MICROPLASTIC RELAXATIONS OF SINGLE AND POLYCRYSTALLINE MOLYBDENUM

The microplasticity of high-purity molybdenum single crystals and of M o polycrystals of technical purity has been investigated by relaxation step tests in uniaxial compression. A new model for the evaluation of relaxation tests in the microplastic range of b.c.c metals is present ed which takes into account the decrease of the mobile dislocation den sity due to exhaustion of non-screw dislocations. The model allows an independent determination of the activation volume and of the microstr ucture parameters controlling dislocation exhaustion. The results indi cate that in the high-purity single crystals the deformation rate is c ontrolled by interactions of non-screw dislocations with the grown-in network. In the Folycrystals additional interactions with impurity ato ms seem to occur. In the single crystals the activity and subsequent e xhaustion of two different glide systems was observed, followed by a g radual onset of screw dislocation motion.