Laser Powder Bed Fusion of NiTi-Based Metastructures

Additive manufacturing facilitates the creation of intricate, architecturally designed structures, providing the capacity to fine-tune their functional attributes. The integration of shape memory alloys (SMAs) into such structures offers a distinctive capability for achieving recoverable deformations. This study focuses on the design and production of a NiTi-based metastructure, fabricated utilizing the laser powder bed fusion (LPBF) technique. Spherical Ni-rich NiTi powder with functional properties at body temperature (37°C) was chosen as the primary material. LPBF process parameters were meticulously optimized to attain nearly full density, achieving levels as high as 99.5%.

To assess the quality of the lattice samples, micro-Computed Tomography (micro-CT) was employed to analyze potential residual defects. For the enhancement of functional attributes in the printed samples, a specific low-temperature heat treatment (HT) approach was implemented. Four distinct HT scenarios were applied, entailing annealing the NiTi lattices at varying temperatures followed by rapid water quenching. A comprehensive array of characterization techniques was deployed to evaluate the mechanical and functional properties of both the as-built and heat-treated samples. In particular, cyclic compression testing was conducted to assess the pseudo-elastic behavior of the NiTi lattices.

The results underscore the efficacy of the HT process in improving the microstructure and transformation temperature of the printed samples, directly influencing their functional performance.