Cyclic phase transformations in the directed energy deposited TRIP steels

Laser Additive Manufacturing (LAM) is a promising technology producing highly complex, near net-shape components. However, LAM components suffer from detrimental quality issues governed by the rapid solidification process and localized thermal contraction. The resulting textured columnar grains and significant inherent residual stress directly influence the static and cyclic mechanical properties. Transformation Induced Plasticity (TRIP) alloys, which can produce a non-textured fine-grained microstructure due to the multi-phase transformation during layer-wise AM process, provide a potential mitigation to LAM challenges. However, the phenomenon is poorly understood and therefore can only crudely be exploited because no one has been able to observe the microstructures layer by layer in 3D. Here, we propose to use Dark Field X-ray Microscopy and the capability of in situ observation to understand the mechanism of cyclic microstructure transformation of TRIP steel during LAM process.