Decoding Residual Stresses in Directed Energy Deposition

Residual stresses (RS) are a critical challenge in metal additive manufacturing (AM). This challenge is especially significant in directed energy deposition (DED), where larger part sizes and melt pools, together with heat accumulation and repeated thermal cycling, promote substantial stress accumulation. Control of RS is further complicated by the many tunable process parameters. Existing reviews either isolate individual parameters or cover RS in AM generally, and rarely address how parameters interact to shape the final stress state. This review addresses that gap with a framework that breaks RS formation into sequential steps: process parameters, intermediate variables, thermal drivers, and RS mechanisms. Using this framework, it analyses how changes in individual parameters propagate through the process to the resulting RS, focusing on experimental studies in DED. It then examines energy density as a unifying metric that captures the combined effect of interacting parameters, collecting published data to correlate calculated energy densities with reported RS levels. Normalised enthalpy is also evaluated as a complementary metric that accounts for intrinsic material properties. Beyond parameter optimisation, the review evaluates the effectiveness of in-situ and post-process mitigation strategies. This work consolidates current knowledge and provides a structured foundation for reducing RS in DED-fabricated parts.