Laser powder bed fusion of nitinol for medical applications

Additive manufacturing of Nitinol via Laser Powder Bed Fusion (LPBF) offers new design freedoms and enables enhanced functionality for medical implants. However, LPBF processing of Nitinol remains challenging due to issues such as porosity, nickel evaporation and oxidation, which must be mitigated to ensure high-quality and reliable components.

This study systematically investigates the influence of key LPBF parameters on the microstructure and mechanical properties of Nitinol. Two post-processing routes are compared: (1) solution annealing followed by age hardening, and (2) direct ageing. A comprehensive characterization approach was applied across multiple stages of the process chain to capture the evolution of microstructure and functional behavior.

This presentation showcases thermomechanical properties of LPBF-processed Nitinol with performance levels that surpass currently published data. A process window enabling the fabrication of nearly fully dense, crack-free parts was identified. Phase transformation temperatures in the annealed state can be tailored within a range of approximately 20 °C by adjusting LPBF parameters. Subsequent heat treatments allow setting the austenite finish temperature up to 37 °C, matching target functional properties. The heat-treated material exhibits superelasticity under tension, recovering strains up to 8 % with residual elongations below 0.2 %. Plateau stresses are tunable toward values typical of conventionally processed Nitinol products. The advantages and limitations of two-step heat treatment and direct ageing are discussed with respect to resulting material properties and process robustness.

These findings provide essential insights for optimizing LPBF of Nitinol, paving the way toward reliable, high-performance implants with customized superelastic properties.