Designing alloy microstructures with desired properties and parts with desired responses is a significant challenge, particularly during metal additive manufacturing, popularly known as 3D printing. The heat-matter interactions occurring during 3D printing result in a sequence of highly non-equilibrium processes: melt-pool dynamics and fast solidification followed by solid-state thermal cycling (SSTC) until the end of the process. As a consequence of these non-equilibrium processes, the finished parts exhibit microstructures that have a plethora of physical and chemical heterogeneities that are more varied than the ones occurring in conventionally processed alloys. These heterogeneities are sensitive to a large number of 3D printing parameters and minor changes to these parameters can result in very different microstructures exhibiting a large spread in the alloy’s mechanical response. This makes it very difficult to perform quality control checks and certification of parts.
The key to control the process-microstructure-properties-performance relationship in metal 3D printing lies in understanding microstructure formation during manufacturing. Prior to the start of project GAMMA, most experiment and modeling efforts in metal 3D printing were overwhelmingly focused on studying the role of melt-pool dynamics and solidification. While these processes are necessary to study microstructure genesis, they are highly insufficient to understand the formation of final microstructures, which also requires investigating the role of SSTC. The thermo-mechanical driving forces occurring during SSTC can trigger a plethora of solid-state mechanisms e.g. dislocation dynamics, phase transformation, grain growth, recrystallization, precipitation, etc. These mechanisms can alter the solidified microstructure and induce residual stresses, all of which determines the mechanical response of as-built parts. Only once an understanding of different phenomena has been gained, can the knowledge be transformed for industrial use to design parts with desired responses.
To that end, the overarching aim of project GAMMA (conducted in the group of Dr. Manas V. Upadhyay
https://www.manas-upadhyay.com(s’ouvre dans une nouvelle fenêtre)) is to highlight the important role of SSTC on microstructure evolution during metal 3D printing, and to show how SSTC can be harnessed to design microstructures with desired mechanical responses.
The objectives to achieve the overarching aim are:
1) To propose and perform experiments to quantify the microstructural changes brought about solely by SSTC, and to identify the underlying micro-mechanisms.
2) To develop and validate theoretical and fast numerical models to gain deep insight on dynamics of micromechanisms and predict polycrystalline evolution due to SSTC.
3) To use the novel models in synergy with experiments to tailor 3D printing parameters and suggest in-process/post-process thermomechanical treatments to engineer microstructures with desired material properties and part performance.
