Magnetic properties and phase transformations of bulk amorphous Fe-based alloys obtained by different techniques

摘要

Bulk amorphous Fe{sub}65.5Cr{sub}4Mo{sub}4Ga{sub}4P{sub}12C{sub}5B{sub}5.5 rods with diameters of 1.5-3 mm were prepared by copper mold casting. Besides casting, bulk amorphous Fe{sub}77Al{sub}2.14Ga{sub}0.86P{sub}8.4C{sub}5B{sub}4Si{sub}2.6 samples in the shape of discs (diameter of 10 mm and thickness of 3 mm) were prepared from melt-spun ribbons by high-energy ball milling and subsequent compaction of the resulting powders in the supercooled liquid region. The ascast amorphous FeCrMoGaPCB samples exhibit a low coercivity, below 10 A·m{sup}(-1). In the case of the FeAlGaPCBSi alloy, the milling-induced stress causes significant differences in coercivity between the ribbons and the powders. The relatively low coercivity of about 5-10 A·m{sup}(-1) characteristic for the melt-spun ribbons increases after 1 hour of ball milling to a value of about 2200 A·m{sup}(-1). Subsequent annealing of the ball-milled powders leads to a decrease of H{sub}c by a factor of 10 to about 220-250A·m{sup}(-1). The bulk samples prepared by hot pressing of the crushed ribbons show a coercivity of about 120-140 A·m{sup}(-1). For both alloys, thermal stability measurements show a distinct glass transition, followed by a supercooled liquid region of 60K for Fe{sub}65.5Cr{sub}4Mo{sub}4Ga{sub}4P{sub}12C{sub}5B{sub}5.5 and of 30K for Fe{sub}77Al{sub}2.14Ga{sub}0.86P{sub}8.4C{sub}5B{sub}4Si{sub}2.6. For the Fe{sub}65.5Cr{sub}4Mo{sub}4Ga{sub}4P{sub}12C{sub}5B{sub}5.5 alloy, crystallization of the amorphous phase as observed by in-situ X-ray diffraction measurements in transmission configuration occurs via the formation of a metastable intermediate phase. The phases observed in the crystalline state obtained by heating do not correspond to those occurring after slow cooling.