Experimental identification of the degenerated equilibrium in extreme Al end of the Al-Cr system

The invariant equilibrium in extreme Al side of the Al-Cr system has been the subject of several investigations. Due to its degenerated nature, which means that the invariant reaction temperature is very close to the melting point of Al, the temperatures reported in these studies show noticeable discrepancies. The experimentally observed invariant reaction temperature among (Al), liquid and Al45Cr7 have been summarized. All of the temperatures quoted in the present work have been converted into international temperature scale of 1990. The formula Al45Cr7 is based on crystal structure data. In the literature five groups of authors reported an eutectic reaction type (L | (Al) + Al45Cr7), whereas the remaining two groups suggested a peritectic one, L + Al45Cr7 < -- > (Al). In the phase diagram assessed by Murray, the peritectic reaction type is adopted. The purpose of the present work is to identify the degenerated nature for the invariant reaction among (Al), liquid, and Al45Cr7 by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD) and electron probe microanalysis (EPMA) methods.