Synthesis And Properties Of Co-Based (Co,Fe)–(B,Si,P) Bulk Metallic Glasses

Due to their excellent soft magnetic properties,i.e.,low coercivity?H_c?and core loss,Fe-and Co-based soft magnetic metallic glasses have been applied in power and electronic components.Among them,the Co-based metallic glasses possess extremely low H_c and magnetostriction,high magnetic permeability.Especially in high-frequency range,the characteristic of high permeability and low loss can be maintained.Besides,Co-based metallic glasses have excellent mechanical properties such as high strength and wear resistance.However,the glass-forming ability?GFA?of Co-based metallic glasses is poor for one thing,which increases the production difficulty and restrains their widespread applications.But also,the saturation magnetic flux density?B_s?of Co-based metallic glasses is limited and thus making it difficult to achieve miniaturization of electronic components.In recent years,some Co-based bulk metallic glasses?BMGs?have been developed by adding early transition metals?ETMs?or rare-earth elements?REs?.Although the GFA has been improved,the introductions of ETMs or RE lead to a severe decrease of the B_s and rising cost.Therefore,it is of great significance to develop a new Co-based BMGs containing no ETM or RE with high GFA and B_s.Co-B-Si system is one of typical soft magnetic Co-based amorphous alloy system,whereas the GFA is insufficient.In this paper,the effects of additions of P and Fe on the thermal properties,GFA,magnetic and mechanical properties of the Co₇₅B₁₅Si₁₀ amorphous alloy were investigated.Co-based?Co,Fe?–?B,Si,P?bulk metallic glasses without any ETM or RE have been successfully developed,which possess outstanding soft magnetic properties with high B_s and good mechanical properties.The main results of this paper are as follows:?1?Addition of P stabilizes the supercooled liquid and promotes the occurrence of the glass transition for the Co₇₅B₁₅Si_10-xP_x?x=3–5?metallic glasses.It exhibits the largest?T_x of 33 K for the alloy with x=3.Although P causes the B_s to decrease slightly,the soft magnetic properties are improved.The H_c at x=3 reaches its minimum of 1.8 A/m.?2?For the Co_75-xFe_xB₁₅Si₇P₃?x=0–35?metallic glasses,the?T_x maintains at29–33 K without a significant variation.The GFA increases with the increase of Fe content and the BMG rods can be obtained for the alloys with x=15–35.When x?30,the GFA reaches its maximum and the critical diameter for glass formation?d_c?is2.0 mm.?3?The Co_75-xFe_x B₁₅Si₇P₃?x=15–35?BMGs possess relatively high B_s and Curie temperature?T_c?.The B_s of 1.24 T and T_c of 789 K for the alloy with x=35 are superior to those of other reported Co-based BMGs.Meanwhile,the BMGs possess outstanding soft magnetic properties,i.e.,low H_c of 0.8–4.6 A/m,and high effective permeability??_e?of 12700–18500 at 1 kHz.?4?The Co_75-xFe_xB₁₅Si₇P₃?x=15–35?BMGs exhibit good mechanical properties,i.e.,high compressive yield strength(?_c,y)of 3343–3590 MPa with distinct plastic strain(?_c,p)of 0.2–2.7%and high Vickers hardness?H_V?of 1150–1175.?5?By increasing the?Co,Fe?content of the?Co,Fe?–?B,Si,P?BMGs,the B_s is further increased while maintaining the GFA.The d_c and B_s of(Co_0.6Fe_0.4)₇₇(B_0.6Si_0.28P_0.12)₂₃ BMG are 2.0 mm and 1.30 T,respectively.