Laser Metal Deposition of NiTi Shape Memory Alloys

Laser metal deposition (LMD) has unlocked a unique capability for designing and manufacturing large-sized products at an efficient printing speed. This study focuses on the LMD process for NiTi-based shape memory alloys, in particular employing Ni-rich NiTi wire with a 1 mm diameter and a transformation temperature of +95°C as our primary material. The printing process is carefully optimized to achieve high-quality prints with near-full density. Furthermore, we employ a heat treatment (HT) approach to enhance the functional performance of the printed samples. A comprehensive array of characterization techniques is employed to assess the mechanical and functional properties of both the as-built and heat-treated samples.

The printed samples are examined using micro-Computed Tomography (micro-CT) to detect potential microstructural defects. Differential scanning calorimetry (DSC) analysis is performed to determine the transformation temperature of both the as-built and heat-treated samples. Notably, tensile and cyclic compression testing is conducted to evaluate the mechanical and functional behavior of the NiTi samples. The results highlight the significant impact of the HT process on the microstructure and transformation temperature of the printed samples, thereby influencing their functional performance.