Preparation And Properties Of Al-Fe-Zr(-Nd)Amorphous Alloys

Nd-based and Zr-based amorphous alloys have been drawn profound attention due to their preparation and properties, because of strong thermal stability、hard magnetic properties at room temperature.In this study, Al-Fe-Zr and Al-Fe-Zr-Nd amorphous alloys can be prepared by casting and milling. The evolution of microstructure, morphology, thermal stability and crystallization procedure of alloys were analyzed by X-ray diffraction, Scanning electron microscopy and Differential scanning calorimetry, respectively.Firstly, the composition range of amorphous forming for Al-Fe-Zr system has been summarized by the previous studies. Twelve components were choosed in the Al-Fe-Zr system milled by mechanical alloying. The evolution of microstructure, morphology, the amorphous forming ability and the composition range of amorphous forming of Al-Fe-Zr alloys were systematically studied. Most importantly, make a comparison between amorphous formation range predicted by Miedema theory and the experiments.The results show that the Zr70Al5Fe25, Zr70Al10Fe2o, Zr7oAl2oFe10, Fe50Al4oZr10, Fe5oAl3oZr20amorphous alloys have the largest GFA, whlie the GFA of the Fe5oAl4oZr10, Fe7oAl10Zr2o amorphous alloys are the weakest. The mechanical stability of Zr70Al5Fe25, Fe5oAl4oZr10, Fe5oAl3oZr20amorphous alloys are high, while Fe5oAl4oZr10, Fe70Al10Zr2o are low. Zr rich Al-Fe-Zr amorphous alloys show the broad diffuse peak, while Fe rich Al-Fe-Zr amorphous alloys show the narrow diffuse peak. The intermetallic formed after casting, during the milling, only the intensity of the diffuse peaks changed, and finally the amorphous formed. The predicted amorphous formation range obtained by the experimental results was in good agreement with that by the theory.Secondly, The composition range of amorphous forming of Al-Fe-Zr-Nd was also predicted by the thermodynamic point of view. The enthalpies of formation for crystalline and amorphous states can be estimated with Miedema’s theory and a geometric model. Effect of Zr on the glass forming ability and thermal stability of Al-Fe-Nd alloys were systematically studied.We found that, the composition range of glass forming ability for the pseudo-ternary system AlloFe30(ZrNd)6o is x=0-100at%of Zr. As for Nd6o-xFe3oAl10Zrx (x=0,5,15,20,30,50), it is noted that amorphous phase formation is completed for Nd6o-xFe3oAl10Zrx (x=0,5,15,20,30,50) after milling certain time. The agreement between the prediction and the experimental data is excellent. So the composition range of glass forming is x=0-60at%of Zr. After milling for30h, the sample of Nd6oFe3oAl10starts to become amorphous, and the homogeneous amorphous phase is stable until about120h of milling. This indicates that amorphous Nd6oFe3oAl10has good mechanical stability. The broad diffuse peak occurred at the angle of25～35°with the Nd-rich Al-Fe-Zr-Nd, while the broad diffuse peak occurred at the angle of35-45°with the Zr-rich. The diffuse peak is becoming broader with the content of Zr increasing. The layer diffusion mechanism belongs to the amorphous mechanism of the Al-Fe-Zr-Nd system. The two crystallization activation energy of Nd6oFe3oAl10estimated by Kissinger schedule are Epl=133.90kJmol-1, Ep2=409.83kJmol-1, respectively. This shows that it has good thermal stalility. The products of the amorphous Nd6oFe3oAl10after annealing for2h at700K and1000K respectively as follows:Am�'Am+AINd�'AINd+Al8Fe4Nd+Fe17Nd5+Al5Fe2.