Phase boundary of the Zr-rich region in commercial grade Zr–Nb alloys

The α/(α + β)/β transformation temperature, the solubility limit of Nb, and the monotectoid temperature of the Zr–Nb binary system were investigated using commercial grade Zr containing 1400 ppm O and 700 ppm Fe and different Nb levels with a high purity. The microstructure characterization was carried out using OM, SEM and TEM and the phase transformation behavior was also investigated using DSC. From the microstructure examination using OM and SEM, it was revealded that the (α + β) region was expanded in commercial grade Zr containing 1400 ppm O and 700 ppm Fe. From the microstructure characterization using TEM, it was revealed that the Nb solubility in α-Zr of quaternary alloy was 0.2 wt%. And the monotectoid temperature of the commercial grade quaternary system of Zr, O, Fe, and Nb was revealed as 585 °C from the SEM, TEM and XRD analysis. The phase boundary of the Zr-rich region in a restricted quaternary alloy of Zr–0.14O–0.07Fe–xNb system was established on the basis of the results obtained in this study using sponge-type Zr. The results of this study were largely different compared with results of the Zr–Nb binary alloy, however, these results could be used at the case of the Zr-rich corner of the phase diagram for a restricted quaternary alloy of Zr–0.14O–0.07Fe–xNb system.