Ductile Co-based bulk metallic glass with superhigh strength and excellent soft magnetic properties induced by modulation of structural heterogeneity

The development of Co-based bulk metallic glasses (BMGs) with satisfying comprehensive properties, including large glass-forming ability, high strength, large plasticity and excellent soft magnetic properties, is in high need for applications as structural and functional materials. A (Co0.7Fe0.2Ni0.1)(67.7)B21.9Si5.1Nb5Cu0.3 BMG with a record large plasticity of 5.5%, a high fracture strength of 4770 MPa, and a large critical diameter of 3.5 mm is successfully developed. This BMG also shows good soft magnetic properties, i.e. low coercivity (H-e) of 1.33 A/m and higher saturation magnetization (B-s) of 0.60 T. The enhanced strength and plasticity, as well as high B-s of this BMG, are all attributed to the minor addition of Cu in (Co0.7Fe0.2Ni0.1)(68-x)B21.9Si5.1Nb5Cux (x = 0, 0.1, 0.3, 0.5 and 0.7 at.%) system. The reduced average atomic spacing in the BMG, which comes from the squeezed spacing between Co, Fe, Ni and Nb atoms with proper addition of Cu, results in the improvement of fracture strength and B-s. The atomic-scale structural heterogeneity with the formation of crystal-like order structures is induced in the amorphous matrix, and thus the plasticity of (Co0.7Fe0.2Ni0.1)(67.7)B21.9Si5.1Nb5Cu0.3 BMG increases in spite of the decreased average atomic spacing.