Observation of dislocations in molybdenum
Loesch, Herbert William
Brotzen, Franz R.
Master of Science
Single crystals of molybdenum were strained in direct shear on (110) planes along the  direction. Crystals were sheared to approximately 5, 10, 20, and 40 percent shear strain at 195°K, 300°K, and 373°K, and to 2 and 6 percent shear strain at 78°K. Specimens taken from the (110) shear plane were examined in transmission electron microscopy. The dislocation structure was examined at each strain and temperature increment, and measurements of the dislocation density and the density of jogs on primary screw dislocations were made. The results indicated that: (1) The dislocation density of molybdenum single crystals deformed in shear increases with strain at all temperatures investigated except 300°K. (2) This increase in p was linear, and as the deformation temperature is lowered, the rate of increase is accelerated. (3) The density of jogs on primary screw dislocations varies with strain and temperature much as does the dislocation density. (4) Conservative motion of jogs on screw dislocations becomes appreciable above 300°K. (5) The ease and scale of cross-slip of screw dislocations increases with increasing temperature. (6) The amount of secondary slip in crystals oriented for direct shear on (110) planes increases as deformation temperature decreases. (7) At l95°K and 300°K, the proportion of edge dislocation length to screw dislocation length increases as strain and tangling increase. No definite conclusion was reached on the dislocation mechanism controlling the flow stress.