Mechanical Properties of Nb-Zr Solid Solution Alloys

Tensile properties of Nb-Zr solid solution alloys composed of the retained high-temperature β phase were investigated at temperatures from −196°C to +800°C. The room-temperature yield stress increases linearly with the zirconium content up to 15 at% and it reaches a maximum value of about 100 kg/mm2 at 42 at%Zr. The mechanical behavior of Nb-15 at%Zr alloy was found to be similar to that of pure niobium, but the alloys with higher zirconium content, e.g. 26 and 42 at%, showed a different behavior from pure niobium. Nb-26 or 42 at%Zr alloy does not show a sharp yield drop. The work hardening rate of the same alloy is smaller than that of niobium, being insensitive to the test temperature. Nb-26 or 42 at%Zr undergoes twin deformation below −72°C and a distinct serration appears in its load vs. elongation curves. The low-temperature flow stress of these alloys increases significantly with decreasing temperature. The temperature dependence of flow stress of Nb-15 at%Zr is similar to that of niobium whereas that of Nb-26 or 42 at%Zr alloy is small compared with that of Nb and Nb-15 at%Zr alloy. At temperatures above room temperature, the flow stress of niobium is insensitive to the test temperature and keeps constant up to 600°C, while the flow stress of alloys decreases with temperature and becomes constant at some higher temperatures. The higher the alloy content, the greater is the decreasing rate. The temperature at which the flow stress becomes insinsitive to temperature also rises with alloy content. Elongation at room temperature decreases with zirconium content. But at high temperature, the effect of zirconium content disappears due to the large decrease of elongation of niobium. At temperatures above 600°C the elongation of niobium increases with temperature, while that of alloys continues to decrease with temperature.