Experimental study of surface residual stress and hardness of TiBw mesh reinforced titanium matrix composites in rotary ultrasonic grinding

Abstract

TiBw mesh reinforced titanium matrix composites were investigated by rotary ultrasonic grinding experiments using nickel-based electroformed diamond grinding wheel and building a single diamond abrasive grain model and a 2D rotary ultrasonic grinding finite element model. Surface residual stress is obtained by simulation and verified by univariate experiments. Combined with nanoindentation experiments, the changes of residual stress and hardness were acquired. The results show that the reinforced phase fibers will be subjected to high mechanical stress which break the fibers and turn into chips with matrix material. The residual stress of TiBw-rich region is closer to the actual value due to the high elastic modulus and low residual strain of TiB. Residual compressive stress around -500MPa exists in the surface of workpiece under different process parameters. The residual stress decreases remarkably as the spindle speed increases. Meanwhile, the work hardening of workpieces changes similarly as the residual stress. The subsurface microstructure of titanium matrix composites after processing was tested by nanoindentation experiments and backscattered electron diffraction (EBSD). It was found that the surface hardness and dislocation density of the workpiece increased after machining, and the affected depth was about 10~15μm. XRD was further used to measure the surface phase of the workpiece under different processing parameters, the results show that the content of TiB reinforcements on the workpiece surface increases and the grain refinement decreases with the increase of spindle speed.