Oxygen–molybdenum interaction with dislocations in Nb-Mo single crystals at elevated temperatures

Abstract A study using a transmission electron microscope was performed for the deformation microstructures of Nb-20mol%Mo single crystals containing from 0.03 to 0.65 mol% oxygen and a Nb-40mol%Mo-0.05mol%O single crystal, compressed to approximately 4% plastic strain at 298 K, 973 K and 1473 K. At 298 K, screw dislocations are predominant in all alloys. At 973 K, in Nb-20Mo-0.03O and Nb-40Mo-0.05O, the dislocation microstructure contains the same amount of edge dislocations and small edge dipoles that tend to aggregate into clusters. In Nb-20Mo-0.65O, however, the arrangement consists of long glide loops parallel to the screw direction. At 1473 K, edge dislocations are dominant in all alloys. From the results, the following conclusions are made: (1) Oxygen atoms impede screw dislocation motion at 298 K and 973 K; (2) The influence of oxygen on screw segments is significantly strong at 973 K; (3) At 1473 K, oxygen atoms impede edge dislocation motion. It is inferred that O-Mo atmosphere is formed around dislocations.