抄録
In connection with hot shortness of tin bronzes, the ductility of a Cu-8 mass%Sn binary alloy and of the alloys singly 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 poor ductility at temperatures from 673 to 873 K accompanied by intergranular fracture on account of so-called 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 the binary and P-bearing alloys. The marked improvement in 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 excellent ductility together with fine recrystallized structures which was caused by dynamic recrystallization at higher temperatures. Recrystallization temperatures, however, were substantially the same in four sorts of alloys. In the binary and P-bearing alloys, intergranular fracture at higher temperatures was shown to start from 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 the grain boundary strength was surmised to be inhibited in B- and Mg-bearing alloys by the suppression of oxygen penetration through the grain boundary.
