Microflow in niobium alloy crystals

Abstract

Single crystals of dilute NbMo and NbTa alloys have been deformed in tension over a range of temperatures and strain sensitivities. At macrostrains, a large parabolic hardening is observed in NbMo alloys at 295°K; a similar though much smaller effect is observed with NbTa alloys, in spite of the absence of an atomic size difference. Alloying does not appear to affect either the nature of the slip lines or the operative slip system. The transition from microyielding to macroflow has been studied in prestrained crystals using a dynamic microstrain technique. In contradiction to previous results, alloying is found to affect microflow in the same way as macroflow. Solute is believed to affect the mobility of dislocations by a long range elastic interaction; solute has no significant effect on dislocation multiplication. At low temperatures, a solution-softening effect is observed during micro-flow of NbTa alloys, as it is at macroflow.