Microstructure, Martensite Transition and Mechanical Properties Investigations of Polycrystalline Co-Ni-Al Alloys with Er Doping

Using a multi-technique approach, we explore the effect of Er doping on the mechanical properties and phase transition temperature of polycrystalline Co-Ni-Al alloy. The un-doped alloy exhibits poor mechanical properties and a very low phase transition temperature. Therefore, the alloy could not obtain the apparent magnetic-field-induced strain. We show that the microstructure is typical of a multi-phase structure at room temperature. Within the grain boundary, a γ phase exists and is shown to continuously grow surrounding the matrix as the Er is being doped. This results in the appearance of Co 2 Er in the γ phase when Er rises above 0.5 at.%. The phase transformation temperature clearly increases with doping and reaches room temperature when doping is at 1 at.% Er. The yield stress and ductility of the alloy increased remarkably at first and then slightly decreased with further doping. The sample exhibits an interesting shape memory effect that is enhanced by Er doping or thermo-mechanical cycles.