Thermodynamic investigation of the aluminum-chromium system

In the course of a thorough investigation of I:he Al-Cr-Nb ternary system, the intermetallic compounds of the AI-Cr system were investigated by direct reaction calorimetry at high temperatures. New enthalpies of formation wer e determined and compared with literature data. X-ray powder diffraction (X RD), electron probe microanalysis (EPMA), and differential thermal analysis (DTA) were carried out on calorimetric products as well as on heat-treated alloys. A eutectoid decomposition of the Al11Cr2 phase (Al11Cr2 <-> Al7Cr + Al4Cr) was discovered. The eutectic nature of the equilibrium involving Al7Cr with Al solid solution was verified and this contradicts the published phase di agram. The hexagonal (AI,Mn structure type) of Al4Cr was confirmed.