Precipitation Strengthened Ni-Ti-Pd Shape Memory Alloys

Shape memory alloys (SMAs) are metals that can return to their original shape following thermal input and are largely used as actuators for various applications across industries including space, aeronautics, automotive, and biomedical. These alloys can require long processing times to stabilize through repeated training cycles and suffer from loss of strength and stability during use. Precipitation strengthening (using heat treatments to grow small nanoscale regions of distinct metal phases within the base alloy) is one way to mitigate these issues. The NASA inventors have combined a modification of typical NiTi compositions by introducing Palladium (Pd) and small amounts of other metals and specific heat treatments to produce a novel SMA with improved properties. Specifically, the alloy is inherently stable, reducing both the need for extended processing times to stabilize the metal and the possibility of failure during high numbers of actuation cycles. Further, the SMA is specifically designed to have significantly lower hysteresis (the temperature difference between the heating and cooling) than current state of the art SMAs, i.e., at or below 10°C compared to 20°C or above. These properties combine for a SMA with enhanced properties usable across various industries and applications for reliable actuation. The related patent is now available to license. Please note that NASA does not manufacturer products itself for commercial sale. Inventors at the NASA Glenn Research Center have developed a set of chemistries and processing methods to enable improved shape memory alloys (SMAs) through precipitation strengthening and crystallographic phase control. These chemistries and methods yield SMAs with higher strengths, low thermal hysteresis of the actuation temperature, improved structural stability, and faster training processes. The enhanced shape memory properties are enabled by the addition of Palladium (Pd) and small amounts of other metal elements, to base nickel-titanium (NiTi) alloys and precise control of the heat treatments performed on the new alloys that encourage the growth of precipitate phases (i.e., finely dispersed, coherent or semi-coherent, nanometer size precipitates). Components made of the new SMAs may be used as actuators in space, aeronautics, and automotive applications across a wide range of temperatures as well as in biomedical settings as surgical tools, implants, or stents.