U.S. patent application number 14/007335 was filed with the patent office on 2014-01-23 for cemented carbide material.
The applicant listed for this patent is Igor Yurievich Konyashin, Frank Friedrich Lachmann, Bernd Heinrich Ries. Invention is credited to Igor Yurievich Konyashin, Frank Friedrich Lachmann, Bernd Heinrich Ries.
Application Number | 20140023546 14/007335 |
Document ID | / |
Family ID | 44067462 |
Filed Date | 2014-01-23 |
United States Patent
Application |
20140023546 |
Kind Code |
A1 |
Konyashin; Igor Yurievich ;
et al. |
January 23, 2014 |
CEMENTED CARBIDE MATERIAL
Abstract
Cemented carbide material comprising tungsten carbide (WC)
material in particulate form having a mean grain size D in terms of
equivalent circle diameter of at least 0.5 microns and at most 10
microns, and a binder phase comprising cobalt (Co) of at least 5
weight per cent and at most 12 weight per cent, W being present in
the binder at a content of at least 10 weight per cent of the
binder material; the content of the WC material being at least 75
weight per cent and at most 95 weight per cent; and nanoparticles
dispersed in the binder material, the nanoparticles comprising
material according to the formula CoxWyCz, where X is a value in
the range from 1 to 7, Y is a value in the range from 1 to 10 and Z
is a value in the range from 0 to 4; the nanoparticles having a
mean particle size at most 10 nm, at least 10 per cent of the
nanoparticles having size of at most 5 nm; the cemented carbide
material having a magnetic coercive force in the units kA/m of at
least -2.1.times.D+14.
Inventors: |
Konyashin; Igor Yurievich;
(Igor, DE) ; Ries; Bernd Heinrich; (Huenfeld,
DE) ; Lachmann; Frank Friedrich; (Burghaun,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Konyashin; Igor Yurievich
Ries; Bernd Heinrich
Lachmann; Frank Friedrich |
Igor
Huenfeld
Burghaun |
|
DE
DE
DE |
|
|
Family ID: |
44067462 |
Appl. No.: |
14/007335 |
Filed: |
March 27, 2012 |
PCT Filed: |
March 27, 2012 |
PCT NO: |
PCT/EP2012/055427 |
371 Date: |
September 25, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61468445 |
Mar 28, 2011 |
|
|
|
Current U.S.
Class: |
419/18 |
Current CPC
Class: |
B22F 7/008 20130101;
C22C 29/067 20130101; C22C 29/005 20130101; B22F 2003/248 20130101;
B22F 7/00 20130101; B22F 2302/10 20130101; B22F 2005/001 20130101;
C22C 29/08 20130101; B22F 2301/15 20130101; B22F 3/24 20130101 |
Class at
Publication: |
419/18 |
International
Class: |
C22C 29/08 20060101
C22C029/08; B22F 7/00 20060101 B22F007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 28, 2011 |
GB |
1105150.5 |
Claims
1. A method as claimed in claim 6, in which the cemented carbide
material comprises tungsten (W) present in the binder at a content
of at least 10 weight per cent of the binder material; the content
of the WC material being at least 75 weight per cent and at most 95
weight per cent; and nanoparticles dispersed in the binder
material, the nanoparticles comprising material according to the
formula CoxWyCz, where X is a value in the range from 1 to 7, Y is
a value in the range from 1 to 10 and Z is a value in the range
from 0 to 4; the nanoparticles having a mean particle size at most
10 nm, at least 10 per cent of the nanoparticles having size of at
most 5 nm; the cemented carbide material having a magnetic coercive
force in the units kA/m of at least -2.1.times.D+14.
2. (canceled)
3. A method as claimed in claim 1, in which the Co content is at
least 5 weight per cent and at most 8 weight per cent and the
cemented carbide material has a magnetic coercive force in the
units kA/m of at least -1.9.times.D+14.
4. A method as claimed in claim 1, in which the Co content is at
least 8 weight per cent and at most 12 weight per cent and the
cemented carbide material has a magnetic coercive force in the
units kA/m of at least -2.1.times.D+14.
5. A method as claimed in claim 1, containing at least about 0.1
weight percent to about 10 weight percent vanadium (V), chromium
(Cr), tantalum (Ta), titanium (Ti), molybdenum (Mo), niobium (Nb)
and or hafnium (Hf).
6. A method for manufacturing a cemented carbide body comprising
cemented carbide material comprising tungsten carbide (WC) material
in particulate form having a mean grain size D in terms of
equivalent circle diameter of at least 0.5 microns and at most 10
microns, and a binder phase comprising cobalt (Co) of at least 5
weight per cent and at most 12 weight per cent; the method
including providing a sintered body comprising tungsten carbide
(WC) particles and a binder material comprising cobalt (Co), the WC
particles having mean size D of at least 0.5 microns and at most 10
microns, the content of the WC particles in the sintered body being
at least 75 weight percent and at most 95 weight percent, and the
content of the binder material in the sintered body being at least
5 weight percent and at most 20 weight percent; and heat treating
the sintered body at a temperature in the range from 500 degrees
centigrade to 900 degrees centigrade for a period of time; the
period in hours being at least (0.8.times.D)-0.15 and at most
(4.3.times.D)-1.7.
7. A method as claimed in claim 21, in which the binder material
contains at least 10 weight percent tungsten (W).
8. A method as claimed in claim 37, in which the W is present in
the binder material in the form of solid solution or dispersed
particles comprising a compound according to the formula CoxWyCz,
where X is a value in the range from 1 to 7, Y is a value in the
range from 1 to 10 and Z is a value in the range from 1 to 4.
9. A method as claimed claim 21, in which the binder of the
sintered body comprises iron (Fe) or (Ni), or an alloy including at
least one of Fe or Ni.
10. A method as claimed in claim 1, in which the composition and
microstructure of the sintered body is selected such that magnetic
moment (or magnetic saturation) of the sintered body is at least
about 70 percent and at most about 85 percent of the theoretical
value of binder material comprising nominally pure Co or of the
alloy of Co and Ni comprised in the binder material.
11. (canceled)
12. (canceled)
13. (canceled)
Description
[0001] This disclosure relates generally to cemented carbide
material, tools comprising same and method for making same.
[0002] Cemented carbide material comprises particles of metal
carbide such as tungsten carbide (\NC) or titanium carbide (TiC)
dispersed within a binder material comprising a metal such as
cobalt (Co), nickel (Ni) or metal alloy. The binder phase may be
said to cement the carbide particles together as a sintered
compact. Measurements of magnetic properties may be used to measure
indirectly aspects of the microstructure and properties of cemented
carbide materials. The magnetic coercive force (or simply coercive
force or coercivity) and magnetic moment (or magnetic saturation)
can be used for such purposes.
[0003] European patent number 1 043 415 discloses a coated cemented
carbide insert with a 5-50 micron thick, essentially gamma phase
free and binder phase enriched surface zone with an average binder
phase content (by volume) in the range 1.2-2.0 times the bulk
binder phase content. The gamma phase consists essentially of TaC
and TiC and to some extent of WC dissolved into the gamma phase
during sintering. The ratio Ta/Ti is between 1.0 and 4.0.
[0004] Jonsson (Jonsson, H., 1981, "Microstructure and hardness of
heat treated Co-W alloys with compositions close to those of binder
phases of Co-WC cemented carbides", PhD thesis, Chemistry Institute
of the University of Uppsala) discloses that ageing of homogenised
Co--25% W alloys in the temperature range 500 to 800 degrees
centigrade for at least up to about 100 hours is accompanied by an
increase in hardness.
[0005] Cemented carbide materials are relatively wear- and fracture
resistant. However, controlling the composition to increase the
wear resistance may typically be expected to result in compromised
fracture resistance, and vice versa. While heat treatment of
cemented carbide materials for extended periods of time may be used
to alter its properties, this reduces the speed of production and
tends to increase cost.
[0006] Viewed from a first aspect, there can be provided cemented
carbide material comprising tungsten carbide (WC) material in
particulate form having a mean grain size D in terms of equivalent
circle diameter of at least about 0.5 microns and at most about 10
microns (as measured using an electron backscatter diffraction
image of a polished surface of the cemented carbide material), and
a binder phase comprising cobalt (Co) of at least about 5 weight
per cent and at most about 12 weight per cent; the content of the
WC material being at least about 75 weight per cent and at most
about 95 weight per cent; and nanoparticles dispersed in the binder
material, the nanoparticles comprising material according to the
formula CoxWyCz, where X is a value in the range from 1 to 7, Y is
a value in the range from 1 to 10 and Z is a value in the range
from 0 to 4 or Z is a value in the range from 1 to 4; the
nanoparticles having a mean particle size at most about 10 nm, at
least about 10 per cent of the nanoparticles having size of at most
about 5 nm; the cemented carbide material having a magnetic
coercive force in the units kA/m of at least about -2.1.times.D+14.
The mean grain size D is the number average of grain sizes d,
expressed as the equivalent circle diameters of grains evident in
an electron backscatter diffraction image of a polished surface of
a body comprising the cemented carbide material.
[0007] Various examples of cemented carbide material are envisaged
by this disclosure and the following are non-limiting,
non-exhaustive examples.
[0008] W may be present in the binder at a content of at least
about 10 weight per cent of the binder material. The W may be
present in the binder in the form of solid solution or dispersed
particles.
[0009] The binder phase may comprises iron (Fe) or nickel (Ni) or
an alloy including Fe or Ni.
[0010] The Co content may be at least about 5 weight per cent and
at most about 8 weight per cent and the cemented carbide material
may have a magnetic coercive force in the units kA/m of at least
about -1.9.times.D+14.
[0011] The Co content is at least about 8 weight per cent and at
most about 12 weight per cent and the cemented carbide material has
a magnetic coercive force in the units kA/m of at least about
-2.1.times.D +14.
[0012] Viewed from a second aspect there is provided a method for
making a cemented carbide body (i.e. a body comprising cemented
carbide material), the method including providing a sintered body
comprising tungsten carbide (WC) particles and a binder material
comprising cobalt (Co), the WC particles having mean size D of at
least about 0.5 microns and at most about 10 microns, the content
of the WC particles in the sintered body being at least about 75
weight percent and at most about 95 weight percent, and the content
of the binder material in the sintered body being at least about 5
weight percent and at most about 20 weight percent; and heat
treating the sintered body at a temperature in the range from about
500 degrees centigrade to about 900 degrees centigrade for a period
of time; the period in hours being at least about
(0.8.times.D)-0.15 and at most about (4.3.times.D)-1.7.
[0013] W may be present in the binder at a content of at least
about 10 weight per cent of the binder material. The W may be
present in the binder in the form of solid solution or dispersed
particles. The dispersed particles may comprise a compound
according to the formula CoxWyCz, where X is a value in the range
from 1 to 7, Y is a value in the range from 1 to 10 and Z is a
value in the range from 0 to 4, or Z is a value in the range from 1
to 4.
[0014] The binder of the sintered body may comprise iron (Fe) or
(Ni), or an alloy including at least one of Fe or Ni.
[0015] The composition and microstructure of the sintered body may
be selected such that magnetic moment (or magnetic saturation) of
the sintered body is at least about 70 per cent and at most about
85 per cent of the theoretical value of binder material comprising
nominally pure Co or of the alloy of Co and Ni comprised in the
binder material.
[0016] Viewed from a third aspect there is provided a tool or tool
element comprising cemented carbide material according to this
disclosure. The tool; may be a pick for road planing or mining. The
tool may comprise a super hard tip joined to a support body
comprising cemented carbide material according to this
disclosure.
[0017] Disclosed cemented carbide material and bodies comprising
same may have the aspect of exhibiting enhanced fracture resistance
in combination with high wear resistance and or hardness. The
disclosed method may have the aspect of reduced manufacturing time
and enhanced manufacturing efficiency.
[0018] While wishing not to be bound by a particular theory,
cemented carbide material comprising relatively small carbide
particles having mean size of at most about 10 microns and present
at a sufficiently high content of at least about 80 weight per cent
(i.e. the content of the binder material is at most about 20 weight
per cent) is likely to exhibit relatively small mean free path
between the carbide particles and relatively thin inter-layers of
binder material between them. This may have the consequence that
the binder material has relatively high internal strain, which may
have the effect that reduced ageing times are required to provide
material having the desired combination of hardness and fracture
resistance. If the content of the binder material is substantially
greater than 20 weight per cent and or the mean size of the carbide
particles is substantially greater than about 10 microns, then
reduction of the aging time may result in reduced hardness and or
reduced strength of the cemented carbide material. The
precipitation of nanoparticles may have the effect of enhancing the
erosion and other wear resistance of the cemented carbide material
without substantially compromising the resistance to fracture or
the strength.
[0019] Non-limiting examples will be described with reference to
the accompanying drawings, of which
[0020] FIG. 1 shows a side view of an example tip for a pick for
road planing (also referred to as road milling, pavement
degradation or asphalt recycling);
[0021] FIG. 2 shows a side view of an example pick mounted on a
drum and engaging a body; and
[0022] FIG. 3 shows a partially cut away side view of an example
pick.
[0023] With reference to FIG. 1, an example tip for road planing
consists substantially of cemented tungsten carbide material
according to this disclosure.
[0024] FIG. 2 illustrates an example pick 20 for road planing or
mining, mounted on a drum 40 and engaging a formation 30. The pick
comprises a holder system 22 and cemented carbide tip 10 and is
driven in the general direction F in use. FIG. 3 illustrates an
example pick 50 comprising a holder 52 having a bore 54, and an
insert comprising a polycrystalline diamond (PCD) tip 56 joined to
a support body 58 comprising cemented carbide material disclosed
and shrink-fitted into the holder 52.
[0025] Example cemented carbide material may comprise WC particles
and a Co binder, and may have magnetic moment .sigma. (in units of
micro-Tesla times cubic meter per kilogram) of at least
0.11.times.[Co] and at most 0.137.times.[Co], where [Co] is the
weight per cent content of Co in the cemented carbide material. The
concentration of tungsten [W] dissolved in the binder material,
expressed as weight per cent of the binder material, may be at
least about (16.1-.sigma..sub.B)/ 0.275, where .sigma..sub.B is the
magnetic moment of the binder material, obtained by dividing the
magnetic moment a of the cemented carbide material by the weight
percentage of the binder material in the cemented carbide, which is
equal to [Co] in examples where the binder material consists
essentially of Co.
[0026] Example cemented carbide material may be substantially
devoid of eta-phase, which may have the aspect of enhancing the
strength and fracture resistance of the cemented carbide material.
An eta-phase compound has the formula Mx M'y Cz, where M is at
least one element selected from the group consisting of W, Mo, Ti,
Cr, V, Ta, Hf, Zr, and Nb; M' is at least one element selected from
the group consisting of Fe, Co, Ni, and C is carbon. Where M is
tungsten (W) and M' is cobalt (Co), eta-phase is understood herein
to mean Co3W3C (eta-1) or Co6W6C (eta-2), as well as fractional
sub- and super-stoichiometric variations thereof. There are also
some other phases in the W--Co--C system, such as theta-phases
Co3W6C2, Co4W4C and Co2W4C, as well as kappa-phases Co3W9C4 and
CoW3C (these phases are sometimes grouped in the literature within
a broader designation of eta-phase). Particles comprising Co3W3C,
Co6W6C and or theta phase Co2W4C in the face-centred cubic (fcc)
crystallographic structure may be dispersed in the binder and have
respective mean sizes of about 0.213 nm, 0.209 nm and 0.215 nm. The
presence of these nanoparticles can be detected by means of
electron diffraction patterns using transmission electron
microscopy (TEM). Using dark field TEM, the nano-particles can be
seen as dark spots. The presence of the nanoparticles within the
binder may have the effect of reinforcing the binder.
[0027] Cemented carbide materials may have various compositions. In
some examples, the cemented carbide material may contain at least
about 0.1 weight per cent to about 10 weight per cent vanadium (V),
chromium (Cr), tantalum (Ta), titanium (Ti), molybdenum (Mo),
niobium (Nb) and or hafnium (Hf), which may be in the form of a
solid solution in the binder material and or in the carbide form.
Nanoparticles dispersed in the binder material may comprise V, Cr,
Ta, Ti, Mo, Nb and or Hf. In some examples, the cemented carbide
may contain at least 0.01 weight per cent and at most 5 weight per
cent of one or more metals selected from Ru, Rh, Pd, Re, Os, In,
and or Pt. Nanoparticles dispersed in the binder material may
comprise Ru, Rh, Pd, Re, Os, In and or Pt.
[0028] Example cemented carbide material may contain diamond of
cubic boron nitride (cBN) particles. The diamond or cBN particles
may be present at 3 volume per cent to 60 volume per cent and may
be provided with coating comprising a carbide, carbonitride and or
nitride compound of Ti, Ta, Nb, W, Mo, V, Zr, Hf and or Si.
[0029] In example cemented carbide materials, the nanoparticles may
be coherent with the crystal lattice of the binder material and or
the nanoparticles may at least partly have a cubic crystal lattice
structure.
[0030] In one version of an example method for making cemented
carbide material, the sintered body may be provided by a method
including milling WC powder with Co powder (and optionally other
metals or their carbides, nitrides and or carbo-nitrides) to form a
mixture, the powders selected to provide the mixture having
equivalent total carbon content in the range from about 5.70 weight
per cent to about 6.05 weight per cent; compacting the mixture to
form a green body; sintering the green body at a temperature in the
range from about 1,350 degrees centigrade to about 1,500 degrees
centigrade and providing a sintered body having a magnetic
saturation in the range from about 70 per cent to about 82 of the
theoretical value of that of nominally pure Co, i.e. 16.1
.mu.Tm.sup.3/kg. The equivalent total carbon (ETC) in a mixture is
the content of carbon in the mixture, the content being in excess
of the carbon included in WC, expressed as a proportion of carbon
in the whole mixture. The WC powder may comprise WC particles
having a mean size D of at least about 0.5 microns and at most
about 10 microns. An organic binder material such as paraffin wax
may be introduced into the mixture prior to compaction and the
green body should be heat treated prior to sintering to remove
binder material. The green body may be sintered in a vacuum and or
in an atmosphere comprising inert gas such as argon (Ar), by means
of a hot isostatic press (HIP), for example. The ratio [C]/[W] of
the content of carbon present in the binder material [C] to the
content of tungsten present in the binder material [W] will be less
than 1 and the W content dissolved in the binder material of the
sintered body may be at least about 10 weight per cent and may lie,
for example, in the range from 11.7 weight per cent to 17.6 weight
per cent of the binder material.
[0031] The amount of C and W dissolved in the binder material of
the sintered body may be controlled in a number of ways, such as
adding W to the starting powders, using non-stochiometric starting
tungsten carbide powder, carburisation/decarburisation of the green
body. The ratio of [C]/[VV] may be very low, which may be expected
to result in the precipitation of particles of eta phase compounds
in the binder material during the step of sintering the green
body.
[0032] In some versions of the method, the content of WC particles
comprised in the sintered body may be at least about 80 weight per
cent, at least about 85 weight per cent or at least about 90 weight
per cent, and the content of the binder material may be at most
about 25 weight per cent, at most about 20 weight per cent, at most
about 15 weight per cent or at most about 10 weight per cent. In
one version of the method, the WC particles may have a mean size of
at least about 2 microns. In some versions of the method, the
binder material may comprise iron (Fe) or (Ni), or an alloy
including at least one of Fe or Ni, and or Co.sub.7Ni.
[0033] In some versions of the method, the sintered body may have a
magnetic moment (or magnetic saturation) of at least about 70 per
cent and or at most about 85 per cent of the theoretical value of
binder material comprising nominally pure Co or an alloy of Co and
Ni, as the case may be. So for example, where the binder consists
substantially of Co, the sintered body may have a magnetic
saturation of at least about 0.7.times.201.9 .mu.T.m.sup.3/kg=141
.mu.T.m.sup.3/kg; and at most about 0.85.times.201.9
.mu.T.m.sup.3/kg =172 .mu.T.m.sup.3/.
[0034] The sintered body may be heat treated at a temperature in
the range from about 500 degrees centigrade to about 900 degrees
centigrade for a period of time; the period in hours being at least
about (0.8.times.D)-0.15 and at most about (4.3.times.D)-1.7, to
produce a body having a magnetic saturation at least 1 per cent
less than that of the sintered body and a magnetic coercive force
at least about 20 per cent greater than that of the sintered body.
The substantial increase in the magnetic coercive force is expected
to indicate the precipitation of nanoparticles comprising a
non-magnetic material phase. Some versions of the method include
heat treating the sintered body at a temperature of at least about
600 degrees centigrade and or at most about 800 degrees centigrade
for the period of time.
[0035] A tool comprising cemented tungsten carbide material as
disclosed can be provided, for example a tool for pavement
degradation, road planing, asphalt recycling, road reconditioning
or mining can be provided. The tool may also comprise
polycrystalline diamond (PCD) material or polycrystalline cubic
boron nitride (PCBN) material, and may be a cutter element for
machining, boring into or degrading bodies comprising metal,
asphalt, stone, rock, concrete or composite material.
[0036] For example, a tip for a pick may be provided, the tip
comprising or consisting substantially of cemented carbide material
as disclosed. A pick comprising the tip can be provided. A pick
comprising a super-hard tip such as polycrystalline diamond (PCD)
joined to a support body comprising cemented carbide material as
disclosed can also be provided, the super-hard material having
Vickers hardness of at least about 28 GPa. Wear parts, drill bits
and machine tools comprising the disclosed cemented carbide
material can also be provided.
[0037] As used herein in relation to grains or particles such as WC
grains comprised in hard-metal material, the term "grain size" d
refers to the sizes of the grains measured as follows. A surface of
a body comprising the hard-metal material is prepared by polishing
for investigation by means of electron backscatter diffraction
(EBSD) and EBSD images of the surface are obtained by means of a
high-resolution scanning electron microscope (HRSEM). Images of the
surface in which the individual grains can be discerned are
produced by this method and can be further analysed to provide the
number distribution of the sizes d of the grains, for example. As
used herein, no correction (e.g. Saltykov correction) is applied to
correct the grain sizes to account for the fact that they were
obtained from a two dimensional image in this way. The grain size
is expressed in terms of equivalent circle diameter (ECD) according
to the ISO FDIS 13067 standard. The ECD is obtained by measuring of
the area A of individual grains exposed at the surface and
calculating the diameter of a circle that would have the same area
A, according to the equation d=square root of (4.times.A /.pi.).
The method is described further in section 3.3.2 of ISO FDIS 13067
entitled "Microbeam analysis--Electron Backscatter
Diffraction--Measurement of average grain size" (International
Standards Organisation, Geneva, Switzerland, 2011). The mean grain
size D of WC grains in cemented WC material is obtained by
calculating the number average of the WC grain sizes d as obtained
from the EBSD images of the surface. The EBSD method of measuring
the sizes of the grains has the significant advantage that each
individual grain can be discerned, in contrast to certain other
methods in which it may be difficult or impossible to discern
individual grains from agglomerations of grains. In other words,
certain other methods may be likely to give false higher values for
grain size measurements.
[0038] The amount of tungsten dissolved in cobalt-based binder
material can be measured indirectly, by measurement of magnetic
moment (or magnetic saturation) of cemented carbides because the
magnetic saturation of Co decreases in inverse proportion to the
content of tungsten in solution. The concentration of tungsten
dissolved in the binder tends to be higher, the lower the total
carbon content, so that the magnetic moment shows indirectly the
total carbon content in cemented carbides.
[0039] The magnetic saturation Ms is proportional to
[C]/[W].times.[Co].times.201.9 in units of .mu.T.m.sup.3/kg, where
[VV] and [C] are the concentrations of W and C, respectively, in
the binder material and [Co] is the weight per cent of Co in the
cemented carbide material. For example, the W concentration at low
C contents is significantly higher. The magnetic saturation of a
hard metal, of which cemented tungsten carbide is an example, is
defined as the magnetic moment per unit weight, .sigma., as well as
the induction of saturation per unit weight, 4.pi..sigma.. The
magnetic moment, .sigma., of pure Co is 16.1 micro-Tesla times
cubic metre per kilogram (.sigma.T.m.sup.3/kg), and the magnetic
saturation, 4.pi..sigma., of pure Co is 201.9 .mu.T.m.sup.3/kg.
[0040] The content of Co in the binder material of cemented carbide
material can be measured by various methods well known in the art,
including indirect methods such as such as the magnetic properties
of the cemented carbide material or more directly by means of
energy-dispersive X-ray spectroscopy (EDX), or the most accurate
method is based on chemical leaching of Co.
[0041] Non-limiting examples of cemented carbide material are
described in more detail below.
EXAMPLE 1
[0042] Ultra-coarse WC powder with mean grain size (the Fischer
number) of 40.8 microns (MAS3000-5000.TM. from H.C.Starck.TM.,
Germany) and super-stoichiometric carbon content of 6.12 weight
percent was blended with about 9.7 weight percent Co powder and
about 2 weight percent W metal powder. Both the W powder and the Co
powder had a mean particle size of about 1 micron. The composition
of the combined powders was therefore 88.3 weight percent WC
(including the excess carbon), 9.7 weight percent Co and 2 weight
percent W. The Equivalent Total Carbon (ETC) of the mixture with
respect to WC was 6.0 weight percent. The powders were milled
together for 10 hours by means of a ball mill in a milling medium
comprising hexane with 2 weight percent paraffin wax, using a
powder-to-ball ratio of 1:3. The powder was dried and green bodies
for sintering bodies configured for carrying out transverse rupture
strength (TRS) measurement according to the ISO 3327-1982 standard
and wear-resistance measurement according to the ASTM B611-85
standard were prepared by compacting the powder mixture. The green
bodies were sintered at 1,420 degrees centigrade for 75 minutes for
produce sample sintered bodies. The sintering cycle including a 45
minute vacuum sintering stage and a 30 minute hot isostatic
pressure (HIP) sintering stage carried out in an argon atmosphere
at a pressure of 40 bars.
[0043] Metallurgical cross-sections of some of the sample bodies
were made for examination of the microstructure, the Vickers
hardness, the micro-hardness and nano-hardness of the sample
bodies. The binder nano-hardness was measured by means of add-on
depth-sensing nano-indentation. Spatial and depth-resolved
information about the micro-mechanical properties of the binder was
measured by means of a nano-indentation device (Hysitron
TriboScope.TM.) mounted on a scanner head of an atomic force
microscope (AFM) (Park Scientific Instruments, AutoProbe CP.TM.).
The direct combination of the nano-indentation device with AFM
allows imaging and indenting the surface with the tip, which
enables the tip to be positioned for indentation with an accuracy
of down to 20 nm. The measurements were carried out at a load of
500 micro-Newton using a Bercovich Indenter.TM.. Transmission
electron microscopy (TEM) and high-resolution TEM (HRTEM) studies
of the binder were carried out on the JEOL-4000FX instrument.
[0044] The microstructure was found to comprise only WC and the
binder material; no eta-phase or free carbon was found. The WC mean
grain size obtained on the basis of the EBSD mapping images was
about 3.1 microns.
[0045] The density of the cemented carbide was about 14.54
g/cm.sup.3, the TRS was 2,050 MPa, the Vickers hardness (HV30) was
10.5 GPa, the magnetic coercive force was 4.8 kA/m (60 Oe), the
magnetic moment .sigma. was 1.16 .mu.T.m.sup.3/kg, the magnetic
saturation 4.pi..sigma. was 14.6 .mu.T.m.sup.3/kg and the wear rate
was 1.9.times.10.sup.-4 cm.sup.3/revolution. The nano-hardness of
the binder material was 7.5 GPa. TEM images of the binder material
indicated the presence of only the face-centred cubic (fcc)
crystallographic structure of Co, indicating the substantial
absence of nanoparticles in the binder material.
[0046] Some of the remaining sample bodies were heat-treated in a
vacuum at 600 degrees centigrade for 10 hours, following which
these samples were analysed as described above. The appearance of
the microstructure of the cemented carbide under visible light had
not substantially changed. The TRS of the of the heat treated
cemented carbide material had increased substantially to 3,200 MPa,
the Vickers hardness (HV30) had increased to 11.5 GPa, the magnetic
coercive force had increased substantially to 13.4 kA/m (168 Oe),
the magnetic moment a was 1.11 .mu.T.m.sup.3/kg, the
correspondingly magnetic saturation 4.pi..sigma. was 13.9 .mu.T
m.sup.3/kg and the wear rate had decreased substantially to
0.6.times.10.sup.-4 cm.sup.3/revolution. The nano-hardness of the
binder had increased to 10.2 GPa. Therefore, the wear resistance
(the ASTM B611 test) of the cemented carbide with the binder
comprising the nanoparticles was found to be higher than that with
that without nanoparticles by about 40%. As a result of the
heat-treatment, the magnetic moment had noticeably decreased (by
about 4 percent) and the magnetic coercive force had significantly
increased (by a factor of nearly 2.8), providing evidence for the
precipitation of nanoparticles consisting of a non-magnetic phase
in the binder material. This seems to have resulted in a dramatic
increase of nano-hardness of the binder material and significantly
higher hardness and improved wear resistance of the cemented
carbide material. The strength (TRS) of the cemented carbide
material had also significantly increased after the
heat-treatment.
[0047] TEM images of the binder material indicated the presence of
reflections from fcc Co and satellite reflections corresponding to
the nanoparticles. The dark field TEM image of the binder material
obtained using the satellite reflections indicated the presence of
nanoparticles having size in the range from about 0.5 to about 7
nm. The mean grain size of the nanoparticles is measured by the
linear intercept method and was found to be equal to 3.1 nm and the
percentage of nanoparticles having size less than 3 nm was found to
be 39 per cent. The nanoparticles are believed to correspond to
eta- (Co3W3C or Co6W6C) or theta-phases (Co2W4C). Although the
crystal lattice of these phases is very similar, the inter-lattice
constant corresponded more closely to that of the theta-phase the
best of all.
EXAMPLE 2
[0048] A sample body was prepared as described in Example 1, except
that the WC powder was blended with about 6.2 weight percent Co
powder and about 2 weight percent W metal powder.
EXAMPLES 3 to 11
[0049] Sample bodies comprising a different grade of cemented
carbide material were made, in which the WC had a mean grain size
of about 1 micron and the content of Co was about 13 weight
percent. These bodies were heat treated at temperatures from 600
degrees centigrade to 800 degrees centigrade for various periods of
time from 0.5 hour, 1 hour and 2 hours as shown in table 1 below.
The density, magnetic saturation and magnetic coercive force of the
sintered body were measured before ageing and after ageing. Before
ageing, the density of the sintered bodies was 14.3 g/cm.sup.3, the
magnetic saturation was 16.2 G.cm.sup.3/g and the magnetic coercive
force was 144 Oe. The table below also shows the respective
density, magnetic saturation, magnetic coercive force and Vickers
hardness for each of the sample bodies aged at different
conditions.
TABLE-US-00001 TABLE 1 Ageing temperature, Magnetic Magnetic
degrees Ageing saturation, coercive Example centigrade time, hours
G cm.sup.3/g force, Oe 3 600 1 15.6 261 4 600 2 15.5 286 5 680 1
15.7 207 6 680 2 15.7 209 7 750 0.5 15.4 190 8 750 1 15.7 152 9 800
0.5 15.5 159 10 800 1 15.8 155 11 800 2 15.9 151
[0050] In order to observe the effect of longer aging periods,
samples of the material were heat treated for cumulative periods of
5 hours and 10 hours at each of 600 degrees centigrade, 680 degrees
centigrade and 800 degrees centigrade, and these results are shown
in table 2 below.
TABLE-US-00002 TABLE 2 For Ageing comparison temperature, Magnetic
Magnetic with degrees Ageing saturation, coercive Example
centigrade time, hours G cm.sup.3/g force, Oe 3 and 4 600 5 15.4
270 3 and 4 600 10 15.4 297 5 and 6 680 5 15.6 203 6 and 7 680 10
15.6 195 9, 10 and 11 800 5 15.8 142 9, 10 and 11 800 10 15.9
139
[0051] The magnetic coercive force increased substantially after
just 0.5 hours of ageing at 600 degrees centigrade, indicating the
precipitation of highly dispersed particulates in the binder
material. However, the further ageing did not result in
substantially further increase in magnetic coercive force.
[0052] Various example embodiments of pick tools and methods for
assembling and connecting them have been described above. Those
skilled in the art will understand that changes and modifications
may be made to those examples without departing from the scope of
the claimed invention.
* * * * *