Plastic Anisotropy of Tantalum, Niobium, and Molybdenum

The stress–strain behavior of single crystals of tantalum, niobium, and molybdenum has been studied in both tension and compression in the temperature range 4.2–400 °K. The crystals were stressed in both the [Formula: see text] and the [Formula: see text] directions.At high temperatures, the yield stress of all three metals is independent of the direction and sense of the applied stress. At low temperatures, the yield stress depends markedly on the orientation of the crystals and the sense of the applied stress. This anisotropic behavior cannot be satisfactorily explained in terms of any of the mechanisms proposed so far, such as the mobility of jogs in screw dislocations, or the dissociation of a/2 [Formula: see text] screw dislocations on {112} planes.