ABSTRACT
The highly interrelated process variables and difficulty in controlling the occurrence of defects makes the LPBF process highly challenging. The requirement of spherical powders with excellent flowability, achieving uniform spreading of powders with good packing density, amenability for re-use, preventing O2 pick-up are critical in reducing defects in the as-built Ti6Al4V alloy parts. Formation of α’ martensite phase due to rapid cooling enables an increase in strength but decreases the ductility of the as-built Ti6Al4V alloy parts. Higher concentration of O2 also impairs the ductility. It is essential to use Ar with a proper flow rate to reduce the O2 concentration of the build environment to < 0.1% and to prevent re-deposition of process by-products. Pre-heating of the powders helps to reduce distortion of the part, decrease porosity and increase the density of parts. In situ remelting helps to eliminate LOF pores, reduce the residual stress and decrease the surface roughness of Ti6Al4V alloy parts. In situ alloying by LPBF is indeed a viable option for the development of new alloys. However, achieving homogeneity is the biggest challenge. Much remains to be explored, which makes the field of research on LPBF process wide open.
