Effect Of Element Additions On Glass Forming Ability, Crystallization And Properties Of Fe-based Glassy Alloys

In the present thesis, the effect of Ni, Zr and Y on the glass forming ability (GFA), thermal expansion behavior, mechanical properties, magnetic properties and corrosion resistance of the Fe-based glassy alloys have been investigated. In addition, the influence of Ni and Y on the primary crystalline phases, precipitation mechanism, and soft magnetic properties in isothermal annealing and rapid solidification process of Fe-based glass alloys have been discussed as well.The influence of Ni on the GFA, magnetic properties and corrosion resistace of Fe78Si9Bi3 glassy alloys were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), vibrating sample magnetometer (VSM), electrochemical workstation and scanning electron microscopy (SEM). The results show that the addtion of Ni decreases the GFA and soft magnetic properties of Fe78Si9B13 glassy alloys. The additon of Ni can induce:(1) the deviation of Fe-Si-B-Ni from eutectic point into the hypereutetic regime; (2) the deviation of Si atoms from Fe-Si region which promotes the nucleation of primary?-Fe phase. The addition of Ni enhances the corrosion resistance of (Fe0.78Si0.09B0.13)100-x.Nix(x= 0,2,3,5) glassy alloys. The improvements of the passive protective properties attribute to the addition of Ni which can promote the diffusive of the Si atoms to the surface of the alloys, and subseqently the Si atoms form a stable and continouos protective SiO2 film.The influence of Ni on the structure and primary crystalline precipitation mechanism of (Fe0.78Si0.09B0.i3)100-x-Nix (x= 0,2,5) glassy alloys, and the mechanical properties of the (Fe0.78Si0.09B0.13)95Ni5 alloy after rapid solidification have been investigated by XRD, transimission electron microscopy (TEM) and microhardness tester. The resuls show that the primary crystalline phases of Fe-Si-B-Ni glassy alloys are a-Fe(Si) solid solution in the rapid solidfication and isothermal annealing process. In the isothermal annealing process, the addition of Ni promotes the nucleation of primary crystalline a-Fe phase, inhabites the decompositon of residual glassy matrix. As the annealing time increases, the lattice constant and grain size of the primary phase show an opposite trend in the crystallization process. The results are related to that the concentration of Si atoms increases in the crystallization interface as the primary a-Fe phase grows up. The microhardness values (H?) between the wheel side and the free side are different, both in glassy and partial crystalline ribbons of the as-cast (Fe0.78Si0.09B0.13)95Ni5 alloy ribbons. The H?of the wheel side is larger than that of the free side, and the glassy ribbon is smaller than that of the partial crystalline ribbon both in the wheel side and the free side. It is ascribed to precipitation and grain boundary strengthening which caused by the fabricating equipment and the different spinning conditions.The effect of Zr on the GFA, thermal expansion properties and magnetic properties of (Fe0.78Si0.09B0.13)100-xZrx(x=0,1,2) alloys were investigated by XRD, DSC, dilatometer (DIL) and VSM. The results show that appropriate Zr addition (1 at. %) can improve the GFA and thermal stability of the Fe-Si-B-Zr alloys. However, further increase of Zr addition deteriorates the GFA. Appropriate addition of Zr can form a reinfoced backbone structure with B atoms, and this kind of structure enhances the stability of the undercooled melt, suppresses primary crystallization, all these induce the improvement of GFA. The thermal expansion coefficient curves and the DSC curves have a similar trend, suggesting that the contraction process on the DIL curve is mainly ascribed to the crystallization process of the Fe-based glassy alloys. The Curie transition temperature T?on the temperature-magnetization(M-T) curves is agree well with the Curie transition temperature on the DSC and DIL curves, implying that the Curie transition temperature can be characterized by M-T, DSC and DIL method.The effect of Y on the GFA of the commercial Fe79.77M0.23B20 (M= impurity elements) alloy were investigated by XRD, DSC, TEM. The results show that Y can improve the GFA. It is attributable to that Y has a scavenging effect on the alloy melt, which can improve the stability of undercooled melt and suppress the cyatallization. The variety of the soft magnetic properties of the Fe71.51M0.49Y6B22 (M= impurity elements) in the isothermal annealing process was investigated. With the annealing time extending, the saturation magnetization Ms presents an opposite to the trend coercivity Hc. In the isothermal annealing process, the large atom Y and the small atom B will be rejected by primary crystalline a-Fe phase, and form a different concentrantion gradient around the a-Fe in the residual amorphous matrix. It promotes to the refine of a-Fe grain as well as result in the opposite trend between Ms and Hc.The corrosion resistance of the Fe75.77M0.23Y4B20 and Fe71.51M0.49Y6B22(M impurity elements) glass alloys were investigated by electrochemical workstation and SEM. The results show that the corrosion resistance properties of Fe75.77M0.23Y4B20 glass alloy is better than that of Fe71.51M0.49Y6B22. The addition of large atom Y can change the nearest neighbor distance of the (FeM)-Y-B (M= impurity elements) alloys, and result in the change of the free energy level and the internal stress of the alloy. Furthermore, it changes the electrochemical activation energy of the alloys and the amount of activated atoms on the surface. All these result in the variation of corrosion resistance of the glassy alloys.