HIGH DUCTILITY OF POLYCRYSTALLINE 70-30 B RASS AT INTERMEDIATE TEMPERATURES

For a further understanding of intermediate temperature embrittlement of alpha brass, the ductility of a Cu-30 mass%Zn binary alloy was inve stigated in detail at elevated temperatures up to 803 K under three st rain rates of 6.7 x 10(-4), 2.0 x 10(-2), 2.0 x 10(-1) s-1 using speci mens with six grain sizes ranging from 0.009 to 0.209 mm diameter. The coarse-grained specimens show a markedly poor ductility near 673 K ac companied with intergranular fracture, i.e., intermediate temperature embrittlement, while fine-grained specimens show an excellent ductilit y together with the formation of fine recrystallized structures due to dynamic recrystallization. In the necked regions near the fractured p ortion, many cavities are present in the fine-grained material. The sh ape and number of cavities are significantly changed with decreasing g rain size. Small round holes are observed at the grain boundaries of t he fine-grained specimens. As the grain size decreases, small isolated cavities are frequently observed. In the fine-grained specimens, grai n refinement by dynamic recrystallization leads to high ductilitily, a lthough cavities are introduced.