Effectiveness of hydrogen microalloying in bulk metallic glass design

Abstract

We investigate the effect of hydrogen microalloying in Pd-based and Zr-based bulk metallic glasses (BMGs). To this end, we study the solubility and diffusivity of hydrogen in glassy Pd77.5Si16.5Cu6 and Zr64Cu22Al12, and focus on its beneficial effect on glass-forming ability and malleability. Each system reveals a different affinity with hydrogen and hence a different stability of hydrogen incorporation. In the case of the Pd-based BMG, large hydrogen pressures are required during processing and only small amounts of hydrogen can be incorporated into the glassy structure. This hydrogen, however, can rapidly diffuse out of the sample even at room temperature, with a calculated diffusion coefficient that agrees with literature results. In contrast, the Zr-based BMG features much greater hydrogen solubility and the incorporated hydrogen is strongly bonded to Zr. Thus hydrogen microalloying is found to have a beneficial long-term effect on BMG malleability only for systems where sufficient amounts of incorporated hydrogen can bond strongly to the base element. We also discuss the implications of these findings for future BMG design.