スズ青銅の高温延性に及ぼす微量添加元素の影響

抄録

In connection with hot-shortness of tin-bronze, the ductility of a Cu-8 mass%Sn binary alloy and of the alloy containing B, Mg or P of about 0.1 mol% was investigated in detail at elevated temperatures up to 1073 K. All the alloys showed markedly a poor ductility near 673 K accompanied by intergranular fracture, i.e., intermediate temperature embrittlement. The ductility was improved to a greater extent at higher temperatures in B-bearing and Mg-bearing alloys, but to a lesser extent, in binary and P-bearing alloys. The improved ductility which was accompanied by transgranular fracture was commonly observed regardless of strain rate and grain size in the B-bearing alloy. This alloy showed an excellent ductility together with fine recrystallized structures due to dynamic recrystallization at higher temperatures. Recrystallization temperatures, however, were almost the same in the four sorts of alloys. In the binary and P-bearing alloys, intergranular fracture at higher temperatures was shown to start at the specimen surface. This fact suggested that the strength of the grain boundary of these alloys was reduced especially near the surface. Based on the result of oxidation experiment, the decrease in grain boundary strength was surmised to be caused by internal oxidation along grain boundaries.