Formation And Properties Of Soft Magnetic Fe-based Bulk Metallic Glasses With Wide Supercooled Liquid Region

Fe-based metallic glasses have been attracting great attention due to their high strength, high hardness, good corrosion resistance, excellent soft magnetic properties and low cost. They have been used as core materials in the energy efficiency transformer. Fe-based metallic glasses can be expected to produce highly functional magnetic micro-/nano parts and electromechanical devices by superplastic processing, which takes advantage of the viscous flow of metallic glass in their supercooled liquid region. However, developed soft magnetic Fe-based metallic glasses can not simultaneously possess low Tg, wide ΔTx and good glass forming ability (GFA), which is important factor for superplastic processing. In the present work, with the aim of developing Fe-based metallic glasses suitable for superplastic processing, we investigated the effects of Mo,(Co, Ni) and Cr additions on the thermal stability and GFA of a base Fe75P10C10B5metallic glass with low Tg and good soft magnetic properties. Series of Fe-based metallic glasses with low Tg, large ΔTx, good GFA were developed. In addition, the magnetic and mechanical properties, viscosity in supercooled liquid region and corrosion resistance of these alloys were evaluated.The thesis consists of following parts mainly:1. With the increasing of Mo content, Tg of Fe-Mo-P-C-B metallic glasses increases from723K to760K; the thermal stability of supercooled liquid and GFA were enhanced remarkablely with the increaseing of ΔTx and dc from37K. and lower than1mm to96K and3mm of Fe67.5Mo7.5P10C10B5alloy, respectively.2. Fe3(P, B) and (Fe, Mo)23(C, B) plaseses formed simultaneously during the crystallization process of Fe67.5Mo7.5P10C10B5alloy, whice is different from the base alloy with Fe3(P, B) phase first appearing. The crystallization mode of various phase appear simultaneously and presence of complex (Fe, Mo)23(C, B)6phase account for the excellent thermal stability of supercooled liquid of Fe67.5Mo7.5P10C10B5alloy.3. The substitutions of Co, Ni for Fe lower the Tg of Fe67.5Mo7.5P10C10B5alloy with727K for Fe60Ni7.5Mo7.5P10C10B5alloy; enhance the thermal stability of supercooled liquid with ATX of100K for Fe60Co5Ni2.Mo7.5P10C10B5alloy; improve GFA with dc of4mm. The further substitution of Cr for Mo decreases Tg, while don’t enhance the thermal staility of the supercooled liquid and GFA. 4.(Fe, Co, Ni)-(Mo, Cr)-P-C-B metallic glasses exhibit low viscosity of107Pa·s in their spuercooled liquid regions, indicating the good superplastic formability of the developed Fe-based metallic glasses5.(Fe, Co, Ni)-(Mo, Cr)-P-C-B metallic glasses possess good soft magnetic properties with saturation magnetization (Is) of0.77～0.83T and coercive force (Hc) of2.07～12.36A/m. These alloys also exhibit high yield strength (δc,y) of3263-3479MPa, Young’s modulus (E) of165-181GPa, plastic deformation (εc, y) of0.5～1.5%, high Vickers hardness (Hv) of943-992.6.(Fe, Co, Ni)-(Mo, Cr)-P-C-B metallic glasses possess good corrosion resistance in IN H2SO4,1N HC1and3mass%NaCl solutions. Specially, the Cr contained (Fe, Ni)-(Mo, Cr)-P-C-B alloys exhibit comparable resistance with SUS316L stainless steel.