Laser processing of bulk metallic glass: A review

The emergence of bulk metallic glasses and their identification as versatile advanced engineering materials with attractive properties has led to a surge in research efforts to investigate processing methods, which can be used either to synthesise new BMG alloys or to shape BMG workpieces into final components with specific geometries. Among such technologies, the number of studies focussing on the laser processing of BMGs has gradually increased over the past decade. For this reason, a comprehensive summary of the state-of-the-art in this particular field of research is presented in this review. The reported studies are categorised into the different laser applications that have been proposed so far by the research community, namely the welding, cladding, additive layer manufacturing, micro machining and microstructure modification of BMG substrates. Due to the attractive properties of BMGs stemming from their amorphous nature, results are also presented, when available, concerning the effect of laser irradiation on the generation of crystalline precipitates during processing and the effect of these changes on the resulting material properties. This review has identified a number of gaps in the knowledge surrounding the laser processing of bulk metallic glasses. Understanding the fundamental interaction of laser energy with multi-component alloys will be necessary, as the development of lasers continues and the amount of available bulk metallic glasses increases. In particular, the crystallisation kinetics of bulk metallic glasses during laser irradiation needs to be understood to aid in the development and optimisation of processes such as welding and cladding. This could be helped by created an accurate simulation model to predict the onset of crystallisation although this is not a minor challenge, developing a complete temperature field model during laser irradiation is a complex task when considering vaporisation, plasma effects as well as chemical composition changes in the material. Besides, there is also the issue of variations in material properties as the temperature increases, particularly for BMGs whose temperature dependent properties are not well-documented. The research into the additive layer manufacturing of bulk metallic glass should continue to grow. Parametric effects need to be addressed to complete the optimisation of this process. Further investigations of the resulting crystallisation processes upon repeated melting and solidification should also aid in the process being able to be controlled more effectively. Finally, the use of laser processing of bulk metallic glass for specific application needs to be investigated further.