Dislocation evolution during thermal creep deformation in V-4Cr-4Ti with various thermal and mechanical treatments

Dislocation evolution during thermal creep deformation was investigated at 1023 K for V-4Cr-4Ti alloys with various thermal and mechanical treatments. Changes in the density and Burgers vector of dislocations were examined with various materials and experimental variables (e.g., cold work introducing dislocations, thermal aging introducing high density of Ti-rich precipitates, applied stress, and creep deformation levels). The Burgers vector analysis showed that, in the annealed specimens, dislocations induced by the thermal creep were predominantly of a/2〈1 1 1〉 type. The densities of a〈1 0 0〉 and a/2〈1 1 1〉 type dislocations were comparable for the cold worked V-4Cr-4Ti, but the fraction of a/2〈1 1 1〉 type dislocations increased with the creep deformation. Similar changes to the Burgers vector fraction were observed for specimens with a high density of precipitation prior to the cold work. On the other hand, cold work followed by aging (i.e., strain aging) was effective in keeping dislocation structures during the creep deformation.