Tunability of martensitic behavior through coherent nanoprecipitates and other nanostructures

Molecular dynamics simulations show that coherent precipitates can significantly affect the properties of martensitic transformations in Ni$_{63}$Al$_{37}$ alloys. The precipitates, consisting of non-martensitic Ni$_{50}$Al$_{50}$, modify the free energy landscape that governs the phase transformation and result in a significant reduction of the thermal hysteresis, at comparably minor expense of transformation strain, and modification of transformation temperatures. Importantly, this paper shows that free energy landscape engineering is possible with nanostructures potentially accessible through standard metallurgical processing routes. The atomistic-level nucleation and transformation mechanisms within the nanoprecipitate systems are explored and compared with epitaxial nanolaminates and nanowires. The simulations reveal three distinct regimes of transformation mechanisms and martensitic nanostructure as a function of volume fraction of the non-martensitic phase. Free energy landscape engineering is generally applicable and could contribute to the design of new shape memory alloys with novel properties, such as light weight alloys that operate at room temperature.