On the formability of bulk metallic glass in its supercooled liquid state

A method is introduced as a standard to characterize the formability, the maximum strain a bulk metallic glass (BMG) can undergo in its supercooled liquid state before it eventually crystallizes. When considering accuracy and practicality it was found that the maximum diameter to which a 0.1 cm3 BMG sample can be formed during heating through the supercooled liquid temperature region under a constant load of 4500 N is best suited as a measure of formability. Among the ten different alloys considered, by far the highest formability was found for Pt57.5Cu14.7Ni5.3P22.5. More generally, the results suggest that fragile liquid behavior, large Poisson ratio, and a low glass transition temperature are attributes indicating good formability. Various parameters, as well as an analytical expression for the formability, are tested against the experimentally determined formability to assess the degree of correlation.