Experimental Investigation and Thermodynamic Assessment of the Hf-Mn System

The Hf-Mn binary system was investigated via experiment and thermodynamic assessment. Six alloys, which were prepared by arc melting the elements, were annealed at 1223 K for 240 h or at 923 K for 408 h, followed by analysis using x-ray diffraction, optical microscopy, scanning electron microscopy, and electron probe microanalysis. The homogeneity range of HfMn2 was determined to be from 66.4 to 73.5 at.% Mn at 1223 K and from 65.3 to 73.0 at.% Mn at 923 K, while that for HfMn was measured to be very limited (48.4-49.0 at.% Mn at 1223 K). The invariant equilibrium of beta Hf <->alpha Hf + HfMn, which was previously proposed to occur at 1123 K, was not observed according to the present differential thermal analysis. The thermodynamic optimization for the Hf-Mn system is then conducted by taking into account the reliable experimental data from the literature and the present work. The calculation using the obtained parameters can reproduce most of the experimental phase diagram data and thermodynamic properties.