Glass-forming ability, fragility parameter, and mechanical properties of Co–Ir–Ta–B amorphous alloys

• We developed a new family of Co–Ir–Ta–B bulk metallic glasses.
• The Co47Ir10Ta8B35 amorphous rod with a diameter of 5 mm was fabricated.
• The extended ΔTx is accompanied by a change in the fragility parameter m.
• The Co47Ta10Ta8B35 bulk metallic glass exhibits super-high strength of 5500 MPa.

The effect of partial substitution of Co by Ir in Co57−x IrxTa8B35 (at.%, x = 0, 5, 10, and 15) alloys on glass-forming ability (GFA), fragility parameter m, and mechanical properties was investigated. It was found that the glass-forming ability reflected by critical diameter for glass formation is in good agreement with the width of supercooled region (ΔTx). The Co47Ir10Ta8B35 BMG exhibits the best GFA yielding the formation of an amorphous rod with a diameter of 5 mm, along with the largest ΔTx value of 64 K. The Ir-bearing Co47Ir10Ta8B35 BMG presents a lower fragility parameter m than Co57Ta8B35 BMG, which indicates better thermal stability and GFA. In addition, the Co47Ir10Ta8B35 BMG shows super-high yield strength of ∼5200 MPa and ultimate compressive strength of ∼5600 MPa as well as significant plasticity of ∼1.2%. The combination of good GFA, large ΔTx and excellent mechanical properties for the new Co–Ir–Ta–B BMG is significant for scientific research and industrial application.