DEFORMATION STRUCTURES IN ZONE-MELTED MOLYBDENUM ABOVE ROOM TEMERATURE.
FRANKLIN INST RESEARCH LABS PHILADELPHIA PA
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Stress-strain behavior of single crystal molybdenum oriented for slip on the 011 111 slip system has been examined at 578K the associated glide dislocation configurations have been characterized by thin film transmission electron microscopy. A high density of prismatic loops is observed elongated along 211. Few long segments of primary screw dislocation exist, but there are serrated, angular, and cusp-shaped segments of short length. The debris of dislocation loops has the same Burgers vector as the primary screw dislocations. Dislocation tangling is restricted to the immediate vicinity of inclusions or pinned grown-in dislocations. In comparison, the slip band structure in the range 4.2 - 300K is characterized by the presence of long primary screw dislocations of Burgers vector plus or minus a2 111. Jog formation at 578K is most likely the result of thermally activated cross-slip. However, it is possible that the magnitude of the dislocation uncertainty perpendicular to the slip plane in molybdenum at this temperature is sufficient to provide job heights consistent with the width of the observed elongated prismatic loops. The work-hardening level is controlled by the extent of secondary slip, and by the recovery occurring through cross-slip. Author
- Metallurgy and Metallography