Fabrication and Properties of (Ti, W, Mo, Nb, Ta)(C, N)-Co-Ni Cermets
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Fabrication and Properties of (Ti, W, Mo, Nb, Ta) (C, N)-Co-Ni Cermets Houan Zhang, Ming Fu, Lili Ma, Siyong Gu, Jiawei Liu, and Ying Chen (Submitted March 30, 2019; in revised form August 8, 2019) Fine single-phase (Ti, W, Mo, Nb, Ta)(C, N) solid solution powders were synthesized through the carbothermal reduction method. (Ti, W, Mo, Nb, Ta)(C, N)-Co-Ni cermets were fabricated via vacuum sintering. Micrographs of powders and microstructures of the cermets were observed using transmission electron microscopy and scanning electron microscopy in combination with energy-dispersive spectroscopy. Phase compositions were investigated using x-ray diffraction. The C and N contents were measured using elemental analysis (CHNS/O). The optimized conditions for the synthesis process of single-phase (Ti, W, Mo, Nb, Ta)(C, N) solid solution powders with high nitrogen content were 1500 °C for 2 h under a 2 kPa nitrogen atmosphere. Under such conditions, the particle size of the synthesized powder was less than 140 nm, and its carbon and nitrogen contents were 9.174 and 7.040 wt.%, respectively. The synthesized fine (Ti, W, Mo, Nb, Ta)(C, N) solid solution powders had a significant positive impact on the strengthening and hardening of Ti(C, N)-based cermets. The values of hardness and transverse rupture strength of the (Ti, W, Mo, Nb, Ta)(C, N)-Co-Ni cermets sintered at 1450 °C for 1 h in vacuum (SSC3) increase by 14.7 and 20.2% compared to those of traditional Ti(C, N)-WC-Mo2C-NbC-TaC-Co-Ni cermet (TC), respectively. However, the KIC value of SSC3 decreases by 14.1% compared to that of TC. The mechanism of strengthening and hardening and the cause of the low fracture toughness of the SSC were revealed by comparing the differences in the microstructures of SSC and TC.
Keywords
electron microscopy, powder metallurgy, sintering, x-ray
1. Introduction Ti(C, N)-based cermets are advanced cutting tool materials that have been developed from TiC-based cermets. Because of their high red-hardness, excellent chemical resistance, and good resistance to temperature oxidation, Ti(C, N)-based cermets are widely used in automobile manufacturing, aerospace industries, and other fields (Ref 1-4). For complex cutting environments, the low flexural strength restricts the application of Ti(C, N)based cermets. Traditional Ti(C, N)-based cermets are usually fabricated from mixtures of Ti(C, N), Co, Ni, and other carbides powders by steps, such as ball-milling, compaction, and sintering. Additions of carbides (i.e., WC, Mo2C, TaC, NbC, etc.) improve the mechanical properties of Ti(C, N)-based cermets (Ref 5-7). However, after added carbides, it is difficult to control the solid solution during sintering process. As a result, this process increases the strain at the interfaces between the core and rim, and this can impair the mechanical properties of the materials (Ref 8, 9). It was recently reported that using the solid solution powders of (Ti, Ta, W)(C, N) improved the Houan Zhang, Ming Fu, Lili Ma, Siyong Gu, Jiawei
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