THE INTERPOLATED TM-MG PHASE-DIAGRAM

The alloying behavior of the different rare earths, which varies accor ding to systematic patterns, can be used to predict constitutional pro perties of rare earth alloys with the same element. The applicability to prediction of the Tm-Mg phase diagram is presented here. The predic ted version is compared with that determined experimentally by analyzi ng a few key compositions using X-ray powder diffraction, optical and scanning electron microscopy, electron probe microanalysis (EPMA) and differential thermal analysis (DTA). The following phases were identif ied and their crystal structures confirmed or determined: beta phase, approximate to Tm2Mg (cubic, cI2, W type), TmMg (cubic, cP2, CsCl type ), TmMg, (hexagonal, hP12, MgZn2 type) and approximate to Tm5Mg24 (cub ic, cI58, alpha-Mn type). All the phases show peritectic formation. Tw o other equilibria were also observed: a eutectic reaction at 575 degr ees C and 89 at.% Mg and the eutectoid decomposition of the beta phase at 670 degrees C and approximately 30 at.% Mg.