Influence of TaC content on microstructure and mechanical performance of Ti(C,N)-based cermets fabricated by mechanical activation and subsequent in situ carbothermal reduction

Abstract

Ti(C,N)-based cermets with different levels of Tantalum carbide (TaC) were fabricated through mechanical activation and subsequent in situ carbothermal reduction method, and microstructure and mechanical performance were studied. It was found the core-rim structure of the cermets became progressively pronounced as the TaC content increased, and when content of TaC reached at 6 wt %, a brighter inner rim phase could be observed in some hard phase particles. The grain size of the cermets decreased and then rose, reaching the finest grain size at 2 wt % TaC. As the TaC content increased, the overall comprehensive mechanical properties of the cermet, especially the TRS (Transverse Rupture Strength) value has been improved. Moreover, a new parallel orientation between the (111)R and (110)B planes formed at the solid solution phase/binder interface. Coherency was observed between the (200)R and (111)B planes of the rim/binder interface in the hard particles with a core-rim structure. The cermet with 6 wt % TaC had the optimal comprehensive mechanical properties of 2399 ± 20 MPa for TRS, 87.9 ± 0.2 HRA for hardness and 19.1 ± 0.2 MPa m1/2 for fracture toughness. This was ascribed to the solid solution strengthening of the (Ti,Ta,Mo)(C,N) phase and improved interfaces between the binder and hard phase. The improved properties of the hard particles have also improved the thermal shock resistance of cermets, with a maximum critical thermal shock temperature of 470 °C.