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The stress-velocity relations for screw and mixed dislocations in high purity niobium were studied at 298K and 196K. Etch pitting methods were used to reveal the dislocation positions after stress pulses in tension and compression. Attention was particularly directed towards establishing any asymmetry in the motion of dislocations on the (112). No asymmetry was observed for either screw or mixed dislocations moving on the (112). The motion at 298K at low stresses was limited by extrinsic barriers while that at 196K and high stresses seemed limited by intrinsic dislocation drag. (Author)

Lattice defects and diffusion of atoms in several transition metal alloys have been examined using anelastic and magnetic measuring methods. In pure nickel phenomena associated with vacancies and divacancies have been observed. The thermodynamic properties of these defects have been determined. In nickel-carbon alloys an associated C-C pair has been identified and some of its motional properties determined. A similar C-C pair in the fcc phase of cobalt has been examined extensively. Not only have the parameters describing its diffusion been deduced, but also the probable symmetry axis, (100), has been determined. The tumbling of Ti-Ti substitutional pairs in dilute concentration in cobalt has also been observed. Detailed analysis of the results leads to the conclusion that the pairs responsible for the relaxation occupy next nearest neighbor lattice positions in the crystal. Both the motional energy and the binding energy of the pairs have been determined. Finally, the precipitation out of solid solution of N in deformed Nb has been followed by internal friction techniques. These measurements have been correlated with changes in hardness and yield strength during precipitation. The system shows unusual strain aging effects which will require careful electron microscopy for full understanding. (Author)

A technique for etch-pitting screw and mixed dislocations in high purity niobium is described.

The effect of hydrogen on the mechanical properties of zirconium and the refractory metals is reviewed with particular attention to the effects on fracture and ductility. The various mechanisms proposed for the hydrogen embrittlement of these metals is reviewed. Both the effects of hydrogen in solution and in the surrounding gas phase is considered. New results on the embrittlement of Nb and Nb-N alloys obtained using a variety of experimental techniques is presented and discussed relative to the generic embrittlement phenomena in these metals. The relation of the crack propagation mechanism to stress and temperature induced phase changes is discussed and a model of hydrogen embrittlement is put forth. (Modified author abstract)

The conditions for machining germanium by the spark erosion technique are established. The effects of this machining on the structure of the crystal are studied by etch pitting. Under proper conditions minimal damage to the crystal results. This technique appears to have the advantages of speed, minimal surface damage and flexibility in the shape of the cut. (Author)