Laser additive manufacturing of metallic glasses: issues in vitrification and mechanical properties

Bulk metallic glasses (BMGs), on account of their attractive properties, have now begun to witness a few commercial applications, e.g. in coatings and micro-gears. Additive manufacturing (AM) or 3D printing, although established for crystalline alloys, has only recently been used for synthesising BMG components. The issues arising in 3D printing of BMGs are of current relevance, and this review focuses on the key scientific aspects, namely vitrification (or crystallisation) during printing, mechanical properties of printed glassy alloys and the use of AM in identifying newer BMGs. Available data on crystallisation during printing of a variety of BMGs are analysed in terms of schematic TTT diagrams and the complex interplay between thermal cycles, the presence of quenched-in nuclei in the glass and oxygen contamination in a way that is hoped to be broadly applicable to most alloy systems. Also reviewed are three key factors influencing mechanical properties of printed BMGs, i.e. porosity, crystallinity and oxygen contamination and thereby potential strategies for improvement are suggested. The review concludes with a discussion on the use of AM for combinatorial alloy development aimed at identifying better glass-forming compositions, which may in turn facilitate greater use of AM in manufacturing glassy components with desired properties.