Experimental Determination of the Allotropic Transition Temperature Between Tetragonal and Orthorhombic Al4Sm Metastable Phases

The allotropic transition temperature associated with the metastable -Al4Sm (orthorhombic) and -Al4Sm (tetragonal) phases was investigated experimentally. Low-energy X-ray diffraction and differential scanning calorimetry were found to be inconclusive due to the transient nature of the phases involved, which spontaneously decompose to the stable -Al3Sm and Al-fcc phases. High-energy X-ray diffraction, using synchrotron radiation, however, was able to resolve the transition during continuous heating, enabling detailed analysis of the temperature-dependent diffraction pattern. The - transition temperature was determined to be 896K, based on a well-resolved transition onset.