Co-based ternary bulk metallic glasses with ultrahigh strength and plasticity

A family of ultrahigh strength Co-based bulk metallic glasses (BMGs) with critical diameters up to 2 mm is synthesized in Co65-xTaxB35 (at.%, x = 5-10) alloys by copper mold casting. The improved glass-forming ability associated with near eutectic compositions is attributed to the appropriate addition of Ta. The glassy alloys exhibit high glass transition temperature of 930-975 K, ultrahigh compressive strength of 5.6-6.0 GPa, high specific strength of 639-654 N.m/g, Vickers hardness of 15-16 GPa, and distinct plastic strain of 0.5-1.5%. The strength and the specific strength are the highest values reported for bulk metallic materials known so far. Several universal criteria correlated with the thermal properties, elastic constants, and mechanical properties were validated in the Co-based BMG system. These Co-Ta-B BMGs combining with superior mechanical properties, high thermal stability, and simple elemental composition are significant for scientific research as modeling materials and industrial application as advanced structural materials.