This paper shows that simple crystal chemistry rules may be applied to interpret and predict the solubility limit and phase stability of alloys at nonequilibrium conditions. Twenty-nine liquid-quenched metastable hcp solid solutions containing elements with both bcc and hcp allotropic forms were studied. Hcp solid solutions of Group III elements with Ti, Zr, and Hf obtained by splat cooling showed that the metastable solubility limits were semiquantitatively correlated to the size factors and c/a ratios. TEM studies indicated that the extended solubilities results from trapping of extra solute in the alpha ' martensite matrices during L yields beta yields alpha' transformation. Hcp intra-rare earth solid solutions were controlled by the structural metastability, e.g. these hcp phases were all terminated at c/a ratios near 1.597. Thus, the linear correlation of the c/a deviation from ideality and phase stability proposed by Hodges was demonstrated. The solubility limit and structure stability for liquid-quenched metastable hcp phases, as well as the implication for the equilibrium solubility limits, are discussed.
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