Effect of oxygen on the glass forming ability, mechanical properties and corrosion resistance of Mo-based bulk metallic glass

MoCoB bulk metallic glass (BMG) exhibits very high thermal stability and outstanding mechanical properties. However, their wide applications are still limited due to the poor glass forming ability (GFA) and critical preparing conditions, particularly the need for low oxygen content. This study systematically investigated the effects of oxygen on the properties of MoCoB BMG. A small amount of oxygen incorporation (≤1064 ppm) significantly enhanced the GFA, increasing the critical diameter from 1.2 mm to 2 mm, due to a reduced thermodynamic driving force for crystallization. Moreover, the addition of 676 ppm oxygen simultaneously improves the mechanical properties of MoCoB BMG with the microhardness of 1347 HV, compressive strength of above 5000 MPa, nanohardness of 19 GPa, and Young's modulus of 300 GPa through strengthening local chemical bonds by the addition of oxygen. The high-oxygen-content specimens (2111 ppm) show exceptional corrosion resistance with a self-corrosion current density of 1.259 × 10 –7 A/cm 2 in 3.5 wt. % NaCl solution. This can be attributed to the formation of a denser CoMoO 4 composite oxide layer and suppression of passive film dissolution. These findings could provide a comprehensive understanding of the effects of oxygen on the BMGs, and help with the development of high-performance and cost-effective Mo-based BMGs.