Effects of metalloids on the thermal stability and glass forming ability of bulk ferromagnetic metallic glasses

• Tuning the thermal stability of supercooled liquid can be largely improved by the content of metalloids.
• The width of supercooled liquid does not always correlate with the glass forming ability.
• The utilization of flux-melting technique can largely improve the glass forming ability.

We prepared three types of bulk ferromagnetic glasses, Fe–Mo–P–C, Fe–Mo–Ga–P–B–C, and Fe–(Co, Sb, Cr, Mo, Ga)–P–B–C by a flux-melting and water-quenching technique. We systematically changed the content of both alloying metals and metalloids to improve the glass-forming ability (GFA) and thermal stability – the difference between crystallization temperature Tx and glass transition temperature Tg – of bulk ferromagnetic glasses. One of our flux-melted ferromagnetic alloys with optimized compositions has a critical cooling rate on the order of ∼10 K s−1, suggesting that the flux treatments play an important role in improving the GFA. Tuning the thermal stability of supercooled liquid by modifying the content of alloying metalloids is more effective than by modifying the content of alloying metals. Adding 1 at.% alloying metalloids and metals can increase Tx–Tg by ∼20 K and 4 K, respectively. We found that upon increasing the content of alloying metalloids, Tx–Tg increases and reaches a maximum where the GFA is highest. After Tx–Tg reaches a maximum, a further increase in the content of alloying metalloids lowers the GFA whereas Tx–Tg may either increase or decrease. Bulk ferromagnetic glasses can only be formed by modifying the content of metalloids within a narrow range, ∼2–6 at.%, in our alloy systems. Our experimental results suggest that optimizing the content of metalloids is a powerful tool for improving the GFA and thermal stability of bulk metallic glasses.