Evolution mechanism of microstructure and microhardness of Ti–6Al–4V alloy during ultrasonic elliptical vibration assisted ultra-precise cutting

The ultra-precision Ti–6Al–4V alloy parts are growing used in medical and aerospace industries, and which always work in the extreme working conditions such as high temperature, high pressure, and variable load. Thus, the requirements for machining accuracy and surface quality of parts are getting higher and higher. The ultrasonic elliptical vibration assisted cutting (UEVC) technology has been proved to be an effective method for the ultra-precision machining of Ti–6Al–4V alloy. However, in the UEVC process, the evolution mechanism of microstructure and microhardness, which directly affect the service performance and life, is unrevealed. In this paper, the comprehensive investigations of microstructural plastic deformation, grain refinement, phase transformation and microhardness of machined surface layer under conventional cutting (CC) and UEVC processes are carried out. The experimental results indicated that, due to the effects of UEVC technology, the plastic deformation area show obvious compression deformation, the depth of plastic deformation is less than 10 μm, there is no obvious phase transformation on the machined surface layer material, and the hardening rate of machined surface is more than 20%. These findings show the UEVC technology has a unique influence on the microstructure and microhardness of Ti–6Al–4V alloy, which have important implications for the cutting parameter design of ultra-precision Ti–6Al–4V alloy parts.