Pathways towards grain boundary engineering for improved structural performance in polycrystalline Co-Ni-Ga shape memory alloys

Co-Ni-Ga high-temperature shape memory alloys attracted a lot of scientific attention due to their superior functional material properties in recent years. In the single crystalline state Co-Ni-Ga HT-SMAs feature a good pseudoelastic response up to 500°C. However, in the polycrystalline condition Co-Ni-Ga suffers significant grain constraints and premature fracture at grain boundaries. In this regard, crystallographic orientation of the grain being involved as well as morphology and geometrical orientation of the grain boundaries with respect to the loading direction under pseudoelastic deformation is expected to be of crucial importance. Therefore, this study addresses the structural integrity of engineered grain boundaries, i.e. specifically selected grain boundaries in terms of orientation, grain boundary morphology and crystallographic grain orientation of adjacent grains. Mechanical testing combined with in situ methods and post mortem scanning electron microscopy investigations are used to shed light on the prevailing microstructural features resulting in any kind of structural degradation.