Heterogeneous coherent interface thermodynamics and Wulff construction associated with the cubic-tetragonal-orthorhombic multi-step structural transition in Mn-Ni alloys

Abstract

A variety of heterogeneous coherent interfaces is formed during the cubic (fcc)-tetragonal (fct)-orthorhombic (fco) multi-step structural phase transition in Mn- Ni antiferromagnetic shape memory alloy, which directly affects their shape memory effect, magnetic field-controlled memory effect and damping property. The thermodynamic properties of various types of interface in Mn-Ni alloys have been studied by using a universal chemical-structure model. The chemical energy and structural energy of fcc/fct, fct/fco and fcc/fco interfaces were calculated and compared, and it was found that the structural energy played a leading role in the total interfacial energy and the construction of Wulff shape. Besides the temperature, the interfacial orientation relationship has an important influence on the interfacial energy, which can be used to consider the singularity of coherent interface from the Wulff shapes. Based on this heterogeneous coherent interfacial energy model, the relationship between interfacial specific heat, interface entropy and interfacial enthalpy and temperature of fcc/fct, fct/fco and fcc/fco heterogeneous interfaces were calculated and compared from thermodynamic viewpoint. The effect of the softening modulus and the habit plane index on the interfacial energy was investigated.