CRYSTALLIZATION BEHAVIOR OF AL-SM AMORPHOUS-ALLOYS

Various Al100-xSmx alloys (10 less-than-or equal-to x less-than-or-equ al-to 14) have been rapidly solidified by single-roller melt spinning with careful control of the atmosphere in the quenching device. The st ructural state and subsequent devitrification behaviour of the melt-sp un ribbons are found to be particularly sensitive to the quenching con ditions. Except for the thinnest ribbons, there are inhomogeneities bo th through the ribbon thickness and along the length. Both fully and p artially amorphous ribbons have been obtained. The crystallization pro cesses of the amorphous phases have been followed by X-ray diffraction , transmission electron microscopy and differential scanning calorimet ry (DSC). Al92Sm8 shows primary crystallization of Al, followed by the formation of metastable phases; Al90Sm10 transforms polymorphically t o a metastable intermetallic; Al88Sm12 and Al86Sm14 display eutectic c rystallization into Al and a metastable mixture of compounds. For Al90 Sm10, the DSC traces involve several overlapping peaks. This may be th e result of transformations occurring in distinct parts of the ribbon with different mechanisms. A kinetic analysis of the crystallization p rocesses has been performed by means of isothermal and non-isothermal DSC experiments. A discussion of the kinetic parameters derived from K issinger and Avrami analyses is provided.