Development Of Ferromagnetic High Entropy Bulk Metallic Glasses And Their Properties

High entropy alloys (HEAs) were defined as the alloys consisting of four or more principal elements in equal or near equal atomic percent (at.%) ranging from 5 to 35 at.%. The HEAs exhibit excellent properties such as high strength, high hardness, good wear resistance, and high temperature oxidation resistance, which show great potential for practical applications. Except for the traditional solid-solution type of HEAs, the recently developed high entropy bulk metallic glasses (HE-BMGs) have attracted considerable attention because they have both advantages of the HEAs and metallic glasses. The previous researchers mainly focused on the glass-forming ability (GFA) and mechanical performances of HE-BMGs, while the work referring to functional properties, such as magnetic properties is still limited. Till now, no ferromagnetic HE-BMGs have been reported. On the basis of previous work, here a new type of ferromagnetic Fe25Co25Ni25(B, Si)25 and Fe25Co25Ni25(P, C, B)25 HE-BMGs was successfully fabricated through addition of Co and Ni elements into the base alloys of Fe-B-Si and Fe-P-C-B systems with good soft magnetic properties. The newly developed HE-BMGs exhibit superior soft magnetic and mechanical properties compared with the other pre-reported HE-BMGs.The thesis consists of the following conclusions mainly:1. The Fe25Co25Ni25(B, Si)25 HE-BMGs have large supercooled liquid region(△Tx) of 27-40 K and high GFA with critical sample diameter for glass-formation (dc) of 1.0-1.5 mm. The Fe25Co25Ni25(Bo.7Sio.3)25 HE-BMG exhibits the widest ATx of 40 K and largest dc up to 1.5 mm, indicating the best thermal stability of supercooled liquid and GFA in Fe25Co25Ni25(B, Si)25 alloys.2. The Fe25Co25Ni25(B, Si)25 HE-BMGs possess good soft magnetic properties, i.e., high saturation magnetization (Is) of 0.77-0.87 T, low coercive force (Hc) of 1.1-3.7 A/m and high effective permeability (μe) of 18000-22000. The alloys also exhibit high yield strength (σc.y) of 3239-3624 MPa and large plastic strain (εc,p) of 1.7-3.1%.3. The Fe25Co25Ni25(P, C, B)25 HE-BMGs exhibit excellent thermal stability of supercooled liquid with εTx of 43-53 K, and good GFA with dc of 1.0 mm. The Fe25Co25Ni25(P0.48C0.32B0.2)25 HE-BMG has the widest εTx of 53 K, indicating the best thermal stability. 4. The Fe25Co25Ni25(P, C, B)25 HE-BMGs possess good soft magnetic and mechanical properties. The Is, Hc, σc,y and εc,p of alloys are 0.71-0.86 T,1.2-4.3 A/m,2817-3210 MPa and 0.3-1.2%, respectively.