The influence of powder preparation condition on densification and microstructural properties of WC-Co- Al2O3 cermets

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Contents lists available atScienceDirect

International Journal of Refractory Metals

& Hard Materials

journal homepage:www.elsevier.com/locate/IJRMHM

The in

ﬂuence of powder preparation condition on densiﬁcation and

microstructural properties of WC-Co- Al

2 O

3 cermets

E.A.D. Leal

a,⁎

, U.U. Gomes

b

, S.M. Alves

a

, F.A. Costa

a

a_{UFRN, Department of Mechanical Engineering, University Campus, Lagoa Nova, CEP 59078-970, Natal, RN, Brazil}

b_{UFRN, Department of Theoretical and Experimental Physics (LMCME), University Campus, Lagoa Nova, CEP 59078-970, Natal, RN, Brazil}

A R T I C L E I N F O Keywords:

WC-Co- Al2O3composites

High energy milling Sintering

A B S T R A C T

This study investigated how powder preparation during WC-10Co production with the addition of 10 wt% Al2O3

influenced its microstructural and mechanical properties. Powders were mixed with a mechanical shaker for 10 min and high energy milling for 2, 6, 10, 20, 30, and 50 h. The powders were then compacted at 200 MPa and sintered in a resistive dilatometric furnace for one hour, under an argon atmosphere, at a heating rate of 10 °C / min, and two sintering temperatures (1400 °C and 1550 °C). XRD and SEM/EDS analyses were carried out for both powders, which were sintered in order to examine their composition and morphology. The sintered powders were also characterized in terms of mechanical properties, densification, and dilatometric shrinkage. The results show that samples milled for 50 h and sintered at 1550 °C exhibited microstructures with denser phases than those of samples mixed in the shaker. The properties measured were around 68%, 45%,−0.30, and 280 HV for relative density, densification, dilatometric shrinkage, and hardness, respectively.

1. Introduction

WC-based cermets are widely used in cutting tools, dies, mining tools, and wear-resistant parts due to their high hardness, wear re-sistance, chemical stability, and adequate mechanical capacities at high temperatures. One of the most important binders used in WC-based cermets is Co [1,2]. The percentage of cobalt in the matrix is directly related to the carbide properties. For example, the higher the amount of this element in the material the lower its hardness and greater its fracture toughness. An increase in cobalt in the carbide decreases its ceramic properties and improves features associated with the metallic phase [3].

Although the Co binder enhances the sintering process and sig-niﬁcantly increases impact resistance, it does cause some problems, such as the toxicity of the Co element, low melting point, high cost, and low resistance to corrosion [4,5]. Some studies have shown that sin-tering monolithic WC without agglomerates [6] or metal binder and high sintering temperatures (1700 °C -1900 °C) are necessary to obtain totally dense materials [7,8].

Numerous eﬀorts have been made to partially or totally replace Co with other metallic binders, such as nickel, iron, etc. [9,10]. However, the partial or total replacement of Co by ceramic particles, such as metallic carbide and metal oxides, has yet to be studied due to the high melting point of ceramics and the use of costly production tools

[11,12]. Al2O3, which has recently been investigated as a binder for

carbide tools, has several advantages. These include chemical inertness, a high degree of hardness and high wear resistance, but although these materials have excellent chemical stability, they exhibit low toughness. Another essential feature is that thermal conductivity declines with rising temperature, thereby providing an attractive thermal barrier for its use in cutting tools [13].

Fazili et al. [14] studied the eﬀect of adding Al2O3as an alternative

component in addition to the Co ligand on the electrochemical and mechanical properties of WC-Co-Al2O3 composites. They also

in-vestigated the plasma spark sintering of the WC-6% Al2O3composite,

compared to the WC-6% Co carbide, and concluded it not only led to an increase in the sintering temperature from 1350 °C to 1600 °C, but also reduced resistance and toughness. Conversely, replacing a part of Co with alumina (WC-3% Co −3% Al2O3), resulted in high strength

(1095 MPa), hardness (17.62 GPa) and fracture toughness (19.46 MPa. m1/2). However, there are no literature studies demonstrating whether preparation time inﬂuences the properties of hard metal with the ad-dition of alumina [15].

The main stage in the production of WC-Co cermet is generally preparing raw powders, and the ideal mixing condition can improve cermet characteristics [16]. In addition, sintering may be the dominant process for adjusting the microstructures and mechanical properties of WC-Co cermets [17,18]. Spark plasma sintering, a high-tech sintering

https://doi.org/10.1016/j.ijrmhm.2020.105275

Received 7 February 2020; Received in revised form 17 April 2020; Accepted 27 April 2020

⁎_{Corresponding author.}

E-mail addresses:[email protected],[email protected](E.A.D. Leal).

International Journal of Refractory Metals & Hard Materials 92 (2020) 105275

Available online 29 April 2020

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process, is also successfully applied to prepare high-temperature cera-mics, with advantages such as high heating rate, surface cleaning, va-cuum condition, pressure application, etc. [14], parameters that lead to the best possible properties for ceramics [19,20]. On the other hand, sintering in a dilatometric furnace also showed promising results, due to its high heating rate, controlled atmosphere, high precision, etc. In this respect, Shixian Zhao et al. [21] investigated the effect of WC particle size on thefinal properties of plasma spark sintered samples of the carbide WC-10% Co. They showed that a combination of micro-metric particles could improve the mechanical properties of WC-Co. However, no studies have investigated the influence of powder pre-paration on the properties of WC-Co enriched with Al2O3.

Thus, the present study aimed to determine the inﬂuence of the powder preparation method and sintering temperature (1400 and 1550 °C). on WC-10% Co-10% Al2O3sintered sample properties. The

sintered samples were characterized in terms of microstructure, densi-ﬁcation, dilatometric shrinkage, and mechanical properties.

2. Experimental methodology

Tungsten carbide powder with an average particle diameter of 4.07μm, cobalt powder 24.70 μm and alumina powder 10.97 μm, and 99% pure, were used to prepare the composite (WC– Co- Al2O3).

Initially, the powders underwent mixing and milling. In the former, the powders were mixed in a glass container for 10 min in a mechanical shaker. In the latter, the powders were milled for 2, 6, 10, 20, 30, and 50 h in a high energy mill. The powder mixture consisted of 80% WC, 10% C, and 10% Al2O3,for all powder preparation methods. The

mil-ling was performed in a Planetary Pulverisette-7 mill using carbide balls (5 mm in diameter), in an ethanol slurry, powder weight ratio of 4:1, and speed of 400 rpm.

Twenty-five grams of prepared powder mixtures were then loaded into a cylindrical die with a diameter of 5 mm and compacted by cold uniaxial pressing at 200 MPa. Before each compaction, the matrix was lubricated with zinc stearate to facilitate sample removal. After com-paction, sintering was carried out in a Netzsc DIL 402C resistive tometric furnace. Alumina support stands were used to measure dila-tometric shrinkage, and the tests were performed with an argonflow of 2.5 ml / s, heating rate of 10 °C / min, constant sintering temperature for 1 h and cooling rate of 20 °C / min. Circulating argon was used in the furnace to prevent sample contamination during the heating and cooling process. The samples were cooled inside the oven until they reached room temperature. Sintering occurred at two different tem-peratures: 1400 °C and 1550 °C.

The relative density of the sintered samples was determined by the geometric method, with the aid of a Mitutoyo digital caliper rule from the Shimadzu precision balance. Density measurements were taken for the green compact (ρv) and the sintered sample (ρs), in order to obtain

the experimental densities (ρex), and compare them with their

theore-tical counterparts (ρT). Eq. 1 was used to obtain the relative densities

(ρR): = ρ ρ ρ . 100 ex T R (1) Theoretical density was determined using the rule of mixtures, re-presented by Eq.2: = + + + + ρ_T mmA mB mC ρ m ρ m ρ A A B B C C (2) where:

ρT= theoretical density of the composite (g/cm3),

mA= mass of element A (g),

mB= mass of element B (g),

mC= mass of element C (g),

ρA= density of element A (g/cm3),

ρB= density of element B (g/cm3), and.

ρC= density of element C (g/cm3).

The theoretical densities of WC (ρA), Co (ρB), and Al2O3(ρC) are

15.63 g/cm3_{, 8.9 g/cm}3,_{and 3.98 g/cm}3_{, respectively. Thus, to}_{ﬁnd the}

theoretical density of the WC-10% Co-10% Al2O3composite, the rule of

mixtures was applied using Eq.2, obtaining a value of 11.45 g/cm3_.

The densiﬁcation parameter (D) was determined by Eq.3

= − − D ρ ρ ρ ρ s v T v (3) where:

D= densiﬁcation of the composite.

ρT= theoretical density of the composite (g/cm3).

ρs= density of the sintered sample (g/cm3).

ρv= density of the green compact (g/cm3).

The sintered samples were submitted to the Vickers hardness test using the ASTM 092 standard. The load used was 20 Kgf with a time of 10 s and the measurement was taken in triplicate. The chemical and structural characterizations of the powders and sintered samples were analyzed by scanning electron microscopy (SEM) and energy dispersive scanning (EDS) under a HITACHI TM-3000 microscope. The crystalline structure was determined using a Bruker D8 Advance X-ray dif-fractometer, with nickelﬁlter, Cu Kα radiation, 40 kV voltage, current of 40 mA, and scanning range (2θ) between 10° and 80°. Average powder particle size was determined with a Zetatrac Legacy Particle Size and Potential Analyzer.

3. Results and discussion

3.1. Starting powder characterization

Figs. 1-3show the characterization of starting powders (WC, Co, and Al2O3) in terms of shape, size distribution, elementary analysis, and

crystalline phases. SEM images (a) and size distribution (c) for all the powders reveal that they are homogeneous, and that size is normally distributed, with an average diameter of 4.07, 24.70, and 10.97μm for WC, Co, and Al2O3, respectively. In addition, powder purity was

con-ﬁrmed by EDS (b) and XRD (d) analysis. The former identiﬁed only elements present in the molecular formula of powders and the latter demonstrated that the ceramics of WC and Al2O3 powders exhibit

phases with well-deﬁned high-intensity peaks, while cobalt powder shows phases with poorly-deﬁned low-intensity peaks between 40° and 50°, as expected.

3.2. Eﬀect of powder preparation on the crystalline structures

Figs. 4 and 5present the X-ray diﬀractograms for mixed and milled WC-10% Co-10% Al2O3composite powder. The results show the

evo-lution of the crystalline structure collected from the powder mixed for 10 min and that milled for 2, 6, 10, 20, 30 to 50 h.

Fig. 4exhibits low-intensity peaks of alumina for milling times of 10 min and 2 and 6 h, evidencing that the mixture was not homo-genized, and after 6 h these peaks were no longer visible. The Co peaks could not be visualized in the diﬀractogram because of the XRD de-tection limit. The diﬀractogram (Fig 4) shows that with an increase in milling time, there was a greater trend towards amorphization of the crystalline powder mixture during the milling process, which is char-acterized by a decline in WC peak intensity. For the WC-10% Co-10% Al2O3composite powder, the highest tungsten carbide peak displayed

intensity values of approximately 6800 u.a when mixed, decreasing to around 400 u.a for 50 h of milling. The diﬀractogram shows a decrease in the peaks with a rise in milling time, demonstrating that the initial elements of tungsten carbide and alumina were being reﬁned, deformed and welded in the cobalt matrix. This is shown in greater detail in Fig. 5, when the peak was enlarged to 35.5° for powder mixed for 10 min and milled for 2, 6, 10, 20, 30, up to 50 h. Peak intensity

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decreased sharply with an increase in milling time. Comparison be-tween the powder mixed for 10 min and that milled for 50 h shows that the WC and Al2O3particles of the latter were reﬁned, fractured and

embedded in the ductile Co binder matrix, trending to greater particle amorphization and homogenization in the microstructures. The powder was also more uniformly distributed over 50 h of milling, as can be seen inFig. 5.

3.3. Eﬀect of powder preparation method on microstructural and morphological properties

Given that the powders mixed for 10 min and milled for 50 h ex-hibited crystalline phases with diﬀerent peak intensities, we analyzed the eﬀect of these times and preparation methods on the micro-structural and morphological characteristics of the powders. Fig. 6 shows SEM image (Fig. 6a), EDS mapping (6b), and particle size dis-tribution (6c) for WC-10% Co-10% Al2O3mixed for 10 min. According

toFig. 6c, the average particle diameter is 16.15μm, an intermediate value between the particle diameter of the starting powder, indicating that it was a mixture, as shown in the SEM image, but no welding was observed in the fragile phase in the ductile matrix. EDS mapping re-vealed well-dispersed cobalt particles (yellow dots), alumina particles (orange), and WC (green).

In the high-energy milling process, the powders were subjected to

high energy collisions, which cause plastic deformation, cold-welding, and powder fracturing. The more fragile particles (WC, Al2O3)

frac-tured, which refined and welded them in the ductile matrix (Co), as confirmed by SEM and EDS analysis (Fig. 7a and b, respectively). These figures illustrate the change in chemical element morphology and dis-tribution. The starting powders are well dispersed in this preparation condition, promoting an increase in particle size (Fig. 7c). For powder milled for 50 h, the average diameter was 53.81μm, a 70% increase over those mixed for 10 min.

3.4. Eﬀect of sintering temperature on microstructure and mechanical properties

Figs. 8 and 9show the X-ray diﬀractograms of samples sintered at 1400 °C and 1550 °C, mixed for 10 min and milled for 50 h, respec-tively. The diﬀractograms reveal new phases for the samples sintered at 1400 °C and 1550 °C, in contrast to initial powder phases before sin-tering. The sample sintered at 1400 °C (Fig. 8) exhibited peaks at dif-fraction angles (2θ) of 40.5, 42, 43 and 73°, corresponding to the (WC; Co3W), (Al2(WO4)3; CCo2W4), (Al2(WO4)3; Co3W) and (WC; CoCo2O4;

Co3W) phases, respectively. On the other hand, the sample sintered at

1550 °C showed higher peaks (approximately 40 and 73°), corre-sponding to the (Co6W6C; AlWO3) and Co6W6C phases, respectively.

With respect to the samples milled for 50 h and sintered at 1400 °C, Fig. 1. WC powder characterization: (a) SEM image (b) EDS analysis, (c) laser particle size distribution, (d) X-ray diﬀractogram.

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Fig. 9shows higher peaks at diﬀraction angles of 40, 58 and 73°, cor-responding to the (Al4C3; Co2C; WC), Co4(Co)12and WO2phases,

re-spectively. With a temperature increase to 1550 °C, more intense peaks are observed at 40, 58, and 73°, showing the presence of Co4(Co)12,

(WO3; Co4(Co)12) and WO2phases, respectively. Milling for 50 h

ob-tained a microstructure with poorly and well-deﬁned phases, which is also favored by an increase in temperature.

SEM images of samples sintered at 1400 °C exhibit a dividing plane between phases in the microstructures of the samples mixed for 10 min (Fig. 10a) and microstructures with less consolidated sintering phases (Fig. 10b). For the temperature of 1550 °C inFigs. 10(b) and11(b), the sintered samples underwent a complete sintering process, characterized by the formation of more widely distributed and uniform binder regions in the microstructures, especially when milled for 50 h. The non-vi-sualization of the binder phase grain boundary shows greater pore closure, resulting in higher material densification. This densification occurs due to the sintering temperature, which is higher than the eu-tectic temperature of the system, leading to the formation of a liquid phase, dissolving higher amounts of the Co causing greater densi fica-tion [16,22]. Thesefigures demonstrate that sintering temperature and powder preparation have a strong influence on the formation of a more uniform microstructure in the sintered sample.

3.5. Physicomechanical properties

The relative density and densiﬁcation results of mixed and milled WC-10% Co-10% Al2O3 composite samples sintered at 1400 °C and

1550 °C are shown inFigs. 12 and 13. Relative densities (ρ) are strongly influenced by powder preparation and temperature; at 1550 °C, both powder preparation methods were non-significant and relative density was 68% (Fig. 13). On the other hand, for 1400 °C, the sintered sample with powder mixed for 10 min showed higher density. Due to an in-crease in temperature, phenomena such as particle diffusion and cobalt meltfluidity were able to be changed, which resulted in amounts of liquid-phase tofill the pores or cover the solid particles, eliminating the solid-vapor interface [23,24]. Relative density was higher in sintered samples obtained for powder mixed for 10 min, likely because of its average diameter of around 16.15μm, 3.3 times smaller than that of particles milled for 50 h. According to [23], the high specific surface area (due to their small size) and large surface energy of these powders could cause quick dissolution in the liquid phase, promoting an increase in density through substance migration and WC precipitation.

Densification is influenced by sintering temperature (Fig. 13). A rise in this temperature decreases porosity, increasing densification, a strengthening mechanism [25]. These values are relatively lower when compared to other cermets because of the high melting point of Al2O3.

Fazili et al. [14] found that at 1350 °C, the cermet with WC-6 wt% Al2O3exhibited total densiﬁcation of 67%.

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Fig. 3. Al2O3powder characterization: (a) SEM image (b) EDS analysis, (c) laser particle size distribution, (d) X-ray diﬀractogram.

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Fig. 4. Diﬀractogram of WC-10% Co-10% Al2O3composite powder preparation time.

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Fig. 5. Enlarged diﬀractogram of WC-10% Co-10% Al2O3composite powder preparation time.

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Fig. 7. Powder milled for 50 h: a) SEM image, b) EDS mappging, and c) particle size distribuition curve.

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AlWO₃ u CoCo2O4 Co6W6C x ' x x u ) '  Al2(WO4)3 ' WC x Co3W ) CCo2W4

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Sintered at 1550° C Sintered at 1400° C

Fig. 8. Diﬀractogram of the samples sintered at 1400 °C and 1550 °C in the WC-10% Co-10% Al2O3composite when mixed for 10 min.

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Fig. 9. Diﬀractogram of the samples sintered at 1400 °C and 1550 °C in the WC-10% Co-10% Al2O3composite when milled for 50 h.

Fig. 10. Scanning electron micrograph of the samples mixed for 10 min and sintered: (a) at 1400 °C and (b) 1550 °C.

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Fig. 14shows the dilatometric curves for each WC-10% Co-10% Al2O3composite sample sintered from ambient temperature (25 °C) to

1550 °C, with a constant sintering temperature of 1 h. As the sintering temperature increased to 1550 °C both the mixed and milled samples exhibited increased shrinkage. For 50 h of milling, the samples ex-perienced the largest dilatometric shrinkage, indicating an average variation from the initial point of approximately−0.30, thereby con-firming the improved densification of this sintered sample. This shrinkage is depicted in Figs. 12 and 13, with approximate relative density of 68% and 45% higher densification. However, samples mixed for 10 min and sintered at 1550 °C obtained approximate dilatometric shrinkage of−0.15.

Fig. 14 shows that the structure shrinks quickly due to the ca-pillarity force exerted by the open pores and the meniscus at the edges of the samples. In addition, insufficient amounts of liquid are formed. This stage ends with sample densification or when the capillarity force is inadequate to close the remaining pores [22,24]. The relative density and densification obtained for the sample sintered by high energy milling confirm the increasing trend in these mechanical properties

with a rise in sintering temperature [26,27].

The influence of sintering temperature and powder preparation method on Vicker's hardness is shown in Fig. 15. When sintered at 1550 °C, the samples obtained higher hardness values of approximately 280 HV for those milled at 50 h, and 239 HV for those mixed for 10 min. Given that the sintered samples are composed of porous re-gions, the hardness values are generally lower than those of entirely solid materials with the same composition and metallurgical properties [28]. In fact, the penetrator will find less resistance in the sintered sample, and the random presence of pores makes the difference be-tween the minimum and maximum hardness values much higher than those obtained in the entirely solid material [28]. Hardness is lower [14] because in the present study, the cermet contains a larger amount of binder, 20% - Co + Al2O3against 6%- Co + Al2O3[14], promoting a

decrease in hardness. Low densiﬁcation precluded measuring the hardness of samples sintered at 1400 °C.

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Fig. 12. Relative density of the sintered (1400 °C and 1550 °C) WC-10% Co-10% Al2O3composite samples, mixed for 10 min and milled for 50 h.

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Fig. 13. Densiﬁcation of the sintered (1400 °C and 1550 °C) green compact from WC-10% Co-10% Al2O3composite samples, mixed for 10 min and milled for 50 h.

(For interpretation of the references to colour in thisﬁgure legend, the reader is referred to the web version of this article.)

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4. Conclusions

The powder preparation method for sintering inﬂuences the prop-erties of the sintered sample. This paper compared two powder pre-paration techniques: mechanical mixing for 10 min and high energy milling for 50 h, and two sintering temperatures: 1400 and 1550 °C. The following conclusions can be drawn from the results:

•

Mechanical mixing preserves the intrinsic characteristics of starting powders; the particles did not break, but remained clustered.

•

On the other hand, after 50 h of high energy milling, the particles from the WC, Al2O3,and Co phases were reﬁned, deformed, and

welded in the Co agglutinate matrix, exhibiting a more uniform shape, as observed in the diﬀractogram powders throughout the high energy milling process. Moreover, the particle diameters of the milled powders showed an increase over the mixed powders

•

From the microstructural viewpoint, diﬀerent phases were formed during sintering at 1400 °C and 1550 °C. In sintering at 1550 °C, the samples showed dense phase microstructures, mainly when sub-mitted to high energy milling for 50 h, unlike the those sintered at 1400 °C.

•

The best relative density, densification, dilatometric shrinkage, and hardness values were obtained for the samples milled for 50 h and sintered at 1550 °C (68%, 45%,−0.30, and 280 HV, respectively). The addition of 10% by weight of alumina had a significant influ-ence on the sintering of the green compacts, mainly for the tem-perature of 1550 °C, due to the increased sinterability of the milled powders.

Declaration of Competing Interest

The authors declare that they have no known competingﬁnancial

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interests or personal relationships that could have appeared to inﬂu-ence the work reported in this paper.

Acknowledgments

The authors thank CAPES and CETENE/FACEPE for the funding provided to carry out this research.

References

[1] M.F. Rodrigues, Thermobaric Sinterization of the Hard Metal Alloy WC-10% Co, Masters Dissertation, State University of Northern Fluminense, Rio of Janeiro, Science and Technology Center, 2006.

[2] S. Zhao, X. Song, J. Zhang, X. Liu, Eﬀects of scale combination and contact con-dition of raw powders on SPS sintered near-nanocrystalline WC–Co alloy, Mater. Sci. Eng. A 473 (1) (2008) 323–329.

[3] Y. Zhengui, J.J. Stiglich, T.S. Sudarshan, Nano-grained Tungsten Carbide Cobalt (WC/Co), Materials Modiﬁcation, Inc., 2929 Eskridge Road, P-1, 1998. [4] J.D. Lamim, Sintering and Characterization of Carbide Alloys Containing Cobalt and

Titanium Using WC Nanometric Powders, Dissertation (Master), State University of North Fluminense Darcy, Rio de Janeiro, 2009 (in Portuguese).

[5] L. Prakash, Fundamentals and General Applications of Hardmetals, Comprehensive Hard Materials, Elsevier, 2014.

[6] S.K. Sun, G.J. Zhang, W.W. Wu, J.X. Liu, J. Zou, T. Suzuki, Y. Sakka, Reactive spark plasma sintering of binderless WC ceramics at 1500° C, Int. J. Refract. Met. Hard Mater. 43 (2014) 42–45.

[7] P.K. Nayak, H.T. Lin, M.P. Chang, W.H. Chen, J.L. Huang, Microstructure analysis and mechanical properties of a new class of Al2O3–WC nanocomposites fabricated

by spark plasma sintering, J. Eur. Ceram. Soc. 33 (15) (2013) 3095–3100. [8] D. Zheng, X. Li, X. Ai, C. Yang, Y. Li, Bulk WC–Al2O3composites prepared by spark

plasma sintering, Int. J. Refract. Met. Hard Mater. (2012),https://doi.org/10.1016/ j.ijrmhm.2011.07.003.

[9] H. Cheol Kim, I.J. Shon, J.K. Yoon, J.M. Doh, Z.A. Munir, Rapid sintering of ul-traﬁne WC–Ni cermets, Int. J. Refract. Met. Hard Mater. 24 (6) (2005) 427–431. [10] I.F. Machado, L. Girardini, I. Lonardelli, A. Molinari, The study of ternary carbides

formation during SPS consolidation process in the WC–Co–steel system, Int. J. Refract. Met. Hard Mater. 27 (5) (2009) 883–891.

[11] I.J. Shon, I.K. Jeong, I.Y. Ko, J.M. Doh, K.D. Woo, Sintering behavior and me-chanical properties of WC–10Co, WC–10Ni and WC–10Fe hard materials produced by high-frequency induction heated sintering, Ceram. Int. 35 (1) (2009) 339–344. [12] W.H. Chen, H.T. Lin, P.K. Nayak, M.P. Chang, J.L. Huang, Sintering behavior and mechanical properties of WC–Al2O3composites prepared by spark plasma sintering

(SPS), Int. J. Refract. Met. Hard Mater. 48 (2015) 414–417.

[13] R.T. Coelho, E.J. Silva, Materiais para ferramenta de corte em usinagem, Universidade de São Paulo -USP, São Paulo, 2018.

[14] A. Fazili, L. Nikzad, M.R. RahimiPour, M. Razavi, E. Salahi, Eﬀect of Al2O3ceramic

binder on mechanical and microstructure properties of spark plasma sintered WC-Co cermets, Int. J. Refract. Met. Hard Mater. (2017),https://doi.org/10.1016/j. ijrmhm.2017.08.010.

[15] A. Fazili, M.R. Derakhshandeh, S. Nejadshamsi, L. Nikzad, M. Razavi, E. Ghasali, Improved electrochemical and mechanical performance of WC-Co cemented car-bide by replacing a part of Co with Al2O3, J. Alloys Compd. 823 (2020) 153857.

[16] F.A.C. Milheiros, Production and Characterization of Nanostructured Composite Powders of WC-10Co Cemented Carbide by High Energy Milled, Dissertation (Master), State University of Norte Fluminense, Rio de Janeiro, 2006 (in Portuguese).

[17] J. Poetschke, V. Richter, A. Michaelis, Fundamentals of sintering nanoscaled bin-derless hardmetals, Int. J. Refract. Met. Hard Mater. 49 (2015) 124–132. [18] Z.Z. Fang, X. Wang, T. Ryu, K.S. Hwang, H.Y. Sohn, Synthesis, sintering, and

me-chanical properties of nanocrystalline cemented tungsten carbide–a review, Int. J. Refract. Met. Hard Mater. 27 (2) (2009) 288–299.

[19] E. Ghasali, A.H. Pakseresht, M. Alizadeh, K. Shirvanimoghaddam, T. Ebadzadeh, Vanadium carbide reinforced aluminum matrix composite prepared by conven-tional, microwave and spark plasma sintering, J. Alloys Compd. 688 (2016) 527–533.

[20] E. Ghasali, A. Pakseresht, A. Rahbari, H. Eslami-shahed, M. Alizadeh, T. Ebadzadeh, Mechanical properties and microstructure characterization of spark plasma and conventional sintering of Al–SiC–TiC composites, J. Alloys Compd. 666 (2016) 366–371.

[21] Z. Shixian, X. Song, J. Zhang, X. Liu, Eﬀects of scale combination and contact condition of raw powders on SPS sintered near-nanocrystalline WC–Co alloy, Mater. Sci. Eng. A 473 (2008) 323–329.

[22] J.R. Savi, Eﬀect of the Addition of Nb, Mo, Cr and Ti on the WC-6Co Carbide Microstructure, Dissertation (Master), Federal University of Rio Grande of Sul, Porto Alegre, 2011 (in Portuguese).

[23] Q. Yang, J. Yang, H. Yang, J. Ruan, The effects of fine WC contents and temperature on the microstructure and mechanical properties of inhomogeneous WC - (fine WC-Co), Ceram. Int. 42 (2016) 18100–18107.

[24] A.G.P. Silva, C. Alves, Theory of Sintering by solid phase: a critical analysis of its application, Ceramics 44 (289) (2008) São Paulo.

[25] S.H. Chang, S.L. Chen, Characterization and properties of sintered Co and WC-Ni- Fe hard metal alloys, J. Alloys Compd. 585 (2014) 407–413.

[26] W. Acchar, A.E. Martinelli, C.A.A. Cairo, Sintering behaviour of alumina tungsten carbide composites, Mat. Sci. Eng. A. 284 (2000) 84–87.

[27] T.P. Oliveira, Eﬀect of High Energy Milled on the Densiﬁcation and Microstructure of the Al2O3-Cu Composite. Dissertation (Master), Federal University of Rio Grande

of Norte, Porto Alegre, 2014, pp. 1–87 (in Portuguese).

[28] C.A.S. Filho, Surface Treatment of Iron-Based Sintered Structural Parts, Campinas State University, Campinas-SP, 2007.