EXHAUSTION OF A[101BAR](111) SLIP TO EXPLAIN THE STRENGTH ANOMALY IN NI3(AL,TI)

The dislocation structure of Ni3(Al, Ti) deformed in the temperature range where the flow stress increases with increasing temperature (room temperature up to 450-degrees-C) has been investigated. Long straight screw superlattice dislocations transformed into Kear-Wilsdorf locks have been observed after room temperature deformation. Also frequently observed are dislocations curved on the cube (010) cross slip planes. With increasing temperature the tendency for cube cross slip and dislocation movement on cube planes increases. This is consistent with thermally assisted exhaustion of primary octahedral slip by cube cross slip which is responsible for the flow stress anomaly. Dislocations of the primary cube slip system (+/- a[110BAR](001)) are activated at deformation temperatures already below the temperature of the flow stress maximum. Their density increases markedly with increasing deformation temperature. Dislocation interactions of octahedral (111) and cube (001) slip could also contribute to the flow stress, but it is more likely that they control the work-hardening rate. A little above the peak in the flow stress octahedral slip is totally replaced by primary cube slip.