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

• Published in: Advanced engineering materials Vol. 16; no. 9; pp. 1140 - 1146
• Main Authors: Dadbakhsh, Sasan, Speirs, Mathew, Kruth, Jean-Pierre, Schrooten, Jan, Luyten, Jan, Van Humbeeck, Jan
• Format: Journal Article
• Language: English
• Published: Blackwell Publishing Ltd 01.09.2014
• Subjects: Intermetallics; Lasers; Martensitic transformations; Nickel; Nickel titanides; Shape memory alloys; Titanium compounds; Transformation temperature
• ISSN: 1438-1656; 1527-2648; 1527-2648
• DOI: 10.1002/adem.201300558

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. Selective laser melting (SLM) of nickel titanium represents a promising future owing to SLM ability to manufacture complex shapes. This work presents original experimental data to successfully manufacture NiTi parts using the SLM process. It also describes a systematic study to illustrate the effect of different sets of SLM parameters on the transformation temperatures, mechanical behavior, microstructure, and shape memory response of the products.