Phase Changes in Mg-Cd Alloys in the Region of Mg3Cd

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Abstract
A magnesium‐rich phase and a cadmium‐rich phase have been found to coexist for 25 and 30 at.% cadmium over temperature ranges of about 10 and 2 C°, respectively. With changing temperature, x‐ray diffractometer tracings of the (004) and (110) reflections showed a pair of peaks associated with each phase, one increasing in intensity while the other decreased. The appearance or disappearance of one pair of peaks established the temperature boundaries of the two‐phase region. Lattice parameters, calculated from the positions of these peaks, changed with temperature in a nonrectilinear manner which indicated maximum changes in composition of 2% and 1% for the 25% and 30% alloys, respectively. The sudden increase or decrease in the intensity of the (101) superlattice line confirmed the upper boundary of the region. Relative amounts of the phases, as determined from areas of the peaks, agreed with the relative amounts determined by applying the ``lever law'' to the revised phase diagram. These results suggest an ordinary first‐order phase transformation. Moore and Raynor reported two phases of the same composition for Mg3Cd. However, Kamath, Craig, and Wallace found phases of different composition for MgCd3.

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