Effect of crystallite size on Vickers microhardness in nanostructured Heusler Ni39+xMn50Sn11−x (x≤2)alloys

A series of nanostructured Heusler Ni_39+xMn₅₀Sn_11-x (x = 0.5, 1.0, 1.5 and 2.0) alloys has been developed in exploring the effect of microstructure on the mechanical, magnetic, and electric properties. Alloying Ni_39+xMn₅₀Sn_11-x by cooling a molten mixture in shape of a cylindrical disc (15 mm diameter and 8 mm width) results in a nanostructure consisting of thin laminates with an average crystallite size D ~20 nm of the martensite phase (x = 2.0), with a Vickers microhardness H_V ~ 2.584 GPa. A lower H_V- value 2.254 GPa (D~ 50 nm) arises in an austenite-martensite composite phase at larger Sn-content 9.5 at% (x = 1.5). In further Sn-rich compositions, x = 1.0 to 0.5, a single austenite phase transforms with pretty larger H_V-values 3.321 and 2.794 GPa, respectively. These alloys have D ~ 19 nm and 55 nm, respectively. Local strain strongly depends on the D-value.