Glass Forming Ability, Magnetic Properties And Microstructure Of Nd-Al-Fe-Co Bulk Metallic Glasses

Since the first report of successful preparation of metallic glasses by P. Duwez et al. in Caltech, the materials have attracted increasing interests due to their unique mechanical, magnetic, electrical and chemical properties. As one of the important magnetic amorphous materials, RE-Fe (RE=Nd, Pr) metallic glasses with promising magnetic properties were developed by J. J. Croat and have been intensively investigated because of their great significance in material science and their considerable technological promise. The glass-forming alloys studied include Nd(Pr)-Al-Fe, Nd(Pr)-Al-Fe(Co), Nd(Pr)-Al-(Fe, Co)-B and so on. Among these, Nd-Fe(Co)-Al bulk metallic glasses (BMGs) have shown attractive glass-forming ability (GFA) and high coercivity at room temperature. However, neither distinct glass transition nor supercooled liquid region has been observed in their differential scanning calorimetry (DSC) traces, while the distinct glass transition and wide supercooled liquid region are common features for other BMGs. And the high coercivity of the BMGs is anomalous because of their disordered structure.In this work, we studied the glass forming ability, microstructure and magnetic properties, thermal stability and kinetics of the alloys. The details of our research work are listed as follows:1. We calculated the forming enthalpies of glasses, solid solutions and intermetallic compounds using Miedema's method and denoted a new parameter x to evaluate the effects of the forming enthalpies on GFA of the alloys. The parameter was confirmed by experimental results to be useful for the prediction of the compositional range of the BMGs in Nd-Al-Fe-Co alloy systems.2. We obtained Nd-Al-Fe-Co BMGs such as Nd55Al20Fe25, Nd60Co40-xAlx (x=5, 10, 15) and Nd50Al15Fe15Co20 with distinct glass transition. The glass forming ability of the alloys was studied by reduced glass transition temperature and parameterγ. The critical thickness of Nd47Al23Fe20Co10 BMG calculated to be about 16.5 mm indicates the excellent GFA of the alloy.