Microstructure and Mechanical Properties of Ti-6Al-4V Fabricated by Selective Laser Melting

Selective laser melting has been recently proposed as a new powder bed manufacturing technology for Ti alloys. In this research, the 3D microstructure characterization of the Ti-6Al-4V pre-alloyed plasma atomized powder material was carried out. Cubic components were then built from the same powder directly onto the build plate or on top of secondary supporting structures using a modulated pulsed fibre laser. The microstructure and mechanical property of the components were analyzed. Spherical and flat pores were found, with supported components showing a larger average porosity probably due to a slower experienced cooling rate. The microstructure of the parts consists mainly of acicular alpha' needles with only a small volume fraction of retained beta phase. Transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD) studies confirmed the crystallographic nature and the orientation of the alpha' needles, respectively. The a' needles are mainly arranged in a colony pattern, but basketweave morphology is visible in the bottom region of the supported components. Columnar grains extending across deposited layers were observed as a result of the several thermal cycles which are typical in selective laser melting.