Effects of oxygen on glass formation in the ${\text{Fe}}_{73}{\text{Mo}}_{3.0}{\text{C}}_{7.0}{\text{Si}}_{3.3}{\text{B}}_{5.0}{\text{P}}_{8.7}$ bulk metallic glass were studied in detail. Surprisingly, it was found that a critical level of oxygen is effective in enhancing the glass-forming ability of the current Fe-based bulk metallic glass due to the facts that (i) oxygen can increase the crystallization resistance via suppressing the precipitation of the competitive primary phase and (ii) oxygen can stabilize the glass-forming liquid as manifested by the decrease in the liquidus temperature. However, excess oxygen additions will destabilize the liquid and induce the formation of more stable oxygen-containing crystalline phase, thus deteriorating the glass-forming ability.

We developed several Fe-based bulk metallic glasses with a unique combination of large glass-forming ability and excellent soft magnetic properties by minor doping of Cu in the Fe₇₆C_7.0Si_3.3B_5.0P_8.7 alloy. Proper additions of the non-magnetic copper element which has a positive heat of mixing with Fe, coupled with adequate annealing, can stimulate formation of ∼5 nm αFe ferromagnetic nanocrystals, which results in the increment in the saturation magnetization. Over-annealing which induced coarsening of the α-Fe nanocrystals reduces the ferromagnetic exchange interaction between the nanosized α-Fe crystals and increases the effective magneto-crystalline anisotropy, thereby deteriorating the soft magnetic properties.

The glass-forming ability (GFA) of alloys with a high-solvent content such as soft magnetic Fe-based and Al-based alloys is usually limited due to strong formation of the solvent-based solid solution phase. Herein, we report that the GFA of soft magnetic Fe-based alloys (with >70 at.% Fe to ensure large saturation magnetization) could be dramatically improved by doping with only 0.3 at.% Cu which has a positive enthalpy of mixing with Fe. It was found that an appropriate Cu addition could enhance the liquid phase stability and crystallization resistance by destabilizing the α-Fe nano-clusters due to the necessity to redistribute the Cu atoms. However, excessive Cu doping would stimulate nucleation of the α-Fe nano-clusters due to the repulsive nature between the Fe and Cu atoms, thus deteriorating the GFA. Our findings provide new insights into understanding of glass formation in general.