Super-high hardness of (Fe,Co)-B-Si-Zr/Hf bulk glassy alloys

In this work, the alloying effect of similar atom substitution of Co for Fe on the glass-forming ability as well as mechanical and magnetic properties of Fe71.7-xCoxB16.7Si8.3Zr3.3 and Fe72.5-yCoyB16.7Si8.3Hf2.5 (x, y = 0, 5, 10, 15, 20 and 25) glassy alloys has been studied. Our experiments show that the substitution of Co for Fe causes a decrease in the glass-forming ability. By increasing the content of Co, the critical glass formation size gradually decreases from 2.5 mm to 1 mm. Nano-indentation results indicate that both the Young's modulus and hardness increase with increasing Co content in the bulk glassy alloys. The Fe51.7Co20B16.7Si8.3Zr3.3 bulk glassy alloy exhibits a microhardness, Hv = 13.5 GPa, and a Young's modulus, E = 230 GPa, the microhardness being the highest among all the Fe-based metallic bulk materials reported to date. All of the glassy alloys exhibit good soft magnetic properties with high saturation magnetization (1.12-1.33 T) and low coercive force (0.6-5.2 A/m).