Multi-laser powder bed fusion of Ti6Al4V: Diode area melting utilizing low-power 450 nm diode lasers

Abstract

Diode Area Melting (DAM) is an innovative approach to laser powder bed fusion. This research for the first time utilized multiple low wavelength (450 nm) and low power lasers (4 W each) to simultaneously process Ti6Al4V from a powder bed, resulting in high density samples (> 99%). The use of nine lasers perpendicular to the scanning direction allowed for the creation of melt pools with widths larger than 1000 µm, reducing the number of passes within a layer compared to traditional single laser LPBF systems. However, the increase in melt pool width creates challenges related to maintaining uniform melt pool penetration depths, this intern creates issues achieving high density in multi-layer parts. A parameter map based on normalized energy density was created. The research also investigated the effect of variable process conditions (scanning speed, hatch distance, and layer height), normalized energy density on densification, microstructure, and hardness. Implementing a rescanning strategy on each layer reduced average surface roughness and increased density while reducing hardness by approximately 40%. X-ray Diffraction analyses showed that the β phase occurred with increased energy density in as-built samples. Coarser lamellar structures were observed in the lower sections due to slower cooling rates, while finer, more martensite structures were observed towards the top, resulting in a basket-weave type microstructure throughout the sample. Furthermore, the lamellar sub-grains were visible without etching. This innovative technology shows that an array of low-power lasers can melt and fuse Ti6Al4V powder to create dense samples.