Effect of applied stress on fcc-L1₀ transformation of FePd single crystal

The equiatomic Fe-Pd alloy has an order-disorder transformation at about 650°C. Three types of variants of the L1₀ ordered phase are formed with the c-axis parallel to either of the 〈100〉 directions of the disordered fcc matrix. Since the ordered phase is tetragonal with c/a=0.966, the external stress is expected to modify the relative population of variants. This has been examined for a single crystal specimen by applying a compressive stress of 40 MPa during ordering treatment. Two types of ordering treatments were examined: (1) quenched from 800°C followed by under-stress-aging at 400°C for 1 h, and (2) slow cooling from a high temperature across the transition temperature (650°C) down to 600°C followed by furnace cooling to room temperature with the stress kept applied. X-ray diffraction measurement revealed that the specimen contains only one type of variant after treatment (2). The effect of the external stress is discussed quantitatively in the light of the calculation based on the continuum elasticity theory.