The late John Boylan and his team in Temecula, CA, filed a patent in the 1990’s that included a variety of radiopaque ternary additions to a nitinol alloy. Several of these elements including Pt, Pd, and Au, hold potential to not only raise x-ray attenuation, but also to perfect the interface between parent and daughter phases thereby increasing certain material performance aspects. Work is needed to understand and apply specific Ni-Ti-Pt chemistries and understand their practical utility. As early as 1988, one way shape memory, superelasticity, and austenitic transformation temperatures from about 0 to 1000°C were demonstrated for the Ni-Ti-Pt system by Lindquist and colleagues at University of Illinois Urbana-Champaign. Under equilibrium, stress-free conditions, the material composition for maximum austenite-martensite interface compatibility is approximately Ti 50 Ni 42.5 Pt 7.5 . Further study is warranted since improved crystallographic compatibility may improve the structural and functional performance of critical medical and industrial subcomponents where performance gains could pay for higher initial material costs.

Typical processing techniques involve thermo-mechanically treating the material such as cold working and subsequent annealing to control grain and precipitate size, shape, orientation, and morphology. Shape memory alloy (SMA) mechanical properties rely heavily on microstructural features such as precipitates and grain size to extend fatigue life. Novel approaches to control microstructural features have used laser anneal on amorphous NiTi thin films to recrystallize grains and short-time annealing on NiTi after angular extrusion and cold-drawn fine wires. A recent study examined rapid thermal annealing (RTA) on Ni-lean NiTi- 10 at.% Hf wires as an effective method for controlling grain size and extending actuation fatigue; however, flash annealing or RTA on Ni-rich NiTiHf high-temperature SMA (HTMSA) wires has not been investigated. Based on a larger study, Ni-rich NiTi-20 at.% Hf HTSMA was down-selected for further processing. This study investigates the effect of flash annealing on the thermo-mechanical properties of a Ni-rich Ni50.3Ti29.7Hf20 HTSMA. Microstructural changes were examined using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and transmission electron microscopy (TEM). Actuation fatigue properties were also evaluated at 300 MPa. The results indicate that flash annealing HTSMA wires is an effective method for controlling grain size and extending fatigue life. The heating rate and time held are crucial parameters to control microstructural features such as grain size and coherency.