S0301-3-3 α黄銅超微細結晶粒材の創成とその疲労強度(疲労き裂進展と疲労強度)

Abstract

Ultra-fine grain α-brass (UFG brass) thin plates were made by repletion of rolling and heat-treatment. The thickness and the grain size of the plates were 0.1 mm and 10 μm for the plate with the initial thickness of 6 mm, and those were 0.120 mm and 1.5 μm for the initial plate thickness of 3 mm, respectively. The fatigue tests were conducting using an electro-hydraulic testing machine with the loading frequency of 30 Hz and the stress ratio of -1 at room temperature. The tensile strength and the 0.2% proof stress of the UFG brass was twice and five times higher than those of normal grain size a-brass (NG brass), respectively, while the elongation of the UFG brass was 1/3 of the NG brass. The fatigue strength of the UFG brass was scarcely higher than that of the NG brass. In the UFG brass, fatigue cracks usually initiated from pits those were formed during electro-chemical polishing process although they were initiated from slip bands for the NG brass. It indicates that the fatigue strength of the UFG brass is very sensitive to defects. Except for the fatigue strength of the UFG brass, the strengths linearly increased with increasing of the inverse of the square root of the grain size (Hall-Petch relationship). Although the tensile strengths were lower for thinner plates, the 0.2% proof stress and the fatigue strength for 10^7 cycles were almost independent of the thickness.