Synthesis And Properties Of Soft Magnetic Co-based Co-Y-B Bulk Metallic Glasses

Co-based amorphous alloys have been applied in electric power and electronic components and have received extensive attention due to their excellent high-frequency magnetic properties such as high permeability,low coercivity,low core loss,and low magnetostriction together with outstanding mechanical properties including high compressive strength and hardness.However,Co-based alloys are difficult to be prepared into bulk form in large scale because of their poor glass forming ability?GFA?which limits their application.Although series of Co-based bulk metallic glass?BMG?systems are developed by scientists,a large amount of early transition metal elements are added commonly which decrease the B_s significantly.Therefore,the development of new Co-based BMGs with high B_s is of great significance.It is noted that rare earth elements have larger atomic sizes than transition metal elements and negative heat of mixing with Co.Adding rare earth elements to Co-based amorphous alloys can further increase the atomic packing density which may have a stronger effect on the GFA than transition metals.At the same time,there is a strong affinity between rare earth elements and oxygen atoms which can purify the molten melt and inhibit non-uniform nucleation which is also beneficial to GFA.Hence new soft magnetic Co-based BMGs are expected to be developed by adding rare earth elements.In this work,Y element which has large atomic size difference and negative heats of mixing with Co,B atoms was micro-alloyed into a Co₇₅B₂₅ alloy.The effects of Y on thermal stability,GFA and soft magnetic properties were investigated.Nb and Fe were further multi-alloyed to the Co-Y-B alloys.The effects of alloying element on GFA,thermal properties,magnetic properties,and mechanical properties were investigated.The principal conclusions are shown as follows:1.In the Co_75-xY_xB₂₅?x=0–5?alloy system,Y element improves the thermal stability of supercooled liquid.A distinct supercooled liquid region??T_x?appears when x=3–4.and reaches maximum value at x=3.5.,i.e.,33 K.According to the GFA criterion,the alloy with x=3.5 also has the highest GFA.These alloys contain good soft magnetic properties including B_s of 0.64?0.98 T and H_c of 1.5?14.1 A/m.The alloy with x=3.5 has the lowest H_c.2 In the Co_71.5-xY_3.5Nb_xB₂₅?x=0–4?alloy system,Nb element improves the thermal stability of supercooled liquid and GFA significantly.?T_x increases from 33 K to 50 K.BMGs with diameters of 1 and 2 mm can be prepared when x=2 and 4,respectively.3.The Co-Y-Nb-B BMGs exhibit good soft magnetic and mechanical properties.The B_s and H_c are 0.36?0.57 T and 0.9?1.2 A/m,respectively.The alloys also show?_c,y larger than3800 MPa as well as obvious plastic deformation.4.In the(Co_1-xFe_x)_71.5Y_3.5B₂₅?x=0–0.4?alloy system,Co-based BMGs have been prepared successfully when x=0.2?0.4.The GFA of the alloys reaches maximum when x=0.3 with a diameter of 2 mm.?T_x increases from 36 K to 60 K with the increase of Fe content.5.The Co-Fe-Y-B BMGs possess high B_s and?_c,y.The B_s,H_c,?_c,y and?_p are 0.94?1.10 T,4.5?5.6 A/m,3978?4152 MPa and 0.14?0.88%,respectively.