Shape Memory and Thermal Actuation Behavior of Laser Powder Bed Fusion-Fabricated NiTi-20Hf High-Temperature Shape Memory Alloys

Abstract NiTi-20Hf high-temperature shape memory alloys (HTSMAs) were fabricated using laser powder bed fusion (LPBF) additive manufacturing with low laser power and medium scanning speeds. Two alloys S1 (60 W, 120 mm/s) and S2 (70 W, 100 mm/s) were prepared using slightly different processing parameters. Both alloys displayed high strength ~ 2 GPa, partial shape memory effect ~ 1%, and thermal actuation in compression at operating temperatures exceeding 350 °C with recoverable actuation strains ~ 1.3% (1.7%) under compression stress 300 MPa (600 MPa). Alloy S1 prepared using lower laser power 60 W and higher scanning speed 120 mm/s displayed higher strength, higher shape memory effect, and lower actuation strain compared to alloy S2 prepared using higher laser power 70 W and lower scanning speed 100 mm/s. Better functional thermomechanical properties of the alloy S1 were attributed to the high density of dispersed near-spherical nanoprecipitates, which suppresses plastic deformation accompanying martensite reorientation and/or martensitic transformation during thermomechanical loading. These results highlight a promising potential of the LPBF technology to fabricate near-net shape HTSMAs actuator components and demonstrate the key role of processing parameters in LPBF fabrication of NiTiHf alloys.