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Spark plasma sintering of WC, cemented carbide and functional gradedmaterials

Mirva Eriksson, Mohamed Radwan, Zhijian Shen

PII: S0263-4368(12)00057-1DOI: doi: 10.1016/j.ijrmhm.2012.03.007Reference: RMHM 3401

To appear in: International Journal of Refractory Metals and Hard Materials

Received date: 31 October 2011Accepted date: 7 March 2012

Please cite this article as: Eriksson Mirva, Radwan Mohamed, Shen Zhijian, SparkplasmaJournal of Refractory Metals and Hard Materials (2012), doi: 10.1016/j.ijrmhm.2012.03.007

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WC,ofsintering cemented carbide and functional graded materials, International

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Spark plasma sintering of WC, cemented carbide and functional graded materials

Mirva Erikssona,*, Mohamed Radwanb, Zhijian Shena a Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm

University, SE-10691 Stockholm, Sweden b Diamorph AB, Roslagstullsbacken 11, SE-10691 Stockholm, Sweden

*Corresponding author: Tel. +46-8-161258, Fax. +46-8-152187, E-mail:

mirva.eriksson@mmk.su.se, SE-10691

Abstract

Spark plasma sintering (SPS) is an extremely fast solidification technique for compounds that

are difficult to sinter within the material group’s metals, ceramics, or composites thereof. SPS

uses a uniaxial pressure and a very rapid heating cycle to consolidate these materials. The

heating is generated by Joule effect when a strong, pulsed electric current passes the

conductive graphite die and also through the sample, if conductive. Cemented carbides (“hard

metals”) are mostly used for metal cutting and drilling, wood cutting or rock drilling tools and

are consolidated either by pressureless sintering (PLS), hot pressing (HP), or hot isostatic

pressing (HIP). With SPS the main benefit is the ability to control the WC grain size due to

the short sintering times at high temperature. In addition, unwished reactions between WC

and cobalt to form other phases are minimized. By SPS the amount of cobalt can be reduced

towards zero in fully dense WC materials. With this technique it is easy to prepare gradient

materials where a ductile weldable metal can be joined with the cemented carbide part.

Keywords: Spark plasma sintering, binder free WC, WC-Co, Functionally graded materials

1. Introduction

Cemented carbides, sometimes in literature referred as “hard metals”, are a wide group of

dense sintered materials consisting of mainly transition metal carbides with a metal sintering

aid. They are characterized by high hardness and wear resistance resulting from the high

carbide content. Cemented carbides are used in industry as metal or wood cutting tools, wear

parts, machine components, and press-stamping dies. They are also important in rock or oil

drilling either as pure cemented carbide or in tool constructions involving diamond

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composites depending on the rock/sand/soil drilling media. The combination WC-Co is the

most traditionally used system as the WC grains exhibit a “ductility” by sliding atom planes

at high external force resulting in high toughness in applications. Other hard transition metal

carbides are often used in combination with WC to alter the overall mechanical and/or

chemical properties. In some of them all of the WC is replaced and a special group with its

own name is the TiC based cermet. In the cermet’s cobalt is usually replaced by nickel. The

chemical, mechanical and wear properties of these cermets are different and they are

commercially used for other special applications than cemented carbides. The sintering of

transition metal carbides, like WC, without metal sintering aids is very difficult because of

their low atomic self-diffusion coefficients. It requires high temperatures and long times to

achieve acceptable dense parts which lead to microstructures consisting of large grains. The

solidification of pure WC is enhanced by applying high pressures taking advantage of the

plastic deformation mechanism of WC, but other carbides will not deform in this way.

However, the sintering is enhanced dramatically by introducing a liquid or melting metal

phase by adding Co, Fe or Ni which all have good wettability and solubility for WC grains

[1]. In this way plastic deformation of WC grains is not needed and the sintering is achieved

by enhanced atomic diffusion in the liquid phase that facilitates materials transport and a

subsequent reprecipitation mechanism takes place. The key mechanical properties of sintered

cemented carbide parts, e.g. hardness, fracture toughness and transverse rupture strength

(TRS) depend primarily on the density, average WC grain size and the Co content. Sintering

of WC-Co powder by Spark Plasma Sintering (SPS) began as far back as in 1927 [2, 3], and

with improved modern equipment the material development studies are increasing.

SPS, also named as Field Assistant Sintering Technique (FAST), is a sintering method which

uses a strong pulsed electric current for heating. In the SPS system the sample powder is

loaded into a graphite die which works as a heating element when the current is passing

through it. The die is heated by Joule effects and the small thermal mass of the heating die

makes it possible to use heating rates up to 1000°C/min. In the case of a conductive powder,

the current is passing it as well, resulting in that the sample experiences an additional internal

heating. Simultaneously a uniaxial pressure is applied to the sample in the graphite die. In this

way the sintering time and sintering temperature can be minimized. A schematic picture of

the SPS configuration is shown in Figure 1. The sintering process is regulated by the

temperature measured either by a thermocouple inserted in a hole on the surface of the die or

by a pyrometer focused on the small hole on the surface of the die. In some of the apparatus

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the temperature can also be measured by a pyrometer focused through a hole in one of the

punches. Usually there is a temperature gradient inside the sample and die depending on the

design of the die and conductivity of the materials, rating between 30 °C up to 300 °C. For

more details concerning the measurement and modelling of such temperature gradients, the

readers can consult articles published on this topic [4, 5, 6]. Fast heating and short holding at

the sintering temperatures are the unique characteristics of the SPS process, which make it

possible to control the sintering and grain growth [7].

2. Binder free WC

With conventional methods a fully dense binder free WC is very difficult to achieve. Very

high temperatures are demanded that results in very large grains. Binder free WC has been

sintered in SPS in 1998 by Omori et.al. and they achieved a hardness value of 24 GPa and

toughness of 6 MPam½ [8]. SPS has later shown to be able to sinter binder free WC with

grains of sub-micron and nano-grain sizes to nearly full densities. The applied sintering

temperatures have been between 1500°C to 1700°C giving densities from 98 to 99.9 % of the

theoretical density (TD). Microstructures having sub-micron up to micron sized grains

achieved hardness values of 24-28 GPa [9, 10]. The smaller overall grain sizes results in

somewhat harder materials than those reported above by Omori et.al.[8]

Maizza et. al. sintered binder free ultra-fine WC powder in SPS and they showed that when

the sintering temperature exceeds 1900°C (using 20 MPa pressure) the grain growth was

accelerated. Thus, temperature control is important to control grain size growth. Indeed,

controlled grain growth and properties will be dependent on the electrical current intensity

and understanding of the temperature differences occurring along the radius. The core of the

sample that experienced higher temperatures resulted in larger grain sizes [1]. They

demonstrated in this way the effect of the current intensity to the homogeneity of the samples.

In SPS there is also another factor that influences the materials micro-homogeneity; the effect

of the applied pressure, especially when it is too low. The pressure has an indirect influence

on the temperature distribution inside the sample and the die. Grasso et. al. [11] reported that

they can sinter homogeneous and binder free ultra-fine WC using high-pressure, 80 MPa at

the current 1400 A, corresponding to a peak temperature of 1579 °C. The samples showed

very limited grain growth and an overall homogeneous microstructure. It was found that the

measured hardness values were independent to the measured position in the sample, as

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expected from the homogenous grain size. With lower pressures they showed that the

distribution of the temperature caused inhomogeneous properties similar to Maizza et. al. [1].

Recently binder-free nano-WC powder (200 nm) has been sintered by SPS at 1500 °C by B.

Huang et al [12]. The initial ultra-fine particle size was maintained after sintering. The

hardness of samples with such fine grain microstructure were increased to 26 GPa [12]. Shon

et. al. [13] have densified nano-sized WC produced by attrition milling by SPS at 1500 °C.

They achieved the grain sizes of 54 nm and density of 99 % after sintering.

3.WC-Co

3.1 Sintering of WC-Co in SPS

As mentioned above the pure WC is very difficult to sinter to full density with conventional

methods. To overcome this problem sintering aids like Co, Fe and Ni are added to WC, where

the most common addition is cobalt. With Co addition a liquid phase appears in the system

above the eutectic temperature 1320 °C. The sintering is facilitated by a dissolution –

reprecipitation mechanism commonly accompanied by Ostwald ripening of WC grains [14].

The amount of Co is usually tailored according to the customized demands. For metal cutting

application the amount varies between 5-12 w% of Co and for non-cutting applications

between 5 to 30 w% of Cobalt [15].

The key benefits of SPS are assumed to be in the area of grain size control when sintering

ultra-fine and nano particles. Because of the rapid heating and high pressure in SPS it is not

necessary to go above eutectic temperature with these extremely small grains, indicating that

WC/Co can be sintered in solid state or at least with a minimum time close to the liquid phase

temperatures. [16,17,18].

High density is obtained by SPS at temperatures between 1050-1100°C and even using

moderate pressures of 30-50 MPa. Below these temperatures the densities fall rapidly below

90 %. Cha et. al. sintered nano-crystalline WC-10wt% Co powder at 1100°C and stated that

the sintering occurred in liquid state [16]. Sivaprahasam et. al. sintered nano-crystalline WC-

12wt% Co at the same temperature (1100 °C), but they concluded that the WC sintering

occurs in solid state where cobalt binder between WC grains behaves similarly to a liquid

phase. [18]. If the sintering temperatures are considered to be around the eutectic temperature

1320oC in the Co-W-C system the temperature gradient within the sample body would be as

large as ~220-270 °C by SPS. This is higher than experimentally measured by Huang et. al.

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[19]. They measured the temperatures for WC-Co system in PECS (Pulsed Electric Current

Sintering) on the normal position (on the outer surface of the die) and through the upper

punch very close to the centre of the sample. In that way they observed a maximal

temperature gradient of ~150 °C. They concluded that the solidification was solid state

sintering, even though they could see similar morphology changes on the WC grains as

observed in liquid phase sintering (from spherical grains to faceted) [19]. Finally, the

temperature distributions by SPS inside the WC-Co body were modelled by Liu et. al. [24].

They noted that the Co layers on WC grains experience higher temperatures and in that way

localized WC-Co contact areas might reach the eutectic temperature. This would indicate that

even at lower measured sintering temperatures there might be a thin liquid phase present on

the grain boundaries that assists the densification. [20]. The difficulty to ascribe the

densification to either a liquid or a solid state sintering mechanism illustrates very well the

problematic of temperature measurements in the SPS technique. The solid state sintering of

WC-Co gives some inhomogenity in the microstructure. This inhomogenity depends also on

the scale factor between cobalt and WC particles. If the WC particle size is much smaller than

Co size the inhomogenity increases. At the same time it seems also that the solid state

sintering in SPS makes the grain size distribution narrower and in that way improves the

properties [21].

3.2 The effect of SPS to the grain size

The pronounced effect of SPS is the ability to control the grain growth as well to keep the

grain size close to the original particle size. This has not been proven to be the case for

cemented carbides. When sintered at 1000 °C the initial particle size of 100 nm was increased

to 300 nm [16]. Further increase of the sintering temperature to 1100 °C increased the final

grain size to 550 nm. The latter grain size is similar to the sizes what can be achieved by

conventional sintering using grain growth inhibitors. Even though fine-grain structures of

cemented carbide can be achieved in SPS, it has not been succeeded to produce

microstructures consisting of grains less than 200 nm, i.e. to be truly WC nano-ceramics

(defined as materials with grain size less than 100 nm). Without grain growth inhibitors the

grain sizes varies from 200 nm to 800 nm depending on the initial powder and sintering

conditions. The finest microstructure for cemented carbide has been reported to be with an

average grain size of 275 nm when sintered at 1150 °C for 5 min under a pressure of 10 kN

[17]. However, with grain growth inhibitors present somewhat lower mean grain sizes (179

nm) can be achieved [21]).

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In our own work at Stockholm University we have been able to sinter WC-Co (9-10w% Co)

cemented carbides at 1175°C to nearly full densities, 98-99.2 % of TD, under a pressure of 30

MPa within 3 min. holding time. Different amounts of Co were tested along with different

particle sizes. All of the powder mixtures were sintered at the same temperatures using

different WC grain sizes. Although the WC grain size varied from 20 nm to 1 micron, a big

difference were not seen in achieved densities. These results are similar to those achieved by

Zhao et. al. [22]. The sintered WC grains had faceted morphology with sizes varying from 0.4

µm to 0.8 µm proving that these results are in line with previous studies.

3.3 Effect of SPS on the material properties

When comparing the properties of tungsten carbide the transverse rupture strength (TRS) is

often given, it gives a combined mechanical property of cemented carbide. TRS depends on

hardness and fracture toughness when the porosity is negligible and microstructure has minor

affect [23] For commercial products, TRS can vary from 1100 MPa up to 4700 MPa

[24,25,26]. TRS is often considered by inverse relation with hardness but in fact it was shown

by Fang that the relationship is more complicated. At low hardness (below 1200 kg/mm2) the

TRS increases with hardness, while at higher hardness’s the TRS decreases. Unfortunately

their work did not reveal the behaviour at the higher hardness than 1500 kg/mm2. For the

reported results of cemented carbides sintered in SPS, the trend seems to be the same. The

reported values for SPS sintered WC-Co seems to follow the same tendency and they lie in

the range (1100 to 3100 MPa [27,28,29] ) for commercial values when considering the

hardness. There is some anomalous in the values but they were explained by the

inhomogenity in the microstructure and by the present of eta phases which decrease the

mechanical properties [27,28]. For the small amount of work published on TRS of SPS-ed

WC-Co it is hard to draw a conclusion if SPS improves the intrinsic properties or not.

The mean free path of Co would be increased if only solid state sintering was allowed by SPS

leading to less homogeneous grain distribution and experimental observations indicate

therefore some effects similar to a present liquid phase [30]. Another effect noticed in SPS

sintered cemented carbides is the dependency of the WC-Co particle size ratio. In

conventional sintering methods, when the Co particle size is kept constant, the initial particle

size of WC affects the sintering process. This was not observed in the case of SPS sintering.

The sintering behaviour was not affected by the WC particle size when the mean Co particle

size was equal or larger than WC particle size [22]. When the Co particle size was decreased

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below that of the WC particle, the sintering process was affected due to the different path of

the current through the sample and more inhomogeneous local temperature distributions were

achieved [31].

3.4 The reaction sintering in SPS and new approaches to improve properties

In-situ reaction synthesis and sintering of WC-Co by SPS from starting W, C and Co elements

was found to be useful to increase the homogeneity of the dense cemented carbide [32,33].

Locci et. al. showed that the reaction proceeded through the formation of W2C and continued

to fully dense WC-Co with a Vickers micro-hardness of ~15 GPa and a fracture toughness of

12.5 MPam½ [33].

During SPS, the samples are exposed to a reducing atmosphere and an excess of carbon. The

problem with the use of graphite die has not been discussed much in the literature and would

be looked upon in more detail. It is most likely that the carbon might diffuse into the sintered

bodies and move the equilibrium of the WC-Co and thereby introduce small amounts of other

ternary carbide phases (eta phase) in the structure. Such phases are known to deteriorate the

properties of the WC-Co cemented carbide.

Addition of carbon nanotubes (CNTs) as a reinforcement agent to the WC-Co system was

studied during SPS [34]. With 0.3 wt% carbon nanotubes addition to a WC-7wt% Co matrix,

the hardness was 2450 kg/mm2 (HV30) and the fracture toughness was 14.0MPam1/2.

As mentioned above some other additives can be used together with the binder free WC in

order to improve both the sintering and the mechanical properties. One interesting additives

were oxides which have been used in order to improve the fracture toughness. El-

Eskandarany has prepared WC/MgO and WC/Al2O3 composites by high energy ball milling

and SPS. The hardness of such composites was decreased, but a high fracture toughness of 15

MPam½ was achieved [35,36]. Another promising oxide addition has shown to be ZrO2. WC

was sintered in SPS with 6 wt% of yttria stabilized zirconia and it showed comparable

hardness and fracture toughness values with WC-Co composite besides improvement of the

flexural strength [37,38].

4. Functionally Gradient Materials and coatings

4.1 Functionally graded tungsten carbide

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The pure WC-Co cemented carbide can be very hard depending on the reduced amount of the

Co, as shown above. In order to improve the strength and life time of the tools, composition

gradient cemented carbides (also called functionally graded materials, FGMs) can be used.

These combine a hard wear-resistant surface (enriched on WC) with a tough and strong bulk

consisting of cemented carbide with higher amount of Co. If the FGM is densified by

conventional methods there is a risk of Co homogenization between the layers, which is

destroying the advantages of the FGM structure. Thus, the problem is the fast migration of Co

liquid phase over the composition interface during the liquid phase sintering. The problem

might partly be solved by using different grain sizes of WC-Co particles as well as using

different carbon contents between layers [39]. But anyhow a precise control of sintering

condition is required to shorten the holding time at the high sintering temperature.

The advantage of SPS is that the FGM can be sintered either in the solid state or with very

short holding times at the liquid phase sintering temperatures. In this way, the diffusion of Co

can be greatly restricted, which was shown by Tokita et. al. [40]. They prepared large 4-layers

FGM (100 mm x 100 mm x 40 mm) with satisfactory properties and minimal residual stresses

between the layers.

4.2 Laminates and thin films

Laminated WC-Co tools have been also prepared by SPS using a low fraction of Co in the

outer shell in order to improve the wear properties. The laminate outer structure was

introduced by a tape casted foil which was successfully combined with the bulk powder. The

low temperature solid state sintering gave an uneven distribution of Co content in the outer

layer. Nevertheless, tested as metal cutting tools the performance was similarly as using a

conventionally fabricated monolithic tool [30].

Cemented carbide coatings for metal tools are often produced by plasma spraying. The high

temperatures required for this process often result in a deficiency of carbon in the sprayed

WC-Co coating and formation of phases like W2C with poorer wear resistance than WC. To

simulate the process in a better controlled experiment, the reducing atmosphere and graphite

die in SPS was utilized to prepare graphite deficiency of WC-Co samples. It was found that

the stoichiometric WC could be restored by the reaction with W, i.e. by the phase

transformation of W2C back to WC. The method was limited to coatings thinner than 10 µm

[41].

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4.3 WC-Co and diamond

Another possibility to produce even harder cutting tools is to combine cemented carbide with

a diamond composite layer at the top. A problem arises from the instability of diamond. For

example, it burns in air even at 700°C and must be kept in reducing atmosphere. However, at

the very high temperatures needed for sintering, despite the use of reducing atmosphere,

diamond experiences graphitization starting at the surface of the crystals. Thus, also in the

reducing atmospheres of all conventional sintering methods this is a great problem. In an

attempt to prevent the graphitization, diamond has been pre-coated with metallic W, Ni, Cr or

SiC [42,43,44]. Although these materials were composites and not FGMs, it indicates that it

should be possible to prepare a laminates with diamond by SPS on a surface of cemented

carbide. This has been done in our laboratory at Stockholm University with a diamond (4%)

laminate on the top of WC-10w% Co as shown in Figure 2. The sintering condition for the

laminate was 1250°C for 3 min using a pressure of 75 MPa applied at the sintering

temperature. This low sintering temperature and short sintering time prevented the

graphitization of diamond which kept its crystal shape and resulted in a very hard surface

structure.

4.4 WC-Co and steel functionally graded materials

FGMs has not only been prepared with WC-Co but even using other metallic materials such

as Mo, Cu and steel [8,45,46]. Steel is important due to its wide use in many applications.

Thus it is of importance to join cemented carbide towards steel. For instance, the cutting teeth

to a steel backing in wood machining or a drill button onto a steel shaft for drilling etc. Steel

will allow the weldability of cemented carbides. Therefore, studies have been made to reveal

the thermal stability and the reaction products of tungsten carbide and steel [47,48 ]. The

reactions between WC and WC-Co towards steel were investigated by consolidation in SPS at

1100 °C, pressure of 60 MPa and holding time of 5 min. They showed that in the WC-steel

and WC-Co-steel systems there appear phases like W3Fe3C and W4Co2C, respectively [48].

These types of ternary carbides are detrimental for the mechanical properties.

Tsuda et. al have prepared a component for oil drilling tool in SPS where a FGM of WC-Co is

sintered onto a steel substrate [49]. The cemented carbide FGM had a surface layer with 25 %

Co and the core has 40% Co. It was sintered at 1000°C using pressure of 50 MPa and a

holding time of 20 min. The work with WC-Co and steel started in our laboratory at

Stockholm University in 2005 with successful results. The micrograph of a lamination of

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WC-Co on a steel is shown in Figure 3. It is visible that the cohesion between the layers is

nice without any cracks and without any reaction zone. The FGM with a steel base with

increasing content of WC-Co has also been prepared with SPS by Diamorph AB [50].

Different designs with different geometries and different number of layers are possible. One

version has 4 intermediate graded layers and a bulk density of about 95%, see Figure 4.

5. Industrial manufacturing

Although sintering of cemented carbide by SPS is more than 80 years old, details of its

application in industry are scarce. The major benefits of using SPS are the ability to keep a

fine-grained microstructure, to lowering the sintering temperature as well as to shortening the

sintering time.

In SPS, like in HP, the powders are directly sintered in the die where the shape of the parts

can be directly adopted. This is an advantage compared with conventional PLS where dry-

pressing aids (paraffin wax/polyethylene glycol) are needed in making green parts of desired

shape and a pre-sintering step for removal of these organic additives. However, in PLS more

complex shapes can be achieved by machining of green parts before final sintering.

The drawbacks of the SPS technique are the inability for low-cost mass production. The

demand for production has increased the complexity of the machines and they can be

equipped with separate heating and cooling chambers in order to decrease the time needed in

SPS cycles. The time is shortened also when the loading and unloading can be made with

robots as well the die filling prior the loading [51,52]. Another limiting factor for production

is the same as in conventional HP; the limited number of shapes which can be prepared. Even

though more complex shapes are already prepared and investigated, the heating arrangement

in SPS makes the temperature distribution in the sample complicated. In some extent, the

temperature gradient can be decreased by using an additional heating element located around

the die [53].At the moment, the use of optimized sintering process and die design makes it

possible to sinter very large components up to 30 cm diameter with homogeneous temperature

distribution during sintering [54]. The productivity can also be improved by die design and

use of multiple processing tools. The die can be designed such away that several samples can

be sintered simultaneously. For example six similar components can be sintered using one die

[52].

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Manufacturers offer an increased productivity by using a two chamber or even four chamber

solutions. A production line of Fuji Electronic Industrial Co, Ltd is presented in Figure 5. It is

a tunnel type of sintering line where the sintering unit is combined with pre-evacuation and

pre-heating chambers as well as several cooling chambers after sintering.

One commercially available product produced in SPS/FAST is pure WC-plates for sputtering

targets. The plates are produced in a unit using high temperatures (2100°C) and a sintering

cycle of ~30 min, Figure 6a. Both circlular and square shapes are produced in a process using

a two chamber solution with separate cooling chamber. This solution has decreased the

sintering time from 85 min to ~30 min [53]. Pure WC parts produced in SPS is also offered

for pressing moulds for aspheric glass lenses, shown in the Figure 6b.

In general, it is hard to find information about industrial products with WC-Co and FGMs

produced by SPS. There are some patents using SPS for sintering WC-Co/ WC FGMs [45,

55-57]. In the literature, a very promising industrial product seems to be parts for oil drilling

tools where FGM with different amounts of Co in WC are sintered on a bulk steel substrate by

SPS. These parts showed longer life time and better wear resistance than conventionally

manufactured parts [49,57].

Further information of the industrial production seems to be hard to find. SPS/FAST

equipment manufacturers give more examples of possible industrial production in their

homepages, but no further information of specific companies or sintering details are given. It

is clear that the industrialization of SPS/FAST is an on-going process which is also indicated

by the fact that there are new actors in the market who offer the SPS/FAST units in different

sizes and purposes.

Acknowledgments

We would like to thank Thommy Ekström for valuable comments and also FCT systeme

GMbH and Fuji Electronic Industries Ltd for providing the help with the Figures.

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Figure Captions

Figure 1. Schematic illustration of the SPS configuration.

Figure 2. SEM micrographs showing a diamond laminate on top of a WC-Co substrate

sintered by SPS. Sharp diamonds can be seen illustrating that no degenerative graphitization

has taken place.

Figure 3. WC-Co laminate on the steel substrate sintered in SPS.

Figure 4 WC-Co –Steel FGM produced by Diamorph with four intermediate layers and the

bulk density of 95 %. Courtesy of Diamorph AB.

Figure 5. Example to show a SPS unit equipped with pre-heating and cooling stages. Courtesy

of Fuji Electronic Industries Ltd.

Figure 6: a) Pure WC sputtering targets (courtesy of FCT systeme GMbH. b) Pure WC parts

for the aspheric glass lens mould. (Courtesy of Fuji Electronic Industries Ltd).

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Figures

Figure 1

Figure 2

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Figure 3

Figure 4

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Figure 5

Figure 6

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Highlights The short review of spark plasma sintering of binder free WC, WC-Co and functionally

graded cemented carbides.

Some industrial applications of WC-Co / WC / FGM sintered in SPS

Industrial production in SPS