Analysis of controversial zones of the Zr–Cr equilibrium diagram

Abstract

Zr–Cr alloys were fabricated in an arc furnace by melting pure chromium and zirconium containing two different concentrations of oxygen. Isothermal heat treatments were performed in the range from 840 to 960 °C. The chromium compositions were selected in order to establish equilibria and transformation temperatures near the eutectoid zone and to determine the eutectic reaction in the zirconium rich zone. Phase characterizations and determination of their compositions were carried out by metallographic observations, X-ray diffraction and electron microprobe analysis. Transformation temperatures were obtained measuring the resistivity by the four-point method and by differential thermal analysis. The conditions of the eutectoid and eutectic invariant transformations and general sketches of equilibria in the zirconium-rich zone of the Zr–Cr–O system could be outlined at different temperatures. From the results obtained, β( X Cr ∼ 1.3 at.%) ↔ α( X Cr ⩽ 0.1 at.%) + α-ZrCr 2 at T = 840 °C and L( X Cr = 26.5 at.%) ↔ β( X Cr ∼ 4.7 at.%) + α-ZrCr 2 at T = 1380 °C.