Influence of external fields on some alloys exhibiting FCC-L1₀ phase transformation

Influence of external stress or magnetic fields on the volume fractions of the variants in the ordered phase has been examined for some ordered alloys exhibiting the fcc(disorder)-L1₀(order) phase transformation. The variant fractions are significantly modified under an external field when the heat-treatment temperature for ordering is relatively high, but the effects of a field are markedly diminished below a certain critical temperature. The critical temperature does not depend on kinds of external fields. A theoretical analysis indicates that the temperature is close to the spinodal-ordering temperature, that is, the "nucleation and growth" process is required to alter the variant fractions. When the proportion of the variants is markedly modified, a macroscopic shape change arising from the lattice-constant change is clearly observed. Thus, the shape change at the order-disorder phase transformation can be utilized as a shape-memory function with applying an external field. It was confirmed that a trial actuator composed of FePd and conventional inconel alloys works properly by heating and cooling.