Vickers micro-hardness variation during change in concentration of constituent elements in Ni50–xFexMn30Sn20–yIny, Heusler alloys

Present work is on Heusler alloys of the sequence Ni50–xFexMn30Sn20–yIny, were prepared in order to investigate the relationship between microstructure and mechanical property. The work represents the variations in the hardness of the alloy when the component elements are changed. Alloys show Vickers hardness HV = 3.5 GPa at x = 2 and y = 4. At x = 4 and y = 8, alloy exhibits an L10 tetragonal structure, whereas at x = 3 and y = 6 L21 austenite phase structure is observed. Interface piling up occurs which greatly reduces fracture propagation and dislocation at neighboring interfaces. Large piled-up interfaces available in the martensite phase due to the sub-strips significantly contribute this process resulting in large hardness value. In spite of thicker laminates in the austenite phase, the alloy exhibits higher hardness than martensite phase or even the composite. Hardness is particularly low in the martensitic phase (x = 4, y = 8), which is produced owing to interfacial motion. The hardness value falls as the Sn concentration increases due to weak pinning between the strips. A drastic increase in hardness of 3.5 GPa has been observed when x = 2 and y = 4.