U.S. patent application number 11/813643 was filed with the patent office on 2009-05-14 for metallic powder mixtures.
This patent application is currently assigned to H.C. Starck GmbH. Invention is credited to Roland Scholl, Stefan Zimmermann.
Application Number | 20090123690 11/813643 |
Document ID | / |
Family ID | 36190685 |
Filed Date | 2009-05-14 |
United States Patent
Application |
20090123690 |
Kind Code |
A1 |
Scholl; Roland ; et
al. |
May 14, 2009 |
Metallic Powder Mixtures
Abstract
The invention relates to blends of metal, alloy or composite
powders having a maximum mean particle diameter D50 of 75,
preferably a maximum of 25 .mu.m, which are produced according to a
process in which a base powder is first transformed into flake-like
particles and these are then crushed in the presence of milling
auxiliary agents, with further additives and also the use of these
powder blends and moulded objects produced from them.
Inventors: |
Scholl; Roland; (Gorwihl,
DE) ; Zimmermann; Stefan; (Laufenburg, DE) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ, LLP
P O BOX 2207
WILMINGTON
DE
19899
US
|
Assignee: |
H.C. Starck GmbH
Goslar
DE
|
Family ID: |
36190685 |
Appl. No.: |
11/813643 |
Filed: |
January 7, 2006 |
PCT Filed: |
January 7, 2006 |
PCT NO: |
PCT/EP06/00085 |
371 Date: |
July 26, 2007 |
Current U.S.
Class: |
428/97 |
Current CPC
Class: |
B22F 2998/00 20130101;
B22F 1/0055 20130101; C22C 33/0207 20130101; B22F 1/0003 20130101;
B22F 2003/023 20130101; Y10T 428/23993 20150401; B22F 2998/00
20130101; B22F 1/0055 20130101 |
Class at
Publication: |
428/97 |
International
Class: |
D03D 27/00 20060101
D03D027/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 10, 2005 |
DE |
10 2005 001 198.5 |
Claims
1-18. (canceled)
19. A metallic powder blend comprising a Component I, which
comprises a metal, alloy and composite powder having a mean
particle diameter D50 of no more than 75 .mu.m, measured with a
Microtrac.RTM. X100 particle size analyzer according to ASTM C
1070-01, obtainable by a process, wherein the particles of a base
powder with a larger or smaller mean particle size are processed in
a deformation step into flake-like particles, whose ratio of
particle diameter to particle thickness is 110:1 to 10000:1 and
these flake-like particles are subjected in a further process step
to pulverization in the presence of a milling auxiliary agent,
optionally a Component II, which is a metal powder (MLV) for powder
metallurgy applications and optionally a Component II, which is a
functional additive.
20. A metallic powder blend comprising a Component I, which
comprises a metal, alloy and composite powder, of which the
contraction, measured with a dilatometer according to DIN 51045-1,
up to the point at which the temperature of the first contraction
maximum is reached, is at least 1.05 times the contraction of a
metal, alloy or composite powder of the same chemical composition
and the same mean particle diameter D50 produced by atomization,
wherein the powder to be analyzed is compacted before measuring
contraction to a pressed density of 50% of theoretical density,
optionally a Component II, which is a metal powder (MLV) for powder
metallurgy applications and optionally a Component III, which is a
functional additive.
21. The metallic powder blend according to claim 19, wherein
Component I or II, independently of each other, are the same or
different and have a composition of Formula (I) hA-iB-jC-kD (I)
wherein, A stands for one or more of the elements Fe, Co or Ni, B
stands for one or more of the elements V, Nb, Ta, Cr, Mo, W, Mn,
Re, Ti, Si, Ge, Be, Au, Ag, Ru, Rh, Pd, Os, Ir or Pt, C stands for
one or more of the elements Mg, Al, Sn, Cu, or Zn, and D stands for
one or more of the elements Zr, Hf, Mg, Ca, or rare earth metal,
and h, i, j and k give the proportions by weight, wherein h, i, j
and k, independently of each other, each mean 0 to 100 wt. %
provided that the total of h, i, j and k amounts to 100 wt. %.
22. The metallic powder blend according to claim 20, wherein
Component I or II, independently of each other, are the same or
different and have a composition of Formula (I) hA-iB-jC-kD (I)
wherein, A stands for one or more of the elements Fe, Co or Ni, B
stands for one or more of the elements V, Nb, Ta, Cr, Mo, W, Mn,
Re, Ti, Si, Ge, Be, Au, Ag, Ru, Rh, Pd, Os, Ir or Pt, C stands for
one or more of the elements Mg, Al, Sn, Cu, or Zn, and D stands for
one or more of the elements Zr, Hf, Mg, Ca, or rare earth metal,
and h, i, j and k give the proportions by weight, wherein h, i, j
and k, independently of each other, each mean 0 to 100 wt. %
provided that the total of h, i, j and k amounts to 100 wt. %.
23. The metallic powder blend according to claim 21, wherein B
stands for one or more of the elements V, Cr, Mo, W or Ti, C stands
for one or more of the elements Mg or Al and D stands for one or
more of the elements Zr, Hf, Y or La.
24. The metallic powder blend according to claim 23, wherein said
composite powder having a mean particle diameter D 50 of no more
than 25 .mu.m, h stands for 50 to 80 wt. % i stands for 15 to 40
wt. % j stands for 0 to 15 wt. % and k stands for 0 to 5 wt. %
provided that the total of h, i, j and k amounts to 100 wt. %.
25. The metallic powder blend according to claim 22, wherein B
stands for one or more of the elements V, Cr, Mo, W or Ti, C stands
for one or more of the elements Mg or Al and D stands for one or
more of the elements Zr, Hf, Y or La.
26. The metallic powder blend according to claim 25, wherein h
stands for 50 to 80 wt. % i stands for 15 to 40 wt. % j stands for
0 to 15 wt. % k stands for 0 to 5 wt. % provided that the total of
h, i, j and k amounts to 100 wt. %.
27. The metallic powder blend according to claim 20, wherein
Component I and/or II is an alloy selected from the group
consisting of Fe20Cr10Al0.3Y, Fe22Cr7V0.3Y, Ni117Mo15Cr6Fe5W1Co,
FeCrVY, Ni20Cr16Cu2.5Ti1.5Al, Ni53Cr20Co18Ti2.5Al1.5Fe1.5 and
Ni57Mo17Cr16FeWMn.
28. The metallic powder blend according to claim 20 which further
comprises a processing auxiliary agent or a pressing auxiliary
agent.
29. The metallic powder blend according to claim 19, which is a
blend of Components I and II.
30. The metallic powder blend according to claim 19, which is a
blend of Components I and III.
31. The metallic powder blend according to claim 19, which is a
blend of components I, II and III.
32. The metallic powder blend according to claim 20, which is a
blend of Components I and II.
33. The metallic powder blend according to claim 20, which is a
blend of Components I and III.
34. The metallic powder blend according to claim 20, which is a
blend of components I, II and III.
35. The metallic powder blend according to claim 20, which contains
as Component III a hard material, a slip agent or an intermetallic
compound.
36. The metallic powder blend according to claim 20, wherein
Component III comprises carbides, borides, nitrides, oxides,
silicides, hydrides, diamonds, or sulfides.
37. The metallic powder blend according to claim 20, wherein
Component III comprises carbides of the elements of groups 4, 5 and
6 of the periodic system, borides of the elements of groups 4, 5
and 6 of the periodic system, nitrides of the elements of groups 4,
5 and 6 of the periodic system, oxides of the elements of groups 4,
5 and 6 of the periodic system, oxides of aluminium and rare earth
metals; silicides of aluminium, silicides of boron, silicides of
cobalt, silicides of nickel, silicides of iron, silicides of
manganese, silicides of molybdenum, silicides of tungsten,
silicides of zirconium, hydrides of tantalum, hydrides of niobium,
hydrides of titanium, hydrides of magnesium, hydrides of tungsten,
graphite, oxides, molybdenum sulfide, zinc sulfide, tin sulfide
(SnS, SnS.sub.2), copper sulfide; boron nitride, titanium boride or
intermetallic compounds with particular magnetic or electrical
properties on a rare earth-cobalt or rare earth-iron base.
38. The metallic powder blend according to claim 19, wherein
Component III comprises long-chain hydrocarbons, waxes, paraffins,
plastics, fully-degradable hydrides, refractory metal oxides,
organic or inorganic salts or mixtures thereof.
39. The metallic powder blend according to claim 20, wherein
Component III comprises low-molecular polyethylene or
polypropylene, polyurethanes, polyacetal, polyacrylates,
polystyrene, rhenium oxide, molybdenum oxide, titanium hydride,
magnesium hydride or tantalum hydride.
40. A process for the production of a molded object, which
comprises subjecting a metallic powder blend according to claim 20
to a powder-metallurgic molding process.
41. The process according to claim 40, wherein the
powder-metallurgic molding process is selected from the group
consisting of pressing, sintering, slip casting, sheet casting,
wet-spraying, powder rolling (both hot, cold or warm powder
rolling), hot pressing, and hot isostatic pressing (HIP),
sinter-HIP, sintering of powder charges, cold isostatic pressing
(CIP), green processing, thermal spraying and deposition
welding.
42. A molded object obtainable by a process according to claim
41.
43. A molded object containing the metallic powder blend according
to claim 20.
Description
[0001] The invention relates to blends of metal, alloy or composite
powders having a mean particle diameter D50 of no more than 75,
preferably of no more than 25 .mu.m, produced according to a
process in which a base powder is first transformed into flake-like
particles and these are then crushed with further additives in the
presence of milling auxiliary agents and also the use of these
powder blends and moulded objects produced from them.
[0002] From the patent application PCT/EP/2004/00736, not yet laid
open for public inspection, powders are known that can be obtained
by a process for the production of metal, alloy and composite
powders having a mean particle diameter D50 of no more than 75,
preferably of no more than 25 .mu.m, measured with a Microtrac.RTM.
X 100 particle size analyser according to ASTM C 1070-01, from a
base powder with a larger mean particle diameter, the particles of
the base powder being processed in a deformation step into
flake-like particles having a ratio of particle diameter to
particle thickness of 10:1 to 10000:1 and these flake-like
particles being subjected in a further process step to
pulverisation or to a high-energy load in the presence of a milling
auxiliary agent. This process is advantageously followed by a
de-agglomeration step. This de-agglomeration step, in which the
powder agglomerates are broken down into their primary particles,
can be carried out for example in a gas counter-current mill, an
ultrasound bath, a kneader or a rotor-stator. In this specification
such powders are called PZD powders.
[0003] These PZD powders have various advantages over conventional
metal, alloy and/or composite powders used for powder metallurgy
applications, such as improved green strength, compressibility,
sintering behaviour, a wider sintering temperature range and/or a
lower sintering temperature, but also better strength, oxidation
and corrosion behaviour of the moulded parts produced and lower
production costs. A disadvantage of these powders is, for example,
poorer flowability. The changed contraction characteristics
combined with the lower tap density may cause problems during
powder-metallurgic processing as a result of greater sintering
contraction. These characteristics of the powders are disclosed in
PCT/EP/2004/00736, to which reference is made.
[0004] Conventional powders, obtained for example by atomisation of
metal melts, also have disadvantages. For certain alloy
compositions, known as high-alloy materials, in particular, these
are lack of sintering activity, poor compressibility and high
production costs. These disadvantages are less significant in
particular for metal injection moulding (MIM), slip casting,
wet-spraying and thermal spray coating. As a result of the poorer
green strength of conventional metal powders (in the sense of
metal, alloy and composite powders, abbreviated to MLV) these
materials are unsuitable for conventional powder-metallurgic
compression, for powder rolling and for cold isostatic pressing
(CIP) with subsequent green processing, as the green compacts do
not have sufficient strength for this.
[0005] The object of the present invention is to provide metal
powders for powder metallurgy, which do not have the
above-mentioned disadvantages of conventional metal powders (MLV)
and the PZD powders, but combine to the greatest possible extent
their respective advantages, such as high sintering activity, good
pressability, high green strength, good pourability.
[0006] A further object of the present invention is to provide
powders containing functional additives, which can provide the
moulded objects produced from PZD powders with characteristic
properties, such as for example additives that increase the impact
strength or abrasion resistance, such as superhard powders, or
additives that facilitate the working of the green compacts, or
additives that function as templates to control the pore
structure.
[0007] A further object of the present invention is to provide
high-alloy powders for the whole spectrum of powder-metallurgic
moulding processes, so that applications in fields that are not
accessible to conventional metal, alloy or composite powders, are
also possible.
[0008] This object is achieved by metallic powder blends containing
a Component I, a metal, alloy and composite powder having a mean
particle diameter D50 of no more than 75, preferably of no more
than 25 .mu.m, or 25 .mu.m to 75 .mu.m, measured with a
Microtrac.RTM. X100 particle size analyser in accordance with ASTM
C 1070-01, which can be obtained by a process in which the
particles of a base powder with a larger or smaller mean particle
diameter are processed in a deformation step to flake-like
particles having a ratio of particle diameter to particle thickness
of 10:1 to 10000:1 and these flake-like particles are subjected in
a further process step to pulverisation in the presence of a
milling auxiliary agent, a Component II, which is a conventional
metal powder (MLV) for powder metallurgy applications, and/or a
Component III, which is a functional additive. The steps of flake
production and pulverisation can be combined directly, by carrying
out one immediately after the other in the same unit under
conditions adapted to the particular objective (flake formation,
crushing).
[0009] This objective is also achieved by metallic powder blends
containing a Component I, a metal, alloy and composite powder, the
contraction of which, measured with a dilatometer according to DIN
51045-1, up to the temperature of the first contraction maximum, is
at least 1.05 times the contraction of a metal, alloy or composite
powder of the same chemical composition and the same mean particle
diameter D50, produced by atomisation, the powder to be
investigated being compacted to a pressed density of 50% of
theoretical density before contraction is measured, a Component II,
which is a conventional metal powder (MLV) for powder metallurgy
applications and/or a Component III, which is a functional
additive. Where a compact that can be handled cannot be produced
from conventional powders of the desired density (50%), greater
densities are also permissible, for example, by using pressing
auxiliary agents. However this should be understood to mean the
same `metallic density` of the powder pressed bodies and not the
average density of the MLV powder and pressing auxiliary agent.
[0010] The use of Component 1 also makes it possible to produce
metallic powder blends in which the contents of oxygen, nitrogen,
carbon, boron, silicon can be precisely set. If oxygen or nitrogen
enter the process, the high energy input can lead to the formation
of oxide and/or nitride phases during the production of Component
I. Such phases may be desirable for certain applications, as they
may have a significant material-strengthening effect. This effect
is known as the Oxide Dispersion Strengthening Effect (ODS).
However, the incorporation of such phases is often associated with
a deterioration in processing properties (for example
compressibility, sintering activity). As a result of the generally
inert properties of the dispersoids towards the alloy component,
the latter may thus inhibit sintering.
[0011] Pulverising immediately distributes the phases referred to
finely in the powder produced. The phases formed (e.g. oxides,
nitrides, carbides, borides) are therefore distributed considerably
more finely and homogeneously in Component I than in
conventionally-produced powders. This again leads to increased
sintering activity in comparison with phases of the same type
incorporated discretely. This improves the sinterability of the
metallic powder blends according to the invention. Such powders
with finely-dispersed intercalations can be obtained in particular
by precise introduction of oxygen during the milling process and
lead to the formation of very finely-distributed oxides. Specific
use of milling auxiliary agents, which are suitable as ODS
particles and undergo mechanical homogenisation and dispersal
during the milling process, is also possible.
[0012] The metallic powder blend according to the present invention
is suitable for use in all powder-metallurgic moulding processes.
Powder-metallurgic moulding processes according to the invention
are pressing, sintering, slip casting, sheet moulding,
wet-spraying, powder rolling (either cold, hot or warm rolling),
hot pressing and hot isostatic pressing (HIP), sinter-HIP, powder
charge sintering, cold isostatic pressing (CIP), in particular with
green processing, thermal spraying and deposit welding.
[0013] The use of the metallic powder blends in powder-metallurgic
moulding processes leads to significant difference in the
processing, the physical and material properties and allows the
production of moulded objects, which have improved properties,
although the chemical composition is comparable or identical to
that of conventional metal powders. The presence of Component II
allows precise `tuning` of component properties such as
high-temperature strength, strength, toughness, wear-resistance,
oxidation resistance or porosity.
[0014] Pure, thermal spray powders can also be used as a repair
solution for components. The use of pure agglomerated/sintered
powders according to the patent application PCT/EP/2004/00736, not
yet laid open for inspection, as a thermal spray powder allows the
characteristic coating of components with a surface layer that has
better abrasion and corrosion behaviour than the base material.
These properties result from very finely-distributed ceramic
intercalations (oxides of elements having an affinity with oxygen)
in the alloy matrix resulting from mechanical loading during
production of the powders according to PCT/EP/2004/00736.
[0015] Component I is a metal, alloy, and composite powder, which
can be obtained by a two-stage process, in which a base powder is
first transformed into flake-like particles and these are then
crushed in the presence of milling auxiliary agents. In particular,
Component I is a metal, alloy and composite powder having a mean
particle diameter D50 of no more than 75, preferably of no more
than 25 .mu.m, measured with the Microtrac.RTM. X100 particle size
analyser according to ASTM C 1070-01, which can be obtained by a
process in which, are obtainable from a base powder with a larger
mean particle size, the particles of the base powder being
processed in a deformation step to flake-like particles having a
ratio of particle diameter to particle thickness of 10:1 to 10000:1
and these flake-like particles being subjected in a further process
stage to pulverisation in the presence of a milling auxiliary
agent.
[0016] The particle size analyser Microtrac.RTM. X100 is
commercially available from Honeywell, USA.
[0017] To measure the ratio of particle diameter to particle
thickness, the particle diameter and the particle thickness are
measured by photo-optic microscopy. For this purpose, the
flake-like powder particles are first mixed with a viscous,
transparent epoxy resin in a ratio of 2 parts by volume of resin to
1 part by volume of flakes. The air bubbles incorporated when
mixing are then removed by evacuation of the mixture. The now
bubble-free mixture is then poured onto a level substrate and
rolled out into a wide sheet with a roller. In this way, the
flake-Like particles align themselves preferably in the field of
flow between the roller and the substrate. The preferred layer is
characterised in that the normal line to the surface of the flakes
is on average aligned parallel to the normal line to the surface of
the level substrate, in other words, the flakes are on average
arranged flat on the substrate in layers. After hardening, samples
of suitable dimensions are worked out of the epoxy resin sheet
lying on the substrate. These samples are studied with a microscope
vertically and parallel to the substrate. Using a microscope with a
calibrated lens and taking account of adequate particle
orientation, at least 50 particles are measured and a mean value is
produced from the measured values. This mean value represents the
particle diameter of the flake-like particles. The particle
thicknesses are measured on a vertical section through the
substrate and the sample to be analysed using the microscope with a
calibrated lens, which was also used to measure the particle
diameter. Care should be taken to ensure that only particles lying
as nearly parallel as possible to the substrate are measured. As
the particles are coated on all sides in the transparent resin, it
is not difficult to select suitably-orientated particles and to
assign reliably the limits of the particles to be evaluated. Once
again, at least 50 particles are measured and a mean value is
produced from the measured values. This mean value represents the
particle thickness of the flake-like particle. The ratio of
particle diameter to particle thickness can be calculated from the
dimensions measured before.
[0018] Fine, ductile metal, alloy or composite powders in
particular can be produced by this process. Ductile metal, alloy or
composite powders are understood to mean those powders that, when
mechanically loaded to breaking point, undergo plastic elongation
or deformation before significant material damage (embrittlement of
the material, breakage of the material) occurs. Such plastic
material changes are dependent on the material and can range from
0.1 percent to several hundred percent, in relation to the initial
length.
[0019] The degree of ductility, i.e. the ability of materials to
achieve plastic i.e. lasting deformation under the influence of
mechanical strain, can be measured or described by means of
mechanical tensile and/or pressure tests.
[0020] To measure the degree of ductility by means of a mechanical
tensile test, a so-called tensile test specimen is produced from
the material to be evaluated. The specimen can be e.g. a
cylindrical specimen the diameter of which is reduced by ca 30-50%
centrally along its length, over a length of ca 30-50% of the
overall length of the specimen. The tensile test specimen is loaded
into the clamping device of an electro-mechanical or
electro-hydraulic tensile test machine. Before actual mechanical
testing, length measurement sensors are placed in the middle of the
specimen over a measuring length amounting to ca 10% of the overall
length of the specimen. These measuring sensors make it possible to
track the increase in length over the selected measurement length
whilst applying a mechanical tensile strain. The strain is
increased until the specimen breaks, and the plastic portion of the
length change is evaluated with the aid of the stress-strain chart.
Materials, which in such an arrangement achieve a plastic length
change of at least 0.1%, are described as ductile according to this
specification.
[0021] Similarly, it is also possible to subject a cylindrical
material specimen, which has a ratio of diameter to thickness of
ca. 3:1, to a mechanical pressure load in a commercially available
pressure testing machine. After exerting sufficient mechanical
compressive strain, the cylindrical specimen also undergoes
permanent deformation. Once the pressure has been released and the
specimen removed, it can be seen that the ratio of diameter to
thickness has increased. Materials, which achieve a plastic change
of at least 0.1% in such a test are also described as ductile
according to this specification.
[0022] Fine, ductile alloy powders having a degree of ductility of
at least 5% are preferably produced according to the process.
[0023] The crushability of alloy or metal powders which, per se,
cannot be further crushed, is improved by the use of mechanically,
mechano-chemically and/or chemically active milling auxiliary
agents, which are added precisely or are produced in the milling
process. A fundamental aspect of this approach is that the chemical
`target composition` of the powder thus produced should not be
changed overall, or even should be influenced in such a way that
the processing properties, such as e.g. sintering behaviour or
flowability are improved.
[0024] The process is suitable for the production of a wide variety
of fine metal, alloy or composite powders having a mean particle
diameter D50 of no more than 75, preferably of no more than 25
.mu.m.
[0025] The metal, alloy and composite powders produced are
characterised conventionally by a small mean particle diameter D50.
The mean particle diameter is preferably no more than 15 .mu.m,
measured according to ASTM C 1070-01 (measuring device:
Microtrac.RTM. X100). For the purpose of improving product
properties for which fine alloy powders tend to be unfavourable
(porous structures, with which a certain material thickness can
better withstand oxidation/corrosion in their sintered state), it
is also possible to set significantly higher D50 values (25 to 300
.mu.m) than are mostly attempted, whilst maintaining the improved
processing properties (pressing, sintering).
[0026] As a base powder, powders can be used for example, that
already have the composition of the desired metal, alloy or
composite powder. However, it is also possible to use a mixture of
several base powders in the process, which produce the desired
composition only through the choice of a suitable mix ratio. In
addition, the composition of the metal, alloy or composite powder
produced can be influenced also by the choice of milling auxiliary
agent, where this remains in the product.
[0027] Powders with spherical or irregularly shaped particles and a
mean particle diameter D50, measured according to ASTM C 1070-01
normally of greater than 75 .mu.m, in particular greater than 25
.mu.m, preferably of 30 to 2000 .mu.m or of 30 to 1000 .mu.m, or of
75 .mu.m to 2000 .mu.m or 75 .mu.m to 1000 .mu.m, or 30 .mu.m to
150 .mu.m, are preferably used as a base powder.
[0028] The required base powders can be obtained for example by
atomisation of metal melts and, if necessary, subsequent
classification or sieving.
[0029] The base powder is first subjected to a deformation step.
The deformation step can be carried out in known devices, for
example in a rolling mill, a Hametag mill, a high-energy mill or an
attritor or agitated ball mill. By selecting suitable process
parameters, in particular by the effect of mechanical strains that
are sufficient to achieve plastic deformation of the material or
the powder particle, the individual particles are transformed, so
that they finally take the form of flakes, the thickness of which
is preferably 1 to 20 .mu.m. This can take place for example by
loading once in a roller or hammer mill, by loading several times
in `small` deformation steps, for example by impact milling in a
Hametag Mill or a SimoIoyer.RTM., or by a combination of impact and
abrasive milling, for example in an attritor or a ball mill. The
high material loading during this transformation produces
structural changes and/or material embrittlement, which can be
utilised in the following step to crush the material.
[0030] Known melt-metallurgy rapid-setting processes can also be
used to produce ribbons or flakes. Like the mechanically-produced
flakes, these are then suitable for the crushing process as
described below.
[0031] The device in which the deformation step is carried out, the
milling media and the other milling conditions are preferably
selected in such a way that the impurities resulting from abrasion
and/or reactions with oxygen or nitrogen are kept at the lowest
possible level and lie below the level critical for the application
of the product, or within the specification applying to the
material.
[0032] This can be achieved, for example, by a suitable choice of
material for the milling vessel and milling medium, and/or the use
of oxidation and nitridation-inhibiting gases and/or the addition
of protective solvents during the deformation step.
[0033] In a particular embodiment of the process, the flake-like
particles are produced directly from the melt in a rapid-setting
step, e.g. by so-called melt spinning, by cooling on or between one
or more, preferably cooled, rollers so that flakes form
immediately.
[0034] The flake-like particles formed in the deformation step are
subjected to crushing. This changes first the ratio of particle
diameter to particle thickness, primary particles (to be obtained
by de-agglomeration) being generally obtained with a ratio of
particle diameter to particle thickness of 1:1 to 100:1, preferably
1:1 to 10:1. Secondly, the desired mean particle diameter of no
more than 75, preferably of no more than 25 .mu.m is set without
again producing particle agglomerates that are difficult to
crush.
[0035] Crushing can be carried out, for example, in a mill, such as
an excentric vibrating mill, but also in material bed roller mills,
extruders or similar devices, which effect material destruction in
the flakes by means of differing movement and loading speeds.
[0036] Crushing is carried out in the presence of a milling
auxiliary agent. Liquid milling auxiliary agents, waxes and/or
brittle powders, for example, can be added as milling auxiliary
agents. The milling auxiliary agents may have a mechanical,
chemical or mechano-chemical action.
[0037] The milling auxiliary agent can be, for example, paraffin
oil, paraffin wax, metal powder, alloy powder, metal sulfides,
metal salts, salts of organic acids and/or hard material
powders.
[0038] Brittle powders or phases act as mechanical milling
auxiliary agents and can be used for example in the form of alloy,
element, hard material, carbide, silicide, oxide, boride, nitride
or salt powders. Pre-crushed element and/or alloy powders are used,
for example, which, together with the base powder used, which is
not readily-crushable, produce the desired compositions in the
product powder.
[0039] Powders which consist of binary, ternary and/or higher
compositions of the elements A, B, C and/or D present in the base
alloy to be used, are preferably used as brittle powders, wherein
A, B, C and D have the meaning given further below.
[0040] Liquid and/or readily-deformed milling auxiliary agents, for
example waxes, can also be used. Examples of these are
hydrocarbons, such as hexane, alcohols, amines or aqueous media.
These are preferably compounds that are required for the subsequent
steps of further processing and/or can easily be removed after
crushing.
[0041] It is also possible to use special organic compounds, which
are known from pigment production, and are used there to stabilise
non-agglomerating single flakes in a liquid environment.
[0042] In a particular embodiment, milling auxiliary agents are
used, which enter into a precise chemical reaction with the base
powder to promote milling and/or to set a particular chemical
composition of the product. These can be, for example, degradable
chemical compounds, of which only one or more constituents are
needed to set a desired composition, and wherein at least one
component or constituent can be largely removed by a thermal
process.
[0043] Examples are reducible and/or degradable compounds, such as
hydrides, oxides, sulfides, salts, sugars, which are at least
partially removed from the crushed material in a subsequent
processing stage and/or powder-metallurgic processing of the
product powder, and which together with the remaining residue
chemically supplement the powder composition in the desired
manner.
[0044] It is also possible, rather than adding the milling
auxiliary agent separately, to produce it in-situ during crushing.
This can be done, for example by producing the milling auxiliary
agent by the addition of a reaction gas, which under the crushing
conditions reacts with the base powder to form a brittle phase.
Hydrogen is preferred as the reaction gas.
[0045] The brittle phases produced during treatment with the
reaction gas, for example by formation of hydrides and/or oxides,
can generally be removed again by corresponding process steps once
crushing is complete or during processing of the fine metal, alloy
or composite powder obtained.
[0046] If grinding auxiliary agents are used, which cannot be
removed, or cannot fully be removed from the metal, alloy or
composite powder produced, these are preferably selected in such a
way that the remaining constituents have a desirable influence on
the properties of the material, such as for example the improvement
of the mechanical properties, the reduction of susceptibility to
corrosion, an increase in hardness and improvement of the abrasion
behaviour or friction and slip properties. An example of this is
the use of a hard material, the proportion of which is increased in
a subsequent step to such an extent that the hard material together
with the alloy component can be further processed into a hard metal
or a hard metal-alloy composite material.
[0047] After the deformation step and crushing, the primary
particles of the metal, alloy or composite powders produced have a
mean particle diameter D50, measured to ASTM C 1070-01
(Microtrac.RTM. X100) of normally 25 .mu.m, advantageously less
than 75 .mu.m, in particular less than or equal to 25 .mu.m.
[0048] In spite of the use of milling auxiliary agents, coarser
secondary particles (agglomerates) with particle diameters
significantly greater than the desired maximum mean particle
diameter of 25 .mu.m, may be formed in addition to the desired
formation of fine primary particles, as a result of the known
interaction between very fine particles.
[0049] For this reason, crushing is preferably followed by a
de-agglomeration step, where the product to be produced allows or
requires no (coarse) agglomerate, in which the agglomerates are
broken up and the primary particles are released. The
de-agglomeration can be carried out, for example, by applying
shearing forces in the form of mechanical and/or thermal stresses
and/or by removing interlayers inserted between the primary
particles earlier in the process. The particular de-agglomeration
method to be used depends on the degree of agglomeration, the
intended use and the susceptibility to oxidation of the very fine
powder and the admissible impurities in the finished product.
[0050] De-agglomeration can take place, for example, by mechanical
methods, such as by treatment in a gas counter-current mill,
sieving, classification or treatment in an attritor, a kneader or a
rotor-stator disperser. A voltage field can also be used, such as
that produced in ultrasound treatment, a thermal treatment, for
example dissolution or conversion of a previously-incorporated
interlayer between the primary particles by cryo- or
high-temperature treatments, or a chemical transformation of
incorporated or purposely created phases.
[0051] De-agglomeration is preferably carried out in the presence
of one or more liquids, dispersion auxiliary agents and/or binders.
In this way, a slip, a paste, a kneading composition or a
suspension with a solid content of 1 to 95 wt. % can be obtained.
Solid contents of 30 to 95 wt. % can be processed directly by known
powder-technology processes, such as for example, injection
moulding, sheet moulding, coating, hot casting, and then converted
to an end product in suitable drying, debinding and sintering
steps.
[0052] For de-agglomeration of particularly oxygen-sensitive
powders, a gas counter-current mill is preferably used, which is
operated under inert gases, such as for example argon or
nitrogen.
[0053] The metal, alloy or composite powders produced are
characterised by a number of particular properties in comparison
with conventional powders with the same mean particle diameter and
the same chemical composition, which are produced for example by
atomisation.
[0054] The metal powders of Component I for example have excellent
sintering behaviour. At a low sintering temperature, the same
sintering densities can mostly be achieved, as with powders
produced by atomisation. At the same sintering temperature, higher
sintering densities can be achieved in relation to the metallic
portion of the pressed body on the basis of powder compacts of the
same pressed density. This increased sintering activity can be seen
for example in the fact that the contraction of the powder
according to the invention during the sintering process is higher
up to the main contraction maximum than that of
conventionally-produced powders and/or that the (standardised)
temperature, at which the contraction maximum occurs, is lower with
the PZD powder, Monoaxially pressed bodies can produce different
paths of contraction parallel and vertically to the direction of
pressing. In this case, the contraction curve is determined
mathematically by addition of the contractions at the relevant
temperature. Here, the contraction in the direction of pressing
contributes one third and the contraction vertically to the
direction of pressing contributes two thirds to the contraction
curve.
[0055] The metal powders of Component I are metal powders whose
contraction, measured by dilatormeter according to DIN 51045-1, up
to the temperature of the first contraction maximum, is at least
1.05 times that of a metal, alloy or composite powder of the same
chemical composition and the same mean particle diameter D50,
produced by atomisation, the powder to be analysed being compacted
to a pressed density of 50% of theoretical density before
contraction is measured.
[0056] The metal powders of Component I are characterised as a
result of a particular particle morphology with a rough particle
surface, also by comparatively better pressing behaviour and as a
result of the comparatively broad particle size distribution, by
high pressed density. This manifests itself in the fact that
compacts of atomised powder with otherwise identical production
conditions, have a lower bending strength (so-called green
strength) than compacts of PZD powders of the same chemical
composition and the same mean particle size D50.
[0057] The sintering behaviour of powders of Component I can also
be influenced specifically by the choice of milling auxiliary
agents. Thus one or more alloys can be used as milling auxiliary
agents, which, as a result of their low melting point in comparison
with the base alloy, form liquid phases already during heating,
which improve particle rearrangement and material diffusion and
thus the sintering and contraction behaviour, and thus allow higher
sintering densities to be achieved at the same sintering
temperature or the same sintering density at lower sintering
temperatures than the reference powder. Chemically degradable
compounds can also be used, whose degradation products, together
with the base material, produce liquid phases or phases with a
raised diffusion coefficient, which are beneficial to
compaction.
[0058] Conventional metal powders (MLV) for powder metallurgy
applications are powders with a substantially spherical particle
shape, as shown for example in FIG. 1 of PCT/IEP/2004/00736. These
metal powders may be element powders or alloy powders. These
powders are known to the person skilled in the art and can be
obtained commercially. Numerous chemical and metallurgic processes
are known for their production. If fine powders are to be produced,
the known processes often begin by melting a metal or an alloy. The
mechanical coarse and fine crushing of metals or alloys is also
frequently used for the production of `conventional powders`, but
produces powder particles with a non-spherical morphology. In so
far as it functions in principle, this constitutes a very simple
and efficient method of powder production. (W. Schatt, K.-P.
Wieters in `Powder Metallurgy--Processing and Materials`, EPMA
European Powder Metallurgy Association, 1997, 5-10). The
atomisation method is also decisive for establishing the morphology
of the particles.
[0059] Where the melt is broken up by atomisation, the powder
particles form directly by setting from the melt droplets produced.
Depending on the method of cooling (treatment with air, inert gas,
water), the process parameters used, such as nozzle geometry, gas
speed, gas temperature or nozzle material, and also the material
parameters of the melt, such as melting and setting point, setting
behaviour, viscosity, chemical composition and reactivity with the
process media, a large number of possibilities arise, and also
restrictions on the process (W. Schatt, K.-P. Wieters in `Powder
Metallurgy--Processing and Materials`, EPMA European Powder
Metallurgy Association, 1997, 10-23).
[0060] As powder production by atomisation is of particular
industrial and economic importance, various atomisation concepts
have become established. Depending on the powder properties
required, such as particle size, particle size distribution,
particle morphology, impurities and properties of the melts to be
atomised, such as melting point or reactivity, and also the
tolerable costs, certain processes are selected. Nevertheless, in
an industrial and economic respect, there are often limits to
achieving powder with a certain property profile (particle size
distribution, impurity contents, yield of `target grain`,
morphology, sintering activity etc.) at reasonable cost (W. Schatt,
K.-P. Wieters in `Powder Metallurgy Processing and Materials`, EPMA
European Powder Metallurgy Association, 1997, 10-23).
[0061] The production of conventional metal powders for
powder-metallurgy applications by atomisation has above all the
disadvantage that large quantities of energy and atomisation gas
must be used, which makes this process very costly. In particular,
the production of fine powder from high-melting alloys with a
melting point >1400.degree. C. is uneconomical, because on the
one hand the high melting point requires a high energy input to
produce the melt and on the other tHe gas consumption increases
sharply as the desired particle size falls. In addition, there are
often difficulties, if at least one alloy element has a high oxygen
affinity. Cost advantages can be achieved in the production of fine
alloy powders by using specially-developed nozzles.
[0062] In addition to the production of conventional metal powders
for powder metallurgy applications by atomisation, other
single-stage melt-metallurgy processes are often also used, such as
`melt-spiming` i.e. pouring a melt onto a cooled roller, producing
a thin, generally easily crushable ribbon, or `crucible melt
extraction` i.e. immersing a cooled, profiled, rapidly-spinning
roller into a metal melt, extracting particles and fibres.
[0063] A further important variant for the production of
conventional metal powders for powder metallurgy applications is
the chemical route, via reduction of metal oxides or metal salts.
However, alloy powders cannot be produced in this way (W. Schatt,
K.-P. Wieters in `Powder Metallurgy--Processing and Materials`,
EPMA European Powder Metallurgy Association, 1997, 23-30).
[0064] Extremely fine particles, which have particle sizes of below
one micrometer, can also be produced by combining evaporation and
condensation processes of metals and alloys, and by gas phase
reduction (W. Schatt, K.-P. Wieters in `Powder
Metallurgy--Processing and Materials`, EPMA European Powder
Metallurgy Association, 1997, 39-41). However, these processes are
very costly on an industrial scale.
[0065] If the melt is cooled in a larger volume/block, mechanical
process steps for coarse, fine, and very fine crushing are
required, to produce metal or alloy powders that can be processed
by powder metallurgy. A summary of mechanical powder production is
given by W. Schatt, K.-P. Wieters in `Powder Metallurgy--Processing
and Materials`, EPMA European Powder Metallurgy Association, 1997,
5-47.
[0066] Mechanical crushing, particularly in mills, as the oldest
method of particle size setting, is very advantageous from an
industrial point of view, because it can be applied at little
expense to a large number of materials. However, it makes
particular demands on the charge material with regard to the size
of the pieces and the brittleness of the material for example. In
addition, crushing cannot be continued for an indefinite time.
Rather, a milling equilibrium forms, which is established even if
the milling process is started with finer powders. The conventional
milling processes are modified when the physical limits of
crushability are reached for the particular milling material, and
certain phenomena, such as for example embrittlement at low
temperatures, or the effect of milling auxiliary agents, improve
the milling behaviour or crushability. The conventional metal
powders for powder metallurgy applications can be obtained by these
aforementioned processes.
[0067] The Components I and IL, independently of each other, can be
chemically the same or different and can be element powders, alloy
powders or mixtures thereof.
[0068] The metal powders of Components I and II may have a
composition of Formula I
hA-iB-jC-kD (I)
wherein, [0069] A stands for one or more of the elements Fe, Co,
Ni, [0070] B stands for one or more of the elements V, Nb, Ta, Cr,
Mo, W, Mn, Re, Ti, Si, Ge, Be, Au, Ag, Ru, Rh, Pd, Os, Ir Pt,
[0071] C stands for one or more of the elements Mg, Al, Sn, Cu, Zn,
and [0072] D stands for one or more of the elements Zr, Hf, Mg, Ca
rare earth metal (Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy,
Ho, Er, Tm, Yb, Lu), and h, i, j and k give the proportions by
weight, wherein h, i, j and k, independently of each other each
mean 0 to 100 wt. %, provided that the sum of h, i, j and k amounts
to 100% wt. %.
[0073] In a further embodiment of the invention [0074] A stands for
one or more of the elements Fe, Co, Ni [0075] B stands for one or
more of the elements V, Cr, Mo, W, Ti, [0076] C stands for one or
more of the elements Mg, Al and [0077] D stands for one or more of
the elements Zr, Hf, Y, La,
in Formula I
[0078] h stands for 50 to 80 wt. % or for 60 to 80 wt. %, i means
15 to 40 wt. % or 18 to 40 wt. %, j means 0 to 15 wt. % or 5 to 10
wt. %, k means 0 to 5 wt. % or 0 to 2 wt. %.
[0079] In a further embodiment of the invention, Components I or II
are element powders or binary alloy powders, so that a moulded
object, which can be obtained from a metallic powder blend
according to the invention, has a corresponding, more complex
composition. For example, in this embodiment of the invention a
moulded object can be obtained, through the use of binary alloys
for Components I and II, that consists of a quaternary alloy.
[0080] In a further embodiment of the invention, Components I and
II are higher alloy powders such as binary or quaternary alloy
powders, so that a moulded object, which can be obtained from a
metallic powder blend according to the invention, has a
corresponding more complex composition. Components I and II,
independently of each other, can thus also consist of alloys
containing two, three, four or five different metals, so that more
complex alloys are possible. For example, in this embodiment of the
invention, a moulded object can be obtained through the use of a
binary alloy for Component I and a quaternary alloy for Component
II, that consists of an alloy containing six metals.
[0081] In a further embodiment of the invention, the compositions
of Components I and II of the metallic powder blend and also of a
moulded object obtained from them are each different from the
other.
[0082] In a further embodiment of the invention, a moulded object,
which can be obtained by subjecting a metallic powder blend
according to the invention to a powder-metallurgic moulding
process, has a composition of Formula I.
[0083] In a further embodiment of the invention, the moulded
object, Component I and/or Component II consist substantially of an
alloy selected from the group consisting of Fe20Cr10Al0.3Y,
Fe22Cr7V0.3Y, FeCrVY, Ni57Mo17Cr16FeWMn, Ni17Mo15Cr6Fe5W1Co,
Ni20Cr16Cu2.5Ti1.5Al and Ni53Cr20Co18Ti2.5Al1.5Fe1.5.
[0084] In a further embodiment of the invention, Component I and/or
II may even be a powder blend of different element powders or alloy
powders. For example a moulded object containing six metals as
alloy components can be obtained in this case by mixing a Component
I, which is a binary alloy with a Component IIa and a Component
IIb, which are each binary alloys, and subjecting them to a
powder-metallurgic moulding process.
[0085] The quantity of Component II in the metallic powder blend
depends on the type and extent of the intended effect to be
achieved and on the desired chemical composition of the moulded
object obtained when the metallic powder blend is subjected to a
powder-metallurgic moulding process. If Components I and II are
identical, the chemical composition of the moulded object is
already established. However, if Components I and II have a
different composition, the composition of the resulting moulded
object depends on the type, composition and content of Components I
and II and these must be adjusted accordingly. According to the
invention, moulded objects can be produced from high-alloy metallic
materials using processes that were previously not suited to their
production. The person skilled in the art is, in principle,
familiar with the effects arising, so that the optimum blends for
the respective application can be established with a small number
of trials. In general, the conventional metal powder is used in
proportions of Component I: Component II of a ratio of 1:100 to
100:1 or of 1:10 to 10:1 or of 1:2 to 2:1 or of 1:1.
[0086] The present invention can be used for the production of
high-alloy materials. Possible procedures are described in more
detail here. The production of complex alloy components for the
metallic powder blend can in general be described as follows, the
sum of the factors a, b and c being made up to 100 percent by
weight and the symbols ABMP-bLEM-cDOT dMHM-eFUZ being used as
follows: [0087] BMP (base metal powder): Fe, Ni, Co [0088] LEM
(alloy element): Cr, Al, Ti, Mo, W, Nb, Ta, V, . . . [0089] DOT
(dopants) SE (rare earth metals), Zr, Hf; Mg, Ca [0090] MHM
(milling auxiliary agents) Paraffin, hydrocarbons, brittle
intermetallic phases, other brittle phases (ceramics, hard
materials) [0091] FUZ (functional additives) Ceramics,
hydrocarbons, sulfides,
[0092] The indices d and e state the quantity of milling auxiliary
agent or functional additive that can be obtained additionally.
[0093] In one embodiment of the invention, the alloy composition is
retained. The composition of the metallic powder blend is as
follows:
Component I: a.sub.1BMP-b.sub.1LEM-c.sub.1IDOT-d.sub.1MHM Component
II: a.sub.2BMP-b.sub.2LEM-c.sub.2DOT Component III: -e.sub.3FUZ
[0094] (where e.sub.3=0)
[0095] In this case, the alloy of which the moulded object
consists, which is obtained from the metallic powder blend, is
composed as follows:
(a.sub.1+a.sub.2)BMP-(b.sub.1+b.sub.2)LEM-(c.sub.1+c.sub.2)DOT
(without milling auxiliary agents)
[0096] In this case a.sub.1a.sub.2 and b.sub.1=b.sub.2 and
c.sub.1=c.sub.2, which means that this is a mixture of the same
alloys, in which Component I is a PZD powder. The (organic) milling
auxiliary agent (MHN) is not mentioned, as it is completely removed
during processing and does not change the alloy. The proportions of
Components I and II can vary between 100% Comp. I and 0% Comp. II
and 1% Comp. I and 99% Comp. II, depending on the requirements of
processing or functional properties.
[0097] In a further embodiment of the invention, the alloy
composition changes according to the proportions of Components I
and II. The metallic powder blend is composed as follows:
Component I: a.sub.1BMP-b.sub.1LEM-d.sub.1MHM Component II:
a.sub.2BMP-c.sub.2DOT Component III: . . . not present
[0098] In this case, the alloy of which the moulded object
consists, which is obtained from the metallic powder blend, is
composed as follows:
(a.sub.1+a.sub.2)BMP-(b.sub.1)LEM-(c.sub.1)DOT
(without milling auxiliary agents)
[0099] In this case a.sub.1.noteq.a.sub.2 and b.sub.1.noteq.b.sub.2
and c.sub.1.noteq.c.sub.2, which means that there are two alloys.
Component I consists only of base metal powder (BMP) and alloy
elements (LEM), Component II contains the dopant in concentrated
form as a compound to be added, advantageously with particular
metallurgic (e.g. low melting point) and/or mechanical (e.g.
brittle, easily crushable) properties. In this way, powder
technological advantages (sintering with a liquid phase) can be
used, to form the desired end alloys. Here, the dopant is
introduced in the form of a masterbatch, which can be advantageous
depending on the type and composition of the alloys. The (organic)
milling auxiliary agent is not mentioned, as it is completely
removed during processing and does not change the alloy. The
proportions by volume of Components I and II are selected by the
person skilled in the art according to the target composition.
[0100] In a further embodiment of the invention, the alloy
composition changes according to the proportions of Component I,
IIa and IIb. The metallic powder blend is composed as follows:
Component I: a.sub.1BMP-b.sub.1LEM-d.sub.1MHM
[0101] Component II: a.sub.2BMP-b.sub.2LEM-c.sub.2DOT
Component IIb: A.sub.3BMP
[0102] In this case, the alloy of which the moulded object
consists, which is obtained from the metallic powder blend, is
composed as follows:
(a.sub.1+a.sub.2+a.sub.3)BMP-(b.sub.1)LEM-(c.sub.1)DOT
(without milling auxiliary agents)
[0103] In this case a.sub.1.noteq.a.sub.2.noteq.a.sub.3 and
b.sub.1.noteq.b.sub.2 and c.sub.1.noteq.c.sub.2, which means that
the components are two alloys and a base metal powder. Component I
consists only of base metal powder (BMP) and alloy elements,
Component II contains as a mixture the dopant in `concentrated`
form together with base metal and/or alloy elements in order to
advantageously use particular metallurgic and mechanical
properties. Component IIb contains base metals that can be produced
simply and cost-effectively, which when added to Component I, II
and IIb form the whole alloy. In this way, in addition to the
powder technological advantages of the embodiment disclosed
immediately above, technical and economic advantages can also be
utilised. The (organic) milling auxiliary agent is not mentioned,
as it is completely removed during processing and does not change
the alloy.
[0104] In a further embodiment of the invention, the alloy
composition changes according to the proportions of Components I
and II. A brittle alloy is used advantageously as a milling
auxiliary agent. The metallic powder blend is composed as
follows:
Component I:
a.sub.1BMP-b.sub.1LEM-d.sub.1MHM=(a.sub.2BMP-c.sub.2DOT) Component
II: a.sub.3BMP Component III: -e.sub.3FUZ=paraffin
[0105] In this case, the alloy, of which the moulded object
consists, which is obtained from the metallic powder blend, is
composed as follows:
(a.sub.1+a.sub.2+a.sub.3)BMP(b.sub.1)LEM-(c.sub.2)DOT
(without milling auxiliary agents)
[0106] In this case a.sub.1.noteq.a.sub.2.noteq.a.sub.3, which
means that there is an alloy and a base metal. Component I consists
only of base metal powder (BMP) and alloy elements (LEM). A
particularly brittle composition consisting of BMP and DOT is used
as a milling auxiliary agent. Paraffin in powder form is mixed in
as Component III. With Component II, in this case a base metal
powder, corrections can be made to the composition. In this way the
powder technological advantages of the alloy
(a.sub.2BMP-c.sub.2DOT) can be used. The milling auxiliary agent is
not listed separately, as it disappears into the alloy of which the
moulded object consists.
[0107] In a further embodiment of the invention, the composition
changes according to the proportions of Component I and II. A
brittle alloy a.sub.2BMP-c.sub.2DOT is used as the milling
auxiliary agent, organic constituents and ceramic particles are
used as a functional additive (FUZ). The metallic powder blend is
composed as follows:
Component I:
a.sub.1BMP-b.sub.1LEM-d.sub.1MHM=(a.sub.2BMP-c.sub.2DOT) Component
II: a.sub.2BMP Component III: -e.sub.3FUZ=PVA, ceramic
[0108] In this case, the alloy of which the moulded object
consists, which is obtained from the metallic powder blend, is
composed as follows;
(a.sub.1+a.sub.2+a.sub.3)BMP=-(b.sub.1)LEM-(C.sub.2)DOT
(without grinding auxiliary agents)
[0109] In this case a.sub.1.noteq.a.sub.2.noteq.a.sub.3, which
means that there is an alloy and a base metal powder. Component I
consists of base metal powder and alloy elements. A brittle
composition consisting of base metal and dopant is used as the
milling auxiliary agent. Corrections can be made to the composition
with the base metal powder. Component III contains PVA (polyvinyl
alcohol) and ceramic particles, which are advantageous for farther
processing, for example by spray drying. This blend can be
processed to a thermal spray powder for example. In this way, the
powder technological advantages of the alloy
(a.sub.2BMP-c.sub.2DOT) and the action of functional additives
(hardness, resistance to wear) can be utilised, if the powder is
processed accordingly, for example by thermal spraying.
[0110] The metallic powder blend can contain functional additives
as Component III. Functional additives can give characteristic
properties to objects moulded from PZD powders, such as for example
additives that increase the impact strength or resistance to
abrasion, such as superhard powders, or additives that facilitate
processing of the green compacts by reducing the brittleness of the
green compact and/or increasing the green strength, or additives
that act as templates to control the pore structure or surface
properties.
[0111] Functional additives are understood to mean additives to be
incorporated homogeneously, which are either largely or completely
retained in the finished product, a moulded object, or which are
largely or completely removed from the product.
[0112] The first of these are functional additives, which control
the mechanical properties, such as for example hardness, strength,
damping or impact strength, or the chemical properties such as
oxidation/corrosion behaviour or functional properties such as
tribology, haptics, electrical and magnetic conductivity, modulus
of elasticity, electrical burn off behaviour, magnetostrictive
behaviour, electrostrictive behaviour by their proportions and
primary properties.
[0113] The complex mechanical, chemical and Functional properties
can be brought about by the incorporation of various
phases/constituents, such as chemical particles or hard materials,
for example carbides, borides, nitrides, oxides, silicides,
hydrides, diamonds, in particular carbides, borides and nitrides of
the elements of groups 4, 5 and 6 of the periodic system, oxides of
the elements of groups 4, 5 and 6 of the periodic system and also
oxides of aluminium and rare earth metals, silicides of aluminium,
boron, cobalt, nickel, iron, molybdenum, tungsten, manganese,
zirconium, hydrides of tantalum, niobium, titanium, magnesium and
tungsten; slip additives with lubricant properties such as
graphite, sulfides, oxides, in particular molybdenum sulfide, zinc
sulfide, tin sulfides (SnS, SnS.sub.2), copper sulfide and also
intermetallic compounds with particular magnetic or electrical
properties on a rare earth-cobalt or rare earth-iron base.
[0114] By this means, the coating of superhard powders with PZD
powders can also be achieved using a metallic powder blend. This is
advantageously achieved by fluidised bed granulation.
[0115] Coarse (50-100 .mu.m) hard material particles of BN and
TiB.sub.2 for example, can be used as feedstock for fluidised bed
granulation and can be provided with a corrosion--resistant
coating. Thus it is possible to serve new applications in the field
of wear under high corrosive and mechanical loads. After coating,
the agglomerates are debound, sintered in an inert atmosphere and
applied by thermal spraying.
[0116] In the second case, in other words when using functional
additives that are largely or completely removed from the product,
the additives used are so-called place-holders which are removed by
suitable chemical or thermal processes and thus function as a
template. These can be hydrocarbons or plastics. Suitable
hydrocarbons are long-chain hydrocarbons such as low-molecular waxy
polyolefins, such as low-molecular polyethylene or polypropylene,
and also saturated, wholly or partially unsaturated hydrocarbons
having 10 to 50 carbon atoms, or having 20 to 40 carbon atoms,
waxes and paraffins. Suitable plastics are in particular those with
a low ceiling temperature, in particular with a ceiling temperature
of less than 400.degree. C., or lower than 300.degree. C. or lower
than 200.degree. C. Above the ceiling temperature, plastics are
thermodynamically unstable and tend to degrade into monomers
(depolymerisation). Suitable plastics are, for example,
polyurethanes, polyacetals, polyacrylates, in particular polymethyl
methacrylate, or polystyrene. In a further embodiment of the
invention, the plastic is used in the form preferably of foamed
particles, such as for example foamed polystyrene beads, as used as
a preliminary material or intermediate in the production of
packaging or thermal insulation materials. Inorganic compounds
tending towards sublimation can also act as place-holders, such as
for example some oxides of refractory metals, in particular oxides
of rhenium and molybdenum, and also partially- or fully-degradable
compounds such as hydrides (Ti hydride, Mg hydride, Ta hydride),
organic (metal stearate) or inorganic salts.
[0117] By adding these functional additives, largely dense
components (90 to 100% of theoretical density), low-porosity (70 to
90% of theoretical density) and high-porosity (5 to 70% of
theoretical density) components can be produced, by subjecting a
metallic powder blend according to the invention containing such a
functional additive as a place-holder to a powder-metallurgic
moulding process.
[0118] The quantity of functional additives depends on the type and
extent of the intended effect to be achieved, with which the person
skilled in the art is, in principle, familiar, so that the optimum
blends can be established with a small number of trials. When using
these compounds, care should be taken to ensure that the compounds
used as place-holders/templates are present in the metallic powder
blends in a structure suitable for their purpose, in other words in
the form of particles, as a granulate, powder, spherical particles
or similar.
[0119] In general, the functional additives are used in proportions
of Component I Component III in a ratio 1:100 to 100:1 or of 1:10
to 10:1 or 1:2 to 2:1 or of 1:1. If the functional additives are
hard materials, for example tungsten carbide, boron nitride or
titanium nitride, these are advantageously used in quantities of
3:1 to 1:100 or of 1:1 to 1:10 or of 1:2 to 1:7 or of 1:3 to
1:6.3.
[0120] In a further embodiment of the invention, the functional
additives are advantageously used in quantities of 3:1 to 1:100 or
of 1:1 to 1:10 or of 1:2 to 1:7 or of 1:3 to 1:6.3. In a further
embodiment of the invention the metallic powder blend is a mixture
of Component I with Component II and/or Component III, provided
that the ratio of Component I to Component III is 3:1 to 1:100 or
1:1 to 1:10 or 1:2 to 1:7 or 1:3 to 1:6.3
[0121] In a further embodiment of the invention the metallic powder
blend is a mixture of Component I with Component II and/or
Component III, provided that, if a hard material is present in
Component III, the ratio of Component I to Component III is 3:1 to
1:100 or 1:1 to 1:10 or 1:2 to 1:7 or 1:3 to 1:6.3.
[0122] In a further embodiment of the invention, the metallic
powder blend is a mixture of Component I with Component II and/or
Component III, provided that, if tungsten carbide is present in
Component III, the ratio of Component I to Component III is 3:1 to
1:100 or 1:1 to 1:10 or 1:2 to 1:7 or 1:3 to 1:6.3.
[0123] Further additives will improve in particular the processing
properties such as pressing behaviour, strength of the agglomerates
or re-dispersibility. These can be waxes, such as polyethylene
waxes or oxidised polyethylene waxes, ester waxes such as montanic
acid ester, oleic acid ester, esters of linoleic acid or linolenic
acid or mixtures thereof, paraffins, plastics, resins such as for
example colophony, salts of long-chain organic acids, such as metal
salts of montanic acid, oleic acid, linoleic acid or linolenic
acid, metal stearates and metal palmitates, for example zinc
stearate, in particular of the alkali and earth alkali metals, for
example magnesium stearate, sodium palmitate, calcium stearate, or
slip agents. These are substances that are normal in powder
processing (pressing, MIM, sheet moulding, slip casting) and are
known to the person skilled in the art. The compaction of the
powder to be analysed can be carried out with the addition of
conventional auxiliary agents which assist pressing, such as for
example paraffin waxes, or other waxes or salts of organic acids
e.g. zinc stearate. Suitable additives are further described in W.
Schatt, K.-P. Wieters, `Powder Metallurgy--Processing and
Materials`, EPMA European Powder Metallurgy Association, 1997,
49-51`, to which reference is made.
[0124] The following examples serve to explain the invention in
more detail. The examples are intended to facilitate understanding
of the invention, and should not be understood as a restriction
thereof.
EXAMPLES
[0125] The mean particle diameters D50 given in the examples were
measured with a Microtrac.RTM. X100 from Honeywell, US, according
to ASTM C 1070-01.
Example 1
[0126] An argon-atomised alloy melt of the type Nimonic.RTM. 90,
with the composition Ni20Cr16Co2.5Ti1.5Al was used as the base
powder. The alloy powder obtained was sieved to between 53 to 25
.mu.m. The density was ca 8.2 g/cm.sup.3. The particles of the base
powder were largely spherical.
[0127] The base powder was subjected to deforming pulverisation in
a vertical agitated ball mill (Netzsch Feinmalitechnik; type: PR
1S), so that the originally spherical particles became flake-like.
The details of the parameters used are as follows:
TABLE-US-00001 Pulverisation vessel volume: 51 Speed: 400 rpm
Peripheral speed: 2.5 m/s Ball charge: 80 vol. % (bulk volume of
balls) Pulverisation vessel material: 100Cr6 (DIN 1.3505: ca 1.5
wt. % Cr, ca 1 wt. % C, ca. 0.3 wt. % Si, ca 0.4 wt. % Mn, <0.3
wt. % Ni, <0.3 wt. % Cu, rest Fe) Ball material: Hard metal
(WC-10Co) Ball diameter: Ca 6 mm (total mass: 25 kg) Powder weighed
in: 500 g Duration of treatment: 2 h Solvent: Ethanol (ca 2 l).
[0128] This was followed by pulverisation. A so-called excentric
vibrating mill (Siebtechnik GmbH, ESM 324) was used for this, with
the following process parameters:
TABLE-US-00002 Pulverisation vessel volume: 5 l, operated as a
satellite (diameter 20 cm, length ca 16 cm) Ball charge: 80 vol. %
(bulk volume of balls) Pulverisation vessel material 100Cr6 (DIN
1.3505: ca 1.5 wt. % Cr, ca 1 wt. % C, ca. 0.3 wt. % Si, ca 0.4 wt.
% Mn, <0.3 wt. % Ni, <0.3 wt. % Cu, rest Fe) Ball material:
100 Cr6 Ball diameter: 10 mm Powder weighed in: 150 g Pulverisation
auxiliary agent: 2 g paraffin Vibration amplitude: Ca 10 mm
Pulverisation atmosphere: Argon (99.998%)
[0129] After a pulverising time of 2 hours very fine particle
agglomerates are obtained. In an REM image of the product obtained
at a magnification of 1000, the cauliflower-like structure of the
agglomerate (secondary particles) can be seen, the primary
particles having particle diameters of far less than 25 .mu.m.
[0130] A sample of the primary particles or very fine particle
agglomerates was subjected in a third process step to
de-agglomeration by a 10 minute-long ultrasound treatment in
isopropanol in a TG 400 ultrasound apparatus (Sonic
Ultraschallanlagenbau GmbH) at 50% of the maximum output in order
to obtain separated primary particles.
[0131] The particle size distribution of the de-agglomerated sample
was measured by Microtrac.RTM. X100 (manufacturer: Honeywell/US)
according to ASTM C 1070-01. The D50 value of the base powder
amounted to 40 .mu.m and had fallen to ca 15 .mu.m as a result of
the treatment.
[0132] The residual quantity of primary particles from
pulverisation was subjected in an alternative third process step to
de-agglomeration by treatment in a gas counter-current mill with
subsequent ultrasound treatment in isopropanol in a TG 400
ultrasound apparatus (from Sonic Ultraschallanlagenbau GmbH) at 50%
of maximum output. The particle size was again measured by
Microtrac.RTM. X100. The D50 value was now only 8.4 .mu.m.
[0133] The paraffin pulverisation auxiliary agent incorporated can
be removed during powder-metallurgic further processing of the
alloy powder by thermal degradation and/or evaporation or can serve
as a pressing auxiliary agent.
[0134] A metallic powder blend according to the invention was
produced as follows from the PZD powder obtained as disclosed
above:
[0135] 5 kg Nimonic.RTM. 90 PZD powder (d50: 10 .mu.m and d90; 20
.mu.m), produced as disclosed above and 5 kg spherical
(gas-atomised) Nimonic.RTM. 90 powder (d50: 10 .mu.m and d90: 20
.mu.m) are added to an Eirich mixer together with 233 g of a
pressing auxiliary agent in powder form (Licowax C). Over a period
of 20 minutes the three constituents are intensively mixed with
each other. This powder is called VSP-711.
[0136] Analogously to this, 10 kg purely atomised (conventional)
powder (Nimonic.RTM. 90 powder (d50: 10 .mu.m and d90: 20 .mu.m))
is processed in the same way, however 300 g Licowax is added. This
powder is called KON-711.
[0137] Both powders are processed by monoaxial pressing at a
pressure of 500 MPa to cylinders 10 mm in length with a diameter of
30 min. The pressed density of KON-711 was 75% of theoretical
density, however the test specimen had only a low green strength.
The specimens obtained from VSP-711 had significantly improved
strength, in spite of their lower theoretical density (70%).
[0138] For the exact measurement of green strength, square-shaped
pressed bodies are produced at a pressing pressure of 500 MPa. FIG.
1 shows a connection in principle between the powder grades
VSP.sub.--711 and KON.sub.--711 with various contents of pressing
auxiliary agent and the green strength. The green strength of the
pressed bodies produced from VSP.sub.--711 is up to 2.5 MPa under
the conditions described and is thus at least twice that of the
reference sample KON.sub.--711. The pressed body strength of test
specimens with a right-angled cross-section under bending strain
was determined in accordance with DIN ISO 3995/1985. The results of
these measurements are listed in Table 1.
TABLE-US-00003 TABLE 1 Green strength Paraffin content Green
strength [MPa] (pressing auxiliary agent) according to DIN ISO 3995
% KON_711 VSP_711 0.7 nmb 0.7 2 -- 1.7 3 1.2 2.5 4 2.1 -- Nmb: not
measurable, specimen disintegrates on handling
[0139] Both powders (VSP-711 and KON-711) are pressed in a metal
powder press to a further test specimen, a PM tensile test bar in
accordance with DIN ISO 3927 with an area of 6.35 cm.sup.2
(parallel to the direction of pressing) and a length of ca 5 mm.
The pressure is varied from 300 to 800 NWa. The density of the
components increases with the increase in pressure. Table 2
describes this dependency of the influence of the pressing pressure
on the green strength of tensile test specimens pressed directly
from the powders as (A (area in the direction of pressing): 6.35
cm.sup.2; L (length of the specimen in the direction of pressing):
4-5 mm). It should be borne in mind here that the density values
given relate to the mixture of metal powder and pressing auxiliary
agent (3% Licowax).
TABLE-US-00004 TABLE 2 Pressed density Pressed density/g/cm.sup.3
Pressed density/MPa KON_7.1 VSP_7.1 300 5.8 5.65 400 5.95 5.7 500
6.1 5.8 600 6.2 5.95 700 6.3 6 800 6.4 6.05
[0140] The PM tensile test bars are debound in a gas stream under
hydrogen at a heating rate of 2 K/min from room temperature to
600.degree. C. and then sintered in a high vacuum at ca 10.sup.-3
mbar at a temperature of 1290.degree. C. for 2 h. The specimen of
the powder type KON-711 shows damage (cracks, signs of destruction)
after debinding and sintering, which was not visible in the pressed
state. In contrast to this, the tensile test specimens of VSP-711
show no damage and also have an even specimen surface with little
roughness. The specimens are shown in FIG. 2. In addition, partial
quantities of both types of powder after debinding at a heating
rate of 2 K/min from room temperature to 600.degree. C. are
compacted under hydrogen by hot pressing (1150.degree. C./2 h/35
MPa/nitrogen) in a graphite mould. After hot pressing, the
temperature is reduced by ca 5 to 15 K/min, until room temperature
is reached. The discs thus formed have a density of 8.18 g/cm.sup.3
(KON-711) and 8.14 g/cm.sup.3 (VSP-711). These discs (diameter: 100
mm; thickness ca 5 mm) are reduced to a thickness of 3.5 mm by
grinding on both sides. Flat tensile test specimens are produced
from them by water jet cutting as shown in FIG. 3, the mechanical
properties of which are evaluated in a tensile test machine (Rm,
strain at break in the tensile test; Pp0.2, mechanical strain at
which elongation of the tensile test specimen is measured at 0.2%).
The measurement curves of the tensile tests are given in FIG. 4,
and allow a comparison of strength at room temperature.
[0141] Pressed bodies were pressed at 500 MPa and sintered in a
kiln at 1300 and 1330.degree. C. for two hours in an argon-hydrogen
atmosphere (6.5 vol. % H.sub.2), after which the organic pressing
auxiliary agent has been removed up to 600.degree. C. under
hydrogen. The results are presented in Table 2b.
TABLE-US-00005 TABLE 2b Sintering conditions and sintering
densities 3% PHM 3% PHM Changes in density at 1300.degree. C./2 h/
1330.degree. C./2 h/ temperature increase of Specimen ArH.sub.2
ArH.sub.2 30.degree. C. name [g/cm.sup.3] [TD] [TD] KON_7.1 7.35
(90%) 7.72 (94%) 4% VSP_7.1 7.5 (91%) 7.84 (96%) 5%
[0142] A further peculiarity lies in the pore structure of the
specimens produced from KON-711 and VSP-711, which is shown in FIG.
5.
Example 2
[0143] Production of a readily-compressible, flowable and
readily-sinterable granulate in the following manner:
[0144] 5 kg Nimonic.RTM. 90--PZD powder (d50: 10 .mu.m and d90: 20
.mu.m), produced as in Example 1, and 5 kg spherical (gas-atomised)
Nimonic.RTM. 90 powder (d50: 10 .mu.m and d90: 20 .mu.m) are added
to 2-3 l water together with an organic binder (polyvinyl alcohol,
PVA, 3 wt. %) and a surface-active stabiliser. This mixture is
dispersed until a stable suspension has formed. This suspension is
processed by spray-drying to an agglomerate of largely spherical
single particles having a diameter of 1 to 150 .mu.m. Heated
nitrogen (gas temperature 30 to 80.degree. C.) in counter-current
is used as the working gas to dry the suspension. The gas mixture
formed during drying is released into the environment through a
filter at the spray dryer outlet.
[0145] To improve further processability and to ensure compliance
with health criteria, the `powdery` fine content (<10 .mu.m) and
the content of grains >150 .mu.m, which are too coarse are
separated off by sieving. Such a granulate (-150 .mu.m+10 .mu.m)
possesses excellent flow behaviour. The granulate thus obtained is
called VSP-712.
[0146] In parallel with the production of this granulate, an
atomised (conventional) powder (10 kg) (Nimonic.RTM. 90--powder
(d50: 10 .mu.m and d90: 20 .mu.m)) is processed in the same way to
a granulate (-150 .mu.m+10 .mu.m). This powder is called
KON-712.
[0147] Both powders (VSP-712 and KON-712) are evaluated in the same
way--as described in Example 1--for the pressing properties, green
compact strength, sintering behaviour and surface quality
(roughness) of the sintered parts. The result corresponds with the
data determined in the example given above.
Example 3
Production of a Densely-Pouring Granulate
[0148] In each case, a pressed body was produced by cold isostatic
pressing (CIP) using the powder blends VSP-711 and KON-711 produced
in Example 1. For this purpose, the granulate is poured into a
rubber mould, sealed with a gas-tight seal and then compacted at a
hydrostatic pressing pressure of 2000 bar. A compaction of 70% TD
is measured on the pressed bodies of KON-711, however VSP-711
achieves a pressed density of ca 65% TD. The CIP pressed bodies
were then broken down one after the other by machining (loaded into
a lathe and cut into coarse `chips`). In the case of VSP-711 a
large proportion (>50% with a particle size of d50; >100
.mu.m) can successfully be processed into coarse grains. A
primarily powdery product (particles >100 .mu.m (<5%)) is
obtained from the pressed bodies of KON-711.
[0149] These pre-granulates are then processed further with a sieve
granulator plate. This process rounds off the edges of the `powder
chips`, producing a more flowable granulate. After sieving, a
fraction -65 .mu.m+25 .mu.m, that is a fraction with a particle
size of less than 65 .mu.m and greater than 25 .mu.m, is obtained.
This granulate can be further processed by powder-metallurgic
moulding processes. The fractions are called VSP-721 and KON-721.
The total yields from the production of a high-density and flowable
granulate are 20 to 50% in the case of VSP-721 and <20% in the
case of KON-721. The granulate portions not lying within the
desired grain band can be recycled in the production process for
the CIP bodies.
[0150] The investigation of the processing properties of the
metallic powder blends VSP-721 and KON-721 from Example 2 (green
strength, sintering properties) produces comparable results.
VSP-721 has a higher green strength and higher sintering density in
comparison with KON-721 at a pre-determined sintering temperature,
when using the same initial densities.
Example 4
Production of a Porous Body of VSP-721, KON-721 and Atomised Powder
VER-6525 (Fraction: -65+25 .mu.m) of the Same Composition
[0151] The VSP-721 and KON-721 granulates produced previously and a
powder, VER-6525, of the same composition and same particle size as
the granulate used (-65/+25) produced by protective gas
atomisation, are processed in the following way to produce porous
moulded bodies:
[0152] Each of the three grain types is first placed in each of
three identical sintering pans (base area: 6 cm.times.2 cm; pouring
height: 3 cm). These are heated under hydrogen in a kiln at a rate
of 2 K/min to a temperature of 600.degree. C. for debinding. This
is followed by heating to 1250.degree. C. at a heating rate of 10
K/min. The temperature of 1250.degree. C. is maintained for 2 h,
and the kiln containing the sintered bodies is then brought to room
temperature at a rate of 10 K/min.
[0153] The (contracted) moulded bodies formed are removed and
evaluated in the three-point bending test. This shows that the
moulded bodies achieve the following, very different, bending
strengths: VSP-721: 40-ca 20 MPa, KON-721: ca. 20-5 MPa and
VER-6525: <5 MPa. The comparatively high sintering activity of
the variant VSP-721 therefore allows production of sufficiently
strong moulded bodies, as required for example for use in filter
elements. Optimisation of the sintering conditions allows the
strength of VSP-721 to be increased to over 50 MPa.
Example 5
Porous Tube
[0154] Production of a porous body in the form of a tube, by
sintering a powder charge of high-density granulates (VSP-721,
KON-721) and a powder produced by atomisation (VER-6525) of the
same chemical composition and particle size as the granulate. A
correspondingly produced granulate and the roughly-atomised powder
are each put into a ceramic mould with a core that allows full burn
out. The core is in the form of a thin-wall plastic tube, which is
sufficiently stable to withstand the pressure of the powder over
its area after filling. It is filled only with a narrow granulate
or powder fraction (-65+25 .mu.m) produced by sieving.
[0155] In a subsequent step, the organic constituents and the
inserted tube are removed by thermal decomposition or expulsion in
a kiln and at the same time, pre-sintering is started at a higher
temperature (1000.degree. C.). The pre-sintered bodies are then
placed, still vertically, into another kiln, which reaches a
temperature of 1300.degree. C. at high gas purity (vacuum, pressure
of 10.sup.-2 mbar). After sintering, a moulded body of the VSP-721
granulate is obtained, which has sufficient contraction and also
sufficient strength. The moulded body of KON-721, on the other
hand, has less strength. The moulded body of the coarse powder
(VER.sub.--6525) achieved only a strength of ca 5 MPa under the
conditions used, rendering industrial use impossible because of
insufficient strength.
Example 6
Powder-Moulded Bodies of High-Strength Granulates
[0156] The granulates VSP-721 and KON-721 disclosed above are
poured into the cavity of a powder pressing mould of a monoaxial
press. Moulded bodies are produced under monoaxial pressing
pressure of 700 MPa, which have the following densities: VSP-721:
5.3 g/cm.sup.3 (65% of theoretical density) and KON-721 ca 6
g/cm.sup.3 (73% of theoretical density). The green strengths are 10
to 15 MPa for moulded bodies of VSP-721 and 2 to 5 MPa for moulded
bodies of KON-721. After sintering according to the
temperature-time programme disclosed in Example 4, the moulded
bodies of VSP-721 achieve densities of 7.8 g/cm.sup.3 (95% of
theoretical density), the moulded bodies sintered from KON-721
achieve densities of 7.7 g/cm.sup.3 (94% of theoretical density). A
typical structure is shown in FIG. 5.
Example 7
[0157] Fluidised bed granulation for the production of good flow-
and press-ready powders The processing of PZD powders (NIMONIC.RTM.
90 according to Example 1) by fluidised bed granulation (using the
ProCell machine, from Glatt) allows the production of agglomerates
with particle diameters of 10 to ca 300 .mu.m. An aqueous
suspension is produced, which is sprayed into a fluidised bed
chamber. When the material jetted in is dried, tiny agglomerates
are first formed, which are built up from several primary
particles. These act as seeds for fluidised bed granulation.
Further separation and drying of droplets produces agglomerates of
growing diameter. This growth process is accompanied by impacts
between the growing particles, achieving compaction of the surface.
As a result of the binder contained in the suspension the primary
particles adhere to the surface of the seeds and growing
agglomerates. The particle size and agglomeration properties can be
influenced by appropriate setting of flow conditions and air
quantities. Agglomerates produced in this way have particularly
good homogeneity of the components in the single-cell agglomerate
grain.
Example 8
Production of Coarse Powder by Agglomeration in a Mill
[0158] By using pure Nimonic.RTM. 90 PZD powder with a d50 of 10
.mu.m and d90 of 20 .mu.m produced in the same way as Example 1, it
is possible to carry out an agglomeration, in which the primary
properties of the very fine powder (in particular sintering and
pressing behaviour) are largely retained.
[0159] In detail, 600 g of the PZD powder is added to the measuring
container of an excentric vibrating mill. Steel balls of the
material 100Cr6 (DIN 1.3505) with a diameter of 15 mm are used.
After a milling time of 1 h at a speed of 1500 rpm in argon 4.8 as
the medium, a ball fill level of 80% and a milling vessel volume of
51, a clearly `coarsened` powder is removed from the mill. The
particle size d50 is ca 40 .mu.m.
Example 9
Metallic Powder Blend with Functional Components by Spray
Drying
[0160] Production of a readily-flowable granulate for use as a
powder for thermal spraying in the following way:
[0161] A spherically atomised Ni17Mo15Cr6Fe5W1Co alloy with a mean
particle diameter D50 of 40 .mu.m, which is commercially available
under the brand name Hastelloy.RTM. C, was subjected to a
deformation step as disclosed in Example 1.
[0162] The pulverisation of the flake-like particles formed was
carried out in an excentric vibrating mill in the presence of
tungsten carbide as a pulverisation auxiliary agent under the
following conditions:
TABLE-US-00006 Pulverising vessel volume: 51 Ball charge: 80 vol. %
Pulverising vessel material: 100Cr6 (DIN 1.3505) Ball material:
Wc-10Co hard metal material Ball diameter: 6.3 mm Powder weighed
in: 150 g Vibration amplitude: 12 mm Pulverising atmosphere: Argon
(99.998%) Duration of treatment: 90 minutes Pulverising auxiliary
agent: 13.5 g WC (D50 = 1.8 .mu.m)
[0163] Pulverisation produced an alloy-hard material composite
powder, the alloy component of which was crushed to a mean particle
diameter D50 of ca 5 .mu.m and the hard material component to a
mean particle diameter D50 of ca 1 .mu.m. The hard material
particles were distributed largely homogeneously in the volume of
the alloy powder.
[0164] 1.5 kg of the Hastelloy C.RTM. PZD powder thus obtained
having a d50 of 5 .mu.m and d90 of 10 .mu.m and 9.5 kg tungsten
carbide (d50: 1 .mu.m, d90: 2 .mu.m) are processed together by
spray granulation, as described in Example 2 for the production of
VSP-712, to form a granulate. The parameters for spray granulation
were set in such a way as to produce a minimum proportion of fine
particles. In order to remove the portions that were unsuitable for
further processing (thermal spraying), the particles with a
diameter greater than 65 .mu.m were sieved out and the coarse
portion was fed back into the spray-ready suspension (mixed in).
The fraction with a diameter of less than 65 .mu.m is debound in a
sintering boat with a base area of 15 cm.times.15 cm filled to a
level of 3 cm and then debound under hydrogen (heating at a heating
rate of 2 K/min to 600.degree. C.) and sintered at a temperature of
1150.degree. C. The sinter cake is removed after cooling and
processed further by lightly crushing in a mortar. The fine portion
thus formed is classified with a 50 .mu.m sieve for the `top` and
with a 25 .mu.m sieve for the `bottom`. The fraction thus formed
with a particle size of less than 50 .mu.m and greater than 25
.mu.m is applied by thermal spraying (high-speed flame spraying) as
a wear and corrosion-resistant layer to a Hastelloy C material with
low wear-resistance. The part image `B` in FIG. 6 contains the
result of this coating. It can be observed that a homogeneous
matrix alloy is formed, which encloses the hard material particles,
and thus allows the expected corrosion and wear resistance. In
contrast to this, the use of elementary base powders (part image
`A`), which are granulated in s similar way to produce spray-ready
powders, results in inhomogeneities in the layer produced. Under
the conditions of a corrosive environment, this can lead to
increased corrosion.
Example 10
Production of a Readily-Re-Dispersible Spray Granulate [LRDG]
[0165] The granulate is produced following the method in Example 2.
However, a mixture of benzene (ca 10 vol. %) and ethyl alcohol (ca
90 vol. %) is used as the solvent and polymethyl methacrylate
(PMMA) is used as the plastic. Spray drying, taking account of the
conditions for handling highly flammable solvents, produces a
granulate in which the individual particles (Hastelloy C and
tungsten carbide) form a largely strong bond. The parameters for
spray granulation are set in such a way, that coarse granulate with
a low content of fine particles is formed, which has good
flowability (d50: 100 .mu.m, d90: 150 .mu.m). By investigating
individual narrower fractions by x-ray fluorescence analysis it can
be demonstrated quantitatively that the same chemical composition
and therefore the same ratio of powder constituents used is present
in the different fractions. On this basis, it can be concluded that
the granulate produced is homogeneously distributed, and also
because separation is unlikely from a chemical point of view, even
if individual constituents of the fraction separate. Even after a
longer period of movement--for example when determining the capped
density to DIN EN ISO 787-11 or ASTM B 527, only marginal changes
in the particle size distribution arise, from which it can be
concluded that a strong bond between the powder constituents used
has been achieved in the granulate.
Example 11
Production of a Powder-Containing Feedstock of Readily
Re-Dispersible Granulates (LRDG) for Further Processing by Metal
Powder Injection Moulding
[0166] By stirring the granulate produced in Example 10 into
alcohol, the individual particles (Hastelloy C and tungsten
carbide) can be released. The addition of waxes, polypropylene and
stabilisers and the simultaneous exertion of high shear forces on a
shear roller at a sufficiently high processing temperature,
achieves a homogeneous distribution of the powdery functional
materials in the organic environment. The bubble-free composition
is processed via a granulation system into a readily conveyable and
homogeneously melting cold granulate. This can then be added to the
dispenser system of a metal powder injection moulding machine,
heated, and injection moulded under process parameters to be
determined (temperature, pressure, pressure change, after pressure,
cooling time in the injection mould etc). 80 to 95% of the organic
constituents are extracted from these injection-moulded parts by
solvent extraction. This is followed by thermal residual debinding
by slow heating of the test specimens under hydrogen (heating rate
of 1 K/min from room temperature to 600.degree. C.). The parts are
pre-sintered at a temperature of 1000.degree. C. under hydrogen in
the same kiln. The sintering of these specimens is then completed
in a vacuum kiln at a pressure of ca 10.sup.-2 to 10.sup.-3 mbar
(heating at 5 K/min from room temperature to 1250.degree. C., 2 h
holding time at 1250.degree. C. and cooling at 10 K/min to room
temperature).
Example 12
Production of a Constituent by Cold Powder Rolling
[0167] The granulates VSP-712 and KON-712 produced in Example 2 are
placed one after the other into the nip of a vertical powder
rolling machine and compressed. In the case of VSP-712, this
pressing produces in an easy-to-handle sheet with a green strength
of 2 to 10 MPa. With the granulate KON-712, it is not possible to
remove test specimens on which the green strength can reliably be
measured.
[0168] By thermal post-treating, debinding and sintering as
described under Example 11, a sheet of VSP-712 can be produced
which, depending on the sintering temperature selected, can be
dense (93 to 98% of theoretical density) or porous (60 to ca 90% of
theoretical density). In spite of the low density of the porous
structure, these sheets still have a high strength of at least
50-100 MPa.
Example 13
Component Produced by Powder Rolling-Sheet Production
[0169] The granulates VSP-712 and KON-712 produced in Example 2 are
debound as a loose powder charge and pre-sintered to stabilise
(compact) the granulate. This takes place under the conditions
described in Example 5 for debinding/pre-sintering to 1000.degree.
C. After de-fragmentation, including classification to -50+25 .mu.m
as described in Example 9, the granulate thus formed is processed
in each case by powder rolling into a green ribbon. The strength of
the green ribbon is sufficient in the case of the granulate VSP-712
for further processing by sintering. The fragments of KON-712 are
unsuitable for the intended further processing into a sheet. If the
VSP-712 green ribbon is sintered at a temperature of 1300.degree.
C., as described in Example 5, a density of over 92% of theoretical
density can be achieved.
Example 14
Component Produced by Hot Post-Compacting by Rolling
[0170] The green ribbon described in Example 13 must not
necessarily be compacted by sintering. A simple option for
compaction is to heat the green ribbon inductively under an inert
protective gas atmosphere (argon) to 1100.degree. C., before
running it into a roll nip and to subject it to intensive pressure
loading at this temperature. This will very simply produce a
sheet-like component in which complete compaction (>98% of
theoretical density) or a desired residual porosity (50 to 90% of
theoretical density) can be set by varying the roll nip. Here too,
the variant KON-712 has lower green strength to obtain a sintered
component.
Example 15
Component Produced by Sheet Moulding, Debinding and Sintering
[0171] On the basis of and following the method described in
Example 10 for producing a readily re-dispersible powder blend, a
granulate is produced, which consists only of Hastelloy C powder.
The tungsten carbide portion is omitted to allow a sheet to be
produced that consists only of an alloy.
[0172] In the same way as and following the process described in
Example 11, a sheet-mouldable, pore-free composition is produced by
intensive pulverisation.
[0173] This composition is continuously applied to a smooth surface
by blade coating. Drying produces as a green body a
metal-powder-filled sheet with organic constituents, which is
rubber-like in nature. This green body is now subjected to
debinding by heating from room temperature to 600.degree. C. at a
heating speed of 0.1 K/min. The part is then subjected to sintering
under the conditions described in Example 5, to achieve an increase
in strength. Linear contraction typically occurs in this step. This
can amount to 10- to 25%, depending on the sintering temperature
and time.
Example 16
Component with `Normally` Set Porosity
[0174] A green compact produced as in Example 15 is treated in a
stamping tool in the shape of a needle press (stamp formed from
needles with a diameter of 0.1 to 0.5 mm) in such a way that
tube-like deformations remain vertically to the normal line to the
surface.
[0175] After debinding and sintering under the conditions described
in Example 5, a sheet is formed, which consists of dense material
areas and pore channels lying on a normal line to the surface. The
flow resistance can easily be set by the number and diameter of the
channels, without the particle size of the powder particles
directly playing a role, which can be important for the setting of
any corrosion and oxidation properties, if very fine powder
particles are used.
Example 17
Blend of VSP and Organic Place-Holders for the Production of
Fine-Cell Porous Structures
[0176] A bubble-free feedstock of `honey-like` viscosity is
produced in a kneader from 3.7 kg PZD powder (VSP-711), 148 g
powdery (<30 . . . 50 .mu.m) polymethyl methacrylate (PMMA) and
a sufficient quantity of a mixture of benzene (ca 10 vol. %) and
ethyl alcohol (ca 90 vol. %). 0.671 foamed polystyrene beads (O 1
to 1.5 mm) are added to this feedstock in the kneader. This
composition (volume ca 0.9 . . . 1.1 l) is placed into a flat
ceramic mould (ca 30.times.30.times.1.5 cm.sup.3) and dried. The
green body thus produced is freed from the organic constituents
polystyrene place holders, PMMA, residual solvent) by slowly
heating to ca. 400.degree. C. (0.5 K/min) under hydrogen. The mould
is then heated in the same kiln at 5 K/min from room temperature to
1000.degree. C. Sintering is completed in a vacuum kiln
(10.sup.-2-10.sup.-3 mbar), the pre-sintered specimens being
brought from room temperature to 1300.degree. C. at 10 K/min and
maintained at this temperature for 2 h. The volume of the
fully-sintered specimens is ca 0.4 l lower than the initial volume
(ca 1 l). This is equivalent to a linear contraction of ca 26%. The
pores (as a result of the place-holders) have reduced from 1 mm
originally to 1.5 mm in the green state, equivalent to a reduction
of 0.74 to 1.1 mm and a material density of ca 7.4 g/cm.sup.3 is
achieved in the metallic area.
Example 1.8
Mechanical Properties of a Hot-Pressed Fe22Cr7V0.3Y-Alloy
[0177] The PZD powder is produced as described in Example 1,
although unlike in Example 1 an atomised Fe22Cr7V0.3Y alloy is used
as the educt (instead of Nimonic.RTM. 90 powder).
[0178] The processable powder blends summarised in Table 3 were
produced in an Eirich mixer from the PZD powder produced
accordingly and conventional spherical powders (-25 .mu.m, -53
.mu.m/+25 .mu.m).
TABLE-US-00007 TABLE 3 Fe22Cr7V0.3Y powder with varying contents of
PZD powders Contents in the relevant blend [wt. %] KON_718 (F)
KON_178 (G) PZD_718 (-25 .mu.m) (-53 .mu.m + 25 .mu.m) Description
[D50: 12 .mu.m] [D50: 13 .mu.m] [D50: 13 .mu.m] 18.1 0 100 -- 18.2
100 0 -- 18.3 50 50 -- 18.4 50 -- 50
[0179] Before processing by hot pressing, partial quantities of
18.2, 18.3 and 18.4 are subjected to debinding at a heating rate of
2 K/min from room temperature to 600.degree. C. under hydrogen. The
hot pressing takes place under the following conditions:
1150.degree. C./2 h/35 MPa/argon 4.8 in a graphite mould. After hot
pressing, the temperature is reduced by ca 5 to 15 K/min, until
room temperature is reached. The discs thus produced have a
diameter of ca 100 mm. Tensile test specimens are produced from
them by water jet cutting as in Example 1 and are ground to the
same thickness (ca 3.4 mm). All samples have virtually the same
material densities of 7.55 to 7.50 g/cm.sup.3. The results of the
mechanical tensile test at room temperature are given in Table
4.
[0180] Table 4 shows that the strength values Rp0.2 and Rm are
better for all PZD powders containing variants (Rp0.2: +5-70%/Rm;
+20-50%). 18.1 has the best values for elongation (At-Fmax: elastic
and plastic part), the PZD-containing variants achieve At-Fmax
values of 95 to 45%. In view also of the fact that variants 18.2,
18.3 and 18.4 are at all processable by pressing and sintering
techniques, the basic advantages of metallic powder blends
according to the invention result.
TABLE-US-00008 TABLE 4 Results of the mechanical test (Rp0.2, Rm
and At-Fmax) for hot-pressed FeCrVY specimens Mechanical properties
(at room temperature) Rp0.2 Rm At-Fmax Name [MPa] [MPa] [%] 18.1
405 730 17.5 18.2 700 1100 8 18.3 430 870 16.5 18.4 480 870
15.5
Example 19
Mechanical Properties of `Freely-Sintered` Fe22Cr7V0.3Y Powder
Compacts
[0181] By mixing the powder blends 18.1, 18.2, 18.3 and 18.4 listed
in Table 3 with Licowax as a pressing auxiliary agent, the powder
mixtures 19.1, 19.2, 19.3 and 19.4 are obtained. With these, it is
possible to obtain, by monoaxial pressing, moulded bodies in the
form of tensile test bars (A (area in direction of pressing): 6.35
cm.sup.2 l (length in the direction of pressing): 4-5 mm, p: 700
Mpa). The quantity of Licowax is selected in each case so that the
compacts contain a total of 4 wt. % of organic constituents. This
high content is necessary only for the PZD-free variant (18.1 and
19.1), to make it at all possible to obtain the compacts with
sufficient green strength. To improve comparability, the remaining
powders were provided with the same quantities of pressing
auxiliary agents.
[0182] After production the moulded bodies were subjected to
debinding (2 K/min from room temperature to 600.degree. C.) under
hydrogen. Sintering then takes place in a cool-wall kiln with a Mo
heater (Thermal Technology) at four different temperatures (1290,
1310, 1340 and 1350.degree. C.) under argon 4.8. Heating is carried
out at 10 k/min, and the maximum temperature is maintained for 2 h.
After sintering, the specimens were cooled to room temperature at a
cooling rate of 10 to 15 K/min.
[0183] The results are summarised in the tables below. Although the
greatest care was taken, it was not possible to produce testable
specimens of 19.1 for 1310 and 1340.degree. C. This is not due to
the sintering temperature, but to the defects arising after
pressing, which are not immediately visible, but frequently result
in destruction after debinding. Such problems did not arise with
19.2 to 19.4.
[0184] It can be established that (in so far as can be determined)
all properties of the specimens according to the invention (19.2,
19.3 and 19.4) were the same as or better than those of the
conventional powder 19.1. At optimum temperatures, an improvement
in Rm of +40-130% (Table 5.1), in Rp0.2 of 5-45% (Table 5.2), in
At-Fmax of +0-270% (Table 5.3) and in of 0-2% (Table 5.4) was
achieved. It should be stated, nevertheless, that the sintering
process has so far not been optimised. Once this has been done, an
improvement in the properties of 19.2 to 19.4 can be expected, as
they have considerable advantages in the reproduction of properties
as a result of their significantly lower tendency to `pressing
defects`
TABLE-US-00009 TABLE 5.1 `Influence of sintering temperature on the
strain at break of freely-sintered Fe22Cr7V0.3Y specimens`
Sintering temperature [.degree. C.] (2 h, Ar 4.8)) Rm/MPa 1290 1310
1340 1350 19.1 350 240 19.2 525 515 565 550 19.3 332 330 360 350
19.4 324 310 170 340
TABLE-US-00010 TABLE 5.2 `Influence of the sintering temperature on
Rp0.2 of freely-sintered Fe22Cr7V0.3Y specimens` Sintering
temperature [.degree. C.] (2 h, Ar 4.8)) Rp0.2/MPa 1290 1310 1340
1350 19.1 290 215 19.2 410 380 425 335 19.3 290 295 305 300 19.4
280 275 290
TABLE-US-00011 TABLE 5.3 `Influence of the sintering temperature on
the elongation (At-Fmax) of freely-sintered Fe22Cr7V0.3Y specimens`
Sintering temperature [.degree. C.] (2 h, Ar 4.8)) At-Fmax/% 1290
1310 1340 1350 19.1 4 0.15 19.2 7 9 12 15 19.3 2 1 4 4 19.4 2 2 0.8
4
TABLE-US-00012 TABLE 5.4 `Influence of the sintering temperature on
the density of freely-sintered Fe22Cr7V0.3Y specimens`
Density/g/cm.sup.3 (theor. density: Sintering temperature [.degree.
C.] (2 h, Ar 4.8)) 7.5 g/cm.sup.3 1290 1310 1340 1350 19.1 6.3 6.6
19.2 6.4 6.5 6.6 6.7 19.3 6.4 6.4 6.3 19.4 6.6 6.7 6.7
Example 20
Sintering Behaviour of Fe20Cl0Al0.3Y Alloys
[0185] The PZD powder is produced in the same way as Example 1.
Instead of Nimonic.RTM. 90 powder, an atomised Fe20Cr10A10.3Y alloy
is used as an educt. The PZD powder produced is called 20.1
(PZD-720) and the reference powder 20.2 (KON-720). Table 6 contains
information about the powder blends processed. Licowax was used as
the pressing auxiliary agent.
TABLE-US-00013 TABLE 6 `FeCrAlY powder containing 4% pressing
auxiliary agent` Content of each blend [wt. %] PHM + organic
PZD_720 KON_720 Constituents Name [D50: 15 .mu.m] [D50: 14 .mu.m]
[wt. %] 20.2 0 100 4 20.1 100 0 4
[0186] The powders contained in Table 6 are processed to tensile
test bars (A:6.35 cm.sup.2, 1:4 . . . 5 nm; p:700 MPa). Test
specimens were produced for dilatometer measurements by abrasive
cutting (vertically to the direction of pressing), which were then
measured vertically to the direction of pressing. Measurement
comprised, in addition to slow heating at a heating rate of 2 K/min
from room temperature to 500.degree. C. for debinding, heating to
1320.degree. C. at 10 K/min (holding time: 10 min) and cooling at a
cooling rate of 10 K/min from 1320.degree. C. to room temperature.
The result is shown in FIG. 7. The heating rate is represented by
the lower, un-annotated curve, the curve for 20.1 is continuous and
the curve for 20.2 is interrupted. The results are collected in
Table 7. The path of contraction shows that the powder compacts of
the conventional powder 20.2 undergo elongation up to ca
1290.degree. C. as a result of the thermal elongation coefficient.
There is no contraction maximum up to a temperature of 1320.degree.
C. To achieve this, the sintering temperature would have to be
increased. However, the sintering shrinkage of the PZD sample 20.1
begins already at ca 1000.degree. C. The first contraction maximum,
which is not shown, is at ca 1300.degree. C. This corresponds to
the behaviour disclosed in patent application PCT/EP/2004/00736 of
conventional powders produced by atomisation and of the PZD powders
produced there. It is noteworthy also, that although 20.1 has a low
starting density of 4.78 g/cm.sup.3 (without organic constituents),
a density of ca 7.5 g/cm.sup.3 is obtained after sintering. In
contrast to this, the conventional specimen 20.2 achieves only a
density of ca 5.7 g/cm.sup.3 at a starting density of 5 g/cm.sup.3.
The advantages of sintering PZD powders, apart from the ability to
produce powder compacts, is thus demonstrated.
TABLE-US-00014 TABLE 7 Sintering conditions (see notes) Starting
density Starting without organ, Sintering Sintering density
constituents contraction density DIL (T, t) [g/cm.sup.3]
[g/cm.sup.3] [%] [g/cm.sup.3] 20.2 5.00 4.8 5.84 5.7 21.1 4.78 4.6
15.17 7.5
* * * * *