Effect of chemical composition on the fracture toughness of bulk metallic glasses

We consider a broad range of 13 BMGs from different alloy systems to represent the material class of bulk metallic glasses (BMGs) and characterize their fracture toughness. To determine the effect of composition on the fracture toughness within one alloy system, we consider alloys in Zr-Al-Ni-Cu and Pd-Ni-Cu-P BMG forming alloy systems, specifically Zrx(Al0.25Ni0.25Cu0.5)100-x (at.%) and Pdx(NiCu2)(80-x)/3P20. Sample preparation follows a thermoplastic forming based method ensuring constant fictive temperature, which allows us to eliminate extrinsic effects and detangle the effect of fictive temperature and alloy chemistry on the fracture toughness. We found that fracture toughness varies significantly with composition, even in a non-monotonic way. Within one alloy system, fracture toughness correlates closely with the ratio of shear modulus over bulk modulus. Such correlation however is not present when comparing BMGs across alloy systems. Observed behavior suggests that shear modulus and bulk modulus serves as an incomplete proxy describing the BMGs ability to resist shear and cavitation. Further, our results reveal a general inverse correlation between fracture toughness and glass forming ability suggesting a trade-off of both desired properties. Such trade-off is not necassary present in metal-metalloid containing BMGs, where our results reveal a possibility to optimize alloys for both GFA and fracture toughness simultaneously.