Formation of metastable low temperature allotropie solid solutions in rare earth-zirconium systems

Abstract

The mutual solid solubilities of the heavy rare earth metals (Gd, Tb, Dy, Ho, Er, and Lu) with zirconium have been greatly extended by splat quenching the alloys from the molten state to room temperature. All the retained solid solutions are in the low temperature allotropie form (hep). X-ray parametric measurements were used to determine the solubility limits. Compared to the solubilities for alloys obtained in the equilibrium condition, the solubility limits of the metastable solid solutions increase more than five times for Gd-Zr and Tb-Zr alloys. Continuous series of solid solutions are obtained in Dy-, Ho-, Er-, and Lu-Zr systems. We believe this is the first observation of the heavy rare earth elements forming continuous solid solutions with a transition metal in their low temperature allotropie forms. The large extension of the metastable solubilities obtained from liquid quenching is in accord with the martensitic phase transformation ofβ → α’ types at a high cooling rate (10⁷°C per sec). The present observations can be qualitatively accounted for by the classical rules; however, a semiquantitative description of the observed increment of the solubility with the increasing atomic number of the rare earth elements is further correlated by thec/a ratios of the hep alloys. Finally, the metastable solid solubility has been demonstrated by the size factor and thec/a ratio for the elemental crystal structure of rare earth element.