Speaker
Description
During laser Additive Manufacturing (AM), a just deposited material undergoes melt-pool dynamics and rapid solidification within a few milliseconds. Then, for the rest of the process, it undergoes cyclic re-heating and cooling in the solid-state i.e., Solid-State Thermal Cycling (SSTC), until the end of the AM process. These non-equilibrium processes result in the formation of metastable hierarchical microstructure with physical and chemical heterogeneities at multiple length scales. Amongst all the microstructural features, precipitates are one of the most important ones due to their direct impact on the mechanical properties of the material.
Microstructure characterization is typically performed via electron and x-ray microscopy/diffraction techniques. However, it is impractical to probe microstructure evolution due to SSTC during the building of an AM part via these techniques. As an alternative, instead of probing microstructure evolution during an AM process, we propose to subject pre-built AM samples to SSTC under controlled conditions.
Recently, we performed a series of novel in-situ rapid/gradual SSTC experiments on Laser Metal Deposited (LMD) 316L Stainless Steel (316LSS) lamellae inside a transmission electron microscope. We evidenced significant changes to the precipitate structure and composition at high resolution.
In order to obtain complementary and statistical information from “bulk” samples, we then performed a series of ex-situ SSTC experiments on micropillars extracted, via focused ion beam, from LMD 316LSS and studied them via Transmission X-ray Microscopy (TXM), also known as 3D nanotomography. These novel experiments provide unprecedented insight on precipitate evolution in the bulk LMD 316LSS during SSTC. Mechanisms such as dissolution, coalescence and formation of new precipitation were observed to govern the evolution of precipitates. In this talk, we present and discuss the results of these ex-situ TXM SSTC experiments.
| Speaker Country | France |
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