A thermodynamic explanation for the martensitic transformation of nanometer-sized γ-iron particles embedded in a copper matrix

The martensitic transformation of nanometer-sized particles precipitating in a copper matrix is analyzed from a thermodynamic viewpoint. It is shown that there exists a critical austenitic particle size below which the austenitic phase becomes more stable than the martensitic phase and the martensitic transformation cannot take place. Prolonged annealing, extraction of particle from the matrix, and plastic deformation would make the austenitic particle size exceed this critical value, and thus, cause the austenitic particles to transform to martensite. The theoretical results can interpret experimental observations well.