Thermodynamic investigation of the aluminum-chromium system

In the course of a thorough investigation of the Al-Cr-Nb ternary system, the intermetallic compounds of the Al-Cr system were investigated by direct reaction calorimetry at high temperatures. New enthalpies of formation were determined and cmpared with literature data. X-ray powder diffraction (XRD), electron probe microanalysis (EPMA), and differential thermal analysis (DTA) were carried out on calorimetric products and on heat-treated alloys. A eutectoid decomposition of the Al sub 11 Cr sub 2 phase (Al sub 11 CR sub 2 < -- > Al sub 7 Cr+Al sub 4 Cr) was discovered. The eutectic nature of the equilibrium involving Al sub 7 Cr with Al solid solution was verified and this contradicts the published phase diagram. The hexagonal (Al sub 4 Mn structure type) of Al sub 4 Cr was confirmed.