Effects of electropolishing on mechanical properties and bio-corrosion of Ti6Al4V fabricated by electron beam melting additive manufacturing

Electron beam melting (EBM) has become one of the most promising additive manufacturing (AM) technologies. However, EBM tends to result in products with rougher surfaces due to the melt pool which causes adjacent powder particles to be sintered to the surface without being melted. Hence, it is necessary to improve the surface quality by post processing. The current study evaluates the tensile response of Ti6Al4V EBMed samples subject to various electropolishing (EP) treatments. The surface roughness Ra readings can be improved from over 24 μmdown to about 4.5 μmby proper EP, resulting in apparent tensile elongation improvement from 7.6% to 11.6%, or a tensile plasticity increment of 53%, without any loss of elastic modulus or tensile strength. Moreover, the in-vitro bio-corrosion test in simulating body fluid (SBF) of the as-EBMed and EP-processed samples is also conducted. The potentiodynamic polarization reveals that the bio-corrosion resistance is improved by the lower Ra through proper EP treatments. This is due to the formation of a denser and more completely passivated oxide layer with less defects after proper EP duration. But when the EBMed samples are over-electropolished, nano pitting would induce a degraded bio-corrosion performance.