Effect of Oxygen on Phase Boundary in Dilute Nb Area of Zr-Nb Alloy

摘要

The phase boundary and Nb solubility of Zr-xNb binary alloys containing 2000 ppm oxygen were investigated by using DSC, metallography and TEM. To obtain the equilibrium phase, the alloys of Zr containing 0 to 10 wt. percent Nb were annealed for a long time at different temperature. The phase transformation temperature from alpha to alpha+beta and alpha+beta to beta in the Zr containing 2000 ppm oxygen was analyzed at 980 deg C and 1025 deg C. The phase transformation temperature of the Zr containing 2000 ppm oxygen was increased than that of the Zr having 700 ppm oxygen. The monotectoid temperature of the Zr-Nb alloys containing 2000 ppm oxygen was revealed at 585 deg C. From the analysis of precipitates using TEM equipped EDS, Nb-containing precipitates were observed on the Zr-0.2Nb alloy that annealed at monotectoid temperature. This means that the maximum Nb solubility in Zr-xNb binary alloy containing 2000 ppm oxygen would he lower than 0.2 wt. percent.