Technical Papers and Notes - Institute of Metals Division - The Antimony-Zirconium System in the Range 0 to 5 At. Pct Antimony

The solubilities of antimony in the a and ß-forms of zirconium were determined between 750" and 1300°C. The a-phase forms by a peritectoid reaction, and the a/(a + ß) and ß/(a + ß) phase boundaries rise in temperature with in- ' creasing antimony. Impurities in the 99.95 pct zirconium were sufficient to influence the phase boundaries and the variation reported is approximate. The restricted solid solubility of the terminal zirconium phases, which is especially characteristic of this system, is thought to result from the low free energy of the Zr2Sb phase. ZIRCONIUM-antimony alloys are important in zirconium alloying studies since antimony is one of the highest valent elements which can be used to make zirconium alloys. The dilute alloys are of further interest as they have somewhat better corrosion resistance' than pure zirconium. The first investigation of the phase diagram was made by Russi and wilhelm2 who found a eutectic reaction, liquid (- 17.5 at. pct Sb) = ß zirconium (- 11 at. pct Sb) + Zr2Sb, at 1430°C'. The Zr2Sb phase was of complicated hexagonal structure, and by thermal analyses of the relatively impure alloys then available, Russi and Wilhelm found evidence for the peritectoid formation of the a-phase. EXPERIMENTAL In the present work, the phase diagram was re-investigated in the region 0 to 5 at. pct Sb and 750" to 1300°C using iodide-zirconium alloys. Details of the procedure have been described earlier. Essentially the alloys were prepared by arc casting and were then examined by the annealing and quenching method. The times of annealing varied from 1 hr at 1300°C to 30 days at 760°C. As in other zirconium phase-diagram studies1"5 the impurities in the zirconium were still sufficient to affect the results, and the experiments will therefore be described in 3 parts. The results from the first 2 parts of the work are shown in Fig. 1. Here the ß/(ß + Zr2Sb) and a/(a + ZrzSb) phase boundaries were determined with alloys made from 99.9 pct zirconium,* and cast under such conditions that the Vickers hardness of a alloys extrapolated to 95 to 110 VPN at 0 at. pct Sb. Such alloys were not suitable for investigations of the (a + ß) region, and the results shown in Fig. 1 near the (a+ ß) and (a +ß + Zr2Sb) regions were determined with purer alloys. These alloys had an extrapolated hardness range of 75 to 85 VPN and were made from 99.95 pct zirconium. A deviation from binary equilibrium occurs in Fig. 1 as indicated by the (a + ß) region of pure