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

Abstract

Glassy Co 43Fe 20Ta 5.5B 31.5 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 × 10 5 N m kg −1 and high specific Young’s modulus of 31 × 10 6 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.