Reducing lack of fusion during selective laser melting of CoCrMo alloy: Effect of laser power on geometrical features of tracks

There is a need to understand how selective laser melting (SLM) parameters affect the size and shape of tracks which are the predominant factor relating to the amount of lack of fusion (LOF) formed during SLM. This study is needed as severe LOF impacts quality. In this work on CoCrMo alloy SLM, experiments and analysis have been conducted to reveal how laser power (P) and thus energy, as other parameters are kept unchanged, affect the geometrical features of SLM tracks and the formation of LOF. It has been found that the track was insufficient to overlap and prevent LOF when the recommended condition (P = 180W) was used. Increasing P increases the size and improves the shape stability of the tracks. It will be shown that there is a rapid decay in the amount of LOF as P increases from 180W to 220 W, as the result of the geometrical effect of the track size on overlapping coverage. However, residual LOF has remained even when P has increased to >300W. Evidence of large size spatters causing this and of the high laser beam penetrating capability to reduce the spatter effect is presented and discussed. (C) 2016 Elsevier Ltd. All rights reserved.