Effect of SLM Parameters on Transformation Temperatures of Shape Memory Nickel Titanium Parts

Selective laser melting (SLM) is used to manufacture dense nickel titanium (NiTi) parts. The reversible martensitic transformation of the NiTi parts is investigated with various SLM parameters. The parameters are in the same energy density range, composed of high laser parameters (HP: high laser power adjusted to high scanning speed) and low laser parameters (LP: low laser power adjusted to low scanning speed). The results are linked to the mechanical behavior and shape memory response achieved from compression and dilatometry tests. It is shown that the products may exhibit distinct transformation temperatures depending on the used SLM parameters. The atomized powders and the HP SLM parts with dominant pseudoelastic properties contain austenite at room temperature (due to their lower transformation temperatures), in contrast to the large thermal memory of the LP parts originating from martensitic phases (corresponding to higher transformation temperatures). The post-annealed samples undergo transformations in a comparable temperature range, implying no significant effect of SLM on composition of the originally used powder. The possible origin of the above findings is postulated and discussed.