Hossein Eskandari Sabzi

A model to predict the conditions for printability is presented. The model focuses on crack prevention, as well as on avoiding the formation of defects such as keyholes, balls and lack of fusion. Crack prevention is ensured by controlling the solidification temperature range and path, as well as via quantifying its ability to resist thermal stresses upon solidification. Defect formation prevention is ensured by controlling the melt pool geometry and by taking into consideration the melting properties. The model’s core relies on thermodynamics and physical analysis to ensure optimal printability, and in turn offers key information for alloy design and selective laser melting process control. The model is shown to describe accurately defect formation of 316L austenitic stainless steels reported in the literature.

Powder bed fusion (PBF) techniques for additive layer manufacturing (ALM) are reviewed with a focus on titanium alloys production. Selective laser melting and electron beam melting are discussed in terms of feedstock production and processing-microstructure relationships. To control the PBF processes, an outline is presented on the computational modelling approaches for simulating process parameters and defects such as residual stresses and porosity at different length scales. It is concluded that by improving powder production techniques, designing new alloys and further developing ALM hardware, PBF techniques can reach commercial maturity. This review was submitted as part of the 2019 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledged.