EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

During an alloy Additive Manufacturing (AM) process, just after the melting of feedstock, the molten material undergoes melt-pool dynamics and rapidly solidifies (typically, within a few milliseconds). Then, for the remaining build time, it undergoes multiple heating-cooling cycles in the solid-state, i.e. Solid-State Thermal Cycling (SSTC) or intrinsic heat treatment, at varying temperature amplitudes and rates. The thermo-mechanical driving forces during SSTC can trigger a plethora of mechanisms such as dislocation dynamics and defect interactions, precipitation, micro-segregation, solid-state phase transformation, recrystallization, grain growth, etc., which manifest as microstructural changes in the form of texture evolution, grain morphology, grain boundary evolution, low-angle grain boundary formation, etc.

A Scanning Electron Microscope (SEM) is well suited to probe polycrystalline microstructures and extract information on features such as texture, grain morphology, high and low grain boundaries, etc. However, it is impractical to probe microstructural evolution during an additive manufacturing process inside a scanning electron microscope. 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 inside an SEM.

To that end, with support from the ERC Starting Grant project GAMMA (ID: 946959), a novel and (at the time of the writing of this abstract) unique coupling between a Continuous-Wave fiber Laser and an environmental-SEM (CWLaser-SEM coupling) has been implemented. In this talk, the details of the design of this CWLaser-SEM coupling and its operation will be presented first. Then, the results of a series of in-situ SSTC experiments performed on a stainless steel using this CWLaser-SEM coupling will be presented; the SSTC will be similar to that occur during an AM process.