Microstructure and Properties of h-BN-Reinforced Titanium Alloy Matrix Composite Fabricated with Optimized Spark Plasma Sintering Parameters

Abstract

The effects of different combinations of spark plasma sintering parameters: temperature, pressure, heating rate and holding time, at three levels on the microstructure, densification, mechanical and wear properties of Ti6Al4V/h-BN binary composite were considered in this work. The design method of Taguchi and signal-to-noise (S/N) ratios analysis and main effects of the parameters were employed to randomize and optimize the levels of the SPS parameters. The microstructure and phase features of the samples sintered were analyzed by using a scanning electron microscope, an optical microscope and X-ray diffractometer respectively. Archimedes’ method, Vickers microhardness tester and a tribometer were used to evaluate the densification, microhardness and wear profiles of the samples. The most important parameter levels for optimum quality characteristics of the sintered composite were obtained at temperature, pressure, heating rate and holding time of 1000 °C, 30 MPa, 100 °C/min and 10 min, respectively. Ti6Al4V/h-BN composite approaching complete theoretical densification of 99.54%, microhardness value of 7.03 GPa, 1.66 GPa yield strength, 2.29 GPa ultimate tensile strength and wear rate of 8.075 x 10-6 mm3/Nm, respectively was produced with the optimized process parameters. The microhardness improved by approximately 216% and the wear rate improved by 97.8% of the Ti6Al4V alloy matrix. The improved microstructure, higher densification, mechanical and wear properties of the optimized composite were promoted by high sintering temperature and low heating rate which ensured adequate diffusional mass transport, achievement of refined grains, better pore filling and formation of solid matrix-reinforcement interfacial integrity.