Experimental determination of the phase relationships in Zr/2.5–8.0 at% Nb/0–6.7 at% Al alloys with 750 at ppm 0 and 250 at ppm N between 730–900° C

Abstract Zr alloys with 2.5 to 8.0 at% Nb and 0 to 6.7 at% Al were subjected to dynamic and static treatments between 730–900° C and studied by qualitative and quantitative optical metallography, electrical resistance, X-ray diffractometry and electron microanalysis. The experimental data were analyzed by taking into account the effects of oxygen and nitrogen impurities. The main results for Zn-Nb-Al alloys with 750 at ppm O and 250 at ppm N are the following: 1. (i) Equilibrium relationships are established between the α (hcp), β (bcc) and Zr 3 Al (Cu 3 Au) phases along isothermal sections at 730, 771 and 800°C. 2. (ii) The β / α + β boundaries are determined along iso-aluminum vertical sections at 6.7, 3.3 and 0 at% Al. 3. (iii) The addition of Al to Zr-Nb alloys increases the solubility of Nb in the α phase, its maximum value at 730° C being about 0.7–0.8 at% for 4 at% Al. 4. (iv) Solubility values for Al in the α-phase of Zr-Al were estimated by extrapolation from ternary alloys. These estimates help to solve an existing discrepancy in the Zr-Al system.