Strain rate sensitivity of the flow stress in a Ti-Al alloy: Analysis of the anomalous strengthening effect

Abstract

An analysis has been made of the mechanisms controlling the strain rate dependence of the flow stress as a function of temperature in a Ti-Al alloy, based on the dislocation configurations observed together with the activation volumes measured at each temperature. At low temperatures (20--200 C), the low values of activation volume measured and their independence on strain have confirmed that a Peierls lattice friction mechanism controls the mobility of screw segments of either ordinary or superdislocations. At the higher temperatures (500--700 C) a climbing process of ordinary 1/2 dislocation segments with variable length is responsible for the slightly strain dependent activation volumes measured. The strongly strain dependent activation volumes obtained between 400--450 C has confirmed that the mechanism responsible for the anomalous peak in flow stress is produced by a jog dragging process as an increased density of jogs is created with increasing temperature, due to the increasing number of forest cutting events between ordinary 1/2 dislocations.