Session: 01-01: Shape Memory Alloy Characterization I

Paper Number: 91014

91014 - Effects of Heat Treatments on the Shape Memory Behavior of Nitihf High Temperature Shape Memory Alloys Fabricated by Laser Powder Bed Fusion 

            Shape memory alloys (SMAs) are functional materials that are used for many applications from biomedical to actuation devices. High-temperature shape memory alloys are the subgroup of SMAs with an operating temperature above 100 ^oC, making them a strong candidate for aerospace.

            Additive manufacturing (AM) is an attractive method to fabricate complex shapes of shape memory alloys (SMAs). Since shape memory properties are highly dependent on composition and microstructure, AM process parameters and subsequent heat treatments are effective methods to control the shape memory behavior. In this study, slightly Ni-rich NiTiHf alloys were fabricated via the Laser Powder Bed Fusion (L-PBF) method, and the shape memory behavior was investigated in consideration of AM parameters and post-processing heat treatments.

            NiTiHf samples were characterized in three conditions consisting of (i) as-fabricated, (ii) solution annealed and (iii) aged (550 ^oC for 3h), where the transformation temperatures (TTs), shape memory strains and superelasticity were quantified. After solution annealing, TTs and hysteresis were decreased while aging resulted in higher TTs and strength due to the formation of Ni-rich precipitates. Aged L-PBF fabricated NiTiHf samples recorded a recoverable strain of 1.03% under stress levels above 500 MPa in compression. Poor superelastic behavior was attained after aging, but additional process refinements are expected to result in improved properties.

Presenting Author: Guher Pelin Toker University of Kentucky