Experimental investigation and thermodynamic calculation of the ternary system Mn-Y-Zr

Abstract

Phase equilibria were established in the ternary system Mn-Y-Zr for an isothermal section at 800 degrees C by use of X-ray powder diffraction, light optical microscopy and quantitative EPMA. No ternary compounds were observed. Mutual solid solubilities among the binary phases were found to be generally less than similar to 2 at.%. Solubility of Mn, Y in alpha Zr at 800 degrees C was 2.1 at.% Mn and 2.9 at.% Y, whereas no Mn dissolves in alpha Y. A reinvestigation of the binary solid solubility limits of Mn2Zr1-x at 800 degrees C by quantitative EPMA and X-ray powder full profile analyses revealed a smaller homogeneous region, Mn2Zr1-x, 0 less than or equal to x less than or equal to 0.20, than previously reported in literature. There is little solubility of Y in stoichiometric Mn2Zr and maximum solubility of Mn, Zr in alpha Y was determined from as cast alloys to be 1.8 at.% Mn and 2.4 at.% Zr. Based on this experimental findings and the literature data relevant to the binary systems a thermodynamic calculation of the ternary system was attempted, requesting a significantly higher heat of formation of Mn2Zr than previously reported. A nearly pseudobinary section was experimentally established for the join Y-Mn2Zr with a maximum eutectic at 1072 +/- 10 degrees C at 57 at.% Y (calculated at 1064 degrees C and 58% Y). Three ternary eutectics were defined: L double left right arrow Mn2Zr + Mn2Y + Mn23Y6 at 1090 +/- 10 degrees C at a composition of Mn75Y23Zr2 (calculated at 1087 degrees C and at Mn72Y26Zr2), L double left right arrow (alpha Y) + Mn2Y + Mn2Zr at 870 +/- 10 degrees C at a composition of Mn40Y57Zr3 (calculated at 883 degrees C and at Mn36Y63Zr1) and L double left right arrow (alpha Y) + (beta Zr) + Mn2Zr at 1054 +/- 10 degrees C at a composition of Mn26Y15Zr59 (calculated at Mn24Y21Zr55 and at 992 degrees C).