High temperature shape memory alloys (HTSMAs) are a type of “smart” material that can generate large amounts of mechanical work due to changes in temperature or strain placed upon the material. HTSMAs are currently an active area of research in the aerospace, automotive, defense, and energy sectors. In this study, a Ni~50.3~Ti~29.7~Hf~20~ (at.%) HTSMA was produced on an industrial scale with a melt size of 11 lbs and then extruded. After extrusion, a portion of the sample was hot-rolled. Some of the extruded and hot-rolled samples were then subjected to a pre-aging treatment plus a conventional aging treatment, while some of the extruded and hot-rolled samples were just subjected to a conventional aging treatment. The pre-age treatment, consisting of a 12hr hold at 300 °C, was performed to create a more coherent interface between the matrix and the nano-precipitate H-phase. Each sample was aged for 3hrs at various temperatures (450, 550, 650, and 750 °C) to nucleate and grow the nano-precipitate H-phase. All of the samples were characterized using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Vickers hardness (HV), synchrotron radiation x-ray diffraction (SR-XRD), and thermo-mechanical testing (TMT). Hot-rolling was shown to induce a significant amount of retained B2 austenite, and, after aging, the volume fraction of B2 austenite increases further. Hot-rolling was also shown, in a previous study, to align the H-phase nano-precipitates. Samples with the aligned H-phase were mechanically tested in order to observe the role that the alignment of H-phase plays on the mechanical properties of the material.


Shape Memory and Mechanical Properties of Pre-Aged Thermo-Mechanically Processed High Hf Containing Nitihf

Division / Sponsors: 
Aerospace Division

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2020/volume/84027

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