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Comparison of Ti(C,N)-based cermets processed by hot-pressing sintering and conventional pressureless sintering
Accepted Manuscript Comparison of Ti(C,N)-based cermets processed by hot-pressing sintering and conventional pressureless sintering Qingzhong Xu, Xing Ai, Jun Zhao, Weizhen Qin, Yintao Wang, Feng Gong PII: DOI: Reference:
S0925-8388(14)02212-9 http://dx.doi.org/10.1016/j.jallcom.2014.08.261 JALCOM 32189
To appear in:
Journal of Alloys and Compounds
Received Date: Revised Date: Accepted Date:
2 July 2014 21 August 2014 21 August 2014
Please cite this article as: Q. Xu, X. Ai, J. Zhao, W. Qin, Y. Wang, F. Gong, Comparison of Ti(C,N)-based cermets processed by hot-pressing sintering and conventional pressureless sintering, Journal of Alloys and Compounds (2014), doi: http://dx.doi.org/10.1016/j.jallcom.2014.08.261
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Comparison of Ti(C,N)-based cermets processed by hot-pressing sintering and conventional pressureless sintering Qingzhong Xu, Xing Ai*, Jun Zhao, Weizhen Qin, Yintao Wang, Feng Gong Key Laboratory of High Efficiency and Clean Mechanical Manufacture of MOE, School of Mechanical Engineering, Shandong University, Jinan 250061, PR China Abstract A suitable sintering method is important to obtain the Ti(C,N)-based cermets with superior properties. In this paper, Ti(C,N)-based cermets were fabricated by hot-pressing sintering (HP) and conventional pressureless sintering (PLS) technology, respectively, to investigate the influence of different sintering methods on the microstructure and mechanical properties of cermets materials. The microstructure, fracture morphology, indention cracks and phase composition were observed and detected using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The transverse rupture strength (TRS), Vickers hardness (HV) and fracture toughness (KIC) were also measured. The results reveals that all of the Ti(C,N)-based cermets exhibit core-rim microstructures with black cores, white cores and grey rims embedded into metal binder phases. The grain size of the samples fabricated by HP is much finer and the structure is more compact than those fabricated by PLS, while there exist pores in the HP sintered samples. The sintering process has no influence on the phase composition of cermets, but affects the phase content and crystallinity. The samples fabricated by PLS present higher transverse rupture strength, fracture toughness and density than samples fabricated by HP. However, the HP sintered samples possess a higher hardness.
Keywords: Ti(C,N)-based cermets; Hot-pressing sintering; Conventional pressureless sintering; Microstructure; Mechanical properties
*
Corresponding author. Tel.: +86 053188392045; Fax: +86 053188392045.
E-mail address: [email protected]. 1
1. Introduction Nowadays, Ti(C,N)-based cermets have been widely used as cutting tools for semi-finishing and finishing of stainless steels and carbon steels because of their unique combination of properties such as high melting temperature, high hardness, wear resistance and thermal conductivities [1-3]. Compared with the conventional WC-based hardmetal tools, Ti(C,N)-based cermet tools can provide excellent chip, tolerance control as well as improved surface finish of machined parts, and can increase feeding speed [4]. The Ti(C,N)-based cermets which belong to hard and wear-resistant materials are commonly fabricated by a powder metallurgy method [5, 6]. In cermet processing, the starting powders are mixtures of Ti(C,N) solid solutions or the binary hard compounds TiC and TiN with the secondary carbides such as Mo2C, WC, TaC or NbC, which are added to improve sinterability, abrasion resistance or thermal shock resistance, and the metal powders of Mo, Ni or Co as the binder [7, 8]. After liquid phase sintering, the hard Ti(C,N) grains with the characteristic core-rim structure are dispersed in tough metallic binder phase [3]. Sintering method is a key process for the fabrication of Ti(C,N)-based cermets, because it largely determines the final characteristics of the hard phases and binder phases, the microstructure of the material and its final properties [6, 9].The most commonly used Ti(C,N)-based cermets production routes are conventional pressureless sintering (PLS), hot-pressing sintering (HP), hot isostatic pressing sintering (HIP) and spark plasma sintering (SPS) [1, 4]. Monteverde et al. [9] prepared the Ti(C,N)-based cermets by hot-pressing sintering at 1620 °C for 30 min (5 MPa of applied pressure), and found that the material exhibited a refined microstructure with some textured flaws of several tenths of microns, which was attributed to not-optimized sintering conditions. Xiong et al. [10] found that the ultra-fine Ti(C0.7N0.3)-based cermets prepared by HIP (1350 °C, 90 min, 70 MPa), had lower porosity, higher densities, finer grain size and a higher hardness of 93.5 HRA and a transverse rupture strength of 1740 MPa than those prepared by PLS at 1450 °C for 1 h. Lei et al. [11] made the comparison of SPS with PLS on the fabrication of ultrafine Ti(C,N)-based cermets, and revealed that the samples fabricated by PLS did not have the ultrafine grained characteristic, but the grain size of the samples fabricated by SPS was still below 0.5 µm. They also found that the mechanical properties of the samples fabricated by SPS were lower than those by PLS, due to the lower 2
densification. Few researchers make the comparison of Ti(C,N)-based cermets processed by hot-pressing sintering and conventional pressureless sintering. In this case, the industry is still lacking in understanding the influence mechanism of different sintering methods on the microstructure and mechanical properties of Ti(C,N)-based cermets. To investigated the effect of pressure and heating rate on the grain size, microstructure feature, phase evolution, dissolution-precipitation mechanism and mechanical properties of Ti(C,N)-based cermets, the cermets materials fabricated by HP were compared with those fabricated by PLS in this paper. The research can provide useful references to tool makers and help them to produce superior tools to meet different properties requirement by selecting a suitable sintering method.
2. Experimental procedures The starting powders and the particle size are listed in Table 1. Two prepared samples were labeled Sample A and Sample B, respectively. Sample A was prepared by powders of (WC + Mo2C) (25 wt.%), NiCo (15 wt.%) and Ti(C,N) (balance). And the composition of Sample B contained (TiC + WC) (20 wt.%), NiCoMo (30 wt.%) and Ti(C,N) (balance). The samples were prepared by the following method. Firstly, the initial powders were mixed by ball-milling in ethanol medium for 48 h, using WC milling pots and cemented carbide balls with a 7:1 ball-to-powder weight ratio. Secondly, the mixed powder was dried at 120 °C in a vacuum oven, and then sieved through an 80 mesh sieve for further use. At last, the dried powders were put in a graphite mold for the hot-pressing sintering and pressed with a pressure of 30 MPa. The heating rate was maintained as 95 °C/min below 950 °C, and then was changed to 40 °C/min till 1430 °C. After sintered at 1430 °C for 1.0 h under vacuum condition, the samples could be cooled to below 200 °C within 2 h. The powders used for the conventional pressureless sintering were mixed with 2.0 wt.% paraffin, and pressed into rectangular specimens under 400 MPa. Dewaxing was carried out below 500 °C in a vacuum furnace at a heating rate of 2 °C/min, and the sintering was conducted at a heating rate of 4 °C/min. Liquid phase sintering was fixed at 1430 °C for 1.0 h. After sintering, it took 5 h to cool the samples to below 200 °C. In this study, the Sample A and B fabricated by HP 3
were labeled A-HP and B-HP, respectively. The Sample A and B fabricated by PLS were labeled A-PLS and B-PLS, respectively. The hot-pressing sintered disks were cut, ground and polished into bars with dimensions of 35 mm × 4 mm × 3 mm. The pressureless sintered specimens were ground and polished to the dimensions of 20 mm × 6.5 mm × 5.25 mm. All of the edges of specimens were chamfered to eliminate the machining flaws. The transverse rupture strength was performed using a three-point bending tester (Model WDW-50E, China) at a loading velocity of 0.5 mm/min. The span for hot-pressing sintered specimens was 20 mm, while for pressureless sintered specimens was 14.5 mm. A Vickers indenter (Model MHVD-30AP, China) was used to measure the hardness with a load of 294 N and a duration time of 15 s. The fracture toughness was determined by the radial crack length around the Vickers indentation and the Shetty formula was applied. The density was tested by the Archimedes method with a densitometer (Model AUY120, Japan). Microstructures and cracks on the polished surfaces were investigated by scanning electron microscopy (SEM, Model JSM-6510LV, Japan) in a back-scattered electron (BSE) mode, the fractured surfaces were observed in a secondary electron (SE) mode, and the chemical compositions of phases were detected by energy dispersive spectroscopy (EDS). Phase identification of the specimens was analyzed by X-ray diffraction (XRD, RAX-10A-X, Hitachi, Japan).
3. Results and discussions 3.1 Effect of sintering process on microstructure The microstructures of Ti(C,N)-based cermets fabricated by HP and PLS methods are shown in Fig.1. All of the Ti(C,N)-based cermets exhibited core-rim microstructures with black cores (Point A in Fig.1), white cores (Point B in Fig.1) and grey rims (Point D in Fig.1) embedded into metal binder phases (Point C in Fig.1). The influence of sintering process on microstructure of Ti(C,N)-based cermets was mainly reflected by grain size and microstructure feature. The grain size of samples fabricated by HP was much finer than those fabricated by PLS. And in the samples fabricated by PLS, the rims forming around the cores were thicker. Due to the applied pressure, the structure of samples fabricated by HP was more compact than that of samples fabricated by PLS, while there existed 4
pores in the HP sintered samples as shown in Fig.1a and c. These pores were formed by the gas which did not completely escape from the cermets, owing to the higher heating rate between 1100 and 1300°C. The gas was mainly nitrogen coming from the decomposition of Ti(C,N). In order to analyze the chemical composition of the phases, EDS was employed to detect the fixed points in Fig. 1, and the result was shown in Table 2 ( since samples fabricated by HP had very small crystal grains, only the black cores and white cores were detected ). Within Ti(C,N)-based cermets, the black cores mainly contained Ti, C and N atoms; the white cores had high W, Mo and Ti contents; the content of W, Mo and Ti in rims was lower than the white cores, but higher than the black cores; and the binder phases had a much higher content of heavy elements, such as Ni, Mo, Co and W. EDS reveals that the Co and Ni contents in the white cores of samples fabricated by HP were lower than those of samples fabricated by PLS, respectively. The reason is that the lower heating rate of 4 °C/min in PLS process can improve the solid phase diffusion reaction more than the higher heating rate of 40 °C/min in HP process. Ostwald’s dissolution-precipitation theory had been used to reveal the formation of core-rim microstructures of Ti(C,N)-based cermets which was different from WC-Co hardmetals [12-14]. The black cores were the remainders of undissolved coarse Ti(C,N) particles and the white cores were formed by the chemical reaction of dissolved fine Ti(C,N) particles with Mo2C and WC [4, 10, 15]; The inner rim phase developed through the diffusion of W, Mo and other atoms during solid sintering, while the outer rim was formed by the precipitation of dissolved carbides during liquid sintering [12, 16-18]. Quach et al. [19] reported that the higher heating rate could result in smaller grain size and the applied pressure was sufficient to break soft agglomerates and caused particle rearrangement, which contributed to densification and avoided grain-coarsening. For Ti(C,N)-based cermets, the temperature range of solid state sintering was from 1000 to 1300 °C, and the liquid phase sintering stage was between 1300 and 1430 °C. Compared with samples fabricated by PLS, the powder compact fabricated by HP could be heated up and cooled down quickly, so the exposure time at the high temperature between 1000 to 1430 °C was shortened, then the grain growth was prevented. Furthermore, during HP sintering, the applied pressure could rearrange particles before liquid sintering, 5
so a fine microstructure of Ti(C,N)-based cermets could be obtained by HP. However, for the cermets fabricated by PLS, many smaller Ti(C,N) particles dissolved and more metal carbides precipitated in the form of solution of (Ti,W,Mo)(C,N) surrounding the undissolved particles, so the reaction in solid sintering and the dissolution-precipitation in liquid phase sintering favorably developed, which resulted in grain growth [15]. 3.2 Influence of sintering process on phase compositions The XRD patterns of Ti(C,N)-based cermets fabricated by different process are given in Fig. 2. For the samples with the same powder components, no difference in the phase composition was found, though the sintering process was different. Taking into account the relationship among metallurgical reactions, elements diffusion, phase evolution and crystal structures during sample sintering [20-22], it is believed that the phase evolution and the dissolution-precipitation mechanism of Ti(C,N)-based cermets during HP process were the same as that during PLS process. However, the diffraction peak of Ti(C,N) in samples prepared by HP was higher than that of the same samples prepared by PLS. Considering that the diffraction peak intensity is proportional to the crystallinity and content of phase, it can be concluded that both the crystallinity and content of Ti(C,N) in samples prepared by HP were higher than those of samples prepared by PLS. This is consistent with the microstructure of cermets as shown in Fig. 1. As a result of the improved solid phase elements diffusion reaction, there were fewer black cores, which were undissolved Ti(C,N) particles, and more white cores, which were formed by elements diffusion, in the samples fabricated by PLS than in the ones fabricated by HP. 3.3 Mechanical properties analysis The transverse rupture strength, Vickers hardness, fracture toughness and density of different samples fabricated by HP and PLS are shown in Fig. 3a–d. Samples fabricated by HP presented lower transverse rupture strength, fracture toughness and density than samples fabricated by PLS, while exhibited higher Vickers hardness. It was reported [23] that the binder phase and a much developed surrounding phase could improve the transverse rupture strength and the fracture toughness of Ti(C,N)-based cermets. For HP process, the higher heating rate was not conducive to the elements diffusion and the gaseous escape during solid sintering, which were detrimental to the 6
formation of inner rims and the decrease of porosity. During liquid sintering, the applied pressure made the binder phases thin (see Fig. 1a and c), which weakened the toughening effect. All of the above reasons would lead to deteriorated transverse rupture strength, fracture toughness and densification for the Ti(C,N)-based cermets fabricated by HP. Compared with samples fabricated by PLS, the HP sintered samples possessed a higher hardness. This is attributed to the finer grains size and the lower binder phase content. In order to further analyze the relationship between fracture toughness and microstructure, both the fracture surfaces of bending strength test specimens and the crack propagation paths of cermets made by indentation are observed as shown in Fig. 4 and Fig. 5, respectively. As shown in Fig. 4, more cleavage fractures of grains were observed in the samples prepared by HP, and the fracture surface was flatter. This was a typical brittle fracture and could result in poor fracture toughness. However, with the cavities formed by the pulling of hard phases and the tearing ridges caused by the metal phase tearing, the fracture surface of samples prepared by PLS was uneven and could absorb more fracture energy, due to the increased amounts of grain boundaries, which contributed to higher fracture toughness. It can be seen from Fig. 5 that cracks made by indentation in samples prepared by HP tended to propagate with transgranular fractures, and the path was nearly straight with less crack deflection. While in samples prepared by PLS, a lot of intergranular cracks were observed, which could increase the toughness of cermets, as a result of the increased area of crack surface by crack deflection.
4. Conclusions Ti(C,N)-based cermets with different powder compositions were prepared by powder metallurgy in order to investigate the effect of HP and PLS process on the microstructure and mechanical properties of cermets materials. The conclusions can be drawn as follows: (1) All of the Ti(C,N)-based cermets exhibit core-rim microstructures with black cores, white cores and grey rims embedded into metal binder phases. Because of the higher heating rate and the applied pressure, the grain size of the samples fabricated by HP is much finer and the structure is more compact than those fabricated by PLS, while there exist pores in the HP sintered samples. 7
(2) The sintering process has no influence on the phase composition, but affects the phase content and crystallinity. Both the crystallinity and content of Ti(C,N) in samples prepared by HP are higher than those of samples prepared by PLS. (3) During the PLS process, the binder phase and surrounding phase trend to develop with lower porosity, hence samples fabricated by PLS present higher transverse rupture strength, fracture toughness and density than samples fabricated by HP. However, the HP sintered samples possess a higher hardness, which is attributed to the finer grains size and the lower binder phase content. (4) The intergranular fractures and intergranular cracks in samples prepared by PLS are more than those in HP sintered samples, in which there exist a lot of cleavage fractures and transgranular fractures. (5) PLS process can be used to fabricate Ti(C,N)-based cermets which require higher transverse rupture strength and fracture toughness. And HP process can be chosen to obtain Ti(C,N)-based cermets with higher hardness.
Acknowledgments This work was sponsored by the National Natural Science Foundation of China (51175310) and the National Basic Research Program of China (2009CB724402).
References [1] S. Cardinal, A. Malchere, V. Garnier, G. Fantozzi, Microstructure and mechanical properties of TiC-TiN based cermets for tools application, Int. J. Refract. Met. Hard Mater. 27 (2009) 521-527. [2] J. Russias, S. Cardinal, Y. Aguni, G. Fantozzi, K. Bienvenu, J. Fontaine, Influence of titanium nitride addition on the microstructure and mechanical properties of TiC-based cermets, Int. J. Refract. Met. Hard Mater. 23 (2005) 358-362. [3] Q. Yang, W. Xiong, S. Li, J. Li, Effect of partial substitution of Cr for Ni on densification behavior, microstructure evolution and mechanical properties of Ti(C,N)-Ni-based cermets, J. Alloys Compd. 509 (2011) 4828-4834. [4] Y. Peng, H. Miao, Z. Peng, Development of TiCN-based cermets: Mechanical properties and 8
wear mechanism, Int. J. Refract. Met. Hard Mater. 39 (2013) 78-89. [5] S. Boudebane, S. Lemboub, S. Graini, A. Boudebane, A. Khettache, J. Le Lannic, Effect of binder content on relative density, microstructure and properties of complex cemented carbides obtained by thermal explosion-pressing, J. Alloys Compd. 487 (2009) 235-242. [6] J.M. Córdoba, E. Chicardi, F.J. Gotor, Liquid-phase sintering of Ti(C,N)-based cermets. The effects of binder nature and content on the solubility and wettability of hard ceramic phases, J. Alloys Compd. 559 (2013) 34-38. [7] V.R. Dizaji, M. Rahmani, M.F. Sani, Z. Nemati, J. Akbari, Microstructure and cutting performance investigation of Ti(C,N)-based cermets containing various types of secondary carbides, Int. J. Mach. Tools Manuf. 47 (2007) 768-772. [8] Z. Shi, D. Zhang, S. Chen, T. Wang, Effect of nitrogen content on microstructures and mechanical properties of Ti(C,N)-based cermets, J. Alloys Compd. 568 (2013) 68-72. [9] F. Monteverde, M. V, A. Bellosi, Microstructure of hot-pressed Ti(C,N)-based cermets, J. Eur. Ceram. Soc. 22 (2002) 2587-2593. [10] J. Xiong, Z. Guo, M. Yang, B. Shen, Preparation of ultra-fine TiC0.7N0.3-based cermet, Int. J. Refract. Met. Hard Mater. 26 (2008) 212-219. [11] Y. Lei, W.H. Xiong, Z.G. Liang, P. Feng, Z.W. Wang, Comparative study of the fabrication of ultrafine Ti(C,N)-based cermets by spark plasma sintering and conventional vacuum sintering, Rare Metals. 24 (2005) 131-136. [12] P.P. Li, J.W. Ye, Y. Liu, D.J. Yang, H.J. Yu, Study on the formation of core-rim structure in Ti(CN)-based cermets, Int. J. Refract. Met. Hard Mater. 35 (2012) 27-31. [13] D. Mari, S. Bolognini, G. Feusier, T. Cutard, C. Verdon, T. Viatte, W. Benoit, TiMoCN based cermets - Part I. Morphology and phase composition, Int. J. Refract. Met. Hard Mater. 21 (2003) 37-46. [14] J. Poetschke, V. Richter, T. Gestrich, A. Michaelis, Grain growth during sintering of tungsten carbide ceramics, Int. J. Refract. Met. Hard Mater. 43 (2014) 309-316. [15] P. Feng, Y.H. He, Y.F. Xiao, W.H. Xiong, Effect of VC addition on sinterability and microstructure of ultrafine Ti(C,N)-based cermets in spark plasma sintering, J. Alloys Compd. 9
460 (2008) 453-459. [16] S. Ahn, S. Kang, Dissolution phenomena in the Ti(C0.7N0.3)-WC-Ni system, Int. J. Refract. Met. Hard Mater. 26 (2008) 340-345. [17] P. Feng, W.H. Xiong, L.X. Yu, Y. Zheng, Y.H. Xia, Phase evolution and microstructure characteristics of ultrafine Ti(C,N)-based cermet by spark plasma sintering, Int. J. Refract. Met. Hard Mater. 22 (2004) 133-138. [18] J. Xiong, Z. Guo, F. Chen, B. Shen, Phase evolution in ultra-fine TiC0.7N0.3-based cermet during sintering, Int. J. Refract. Met. Hard Mater. 25 (2007) 367-373. [19] D.V. Quach, H. Avila-Paredes, S. Kim, M. Martin, Z.A. Munir, Pressure effects and grain growth kinetics in the consolidation of nanostructured fully stabilized zirconia by pulsed electric current sintering, Acta Mater. 58 (2010) 5022-5030. [20] S.Y. Ahn, S. Kang, Formation of core/rim structures in Ti(C,N)-WC-Ni cermets via a dissolution and precipitation process, J. Am. Ceram. Soc. 83 (2000) 1489-1494. [21] H.O. Andren, Microstructure development during sintering and heat-treatment of cemented carbides and cermets, Mater. Chem. Phys. 67 (2001) 209-213. [22] Y. Zheng, S.X. Wang, Y.L. Yan, N.W. Zhao, X. Chen, Microstructure evolution and phase transformation during spark plasma sintering of Ti(C,N)-based cermets, Int. J. Refract. Met. Hard Mater. 26 (2008) 306-311. [23] H. Zhang, H.H. Yan, Z. X, S.W. Tang, Properties of titanium carbonitride matrix cermets, Int. J. Refract. Met. Hard Mater. 24 (2006) 236-239.
Figure captions Fig. 1. SEM micrographs of Ti(C,N)-based cermets fabricated by different processes: (a) A-HP, (b) A-PLS, (c) B-HP, (d) B-PLS. Fig. 2. XRD profiles of (a) A-HP, (b) A-PLS, (c) B-HP, (d) B-PLS. Fig. 3. Effect of sintering process on the (a) transverse rupture strength, (b) fracture toughness, (c) Vickers hardness and (d) density of cermets. Fig. 4. SEM micrographs of fracture surface: (a) A-HP, (b) A-PLS, (c) B-HP, (d) B-PLS. 10
Fig. 5. SEM micrographs of crack propagation paths: (a) A-HP, (b) A-PLS, (c) B-HP, (d) B-PLS.
11
Fig. 1. SEM micrographs of Ti(C,N)-based cermets fabricated by different processes: (a) A-HP, (b) A-PLS, (c) B-HP, (d) B-PLS.
Fig. 2. XRD profiles of (a) A-HP, (b) A-PLS, (c) B-HP, (d) B-PLS. 12
Fig. 3. Effect of sintering process on the (a) transverse rupture strength, (b) fracture toughness, (c) Vickers hardness and (d) density of cermets.
13
Fig. 4. SEM micrographs of fracture surface: (a) A-HP, (b) A-PLS, (c) B-HP, (d) B-PLS.
Fig. 5. SEM micrographs of crack propagation paths: (a) A-HP, (b) A-PLS, (c) B-HP, (d) B-PLS.
14
Table 1 Mean particle size of the raw powders. Powder
Ti(C,N)
TiC
WC
Mo2C
Ni
Co
Mo
Mean particle size (µm)
0.5
0.5
0.6
0.1
0.05
0.03
0.6
Table 2 Results of EDS analysis (correspond to Fig. 1) Element (at%) A-HP
A-PLS
B-HP
B-PLS
C
N
Ti
Co
Ni
Mo
W
A
51.49
6.49
33.91
0
1.76
3.33
3.01
B
55.59
0
36.41
0.29
0.61
3.75
3.34
A
43.24
13.30
34.68
0.98
2.67
2.90
2.23
B
51.17
0
22.51
4.74
14.19
4.04
3.35
C
53.93
0
34.60
0.69
2.45
4.57
3.76
A
52.04
9.04
31.72
1.85
1.28
1.39
2.68
B
60.50
0.46
30.94
0.33
0.85
3.71
3.20
A
49.81
1.88
43.60
0.45
0.64
1.19
2.42
B
55.28
0
35.91
1.20
1.56
2.15
3.91
C
43.83
0
14.46
16.76
21.28
1.49
2.17
D
53.57
0
39.76
0.37
0.52
1.99
3.78
15
16
Highlights: The hot-pressing sintered Ti(C,N)-based cermets exhibit high hardness with fine grain size. The Ti(C,N)-based cermets fabricated by conventional pressureless sintering possess high transverse rupture strength, fracture toughness and density with low porosity. The applied pressure can rearrange particles before liquid sintering and contribute to grain refinement. The heating rate has a great effect on the elements diffusion and the gaseous escape in solid sintering, and the dissolution-precipitation of phases during liquid phase sintering.
17
S0925-8388(14)02212-9 http://dx.doi.org/10.1016/j.jallcom.2014.08.261 JALCOM 32189
To appear in:
Journal of Alloys and Compounds
Received Date: Revised Date: Accepted Date:
2 July 2014 21 August 2014 21 August 2014
Please cite this article as: Q. Xu, X. Ai, J. Zhao, W. Qin, Y. Wang, F. Gong, Comparison of Ti(C,N)-based cermets processed by hot-pressing sintering and conventional pressureless sintering, Journal of Alloys and Compounds (2014), doi: http://dx.doi.org/10.1016/j.jallcom.2014.08.261
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Comparison of Ti(C,N)-based cermets processed by hot-pressing sintering and conventional pressureless sintering Qingzhong Xu, Xing Ai*, Jun Zhao, Weizhen Qin, Yintao Wang, Feng Gong Key Laboratory of High Efficiency and Clean Mechanical Manufacture of MOE, School of Mechanical Engineering, Shandong University, Jinan 250061, PR China Abstract A suitable sintering method is important to obtain the Ti(C,N)-based cermets with superior properties. In this paper, Ti(C,N)-based cermets were fabricated by hot-pressing sintering (HP) and conventional pressureless sintering (PLS) technology, respectively, to investigate the influence of different sintering methods on the microstructure and mechanical properties of cermets materials. The microstructure, fracture morphology, indention cracks and phase composition were observed and detected using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The transverse rupture strength (TRS), Vickers hardness (HV) and fracture toughness (KIC) were also measured. The results reveals that all of the Ti(C,N)-based cermets exhibit core-rim microstructures with black cores, white cores and grey rims embedded into metal binder phases. The grain size of the samples fabricated by HP is much finer and the structure is more compact than those fabricated by PLS, while there exist pores in the HP sintered samples. The sintering process has no influence on the phase composition of cermets, but affects the phase content and crystallinity. The samples fabricated by PLS present higher transverse rupture strength, fracture toughness and density than samples fabricated by HP. However, the HP sintered samples possess a higher hardness.
Keywords: Ti(C,N)-based cermets; Hot-pressing sintering; Conventional pressureless sintering; Microstructure; Mechanical properties
*
Corresponding author. Tel.: +86 053188392045; Fax: +86 053188392045.
E-mail address: [email protected]. 1
1. Introduction Nowadays, Ti(C,N)-based cermets have been widely used as cutting tools for semi-finishing and finishing of stainless steels and carbon steels because of their unique combination of properties such as high melting temperature, high hardness, wear resistance and thermal conductivities [1-3]. Compared with the conventional WC-based hardmetal tools, Ti(C,N)-based cermet tools can provide excellent chip, tolerance control as well as improved surface finish of machined parts, and can increase feeding speed [4]. The Ti(C,N)-based cermets which belong to hard and wear-resistant materials are commonly fabricated by a powder metallurgy method [5, 6]. In cermet processing, the starting powders are mixtures of Ti(C,N) solid solutions or the binary hard compounds TiC and TiN with the secondary carbides such as Mo2C, WC, TaC or NbC, which are added to improve sinterability, abrasion resistance or thermal shock resistance, and the metal powders of Mo, Ni or Co as the binder [7, 8]. After liquid phase sintering, the hard Ti(C,N) grains with the characteristic core-rim structure are dispersed in tough metallic binder phase [3]. Sintering method is a key process for the fabrication of Ti(C,N)-based cermets, because it largely determines the final characteristics of the hard phases and binder phases, the microstructure of the material and its final properties [6, 9].The most commonly used Ti(C,N)-based cermets production routes are conventional pressureless sintering (PLS), hot-pressing sintering (HP), hot isostatic pressing sintering (HIP) and spark plasma sintering (SPS) [1, 4]. Monteverde et al. [9] prepared the Ti(C,N)-based cermets by hot-pressing sintering at 1620 °C for 30 min (5 MPa of applied pressure), and found that the material exhibited a refined microstructure with some textured flaws of several tenths of microns, which was attributed to not-optimized sintering conditions. Xiong et al. [10] found that the ultra-fine Ti(C0.7N0.3)-based cermets prepared by HIP (1350 °C, 90 min, 70 MPa), had lower porosity, higher densities, finer grain size and a higher hardness of 93.5 HRA and a transverse rupture strength of 1740 MPa than those prepared by PLS at 1450 °C for 1 h. Lei et al. [11] made the comparison of SPS with PLS on the fabrication of ultrafine Ti(C,N)-based cermets, and revealed that the samples fabricated by PLS did not have the ultrafine grained characteristic, but the grain size of the samples fabricated by SPS was still below 0.5 µm. They also found that the mechanical properties of the samples fabricated by SPS were lower than those by PLS, due to the lower 2
densification. Few researchers make the comparison of Ti(C,N)-based cermets processed by hot-pressing sintering and conventional pressureless sintering. In this case, the industry is still lacking in understanding the influence mechanism of different sintering methods on the microstructure and mechanical properties of Ti(C,N)-based cermets. To investigated the effect of pressure and heating rate on the grain size, microstructure feature, phase evolution, dissolution-precipitation mechanism and mechanical properties of Ti(C,N)-based cermets, the cermets materials fabricated by HP were compared with those fabricated by PLS in this paper. The research can provide useful references to tool makers and help them to produce superior tools to meet different properties requirement by selecting a suitable sintering method.
2. Experimental procedures The starting powders and the particle size are listed in Table 1. Two prepared samples were labeled Sample A and Sample B, respectively. Sample A was prepared by powders of (WC + Mo2C) (25 wt.%), NiCo (15 wt.%) and Ti(C,N) (balance). And the composition of Sample B contained (TiC + WC) (20 wt.%), NiCoMo (30 wt.%) and Ti(C,N) (balance). The samples were prepared by the following method. Firstly, the initial powders were mixed by ball-milling in ethanol medium for 48 h, using WC milling pots and cemented carbide balls with a 7:1 ball-to-powder weight ratio. Secondly, the mixed powder was dried at 120 °C in a vacuum oven, and then sieved through an 80 mesh sieve for further use. At last, the dried powders were put in a graphite mold for the hot-pressing sintering and pressed with a pressure of 30 MPa. The heating rate was maintained as 95 °C/min below 950 °C, and then was changed to 40 °C/min till 1430 °C. After sintered at 1430 °C for 1.0 h under vacuum condition, the samples could be cooled to below 200 °C within 2 h. The powders used for the conventional pressureless sintering were mixed with 2.0 wt.% paraffin, and pressed into rectangular specimens under 400 MPa. Dewaxing was carried out below 500 °C in a vacuum furnace at a heating rate of 2 °C/min, and the sintering was conducted at a heating rate of 4 °C/min. Liquid phase sintering was fixed at 1430 °C for 1.0 h. After sintering, it took 5 h to cool the samples to below 200 °C. In this study, the Sample A and B fabricated by HP 3
were labeled A-HP and B-HP, respectively. The Sample A and B fabricated by PLS were labeled A-PLS and B-PLS, respectively. The hot-pressing sintered disks were cut, ground and polished into bars with dimensions of 35 mm × 4 mm × 3 mm. The pressureless sintered specimens were ground and polished to the dimensions of 20 mm × 6.5 mm × 5.25 mm. All of the edges of specimens were chamfered to eliminate the machining flaws. The transverse rupture strength was performed using a three-point bending tester (Model WDW-50E, China) at a loading velocity of 0.5 mm/min. The span for hot-pressing sintered specimens was 20 mm, while for pressureless sintered specimens was 14.5 mm. A Vickers indenter (Model MHVD-30AP, China) was used to measure the hardness with a load of 294 N and a duration time of 15 s. The fracture toughness was determined by the radial crack length around the Vickers indentation and the Shetty formula was applied. The density was tested by the Archimedes method with a densitometer (Model AUY120, Japan). Microstructures and cracks on the polished surfaces were investigated by scanning electron microscopy (SEM, Model JSM-6510LV, Japan) in a back-scattered electron (BSE) mode, the fractured surfaces were observed in a secondary electron (SE) mode, and the chemical compositions of phases were detected by energy dispersive spectroscopy (EDS). Phase identification of the specimens was analyzed by X-ray diffraction (XRD, RAX-10A-X, Hitachi, Japan).
3. Results and discussions 3.1 Effect of sintering process on microstructure The microstructures of Ti(C,N)-based cermets fabricated by HP and PLS methods are shown in Fig.1. All of the Ti(C,N)-based cermets exhibited core-rim microstructures with black cores (Point A in Fig.1), white cores (Point B in Fig.1) and grey rims (Point D in Fig.1) embedded into metal binder phases (Point C in Fig.1). The influence of sintering process on microstructure of Ti(C,N)-based cermets was mainly reflected by grain size and microstructure feature. The grain size of samples fabricated by HP was much finer than those fabricated by PLS. And in the samples fabricated by PLS, the rims forming around the cores were thicker. Due to the applied pressure, the structure of samples fabricated by HP was more compact than that of samples fabricated by PLS, while there existed 4
pores in the HP sintered samples as shown in Fig.1a and c. These pores were formed by the gas which did not completely escape from the cermets, owing to the higher heating rate between 1100 and 1300°C. The gas was mainly nitrogen coming from the decomposition of Ti(C,N). In order to analyze the chemical composition of the phases, EDS was employed to detect the fixed points in Fig. 1, and the result was shown in Table 2 ( since samples fabricated by HP had very small crystal grains, only the black cores and white cores were detected ). Within Ti(C,N)-based cermets, the black cores mainly contained Ti, C and N atoms; the white cores had high W, Mo and Ti contents; the content of W, Mo and Ti in rims was lower than the white cores, but higher than the black cores; and the binder phases had a much higher content of heavy elements, such as Ni, Mo, Co and W. EDS reveals that the Co and Ni contents in the white cores of samples fabricated by HP were lower than those of samples fabricated by PLS, respectively. The reason is that the lower heating rate of 4 °C/min in PLS process can improve the solid phase diffusion reaction more than the higher heating rate of 40 °C/min in HP process. Ostwald’s dissolution-precipitation theory had been used to reveal the formation of core-rim microstructures of Ti(C,N)-based cermets which was different from WC-Co hardmetals [12-14]. The black cores were the remainders of undissolved coarse Ti(C,N) particles and the white cores were formed by the chemical reaction of dissolved fine Ti(C,N) particles with Mo2C and WC [4, 10, 15]; The inner rim phase developed through the diffusion of W, Mo and other atoms during solid sintering, while the outer rim was formed by the precipitation of dissolved carbides during liquid sintering [12, 16-18]. Quach et al. [19] reported that the higher heating rate could result in smaller grain size and the applied pressure was sufficient to break soft agglomerates and caused particle rearrangement, which contributed to densification and avoided grain-coarsening. For Ti(C,N)-based cermets, the temperature range of solid state sintering was from 1000 to 1300 °C, and the liquid phase sintering stage was between 1300 and 1430 °C. Compared with samples fabricated by PLS, the powder compact fabricated by HP could be heated up and cooled down quickly, so the exposure time at the high temperature between 1000 to 1430 °C was shortened, then the grain growth was prevented. Furthermore, during HP sintering, the applied pressure could rearrange particles before liquid sintering, 5
so a fine microstructure of Ti(C,N)-based cermets could be obtained by HP. However, for the cermets fabricated by PLS, many smaller Ti(C,N) particles dissolved and more metal carbides precipitated in the form of solution of (Ti,W,Mo)(C,N) surrounding the undissolved particles, so the reaction in solid sintering and the dissolution-precipitation in liquid phase sintering favorably developed, which resulted in grain growth [15]. 3.2 Influence of sintering process on phase compositions The XRD patterns of Ti(C,N)-based cermets fabricated by different process are given in Fig. 2. For the samples with the same powder components, no difference in the phase composition was found, though the sintering process was different. Taking into account the relationship among metallurgical reactions, elements diffusion, phase evolution and crystal structures during sample sintering [20-22], it is believed that the phase evolution and the dissolution-precipitation mechanism of Ti(C,N)-based cermets during HP process were the same as that during PLS process. However, the diffraction peak of Ti(C,N) in samples prepared by HP was higher than that of the same samples prepared by PLS. Considering that the diffraction peak intensity is proportional to the crystallinity and content of phase, it can be concluded that both the crystallinity and content of Ti(C,N) in samples prepared by HP were higher than those of samples prepared by PLS. This is consistent with the microstructure of cermets as shown in Fig. 1. As a result of the improved solid phase elements diffusion reaction, there were fewer black cores, which were undissolved Ti(C,N) particles, and more white cores, which were formed by elements diffusion, in the samples fabricated by PLS than in the ones fabricated by HP. 3.3 Mechanical properties analysis The transverse rupture strength, Vickers hardness, fracture toughness and density of different samples fabricated by HP and PLS are shown in Fig. 3a–d. Samples fabricated by HP presented lower transverse rupture strength, fracture toughness and density than samples fabricated by PLS, while exhibited higher Vickers hardness. It was reported [23] that the binder phase and a much developed surrounding phase could improve the transverse rupture strength and the fracture toughness of Ti(C,N)-based cermets. For HP process, the higher heating rate was not conducive to the elements diffusion and the gaseous escape during solid sintering, which were detrimental to the 6
formation of inner rims and the decrease of porosity. During liquid sintering, the applied pressure made the binder phases thin (see Fig. 1a and c), which weakened the toughening effect. All of the above reasons would lead to deteriorated transverse rupture strength, fracture toughness and densification for the Ti(C,N)-based cermets fabricated by HP. Compared with samples fabricated by PLS, the HP sintered samples possessed a higher hardness. This is attributed to the finer grains size and the lower binder phase content. In order to further analyze the relationship between fracture toughness and microstructure, both the fracture surfaces of bending strength test specimens and the crack propagation paths of cermets made by indentation are observed as shown in Fig. 4 and Fig. 5, respectively. As shown in Fig. 4, more cleavage fractures of grains were observed in the samples prepared by HP, and the fracture surface was flatter. This was a typical brittle fracture and could result in poor fracture toughness. However, with the cavities formed by the pulling of hard phases and the tearing ridges caused by the metal phase tearing, the fracture surface of samples prepared by PLS was uneven and could absorb more fracture energy, due to the increased amounts of grain boundaries, which contributed to higher fracture toughness. It can be seen from Fig. 5 that cracks made by indentation in samples prepared by HP tended to propagate with transgranular fractures, and the path was nearly straight with less crack deflection. While in samples prepared by PLS, a lot of intergranular cracks were observed, which could increase the toughness of cermets, as a result of the increased area of crack surface by crack deflection.
4. Conclusions Ti(C,N)-based cermets with different powder compositions were prepared by powder metallurgy in order to investigate the effect of HP and PLS process on the microstructure and mechanical properties of cermets materials. The conclusions can be drawn as follows: (1) All of the Ti(C,N)-based cermets exhibit core-rim microstructures with black cores, white cores and grey rims embedded into metal binder phases. Because of the higher heating rate and the applied pressure, the grain size of the samples fabricated by HP is much finer and the structure is more compact than those fabricated by PLS, while there exist pores in the HP sintered samples. 7
(2) The sintering process has no influence on the phase composition, but affects the phase content and crystallinity. Both the crystallinity and content of Ti(C,N) in samples prepared by HP are higher than those of samples prepared by PLS. (3) During the PLS process, the binder phase and surrounding phase trend to develop with lower porosity, hence samples fabricated by PLS present higher transverse rupture strength, fracture toughness and density than samples fabricated by HP. However, the HP sintered samples possess a higher hardness, which is attributed to the finer grains size and the lower binder phase content. (4) The intergranular fractures and intergranular cracks in samples prepared by PLS are more than those in HP sintered samples, in which there exist a lot of cleavage fractures and transgranular fractures. (5) PLS process can be used to fabricate Ti(C,N)-based cermets which require higher transverse rupture strength and fracture toughness. And HP process can be chosen to obtain Ti(C,N)-based cermets with higher hardness.
Acknowledgments This work was sponsored by the National Natural Science Foundation of China (51175310) and the National Basic Research Program of China (2009CB724402).
References [1] S. Cardinal, A. Malchere, V. Garnier, G. Fantozzi, Microstructure and mechanical properties of TiC-TiN based cermets for tools application, Int. J. Refract. Met. Hard Mater. 27 (2009) 521-527. [2] J. Russias, S. Cardinal, Y. Aguni, G. Fantozzi, K. Bienvenu, J. Fontaine, Influence of titanium nitride addition on the microstructure and mechanical properties of TiC-based cermets, Int. J. Refract. Met. Hard Mater. 23 (2005) 358-362. [3] Q. Yang, W. Xiong, S. Li, J. Li, Effect of partial substitution of Cr for Ni on densification behavior, microstructure evolution and mechanical properties of Ti(C,N)-Ni-based cermets, J. Alloys Compd. 509 (2011) 4828-4834. [4] Y. Peng, H. Miao, Z. Peng, Development of TiCN-based cermets: Mechanical properties and 8
wear mechanism, Int. J. Refract. Met. Hard Mater. 39 (2013) 78-89. [5] S. Boudebane, S. Lemboub, S. Graini, A. Boudebane, A. Khettache, J. Le Lannic, Effect of binder content on relative density, microstructure and properties of complex cemented carbides obtained by thermal explosion-pressing, J. Alloys Compd. 487 (2009) 235-242. [6] J.M. Córdoba, E. Chicardi, F.J. Gotor, Liquid-phase sintering of Ti(C,N)-based cermets. The effects of binder nature and content on the solubility and wettability of hard ceramic phases, J. Alloys Compd. 559 (2013) 34-38. [7] V.R. Dizaji, M. Rahmani, M.F. Sani, Z. Nemati, J. Akbari, Microstructure and cutting performance investigation of Ti(C,N)-based cermets containing various types of secondary carbides, Int. J. Mach. Tools Manuf. 47 (2007) 768-772. [8] Z. Shi, D. Zhang, S. Chen, T. Wang, Effect of nitrogen content on microstructures and mechanical properties of Ti(C,N)-based cermets, J. Alloys Compd. 568 (2013) 68-72. [9] F. Monteverde, M. V, A. Bellosi, Microstructure of hot-pressed Ti(C,N)-based cermets, J. Eur. Ceram. Soc. 22 (2002) 2587-2593. [10] J. Xiong, Z. Guo, M. Yang, B. Shen, Preparation of ultra-fine TiC0.7N0.3-based cermet, Int. J. Refract. Met. Hard Mater. 26 (2008) 212-219. [11] Y. Lei, W.H. Xiong, Z.G. Liang, P. Feng, Z.W. Wang, Comparative study of the fabrication of ultrafine Ti(C,N)-based cermets by spark plasma sintering and conventional vacuum sintering, Rare Metals. 24 (2005) 131-136. [12] P.P. Li, J.W. Ye, Y. Liu, D.J. Yang, H.J. Yu, Study on the formation of core-rim structure in Ti(CN)-based cermets, Int. J. Refract. Met. Hard Mater. 35 (2012) 27-31. [13] D. Mari, S. Bolognini, G. Feusier, T. Cutard, C. Verdon, T. Viatte, W. Benoit, TiMoCN based cermets - Part I. Morphology and phase composition, Int. J. Refract. Met. Hard Mater. 21 (2003) 37-46. [14] J. Poetschke, V. Richter, T. Gestrich, A. Michaelis, Grain growth during sintering of tungsten carbide ceramics, Int. J. Refract. Met. Hard Mater. 43 (2014) 309-316. [15] P. Feng, Y.H. He, Y.F. Xiao, W.H. Xiong, Effect of VC addition on sinterability and microstructure of ultrafine Ti(C,N)-based cermets in spark plasma sintering, J. Alloys Compd. 9
460 (2008) 453-459. [16] S. Ahn, S. Kang, Dissolution phenomena in the Ti(C0.7N0.3)-WC-Ni system, Int. J. Refract. Met. Hard Mater. 26 (2008) 340-345. [17] P. Feng, W.H. Xiong, L.X. Yu, Y. Zheng, Y.H. Xia, Phase evolution and microstructure characteristics of ultrafine Ti(C,N)-based cermet by spark plasma sintering, Int. J. Refract. Met. Hard Mater. 22 (2004) 133-138. [18] J. Xiong, Z. Guo, F. Chen, B. Shen, Phase evolution in ultra-fine TiC0.7N0.3-based cermet during sintering, Int. J. Refract. Met. Hard Mater. 25 (2007) 367-373. [19] D.V. Quach, H. Avila-Paredes, S. Kim, M. Martin, Z.A. Munir, Pressure effects and grain growth kinetics in the consolidation of nanostructured fully stabilized zirconia by pulsed electric current sintering, Acta Mater. 58 (2010) 5022-5030. [20] S.Y. Ahn, S. Kang, Formation of core/rim structures in Ti(C,N)-WC-Ni cermets via a dissolution and precipitation process, J. Am. Ceram. Soc. 83 (2000) 1489-1494. [21] H.O. Andren, Microstructure development during sintering and heat-treatment of cemented carbides and cermets, Mater. Chem. Phys. 67 (2001) 209-213. [22] Y. Zheng, S.X. Wang, Y.L. Yan, N.W. Zhao, X. Chen, Microstructure evolution and phase transformation during spark plasma sintering of Ti(C,N)-based cermets, Int. J. Refract. Met. Hard Mater. 26 (2008) 306-311. [23] H. Zhang, H.H. Yan, Z. X, S.W. Tang, Properties of titanium carbonitride matrix cermets, Int. J. Refract. Met. Hard Mater. 24 (2006) 236-239.
Figure captions Fig. 1. SEM micrographs of Ti(C,N)-based cermets fabricated by different processes: (a) A-HP, (b) A-PLS, (c) B-HP, (d) B-PLS. Fig. 2. XRD profiles of (a) A-HP, (b) A-PLS, (c) B-HP, (d) B-PLS. Fig. 3. Effect of sintering process on the (a) transverse rupture strength, (b) fracture toughness, (c) Vickers hardness and (d) density of cermets. Fig. 4. SEM micrographs of fracture surface: (a) A-HP, (b) A-PLS, (c) B-HP, (d) B-PLS. 10
Fig. 5. SEM micrographs of crack propagation paths: (a) A-HP, (b) A-PLS, (c) B-HP, (d) B-PLS.
11
Fig. 1. SEM micrographs of Ti(C,N)-based cermets fabricated by different processes: (a) A-HP, (b) A-PLS, (c) B-HP, (d) B-PLS.
Fig. 2. XRD profiles of (a) A-HP, (b) A-PLS, (c) B-HP, (d) B-PLS. 12
Fig. 3. Effect of sintering process on the (a) transverse rupture strength, (b) fracture toughness, (c) Vickers hardness and (d) density of cermets.
13
Fig. 4. SEM micrographs of fracture surface: (a) A-HP, (b) A-PLS, (c) B-HP, (d) B-PLS.
Fig. 5. SEM micrographs of crack propagation paths: (a) A-HP, (b) A-PLS, (c) B-HP, (d) B-PLS.
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Table 1 Mean particle size of the raw powders. Powder
Ti(C,N)
TiC
WC
Mo2C
Ni
Co
Mo
Mean particle size (µm)
0.5
0.5
0.6
0.1
0.05
0.03
0.6
Table 2 Results of EDS analysis (correspond to Fig. 1) Element (at%) A-HP
A-PLS
B-HP
B-PLS
C
N
Ti
Co
Ni
Mo
W
A
51.49
6.49
33.91
0
1.76
3.33
3.01
B
55.59
0
36.41
0.29
0.61
3.75
3.34
A
43.24
13.30
34.68
0.98
2.67
2.90
2.23
B
51.17
0
22.51
4.74
14.19
4.04
3.35
C
53.93
0
34.60
0.69
2.45
4.57
3.76
A
52.04
9.04
31.72
1.85
1.28
1.39
2.68
B
60.50
0.46
30.94
0.33
0.85
3.71
3.20
A
49.81
1.88
43.60
0.45
0.64
1.19
2.42
B
55.28
0
35.91
1.20
1.56
2.15
3.91
C
43.83
0
14.46
16.76
21.28
1.49
2.17
D
53.57
0
39.76
0.37
0.52
1.99
3.78
15
16
Highlights: The hot-pressing sintered Ti(C,N)-based cermets exhibit high hardness with fine grain size. The Ti(C,N)-based cermets fabricated by conventional pressureless sintering possess high transverse rupture strength, fracture toughness and density with low porosity. The applied pressure can rearrange particles before liquid sintering and contribute to grain refinement. The heating rate has a great effect on the elements diffusion and the gaseous escape in solid sintering, and the dissolution-precipitation of phases during liquid phase sintering.
17