Phase Equilibria in the Zr-Ti-Cu System

Phase equilibria in the Zr-Ti-Cu system have been studied by differential thermal analysis, scanning electron microscopy, x-ray microanalysis, and x-ray diffraction. Based on the obtained results, a ternary phase diagram was constructed over the entire composition range in the crystallization interval. The results are presented in the form of liquidus and solidus projections, the Scheil reaction scheme, and isopleths for sections of 40 and 70 at.% Cu. Phase equilibria in the system are defined by the ternary compound ZrTiCu₂ (τ₁) and the binary-based phase Zr₁₄Cu₅₁. These phases have the widest fields of primary crystallization on the liquidus projection and form two-phase equilibria with all other phases on the solidus projection. The solidus projection contains 11 three-phase fields. Two of them form by invariant four-phase reactions of the transition type, the rest by eutectic ones. A comparison of the solidus projection with the published isothermal sections at 800 and 750 °C led to the need for two solid-state four-phase invariant equilibria involving binary Ti-Cu intermetallic compounds. They are shown to occur between 840 and 850 °C. The ternary compound Zr₂₂Ti_14.5Cu_63.5 (τ₂) was shown to form in the solid state at 827 °C by three-phase invariant reaction τ₁ + Zr₁₄Cu₅₁ ⇄ τ₂.