Modelling the solidification microstructures of 316L steel produced by additive manufacturing

A numerical simulation model named CA-FE, allows simulating grain structure obtained during the additive manufacturing process call laser powder bed fusion (L-PBF). The CA-FE model links two calculus: temperature field simulation during the process with Finite Elements (FE), then crystallographic grain solidification with Cellular Automaton (CA). Experimental results run in parallel to enrich the program and validate the obtained results. The developed program is thus able to simulate different multi-layer arrangements. It has been tested to simulate manufacturing of 'wall' arrangements obtained by the superposition of mono-cords made in the different layers of deposited powder. The goal is to observe influence of process parameters on microstructure: laser parameters (power, speed), and geometrical parameters (layer thickness, number of ropes). The walls samples were manufactured at ENSAM/PIMM, and were simulated using the same parameters. Experimental/numerical comparison revealed similar results, with grains growing in a columnar way and oriented along the building direction. We observe also an enlargement of grains with number of layers. It is possible to validate the program for simple wall cases.Simultaneously, the influence of the powder was studied using a second 316L powder manufactured by the company PRAXAIR, an argon-atomized 316L powder with varying composition compared to the first powder. Walls samples were manufactured under the same conditions as mentioned above. Equiaxed grains structures were observed on these walls. To be able to simulate the granular structures obtained with this second powder, a germination model was added to the CA-FE program. The resulting walls obtained by simulation exhibit grain structures close to equiaxed. (author)