Effect of Mo–Fe substitution on glass forming ability, thermal stability, and hardness of Fe–C–B–Mo–Cr–W bulk amorphous alloys

Amorphous Fe67 − xC10B9Mo7 + xCr4W3 (x = 1–7 at.%) plates with 640 μm thickness were prepared by copper mold casting. The thermal properties and microstructural development during heat treatments were investigated by a combination of differential scanning calorimetry (DSC), differential thermal analysis, and X-ray diffractometry (XRD). The glass forming ability (GFA) and activation energy for crystallization have a distinct dependence on Mo content. Fe62C10B9Mo12Cr4W3 is the best glass former in this study, demonstrating a supercooled liquid region, ΔTx = 51 K, and an activation energy for crystallization, Q = 453 kJ/mol. The GFA of alloys in this system was governed by elastic strain optimization resulting directly from the variation in Mo content. Heat treatments were performed to demonstrate resistance to crystallization under typical processing conditions. Alloys in this system exhibited a three-phase evolution during crystallization. A second set of heat treatments was performed to identify each phase. Hardness data was collected at each of the heat treatment conditions, and a bulk metallic glasses (BMG)-derived composite containing a Mo-rich phase exhibited Vickers Hardness in excess of 2000. The fully amorphous alloys had an average hardness approaching 1500.