High strength in combination with improvements in failure characteristics and associated gains in fracture toughness have placed bulk-metallic glasses (BMGs) among the most damage-tolerant materials to date. Recent studies show, however, that there can be large variabilities in the mechanical performance of these alloys, particularly in their toughness, which are likely associated with sample-size effects or structural variations from differences in processing. Here, we examine the variation in fracture toughness of the Pdbased metallic glass Pd77.5Cu6Si16.5, using single-edge notched bend specimens but in two different sizes. Although all toughness results on this glass were "valid" in terms of the nonlinear-elastic fracture mechanics J-standard, i.e., one would expect a single value of the fracture toughness for this alloy, marked differences were apparent in the toughness values and failure characteristics of the differently-sized samples. Specifically, significantly larger variations in toughness values were measured in larger-sized samples, which all essentially failed catastrophically, whereas, none of the smaller-sized samples failed catastrophically yet displayed far less scatter in their measured toughness. Additional in-situ tests on the smaller-sized samples in a scanning electron microscope revealed stable crack growth and progressive resistance to crack extension, i.e. rising crack-resistance (R-curve) behavior. Overall, this marked transition from brittle catastrophic failure in large samples where a sizeindependent fracture toughness can be measured, to non-catastrophic, more

No abstract

No abstract

No abstract

We report on advanced insights into the fluxing of Pd–Si–Cu bulk metallic glasses. Flux-induced boron alloying and trapping of oxides are found to be associated with the employed boron oxide fluxing agent, and both influence the attainable glass-forming ability (GFA) in opposite ways. Incorporated boron strongly deteriorates the GFA due to a rising liquidus temperature, while the oxygen reduction improves it. Thus, proper fine-tuning of the fluxing time and overheating characteristics leads to an enhancement of GFA. In the current case, the critical diameter of Pd77.5Si16.5Cu6 bulk metallic glasses can be increased to 15 mm, as compared to 3 mm in the unfluxed case. Based on these results, we illustrate that the development of further fluxing agents is crucial for enhancement of the key properties of bulk metallic glasses.