Effect of C/N ratio on microstructure and properties of Ti(C, N)-based cermets

To address the challenge of balancing hardness, toughness, and strength in Ti(C, N)-based cermets, existing research predominantly focused on composition design and sintering optimization, while comparatively less attention was paid to the critical role of initial Ti(C, N) powder characteristics in determining properties. In this study, high-quality Ti(C, N) powders with varying C/N ratios were synthesized via carbothermal reduction-nitridation (CRN) coupled with Ca treatment, followed by the fabrication of Ti(C, N)-20WC-5Mo-5Ni-5Co (wt%) cermets using vacuum pre-sintering assisted spark plasma sintering (SPS). The prepared powders were characterized by the absence of free carbon, low oxygen content, uniform morphology, superior crystallinity, and excellent dispersibility. After sintering, all samples achieved high densification, comprising the (Ti, W, Mo)(C, N) hard phase, (Co, Ni) binder phase, and trace residual WC. The ceramic grains mainly displayed black core-gray rim, black core-rimless, and white core-gray rim structures, characterized by overall thin rims. As the C/N ratio decreased, the dissolution-precipitation process during sintering was inhibited. Accordingly, hardness exhibited an initial decline followed by an increase, whereas the fracture toughness ( K IC ) showed an opposite trend. Transverse rupture strength (TRS) peaked at an intermediate C/N ratio. Cermet derived from Ti(C 0.44 , N 0.56 ) powder achieved an optimal combination of properties, with hardness, K IC , and TRS values of 1867 ± 12 HV 30 , 9.13 ± 0.21 MPa m 1/2 , and 1748 ± 75 MPa, respectively. The synthesized high-quality Ti(C, N) powders provided a crucial foundation for microstructural control and improved overall properties of cermets, and adjusting the C/N ratio served to further optimize the balance among hardness, toughness, and strength.