EFFECT OF ORDER-DISORDER TRANSITION ON PLASTIC ANOMALY OF TI3AL SINGLE-CRYSTALS DEFORMING BY PRISM SLIP

Plastic behaviour of Ti3Al single crystals was investigated at high te mperatures focusing on the order-disorder transition. When the crystal s deformed above 700 degrees C by the <{10(1)over bar 0}> <<1(2)over b ar 10>> prism slip, yield stress anomalously increased with increasing temperature and showed a peak just below the critical temperature (T- c) for ordering. The critical resolved shear stress (CRSS) for prism s lip did not obey the Schmid law at high temperatures, and the extent o f violation increased as the anomalous strengthening became significan t. The CRSS for the (0001) <<1(2)over bar 10>> basal slip was higher t han that for the prism slip below T-c, while this relation of the two slips was reversed above T-c. A marked difference in deformation subst ructure between the basal and prism slips was observed in crystals def ormed at 1100 degrees C; almost all 1/3 <<1(2)over bar 10>> superlatti ce dislocations on the prism plane were preferentially aligned in dire ctions parallel or perpendicular to [0001], while widely separated sup erpartials bound by an anti-phase boundary were randomly distributed o n the basal plane showing no preferentially oriented alignment. Copyri ght (C) 1996 Elsevier Science Limited