Composition, Compatibility, and the Mechanical Performance of Ternary NiTiX Shape Memory Alloys

The process of designing, manufacturing, and testing new compositions of shape memory alloys (SMAs) can be extremely time-consuming and expensive. We present an alternative procedure that can be used to optimize SMAs for specific engineering performance metrics such as operating temperatures, mechanical work, and life. This is a general procedure that utilizes the relationships between theoretical micromechanical properties and engineering performance and requires only composition and lattice parameter measurements as inputs. Knowledge of thermomechanical processing and measurement of transformation temperatures can provide additional comparisons between microstructural-based and engineering properties. This procedure is outlined and demonstrated through a study of 23 ternary, NiTiX high temperature SMAs, where X=Pd, Hf, and Zr. Through this study, we demonstrate that SMAs can be tuned for specific applications using relatively simple, fast, and inexpensive measurements and theoretical calculations. The results also indicate an overall trade-off between compatibility and strains, indicating that alloys may be optimized for either minimal hysteresis or large transformation strains and work output. However, further analysis of the effects of aging shows better combinations of uncompromised properties are possible through solid solution strengthening.