Ultra-high strength above 5000 MPa and soft magnetic properties of Co–Fe–Ta–B bulk glassy alloys

Abstract Glassy Co43Fe20Ta5.5B31.5 alloy rods with glass transition temperature of 910 K, followed by a large supercooled liquid region of 72 K were produced in the diameter range up to 2 mm by copper mold casting. The glassy alloy rods exhibit ultra-high fracture strength of 5185 MPa, high Young’s modulus of 268 GPa, high specific strength of 6.0 × 105 N m kg−1 and high specific Young’s modulus of 31 × 106 N m kg−1. The fracture strength, specific strength and specific Young’s modulus obtained by compression test are higher than all previous values reported for any crystalline and glassy alloys. The ultra-high strength of over 5000 MPa persists in the temperature range up to 698 K. The fracture occurred on one major shear band which was declined by 44° to the stress axis implying the slight deviation from the maximum shear stress plane. Excellent formability is manifested by large tensile elongation of 1400% and large reduction ratio in thickness above 90% in the supercooled liquid region. The ultra-high strength alloy exhibits simultaneously good soft magnetic properties: low coercivity of 0.25 A/m and an extremely high permeability of 550,000. The novel alloy is promising as a new ultra-high strength material with good deformability and soft magnetic properties.