Strain compatibility issues in mechanically driven martensitic transformations in shape memory alloy polycrystals

Applications of shape memory alloys (SMA) rely on transformation strains in the range of several percents reversibly generated in response to thermomechanical loading. The transformation strain stemming from martensitic transformation (MT) is intrinsically anisotropic leading to elastic interactions at the interface between the austenitic lattice and variants of martensitic lattice. The interactions affect temperature hysteresis, stability of the thermomechanical response and fatigue processes in cyclically loaded SMAs. However, SMAs are being used mostly in polycrystalline form, where the deformation process is further constrained. The creation of martensitic microstructures in individual grains under the external mechanical stress is constrained by neighboring grains. The objective of the present project is to understand at the structural level cooperative deformation processes related to stressinduced MT in SMA polycrystals and experimentally prepare microstructures providing lowest intergranular constraints with hope to engineer resistant strain compatible microstructures