Abstract
α-brass shows the decrease in ductility when deformed over a certain region of elevated temperatures. The phenomenon, so-called “Hot-shortness”, was investigated metallographically on the 70:30 brass specimen tensile-deformed at room temperature∼650°C. As described in the preceding report, the interaction between mobile dislocation and solute atmosphere results in such phenomena as repeated yielding and abnormal work-hardening at about 250°∼550°C. In order to release the stress concentration at grain boundary due to piled up dislocations, local migration of grain boundary occurs, revealing corrugated shape of grain boundary. The abnormal hardening of grain-inside will promote the grain boundary sliding, by which W-type cracks or voids are formed along the corrugated boundary or at the triple point of boundaries. The interlinking of those cracks forms a grain boundary fracture showing hot-shortness. At high temperatures above 550°C, the easy deformability of grain structure and the extensive migration of grain boundaries may dissipate the stress concentration and the crack growth along grain boundaries, leading to the recovery of ductility. Those behaviors are confirmed by the present metallographic study through optical micrography and electron fractography.
