High Temperature Discontinuous Yielding in a New Near β Titanium Alloy Ti-7333

The high temperature discontinuous yielding behavior of Ti-7333 (Ti-7Mo-3Nb-3Cr-3Al), a new near beta titanium alloy, has been examined between 770 and 845 degrees C over strain rates from 10(-3) s(-1) to 1 s(-1). The results show that the discontinuous yielding of the alloy occurs when its strain rate is above 10(-2) s(-1) at all the experimental temperatures. The magnitude of the discontinuous yield drop for Ti-7333 alloy increases with decreasing of strain rate at a fixed temperature, and decreases with decreasing of temperature at a fixed strain rate. The magnitude is more sensitive to the strain rate than the temperature in this investigation. The discontinuous yield phenomena observed is associated with the mobile dislocation generated in grain boundaries during plastic deformation spreading to the grain interior with increasing of strain. The grain boundaries act as the sources of mobile dislocation generation. Further analysis suggests that the discontinuous yield drop is related to unlocking of dislocation sources through a localized dislocation climb, a boundary migration and/or a solute rearrangement.