Effects of local processing parameters on microstructure, texture, and mechanical properties of electron beam powder bed fusion manufactured Ti–6Al–4V

Abstract

Electron beam powder bed fusion scan strategies for parts or part groupings of various sizes and scan line lengths have been found to inadvertently lead to significant variations in crystallographic texture and mechanical properties for Ti–6Al–4V. This occurs over a range of scan line length that is well below the maximum scan line length recommended by the electron-beam powder bed fusion machine manufacturer. The microstructural attributes such as α lath thickness, prior β grain size, and β phase fraction were similar for materials fabricated under short and long scan line length conditions, but the crystallographic textures varied considerably. Electron backscatter diffraction measurements indicate the basal pole [0001]α was strongly aligned with the build direction for long scan line length conditions, whereas 112‾0α were aligned with the build direction for short scan line length conditions. Subsequent prior β reconstructions indicate a preference for alignment of 110β and 100β with build direction for long and short scan line length conditions, respectively. Both yield and ultimate tensile strengths along the build direction were approximately 8% higher for long scan line lengths, consistent with the observed differences in texture. The impact of a sub-solvus hot isostatic pressing was also investigated, however, this did not significantly change the textures of as-built materials or the relative strengths for the two processing conditions.