Surface finishing and change in residual stress of AMed titanium alloy by combination of grit blasting and large-area EB irradiation

Abstract

Additively manufactured (AMed) titanium products are typically produced by electron beam melting (EBM), since oxidation of titanium alloy surface can be suppressed in vacuum ambience. The surface roughness of AMed titanium products becomes more than 200µmRz, and the very rough surface would lead to reduction in surface strength. Therefore, a post surface finishing process is required. Abrasive blasting is one of the common surface smoothing processes of AMed metal products. Large surface roughness can be decreased, and compressive residual stress can be introduced to the surface. However, there is a limitation to reduction of surface roughness to several µmRz. On the other hand, it was recently found that AMed metal surface produced by powder bed fusion with laser beam could be smoothed by large-area electron beam (LEB) irradiation. However, it is difficult to smooth surface with large initial surface roughness, and a tensile residual stress may be generated on the surface. In this study, surface finishing and change in residual stress of AMed titanium alloy were proposed by combination of grit blasting and LEB irradiation. Surface roughness of AMed titanium alloy significantly decreases from 265µmRz to about 2.0µmRz by combination of grit blasting and LEB irradiation. Reduction rate of surface roughness by LEB irradiation linearly increases with decreasing mean width of blasted surface. Influence of the mean width on smoothing effect by LEB irradiation can be explained by thermo-fluid analysis. Moreover, tensile residual stress caused by LEB irradiation can be reduced when LEB is irradiated to blasted surface.