Synthesis And Properties Of High Magnetic Elements Fe-based Bulk Amorphous Alloys

Fe-based bulk amorphous alloys (BAAs) have attracted much attention due to their outstanding properties such as high strength and excellent soft-magnetic properties. Moreover, BAAs have low cost and a borad market application prospect. However, low saturation magnetic polarization, the room-temperature brittleness and relatively low glass-forming ability (GFA) are still serious problems which limit their applications. In this study, fluxing technique and alloying method are adopted to improve the properties of Fe81Mo1P7.5C5.5B2Si3 BAAs. The effects of alloying elements and fluxinvg technique on the GFA, mechanical properties and crystallization behavior of Fe-based BAAs have also been investigated. In addition, a thin electroless Ni coating strongly adhering on a Fe81Mo1P7.5C5.5B2Si3 bulk metallic glass (BMG) has been applied to improve its plasticity by geometric confinement.A significant enhancement in thermal stability and GFA in the Fe81Mo1P7.5 C5.5B2Si3 alloy has been realized through partial substitution of Fe by Co, but substitution of Fe by Co has no obvious effect on compressive plasticity of alloy. The Fe66Co15Mo1P7.5C5.5B2Si3 BAA can be obtained with a diameter of 2.0 mm by fluxing technology and copper mold casting, while the Co-free alloy can be only cast into glassy rod up to 1.0 mm. Stimulated by the successful preparation of Fe66Co15Mo1P7.5C5.5B2Si3 BAA with 2.0 mm diameter, Fe67Co15Mo1P6.5C5.5B2Si3 with 1.4 mm and Fe67Co16Mo1P5.5C5.5B2Si3 with 1.0 mm alloys have also been prepared. In particular, Fe67Co16Mo1P5.5C5.5B2Si3 BAA amorphous alloy is the first reported Fe-based BAA with saturation magnetic polarization up to 1.70 T. The precipitated primary phase a-Fe(Co) forming during isothermal crystallization annealing can be purposefully controled by adjusting different temperature and time, and the metallic-glass-matrix composites exhibitsexcellent soft magnetic properties with a very high saturation magnetic polarization of 2.11T.The compressive plasticity of the Fe81Mo1P7.5C5.5B2Si3 BAA is effectively improved by replacing Fe with Ni.The Fe71Ni10Mo1P7.5C5.5B2Si3 BAA with 2.5 mm has been prepared and possess better GFA than Fe81Mo1P7.5C5.5B2Si3 BAA. The compressive plasticity can also be enhanced with the addition of Ni. The yield strength and compressive plastic strain are 3129 MPa and 0.3%, respectively, for Fe81Mo1P7.5C5.5B2i3 alloy and 2667 MPa and 3.2%, respectively, for Fe61Ni20Mo1P7.5C5.5B2Si3. However, by substitution of Ni for Fe in Fe81Mo1P7.5C5.5B2Si3 BAA, the yield strength and saturation magnetic polarization of the alloyshave been obviously deteriorated.A thin Ni coating strongly adhering on a Fe81Mo1P7.5C5.5B1Si3 BAA has been successfully prepared by electroless plating for improving its plasticity. It has been found that the compressive plasticity of the coated BMG is noticeably increased from 0.3% to 8%. The coating with nanosize grain size could constrain the propagation of shear bands and change deformation into a self-organized critical state. The present result indicates that electroless plating was an effective coating method for improving the ductility of metallic glasses.