Phase equilibria of the ternary Ni-Cr-Zr system and interfacial reactions in the Ni-Cr/Zr couples

The phase equilibria of the ternary Ni-Cr-Zr system and interfacial reactions in the Ni-Cr/Zr couples at 900 degreesC were determined. Fifty alloys were prepared from pure Ni, Cr, and Zr. The alloys were metallographically analyzed. Both X-ray diffraction and electron-probe microanalysis (EPMA) were carried out for structural identification and compositional analysis of phases formed in these alloys. At 900 degreesC, the Cr-Ni10Zr7 two-phase region divides the system into two halves. ZrCr2(C14) exists in the Zr-Cr-Ni10Zr7 half, and the ZrCr2 (C15) phase has an extensive ternary solubility. In the CrNi10Zr7-Ni half, except for the Ni7Zr2 phase, most of the binary Zr-Ni compounds are in equilibrium with either Cr or Ni phase. Reaction-couple techniques were used for the interfacial reaction study. The reaction path was Zr/NiZr2/NiZr/Ni10Zr7/Ni21Zr8/Cr/Ni-Cr alloy in the Ni-Cr/Zr couples examined in this study. The results indicate that Ni is the fastest-diffusing species, while Cr is the slowest one.