Effect of Nanosized TiC_0.37N_0.63 on Unlubricated Wear Responses of Si₃N-Based Nanocomposites under Low Hertzian Stress

Si₃N₄-based nanocomposites containing 0-50 wt% TiC_0.37N_0.63 are directly consolidated at 1700°C by spark plasma sintering, and their reciprocal sliding behavior against a Si₃N₄ counterbody is investigated under a maximum Hertzian stress of 1.27 GPa in unlubricated conditions. The average grain widths of Si₃N₄ and TiC_0.37N_0.63 are about 85 and 90 nm, respectively. The decreasing relative densities of the as-sintered nanocomposites indicate that the nano-TiC_0.37N_0.63 may introduce pores and reduce the hardness and fracture resistance of the materials. The brittleness index for sliding contacts in all the samples is 25-31, indicating brittle fracture taking place on the wear surface and inducing cavities. When the mean free paths of nano-TiC_0.37N_0.63 are slightly greater than grain length of Si₃N₄, the best wear resistance is achieved in Si₃N₄ containing 20/30 wt% TiC_0.37N_0.63 due to the process of surface smoothing by triboproducts. Severe wear response can be observed in Si₃N₄ nanocomposites containing 0, 10, 40, and 50 wt% of TiC_0.37N_0.63. The wear responses are explained by considering the microstructural parameters (like grain characteristics for both phases and mean free path of nano-TiC_0.37N_0.63) and contact-induced fracturing behavior, as well as tribochemical reactions.