Microstructure and machinability of selective laser melted titanium alloy in micro-milling

Abstract

This study thoroughly investigates the relationship between the microstructure of Selective Laser Melted (SLM) Ti6Al4V and improved machinability in micro-milling. The study demonstrates a detailed comparison of grain structure and crystallographic orientation through electron backscatter diffraction and phase mapping with experimental analysis, highlighting the fine, needle-like and acicular α′ martensite of SLM Ti6Al4V and the larger, equiaxed α grains with intergranular β’ phase of wrought Ti6Al4V, has a significant impact on machinability in micro-milling. The exceptional resistance to deformation of SLM microstructure resulting from its inherent hardness and decreased ductility, leads to reduced tool interaction in micro-milling. In contrast, the wrought material exhibits larger grains, which result in greater ploughing, increased burr formation, and significant tool wear. The reduction in burr width on the down-milling side for SLM Ti6Al4V at a feed rate of 1 μm/tooth can reach up to 71.6%. Furthermore, the surface finish of SLM Ti6Al4V is consistently superior to wrought Ti6Al4V in term of surface roughness, emphasizing the microstructural advantages of SLM titanium alloys for machinability. The findings of this study offer a comprehensive understanding of the positive effect of microstructure of SLM titanium alloys on machining performance in micro-milling.