Additive manufacturing by the powder bed fusion process can provide cooling rates high enough to avoid crystallization, i.e. create bulk metallic glasses. The small melting pool connected to a relatively large volume of cooling material gives cooling rates many orders of magnitude larger than the critical cooling rate for the studied glass forming alloy AMZ4. However, subsequent reheating of built material may cause devitrification, i.e. crystallization of the amorphous phase. The present work aims to simulate the thermal cycles of the powder bed fusion process in order to evaluate and mitigate the risk of devitrification. This is done by combining finite elements simulations with a phase transformation model for the amorphous and crystal phases.

The response of AMZ4, in the present case limited to heating of amorphous material from room temperature, was evaluated using DSC measurements with varying low heating rates. This limited set of information is used to construction the lower part of the crystallization diagram based on a JMAK-model.

Previous work has developed simulation techniques for efficient simulations of glass formation in powder bed fusion. Temperatures can be computed with sufficient accuracy and considerable reduced computational time compared to a fully detailed model. The simplifications were based on temporal reduction by consolidating the heat source to strings or entire layers by assuming infinite scanning speed in one or two directions. The JMAK- model will now be used combined with these techniques. Further understanding of when and where crystals may be formed can be acquired by the presented work.