Effect of cyclic deformation on the dislocation structure and mechanical properties of molybdenum, chromium, and tungsten

Abstract

1. We have established that under the effect of elastic vibrations in molybdenum a mosaic structure arises with large angles of misorientation (3–5 °). The mean subgrain size is about 2 μ. 2. We determined that the formation of misoriented mosaic structure in molybdenum, chromium, and tungsten takes place upon cyclic loading with amplitudes and exposure times at which cracks due to fatigue appear. 3. It was shown that the application of intermediate anneals up to 800 °C and electrolytic polishing in order to remove the surface layer can substantially decrease the number of microcracks observed in the surface layer. 4. It was shown that the hardening achieved in molybdenum by low-frequency cyclic loading is comparable to the hardening that can be achieved by 90% plastic deformation in rolling. The yield stress of cyclically loaded samples amounts to 110–120 kg/mm2 as compared to 50–60 kg/mm2 in the initial state. The transition temperature to cold brittleness is lowered by 20–30 °C. 5. We have established that cyclic loading of molybdenum samples leads to a change of the character of brittle fracture. While in the initial, recrystallized state the fracture is primarily intergranular, after cyclic loading we observed transgranular fracture.