U.S. patent application number 15/305760 was filed with the patent office on 2017-03-16 for method of making cermet or cemented carbide powder.
The applicant listed for this patent is SANDVIK INTELECTUAL PROPERTY AB. Invention is credited to Magnus EKELUND, Carl-Johan MADERUD, Johan SUNDSTROM.
Application Number | 20170072469 15/305760 |
Document ID | / |
Family ID | 50513823 |
Filed Date | 2017-03-16 |
United States Patent
Application |
20170072469 |
Kind Code |
A1 |
MADERUD; Carl-Johan ; et
al. |
March 16, 2017 |
METHOD OF MAKING CERMET OR CEMENTED CARBIDE POWDER
Abstract
A method of making a powder of dense and spherically shaped
cemented carbide or cermet granules and a powder produced by the
method is provided. The powder made according to the present method
can be used in additive manufacturing such as 3D printing by the
binder jetting technique. Moreover, a Hot Isostatic Pressing (HIP)
process for manufacturing a product by using the powder is also
disclosed.
Inventors: |
MADERUD; Carl-Johan;
(Stockholm, SE) ; SUNDSTROM; Johan; (Lovstabruk,
SE) ; EKELUND; Magnus; (Jarna, SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SANDVIK INTELECTUAL PROPERTY AB |
Sandviken |
|
SE |
|
|
Family ID: |
50513823 |
Appl. No.: |
15/305760 |
Filed: |
April 23, 2015 |
PCT Filed: |
April 23, 2015 |
PCT NO: |
PCT/EP2015/058790 |
371 Date: |
October 21, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B33Y 70/00 20141201;
B22F 3/1055 20130101; B22F 3/1003 20130101; B22F 1/0048 20130101;
B22F 3/15 20130101; B22F 7/06 20130101; B22F 9/04 20130101; B22F
2302/10 20130101; B33Y 40/00 20141201; C22C 29/02 20130101; B33Y
10/00 20141201; B22F 3/1216 20130101; B22F 3/1021 20130101; B22F
2999/00 20130101; B22F 1/0085 20130101; C22C 29/08 20130101; B22F
2998/10 20130101; Y02P 10/25 20151101; B28B 3/003 20130101; B22F
2301/15 20130101; B22F 1/0014 20130101; C22C 29/16 20130101; C22C
29/10 20130101; B22F 2998/10 20130101; C22C 1/051 20130101; B22F
1/0085 20130101; B22F 3/1021 20130101; B22F 3/1003 20130101; B22F
2999/00 20130101; C22C 1/051 20130101; B22F 9/026 20130101 |
International
Class: |
B22F 3/15 20060101
B22F003/15; B33Y 70/00 20060101 B33Y070/00; B33Y 10/00 20060101
B33Y010/00; B28B 3/00 20060101 B28B003/00; B22F 9/04 20060101
B22F009/04; B22F 3/10 20060101 B22F003/10; C22C 29/02 20060101
C22C029/02; B22F 7/06 20060101 B22F007/06; B33Y 40/00 20060101
B33Y040/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 24, 2014 |
EP |
14165842.7 |
Claims
1. A method of making a powder of dense and spherically shaped
cermet or cemented carbide granules, wherein the method comprises
the steps of: (a) forming spherically shaped granules comprising
metal, hard constituents and organic binder; (b) mixing said
spherically shaped granules with a sintering inhibitor powder to
form a mixture of spherically shaped granules and sintering
inhibitor powder; (c) loading the mixture of spherically shaped
granules and sintering inhibitor powder in a furnace chamber; (d)
heat-treating the mixture obtained in step (b) in the furnace
chamber at a sintering temperature to remove organic binder from
the spherically shaped granules and to sinter the hard constituents
with the metal in each spherically shaped granule and thereby
forming a mixture of sintered dense spherically shaped granules and
sintering inhibitor powder; (e) unloading the mixture of sintered
dense spherically shaped granules and sintering inhibitor powder
from the furnace chamber; and (f) separating the sintering
inhibitor powder from the sintered dense spherically shaped
granules whereby a powder of dense and spherically shaped cermet or
cemented carbide granules is formed.
2. The method in accordance with claim 1, wherein the porosity
inside each cermet or cemented carbide dense spherically shaped
granule is less than 5 vol %.
3. The method in accordance with claim 1, wherein the granule size
of the sintered dense spherically shaped granules of the cermet or
cemented carbide powder is of from 1 to 500 .mu.m.
4. The method in accordance with claim 1, wherein the heat
treatment in the furnace chamber is performed at a sintering
temperature above a solidus temperature of the metal in the
spherically shaped granules.
5. The method in accordance with claim 4, wherein the heat
treatment in the furnace chamber is performed at a sintering
temperature of from 30 to 100.degree. C. above the solidus
temperature of the metal in the spherically shaped granules.
6. The method in accordance with claim 1, wherein the inhibitor
powder includes an oxide.
7. The method in accordance with claim 1, wherein the inhibitor
powder includes carbon.
8. The method in accordance with claim 1, wherein the inhibitor
powder is separated from the sintered dense spherically shaped
granules by sieving, air classification, hydrocyclone, flotation
and/or fluidization.
9. The method in accordance with claim 7, wherein the inhibitor
powder is separated from the sintered dense spherically shaped
granules by a thermochemical method using a gas at elevated
temperature.
10. The method in accordance with claim 9, wherein the
thermochemical method is performed in a rotating tube furnace or in
a fluidized bed furnace.
11. A powder of cermet or cemented carbide made in accordance with
the method of claim 1.
12. The powder made in accordance with claim 11, wherein the powder
is used in Additive Manufacturing.
13. The powder made in accordance with claim 11, wherein the powder
is used in a HIP application.
14. A process for manufacturing a component comprising the
following steps: (a) providing a powder in accordance with claim
11; (b) providing a form; (c) filling the form with the powder; (d)
evacuating air from the form; (e) sealing the form; and (f)
subjecting the form to Hot Isostatic Pressing (HIP) at a
predetermined temperature, a predetermined pressure and for a
predetermined time so that the powder in accordance with claim 11
bond metallurgically and a solid body is formed, wherein the form
is made of an alloy of zirconium or an alloy of titanium.
15. The process according to claim 14, wherein the powder has a
continuous particle size distribution in the range of from 1 to 500
.mu.m.
16. The process according to claim 14, wherein the predetermined
temperature is above 900.degree. C.
17. The process according to claim 14, wherein the predetermined
pressure is above 500 bar.
18. The process according to claim 14, wherein said process is used
for manufacturing a cemented carbide or cermet.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to a method of making a
powder of dense and spherically shaped cemented carbide or cermet
granules. The present disclosure also relates to a powder produced
by the method and use of said powder in additive manufacturing such
as 3D printing by the binder jetting technique.
[0002] Furthermore, the present disclosure relates to a Hot
Isostatic Pressing (HIP) process for manufacturing a product by
using said powder.
BACKGROUND
[0003] Additive manufacturing alias 3D (three dimensional) printing
is a process of making three-dimensional solid components from a
digital model using an additive process. In such a process layers
of material are successively laid down and the component is built
up layer by layer. 3D printing differs from traditional machining
techniques in that it is a process building up the shape, whereas
traditional machining typically relies on the removal of material
from a work piece by methods such as cutting or drilling and
thereby forming the final shape.
[0004] In an example of a binder jetting type of 3D printing
process a first layer of powder, is spread over a surface. A liquid
binder is deposited (printed) over the surface in a pattern
predetermined by a digital model. A second layer of powder is
spread out for the next predetermined pattern to be printed. This
process is repeated until the forming of the 3D printed green body
is completed. A subsequent curing process for improving the
strength of certain thermosetting polymers might also be required.
The 3D printed green body is after removal of loose (binder-less)
powder ready for a subsequent debinding and sintering process. For
example components of cermet, cemented carbide or metal can be
produced by the described procedure. The final density and quality
of the sintered product depends on for example the sintering
conditions and the powder properties. An example of making cermets
with a 3D method from a powder is disclosed in "(Ti,W)C--Ni cermets
by laser engineered net shaping" by Y. Xiong et al published in
Powder Metallurgy 2010, vol 53, No. 1, page 41-46.
[0005] There is a continuous need of making it possible to produce
high quality products of cermets or cemented carbide with 3D
printing techniques. This implies high demands on the powder to be
used in the process. Examples of features that are to be controlled
in the final production of a component are the grain size, the
porosity and the shape retention and shrinkage of the product. This
implies high demands on the powder to be used since the quality and
properties of the powder is essential for the quality of the final
component.
SUMMARY OF THE DISCLOSURE
[0006] It is an aspect of the present disclosure to provide a
method of making a powder that can be used in 3D printing for
production of cermet or cemented carbide products. A further aspect
is to provide a method of making a powder that overcomes at least
some of the above mentioned demands. A further aspect of the
present disclosure is to present a HIP process using the powder as
defined hereinabove or hereinafter which will provide cemented
carbides or cermets with enhanced hardness and wear resistance.
[0007] These aspects are achieved by a method according to claim 1
and a powder in accordance with claim 11 and a process according to
claim 14. Preferred embodiments are disclosed in the dependent
claims.
[0008] One advantage with the method according to claim 1 is that
it is possible to convert powder of spherically shaped granules
comprising agglomerated (porous) constituents of cermet or cemented
carbide to a powder comprising dense and spherically shaped cermet
or cemented carbide granules. Said powder may be produced with less
problems of granules sticking or sintering together (hereafter
denoted "inter-granule sintering") since the inhibitor powder
prevents contact between individual spherically shaped granules
during the sintering densification. Inter-granule sintering
typically causes the sintered powder to stick together and thereby
co-sintered granule agglomerates or even a sintered cake of the
powder is formed. A sintered powder cake could possibly be milled
to form a powder again with a certain degree of breakage of
granules, loss of the spherical shape of some granules and a
decreased amount of the finest spherical granules.
[0009] Another advantage of the method as defined hereinabove or
hereinafter is that the spherical shape from the granulated state
as porous granules can be preserved during sintering and thus
resulting in a powder comprising dense and spherically shaped
cermet or cemented carbide granules. A spherical shape of the
granules is advantageous as a powder of spherically shaped granules
has good flowing properties and good packing properties.
[0010] Further, another advantage of the method as defined
hereinabove or hereinafter is that the produced powder of dense and
spherically shaped cermet or cemented carbide granules exhibits a
high or even full density in every granule and therefore the total
volume of pores in a 3D printed body would be less than the total
volume would be if using porous and less densely packed cermet or
cemented carbide granules. Such aspects of density have large
impact on the shrinkage and ability to conform to the predicted
body geometry after a subsequent sintering or HIP process. It is to
be noted that larger hollow space in a granule originating from a
spray drying might still exist.
[0011] Further, yet another advantage of the method as defined
hereinabove or hereinafter is that the produced powder in virtue of
the dense and spherically shaped cermet or cemented carbide
granules confers high packing density to the green body. This is
advantageous due to limited shrinkage during a subsequent sintering
treatment of the green body.
[0012] Furthermore, a high packing density promotes the achievement
of a high sintered density, which can be decisive for the
achievement of a closed porosity (i.e. not inter-connected
porosity). Only by the obtained state of closed porosity, the body
can be further densified to full density by a subsequent
post-sintering HIP process.
[0013] A powder produced in accordance with the present disclosure
can be used in powder metallurgy (PM) area for example for
manufacturing of near net shaped cermet or cemented carbide
components. The application area of the present disclosure is as
powder feedstock for binder jetting 3D-printing techniques and also
near net shape HIP of encapsulated powder. Alternatively, the
powder can be used in other types of additive manufacturing
techniques as well as other PM-techniques in general.
[0014] One advantage with the process as defined hereinabove or
hereinafter is that the obtained component can be a fully dense
net- or near net shaped component, thus the obtained component will
almost have no voids or have no voids.
[0015] Another advantage with the process as defined hereinabove or
hereinafter is that when zirconium alloy or titanium alloy is used
as capsule material, a layer of ZrC or TiC is formed in the contact
interface between the capsule and the cemented carbide or cermet.
This carbide layer is dense and has almost no cracks and prevents
therefore most of the interdiffusion between the capsule and the
powder as defined hereinabove or hereinafter. Thus, this carbide
layer thereby limits the loss of carbon from the cemented carbide
or the cermet to the capsule material and maintains the chemical
balance and stability of the cemented carbide or cermet.
Furthermore, this carbide layer provides conditions to avoid
formation of low carbon containing carbides such as e.g. M2C, M6C
and M12C. Thus, different grades of the Zr (Zirconium) or Ti
(Titanium) alloy may be used for capsule material. Also, pure Ti or
pure Zr may be used as capsule material.
[0016] Other aspects, advantages and novel features of the
disclosure will become apparent from the following detailed
description of the disclosure when considered in conjunction with
the accompanying drawings and claims.
BRIEF DESCRIPTION OF DRAWINGS
[0017] FIGS. 1 shows a Scanning Electron Microscope (SEM) image at
about 1500.times. magnification of dense cemented carbide granules
made in accordance with Example 2.
[0018] FIG. 2 shows an image of a cross-section of an interface
between a Zr capsule and a cemented carbide component that has been
obtained according to the process as defined hereinabove or
hereinafter, wherein 1=Zr; 2=ZrC; 3=Prior Zr-rich Zr/Co-eutectic
area; 4=sub-carbide phase; 5=Prior particles; 6=Squeezed out
Co-binder phase.
DEFINITIONS
[0019] The term "cermet" is herein intended to denote a material
comprising a ceramic phase, i.e. hard constituents, and a metallic
binder phase.
[0020] The term "cemented carbide" is herein intended to denote a
material comprising a ceramic phase, i.e. hard constituents, and a
metallic binder phase, where the ceramic phase comprises WC and the
metallic phase comprises Co and optionally one or more of Ni, Fe,
Cr and Mo.
[0021] The term "granule" refers to the agglomerated state of a
mixture that is produced by e.g. spray drying.
[0022] The term "dense granule" refers to the sintered and
densified granule.
[0023] The term "sintering" is a generic term for a process wherein
heating under controlled atmosphere is conducted in order to
minimize the surface of a particulate system, which mostly is
associated with generation of bonds between neighboring particles
or granules and shrinkage of the aggregated particles or
granules.
[0024] The term "intra-granule sintering" refers to the sintering
inside a granule causing the individual granules to densify and
shrink and to form a dense and spherically shaped granule.
[0025] The term "inter-granule sintering" refers to the creation of
sintering bonds between neighboring granules.
[0026] The term "green body" refers to a body comprising granules
that are bonded by organic binder.
[0027] The term "solidus" refers to a certain temperature that when
being exceeded leads to the inception of liquid phase
formation.
[0028] The term "about" as used herein is intended to mean +/-10%
of the numerical value.
DETAILED DESCRIPTION OF THE DISCLOSURE
[0029] The present disclosure relates to a method of making a
powder of dense and spherically shaped cermet or cemented carbide
granules, wherein the method comprises the steps of: [0030] (a)
forming spherically shaped granules comprising metal, hard
constituents and organic binder; [0031] (b) mixing said spherically
shaped granules with a sintering inhibitor powder to form a mixture
of spherically shaped granules and sintering inhibitor powder;
[0032] (c) loading the mixture of spherically shaped granules and
sintering inhibitor powder in a furnace chamber; [0033] (d)
heat-treating the mixture obtained in step (b) in the furnace
chamber at a sintering temperature to remove organic binder from
the spherically shaped granules and to sinter the hard constituents
with the metal in each spherically shaped granule and thereby
forming a mixture of sintered dense spherically shaped granules and
sintering inhibitor powder; [0034] (e) unloading the mixture of
sintered dense spherically shaped granules and sintering inhibitor
powder from the furnace chamber; and [0035] (f) separating the
sintering inhibitor powder from the sintered dense spherically
shaped granules whereby a powder of dense and spherically shaped
cermet or cemented carbide granules is formed.
[0036] The forming of spherically shaped granules comprising metal,
hard constituents and organic binder is preferably performed by
spray drying. The organic binder can for example be PEG
(polyethylene glycol). The metal is typically Cobalt (Co) or a
mixture of Co and one or more of Nickel (Ni), Iron (Fe), Chromium
(Cr) and Molybdenium (Mo). The hard constituents may for example be
WC, TiC, TiN, Ti(C,N) and/or NbC. The step of providing the
granules with a spherical shape is important since the subsequent
heating process will ideally make the granules to shrink but
preserve their original spherical shape.
[0037] The step of mixing the spherically shaped granules with a
sintering inhibitor powder to form a mixture of spherically shaped
granules and sintering inhibitor powder may be performed in a
conventional mixing equipment, but care should be taken not to
deform the spherical shape of the granules or to unintentionally
reduce the size of the spherically shaped granules.
[0038] The step of loading the mixture of spherically shaped
granules and sintering inhibitor powder in a furnace chamber may
typically be performed by placing said mixture in a tray or in a
vessel that can be loaded in the furnace chamber.
[0039] The step of heat-treating the mixture of spherically shaped
granules and sintering inhibitor in the furnace chamber at a
sintering temperature is performed in order to remove the organic
binder from the spherically shaped granules and to sinter the hard
constituents with the metal in each spherically shaped granule and
thereby form a mixture of sintered dense spherically shaped
granules and sintering inhibitor powder. At an initial stage of the
sintering, typically even before the sintering temperature has been
reached, the organic binder will evaporate and will leave the
spherically shaped granules by degassing. At the sintering
temperature, the metal and the hard constituents will sinter and
form dense spherically shaped granules.
[0040] The step of unloading the mixture of sintered dense
spherically shaped granules and sintering inhibitor powder from the
furnace chamber may be performed after a cooling step wherein the
mixture of sintered dense spherically shaped granules and sintering
inhibitor powder has reached a temperature of about room
temperature.
[0041] The step of separating the sintering inhibitor powder from
the sintered spherically shaped dense granules may be performed in
one or several subsequent steps using one or several techniques.
The result from the separation is a powder of dense and spherically
shaped cermet or cemented carbide granules and a separate inhibitor
powder. The inhibitor powder may preferably be reused in a
subsequent process following the method in accordance with the
present disclosure.
[0042] The purpose of the inhibitor powder is to prevent the
spherically shaped granules from building inter-granule bonds
during sintering. Without any sintering inhibitor powder, strong
inter-granule bonds will be formed during sintering at temperatures
above the solidus temperature of the metal. Mechanical forces must
then be applied (e.g. in a disintegrator mill) in order to break
the inter-granule bonds. However, during such an operation, a
certain fraction of the granules will most probably be cracked and
fractured, whilst yet another fraction might not be separated into
their individual granule entities. The latter case is mostly
evident for the finest granules that are difficult to break apart
from other fine granules or those bigger in size. Hence, the degree
of sphericity will be decreased under these circumstances. The
usage of inhibitor powder in the sintering heat-treatment will
allow intra-granule sintering while avoiding the extent of
inter-granule sintering. Thus, making it possible to produce cermet
or cemented carbide granules that are both dense and spherical in a
cost effective manner.
[0043] One advantage with the method in accordance with the present
disclosure is that it is possible to produce a powder of dense and
spherically shaped granules with a wide granule size distribution
and/or with a considerable amount of small granules (<30 .mu.m).
Without the use of sintering inhibitor in accordance to the present
disclosure, it becomes subsequently very difficult to separate
these small dense granules from each other or from larger granules
by milling or other methods. This leads to a decreased amount of
fine dense granules in the powder. One important advantage with
using sintering inhibitor powder is that the granules can be
sintered at high temperatures (far exceeding the solidus
temperature) without the disadvantage associated to such high
temperatures when sintering without inhibitor powder. This freedom
may be of importance, especially if the furnace is lacking the
ability to control temperature in a precise manner throughout the
furnace charge; but may also be of importance for the purpose of
high throughput rate in the furnace. A high throughput rate means
here as fast sintering cycle as possible, being equivalent with
high heating loads that inevitably leads to high overheating in
some parts of the batch relative others. Without the use of
sintering inhibitor, the temperature control of the batch must be
very precise, probably within +/-5.degree. C., in order to adjust
between the opposing goals of achieving high density granules
versus avoiding too hard sintered cake.
[0044] The inhibitor powder has to be adapted in particle size and
in amount to reach the advantageous effects as associated with the
present disclosure. The average particle size of the inhibitor
powder should preferably not be larger than the average spherically
shaped granule size, since the mixing of the powders would then
most probably not lead to full separation of the spherically shaped
granules and thereby not fulfil the object of inter-granule
sintering inhibition. The amount of inhibitor powder needed to
separate the spherically shaped granules from each other during the
sintering step demands an optimization to be performed by the
person skilled in the art. The amount of inhibitor powder needs to
be high enough to separate the spherically shaped granules but not
more than necessary in order to maintain high throughput through
the furnace.
[0045] In one embodiment of the present disclosure, the porosity
inside each dense cermet or cemented carbide spherically shaped
granule is less than 5 vol %, such as <1 vol %, such as <0.5
vol %. A low porosity is advantageous in applications benefitted by
high green body densities and for which the obtainment of a high
green density depends upon solid incompressible granules' ability
to redistribute into a dense packing arrangement (e.g. gauged by
TAP density). In such applications, the internal porosity of the
spherically shaped granules adds to the porosity between the
granules to make up the overall porosity and thereby shrinkage of
the finally produced dense body. 3D printing by binder jetting and
HIP constitute examples of such applications.
[0046] In one embodiment of the present disclosure, the size of the
sintered dense spherically shaped granules in the cermet or
cemented carbide powder is distributed between 1-500 .mu.m, more
typically between 5-200 .mu.m. Alternatively, the sintered dense
spherically shaped granules are <50 .mu.m, such as <30 .mu.m.
When using this powder for 3D printing of green bodies aimed to
become subsequently sintered to almost full density or at least
closed porosity, the spherically shaped granule size is preferably
below 50 .mu.m, such as below 30 .mu.m. But even more important for
such an application, the granule size fraction below 10 .mu.m
constitutes more than 10 wt % or more preferably 20 wt % of the
complete distribution. In HIP applications the preferred continuous
particle size distribution of the spherically shaped granules size
is in the range of from about 5 to about 500 .mu.m, such as about
10 to about 200 .mu.m.
[0047] A narrow granule size distribution may be advantageous in
virtue of less segregation problems, e.g. during handling, storage
and transferring of the powder. A wide granule size distribution
can be advantageous in applications relying on high green strength
and high green density; e.g. in HIP when a capsule is being filled
with powder having a wide distribution will obtain a higher packing
density compared to a more narrowly distributed granule size. On
the other hand, if the free flowing properties are of prime
interest for the given application a narrow distribution can be
preferred.
[0048] In one embodiment of the present disclosure, the heat
treatment in the furnace chamber is performed at a sintering
temperature above the solidus temperature of the metal in the
spherically shaped granules. When the sintering temperature is
above the solidus temperature, liquid phase is formed. During
cooling, when the metal cools down to solid phase again, the
spherically shaped granules, as prevented from contact by the
inhibitor powder, will form the dense and spherically shaped
granules separated by inhibitor powder.
[0049] In one embodiment of the present disclosure, the heat
treatment in the furnace chamber is performed at a sintering
temperature ranging of about 30.degree. C. to about 100.degree. C.,
or from 30.degree. C. to 100.degree. C., above the solidus
temperature of the metal in the spherically shaped granules.
Alternatively the sintering is performed at a sintering temperature
of more than about 100.degree. C., or from 100.degree. C., above
the solidus temperature.
[0050] In one embodiment of the present disclosure, the inhibitor
powder comprises an oxide, preferably yttrium oxide. Yttrium oxide
is an oxide that can withstand sintering at a temperature of more
than 1000.degree. C. without chemically reacting with the
granules.
[0051] In one embodiment of the present disclosure, the inhibitor
powder comprises carbon, preferably graphite. An advantage with
using carbon is that in the subsequent steps of separating the
sintered dense spherically shaped granules from the inhibitor
powder, carbon as an inhibitor can be removed by thermochemical
methods besides physical separation, e.g. air classification or
sieving. Another advantage with carbon is that sintering of for
example cemented carbide granules tends to deplete carbon, and with
carbon as the inhibitor this will be compensated for. However, the
main advantage with carbon is that carbon does not bring any
contamination to the sintered dense spherically shaped granules
since carbon already is part of the overall chemistry of cermets
and cemented carbides.
[0052] In a sintering process, the solidus temperature of the
metallic phase is important. Proximity of carbon to the metal
typically influences the solidus temperature of the metal since the
carbon partly dissolves into the metal. This can be analysed in
detail by studying phase diagrams comprising carbon for the
relevant metallic phase. The solidus temperature decreases by
dissolution of carbon, at least until full saturation is achieved.
The optimum sintering temperature can be chosen based on this
influence of solidus temperature exerted by carbon. In fact, it
provides an exact measure of the solidus temperature since the
saturation with respect to carbon is a rule that can be applied in
general.
[0053] In one embodiment of the present disclosure, the inhibitor
powder is separated from the sintered dense spherically shaped
granules by means of physical methods such as sieving, air
classification, hydrocyclone, flotation and/or fluidization.
[0054] In one embodiment of the present disclosure, the inhibitor
powder comprising carbon is separated from the sintered dense
spherically shaped granules by means of thermochemical methods
using a gas at elevated temperature, preferably using a gas
comprising hydrogen.
[0055] In one embodiment of the present disclosure, the
thermochemical method is performed in a continuous belt furnace
loaded with fixed powder beds, a rotating tube furnace or in a
fluidized bed furnace.
[0056] The present disclosure also relates to a powder of cermet or
cemented carbide made in accordance with the disclosed method.
[0057] The present disclosure also relates to the use of a powder
made in accordance with the disclosed method in 3D printing,
preferably 3D printing of green body aimed for sintering to closed
porosity. Closed porosity is considered to be porosity where the
majority of the pores are closed by being surrounded by material,
comparable to open pores which are open to the surroundings, i.e.
not closed.
[0058] The present disclosure also relates to the use of a powder
made in accordance with the disclosed method in HIP
applications.
[0059] Furthermore, the present disclosure relates to a process for
manufacturing a component comprising the following steps: [0060]
(a) providing a powder as defined hereinabove or hereinafter;
[0061] (b) providing a form; [0062] (c) filling the form with the
powder; [0063] (d) evacuating air from the form; [0064] (e) sealing
the form; [0065] (f) subjecting the at least one form to Hot
Isostatic Pressing (HIP) at a predetermined temperature, a
predetermined pressure and for a predetermined time so that the
powder as defined hereinabove or hereinafter bond metallurgically
wherein a solid body is formed; characterized in that the form is
made of an alloy of zirconium or an alloy of titanium. According to
the present process, in a first step the powder as defined
hereinabove or hereinafter is provided. Said powder may have a
continuous particle size distribution in the range of from 1 to 500
.mu.m, such as from 10 to 200 .mu.m.
[0066] In a second step, a form is provided, the form is sealable.
According to one embodiment, more than one form may also be
provided. Even though, the terms "form" and "capsule" are used
herein interchangeably, the term "mould" could be used as well. The
form is manufactured from an alloy of zirconium or an alloy of
titanium and may be a manufactured of e.g. sheets or tubes, which
are welded together. The form may have any shape. The form may also
define a portion of the final component.
[0067] In the next step, the powder as defined hereinabove or
hereinafter is poured/filled into the form, which form defines the
shape of the component. The form is thereafter sealed, for example
by welding. Prior to sealing the form, air is evacuated from the
form. The air is removed (evacuated) as air typically contains
argon, which has a negative effect on ductility. The evacuation is
usually performed by using vacuum pump(s).
[0068] The filled, evacuated, and thereafter sealed form is then
subjected to HIP in a heatable pressure chamber, normally referred
to as a Hot Isostatic Pressing-chamber at a predetermined
temperature, a predetermined isostatic pressure and a predetermined
time so that said powder particles bond metallurgical to each other
and so that the voids between the powder particles are closed and a
solid and dense body is formed, thus a certain shrinkage of the
total volume of said powder is obtained. Hence, the obtained
component has a dense structure.
[0069] The heating chamber is pressurized with gas, e.g. argon gas,
to a predetermined pressure (isostatic pressure) of above 500 bar.
Typically the isostatic pressure is of from about 900 to about 1500
bar, such as of from 1000 to 1200 bar.
[0070] The heating chamber is heated to a predetermined and
suitable temperature allowing said powder particles to
metallurgically bond and thereby allowing the voids in-between the
powder particles to close, whereby a component having a dense
structure is obtained. At low temperatures the diffusion process
slows down and the obtained component will contain residual
porosity and the metallurgical bond between said powder particles
becomes weak. Therefore, the predetermined temperature may be above
900.degree. C., such as of from 900 to about 1350.degree. C., such
as about 1100 to 1350.degree. C. The form is held in the heating
chamber at said predetermined pressure and said predetermined
temperature for a predetermined time period. The diffusion
processes that take place between the powder particles during HIP
are time dependent so long times are preferred. Preferable, the
form should be HIP treated for a time period of about 0.5 to about
3 hours, such as about 1 to about 2 hours, such as about 1
hour.
[0071] A cermet or cemented carbide component obtained according to
the process as defined hereinabove or hereinafter may be used in
any product requiring good wear resistant properties and/or high
stiffness.
[0072] For further illustrating the present disclosure, it is
further described by the following non-limiting examples.
EXAMPLES
Example 1
Inhibitor Powder of Yttrium Oxide
[0073] Granules were formed from a slurry comprising powders of WC,
Co, Cr, PEG and ethanol. The average grain size of the WC and the
Co powder were 0.8 .mu.m any 1.3 .mu.m respectively. The slurry was
spray dried in a Niro-spray drying equipment. The spray dried
granules formed were sieved on a 63 .mu.m net to leave only the
smallest fraction from the granulated powder.
[0074] In this example the final cemented carbide to be formed was
a 10 wt % Co, 0.45 wt % Cr.sub.3C.sub.2 and 89.44 wt % WC material
and the relative composition of the powders in the slurry were
adapted therefor. The spray dried granules comprised about 2 wt %
PEG.
[0075] The granules were mixed with yttrium oxide in a ratio of 50
wt % spherically shaped granule powder and 50 wt % yttrium oxide
powder. The yttrium oxide powder had a particle size of about 3
.mu.m in average.
[0076] The mixture of spherically shaped granules and yttrium oxide
was distributed on yttrium oxide coated graphite trays. The trays
were filled to a height of about 2 cm mixture.
[0077] Two different sintering temperatures were evaluated,
1370.degree. C. and 1410.degree. C. in vacuum environment. The
liquid temperature of the metal (Co and Cr) in the granules is
about 1307.degree. C.
[0078] The sintering was performed in vacuum conditions of about 5
mbar. The heating cycle comprised an increase in temperature in
hydrogen flow, where the temperature was held constant at
300.degree. C. in 60 minutes to allow binder degassing. Thereafter
the temperature was increased by 500.degree. C. per minute. At the
reached sintering temperature (maximum temperature) the temperature
was hold constant for 90 minutes. Thereafter a cooling step was
performed whereby the temperature was decreased down to room
temperature.
[0079] After the sintering the sintered spherically shaped granules
were separated from the yttrium oxide powder by two steps, first
the sintered cake was gently dry milled for 10 minutes and then the
spherically shaped granules were separated from the oxide powder in
a magnetic separation step. In the magnetic separation step, the
spherically shaped sintered granules were separated from the
yttrium oxide utilizing the magnetism of the cemented carbide. The
powder mixture was dispersed in ethanol. The cemented carbide
powder could be kept at the bottom of the vessel by placing a Ferro
magnet close to the bottom of the vessel, while the yttrium oxide
could be decanted together with ethanol. 50 repetitions of the
decanting were performed. After the decantation, the dense cemented
carbide spherically shaped granules were dried in a furnace at a
temperature of 50.degree. C.
[0080] The granule size of the sintered dense spherically shaped
granules of the cemented carbide powder sintered at 1410.degree. C.
was d(0.1): 22.4 .mu.m, d(0.5): 32 .mu.m and d(0.9): 46 .mu.m.
Several through cuts spherically shaped granules were studied
showing a porosity of less than 0.02 vol % (<A02).
[0081] One way of measuring the density of the dense and
spherically shaped granule powder is to study the density of tapped
powder. For the present powder the full theoretical density is
14.45 g/cm.sup.3. The density of the tapped powder produced and
1370.degree. C. and 1410.degree. C. was 8.10 and 7.92 g/cm.sup.3,
respectively. The slight difference in tapped density is most
probably due to differences in particle (granule) size
distribution.
Example 2
Inhibitor Powder of Graphite
[0082] Granules were formed from a slurry comprising powders of WC,
Co, Cr, PEG and ethanol. The average grain size of the WC and the
Co powder were 0.8 my any 1.3 my (Fischer) respectively. The slurry
was spray dried in a Niro-spray drying equipment. The spherically
shaped granules formed were sieved on a 63 .mu.m net to use only
the smallest fraction of the granulated powder.
[0083] In this example, the final cemented carbide to be formed was
a 10 wt % Co, 0.45 wt % Cr.sub.3C.sub.2 and 89.44 wt % WC material
and the relative composition of the powders in the slurry were
adapted therefor. The spray dried spherically shaped granules
comprised about 2 wt % PEG. The size of the granules was <63
.mu.m.
[0084] The spherically shaped granules were mixed with graphite in
a ratio of 75 wt % granule powder and 25 wt % graphite powder. The
graphite powder had a particle size maximum size of about 45 .mu.m.
The shape of the graphite particles was typically flaky.
[0085] The mixture of spherically shaped granules and graphite was
distributed on graphite trays. The trays were filled to a height of
at least 2 cm and sometimes up to 5 or 10 cm.
[0086] Four different sintering temperatures were evaluated:
1270.degree. C., 1290.degree. C., 1310.degree. C. and 1350.degree.
C., see Table 1. The solidus temperature of this cemented carbide
is about 1300.degree. C., but when saturated with carbon falls down
to about 1250.degree. C.
[0087] The heating cycle comprised heating during a constant flow
of hydrogen up to 300.degree. C., whereat the temperature was held
constant for 60 minutes to allow binder degassing. Thereafter the
temperature was increased by 500.degree. C. per hour under vacuum
pumping down to vacuum conditions. At the reached sintering
temperature (maximum temperature), the temperature was hold
constant for 90 minutes. Thereafter a cooling step was performed
whereby the temperature was decreased down to room temperature.
[0088] After the sintering, the sintered spherically shaped
granules were separated from the graphite powder by two steps,
first in an air classification step and then in a decarburization
step.
[0089] The air classification was performed in a laboratory air
classification machine from Hosokawa Alpine (ATP50). By adjusting
the parameters of the air classification machine to optimized
performance a complete separation of loose graphite powder was
obtained.
[0090] Subsequently, to remove the final excess of carbon from the
mixture of sintered dense spherically shaped granules and inhibitor
(graphite), a hydrogen gas decarburization treatment was performed.
The mixture was distributed to 3 mm shallow beds in heat resistant
vessels and charged into a muffle furnace and treated for 8 hours
at 800.degree. C.
[0091] The final dense and spherically shaped cemented carbide
powder was studied in a scanning electron microscope and a cross
section of some granules can be seen in FIG. 1. Several through
cuts granules were studied showing a porosity of about 0 vol % for
the granules that were heat treated with an inhibitor powder of
graphite at a temperature of 1290.degree. C. or above.
[0092] One way of measuring the density of the powder of dense and
spherically shaped granules is to study the density of tapped
powder. For the present powder the theoretical density is 14.45
g/cm.sup.3. The density of the tapped powder of dense granules with
a size distribution between 10-50 .mu.m was 8.8 g/cm.sup.3. A
mixture between 1 part of foregoing powder with 4 parts of similar
powder having a size distribution between 50-200 .mu.m had a tapped
density of 9.7 g/cm.sup.3.
TABLE-US-00001 TABLE 1 Sintering temperature Porosity (.degree. C.)
Inhibitor powder (vol %) 1270 Graphite 5% 1290 No 10% 1290 Graphite
0% 1310 No 5% 1310 Graphite 0% 1350 No 0% 1350 Graphite 0%
[0093] While the disclosure has been described in connection with
various exemplary embodiments, it is to be understood that the
disclosure is not to be limited to the disclosed exemplary
embodiments; on the contrary, it is intended to cover various
modifications and equivalent arrangements within the appended
claims. Furthermore, it should be recognized that any disclosed
form or embodiment of the disclosure may be incorporated in any
other disclosed or described or suggested form or embodiment as a
general matter of design choice. It is the intention, therefore, to
be limited only as indicated by the scope of the appended claims
appended hereto.
Example 3
HIP Process
[0094] The powder manufactured according the method described in
Example 2 having a continuous particle size distribution within the
range of about 10-200 .mu.m was filled in a capsule made of
zirconium grade 702 and which had the form as a simple bottomed
tube in this case. The filling was performed under tapping action
for maximized powder packing density (67 vol-% was reached).
[0095] A press-fitting lid was fitted on top of the tube and the
tube was sealed by welding. The tube interior atmosphere was
evacuated via a manifold and crimped and welded according to
industrial practice for HIP.
[0096] The tube was put in a HIP-furnace and a maximum temperature
was applied in slight excess of the solidus-temperature (e.g.
30.degree. C. above the solidus temperature of the particular
cemented carbide grade). A peak temperature of 1310.degree. C. was
used during 30 minutes. The HIP-pressure was 150 MPa during that
period.
[0097] After the HIP process was performed the tube material was
removed by pickling by using a mixture of 2% HF and 20%
HNO.sub.3.
[0098] The result was the following:
[0099] A fully dense material, with excellent wear properties was
obtained. ASTM B611 wear test was performed:
Physical Properties
[0100] Com (% Co) 8.89
[0101] Hc (k/Am) 16.84
[0102] Density (g/cm.sup.3) 14.35
[0103] Porosity A02B00C00
[0104] WC grain size .about.1 .mu.m
[0105] Hardness (Hv30) 1470
[0106] Mass loss (g)* 0.2412
[0107] The microstructure was characterized by slightly deformed
prior powder-particles from which Co-rich binder phase have been
partially squeezed out to fill the remaining powder inter-particle
interstices.
[0108] FIG. 2 shows an image of a cross-section of an interface
between the Zr capsule and the cemented carbide component, wherein
1=Zr; 2=ZrC; 3=Prior Zr-rich Zr/Co-eutectic area; 4=sub-carbide
phase; 5=Prior particles; 6=Squeezed out Co-binder phase. As can be
seen from FIG. 2, a bulk microstructure (i.e. within a distance of
100-200 .mu.m from the capsule wall) characterized by absence of
detrimental phase formations. Only a thin (about 100 .mu.m) surface
zone of the cemented carbide was found to be severely affected by
sub-carbide formation and capsule metal (Zr-alloy) enrichment of
the binder phase. The ZrC-layer in contact with the Zr-metal was
only about 10 .mu.m thick.
* * * * *