The Influence of Microstructural Texture and Prior Beta Grain Recrystallisation on the Deformation Behaviour of Laser Powder Bed Fusion Produced Ti-6al-4v

Abstract

The control and predictability of mechanical properties during manufacturing is essential in achieving parts that consistently deliver adequate mechanical properties. In laser powder bed fusion produced Ti-6Al-4V, this control is complex and dependent on the build orientation. While studies have identified the columnar prior-β grain structure as a cause in mechanical anisotropy, differences in underlying micro-structure and its influence on anisotropy are not yet well understood. This study investigates micro-structural texture differences in two build orientations before and after post-process heat treatments and in what way the micro-structural features control deformation-and-failure behavior. The study uses uniaxial tensile tests to determine tensile behavior of samples built “vertically” and “horizontally” with reference to the build plate. Microscopy techniques of scanning electron microscopy imaging and back-scatter diffraction are used for micro-structure characterization and deformation mode identification. Results identify key crystallographic and morphological textural differences in the two build-orientations. Heat treatments above the β-transus successfully globularise prior β grains, thereby improving mechanical anisotropy. The use of electron backscatter diffraction demonstrates key morphological features that control slip, micro-crack initiation and final fracture.