Microstructural effects of Ti6Al4V alloys modified by electropulsing treatment on ultraprecision diamond turning

Abstract

The mechanical properties of polycrystalline materials are significantly affected by their microstructures, such as the grain size, phase composition and texture. In this paper, Ti6Al4V alloys with equiaxed grain structure, bimodal structure and martensitic structure are obtained by electropulsing treatment (EPT). The microstructural evolution is primarily caused by the coupling function of thermal and athermal effects of EPT. A theoretical model was built to analyze the temperature evolution induced by the thermal effect of EPT from the perspectives of energy gain, heat transfer and thermal radiation. Ultraprecision diamond turning was then conducted to investigate the effects of microstructures on the machinability of Ti6Al4V alloys. The results show that material swelling and spring-back vary with microstructures due to the various strength and ductility, which significantly affects the turning surface profiles. The alloy with fully martensitic structure shows a best surface roughness of approximately 9 nm after diamond turning, and the cutting and thrust forces are also lower than the alloys with equiaxed and bimodal structures. The paper also qualitatively analyzes the cutting and thrust force evolution of the alloys with various microstructures.