Real time synchrotron studies on amorphous Al_(85)Ce_5Ni_8Co_2 and Al_(85)Y_5Ni_8Co_2 alloys

摘要

The crystallization of Al_(85)Ce_5Ni_8Co_2 and Al_(85)Y_5Ni_8Co_2 alloys was studied using differential scanning calorimetry (DSC) and in situ X-ray diffraction (XRD). Continuous heating DSC measurements revealed that Al_(85)Ce_5Ni_8Co_2 and Al_(85)Y_5Ni_8Co_2 alloys exhibit a glass transition followed by a super-cooled liquid region where crystallization occurs through a two- and three-stage process, respectively. The crystallization sequences were also observed in situ by means of XRD using a third generation synchrotron source. During the first crystallization stage, the primary precipitation of alpha-Al takes place only in the Al_(85)Y_5Ni_8Co_2 alloy while in the Al_(85)Ce_5Ni_8Co_2 alloy, a simultaneous precipitation of a metastable Al_(11)Ce_3 and a-Al was observed. The final microstructure contained alpha-Al, Al_3Y/Ce, Al_9Co_2, and Al_3Ni phases. The crystallization was monitored both during heating of the amorphous alloy and during cooling of the liquid alloy in order to detect possible differences in the nature of the crystallization.