Kinetic nature of hard magnetic Nd 50 Al 15 Fe 15 Co 20 bulk metallic glass with distinct glass transition
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M.B. Tang Institute of Physics, Chinese Academy of Science, Beijing 100080, China
H. Xu Institute of Materials, Shanghai University, Shanghai 200072, China
M.X. Pan, D.Q. Zhao, and W.H. Wang Institute of Physics, Chinese Academy of Science, Beijing 100080, China
Y.D. Dong Institute of Materials, Shanghai University, Shanghai 200072, China (Received 6 August 2003; accepted 15 January 2004)
A hard magnetic Nd50Al15Fe15Co20 bulk metallic glass (BMG) was prepared in the shape of a rod up to 3 mm in diameter by suction casting. The glass transition and crystallization behaviors as well as their kinetic nature have been studied. In contrast to the previously reported hard magnetic Nd–Al–Fe–Co BMGs, Nd50Al15Fe15Co20 as-cast rod exhibits a distinct glass transition and multistep crystallization behaviors in the differential scanning calorimetry traces and lower coercivity. The BMG provides an ideal model for the investigation of glass transition and crystallization of hard magnetic Nd–Al–Fe–Co glass-forming alloys.
Since Croat et al. reported the high coercivity observed in RE–Fe (RE⳱Nd, Pr) melt-spun ribbon,1 rare earth– transition metal (RE–TM) metallic glasses with promising magnetic properties have attracted increasing interest because of their great significance in materials science and their considerable technological promise.2-10 The glass-forming alloys studied include Nd(Pr)–Fe(Co)– Al,2-8 Nd–Fe–Co–Al–B,9 Nd(Pr)–Al–Ni–Cu– Fe(Co), 10,11 Y–Fe–Al, 12 and so on. Among these, Nd–Fe(Co)–Al bulk metallic glasses (BMGs) have shown attractive glass-forming ability (GFA), high coercivity, and absence of glass transition temperature in differential scanning calorimetry (DSC) traces.2-8 Inoue et al. supposed that the high coercivity of the alloys is due to the pre-existence of ferromagnetic clusters, the glass transition temperature might be higher than the crystallization temperature, and the reduced glass transition temperature was estimated to be higher than 0.9.3 Recent experimental results have shown that the BMGs are partially crystalline,13 and the absence of glass transition in DSC traces might be due to the chemical inhomogeneity of the amorphous phase.14 More recently, a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0172 J. Mater. Res., Vol. 19, No. 5, May 2004
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further results obtained in Nd60Al10Fe20Co10 glassforming alloys have revealed that the typical microstructure of nanoscale particles scattering in the amorphous matrix is closely related to the primary crystallization (observed in the DSC traces of the ribbons) of the alloy,13,15 and the reduced glass transition temperature representing the GFA might not match the value reported previously.14,15 Up to now, the glass transition of the alloys can only be obtained in the DSC traces of the paramagnetic Nd60Co30Al10 amorphous rods16 and the partially crystalline Nd60Al10Co30-xFex (x < 10) rods.17 And, it is commonly regarded that both the hard magneti
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