EFFECT OF APPLIED STRESS ON FCC-L1(0) TRANSFORMATION OF FEPD SINGLE-CRYSTAL

The equiatomic Fe-Pd alloy has an order-disorder transformation at abo ut 650 degrees C. Three types of variants of the L1(0) ordered phase a re formed with the c-axis parallel to either of the [100] directions o f the disordered fee matrix. Since the ordered phase is tetragonal wit h c/a=0.966, the external stress is expected to modify the relative po pulation of variants. This has been examined for a single crystal spec imen by applying a compressive stress of 40 MPa during ordering treatm ent. Two types of ordering treatments were examined: (1) quenched from 800 degrees C followed by under-stress-aging at 400 degrees C for 1 h , and (2) slow cooling from a high temperature across the transition t emperature (650 degrees C) down to 600 degrees C followed by furnace c ooling to room temperature with the stress kept applied. X-ray diffrac tion measurement revealed that the specimen contains only one type of variant after treatment (2). The effect of the external stress is disc ussed quantitatively in the light of the calculation based on the cont inuum elasticity theory.