Effect of Post-treatments on the Thermomechanical Behavior of NiTiHf High-Temperature Shape Memory Alloy Fabricated with Laser Powder Bed Fusion

Abstract

Despite increasing interest in Nickel Titanium-based high-temperature shape memory alloys (HTSMAs), machining challenges and limited functionality at elevated temperatures hinder their application in aerospace, energy, and automotive industries. Additive manufacturing, including laser powder bed fusion (LPBF) and subsequent treatments, addresses these obstacles. Employing LPBF, we processed a Ni 50.4TiHf20 HTSMA, maintaining a constant volume energy density of 64 J/mm3. Laser powers of 100 W and 200 W, with scanning speeds of 400 mm/s and 800 mm/s, respectively, were chosen for dense, defect-minimized parts. Process parameter effects on thermomechanical properties were assessed. Post-processing steps (HIP, solution treatment, aging) further enhanced properties. HIP proved more effective for 200 W samples. (Ti/Hf)-rich oxide inclusions formed during processing, impacting phase transformation temperatures. Aging treatments improved strain recovery, attributed to H-phase precipitate strengthening. After heat treatment, 100 W and 200 W samples exhibited 2.33% and 2.10% actuation strain, with negligible and near-zero residual strains.