| In this research, a new type of wear-resistant composite was developed using a TiNi alloy as the matrix reinforced by hard TiC or TiN particles. Due to its pseudoelasticity and good wear resistance, the TiNi alloy is a desirable matrix for high-performance composites. The TiNi-based composite was fabricated using a vacuum sintering process. The effects of powder metallurgy processing and hard particles on the microstructure and mechanical properties of the composite were studied. It has been demonstrated that the TiNi alloy matrix composite can be obtained by sintering elemental Ti and Ni powders with the hard TiC or TiN particles. However, high porosity is typical for such a sintered composite. 52 vol% was found to be the best fraction for TiC particles, and 1500°C and 6 hours were the optimum sintering parameters for making such a composite. Even with high-density porosity, the sintered TiNi-based composite showed a wear resistance that is about three orders of magnitude higher than that of 304 stainless steel, one order of magnitude higher than that of a Ti-51at%Ni alloy, and comparable to that of WC/NiCrBSi, a commercial hardfacing material. In order to further improve the composite's wear resistance, the effects of porosity on the composite's mechanical properties and wear resistance were investigated, and accordingly, hot isostatic pressing (HIP) was used to reduce the porosity of the composite for enhanced wear resistance. Finally, the pseudoelasticity of the TiNi matrix in the composite and corresponding phase transformation were investigated, using nano-indentation, differential scanning calorimetry (DSC), X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques, respectively. It was demonstrated that a reversible R-phase transformation induced by the wearing stress was mainly responsible for the pseudoelasticity of the composite. The pseudoelasticity of the composite affected its wear performance over a relatively wide temperature range. |
