An investigation into the mechanistic origin of thermal stability in thermal-microstructural-engineered additively manufactured Inconel 718

An obstacle hindering the applicability of surface modification techniques such as laser peening (LP) in high temperature systems stems from thermally-driven degradation of desirable, strain-induced material modifications. Illustrated in this work is a novel LP scheme termed laser peening plus thermal microstructure engineering (LP + TME) comprised of cyclic LP and the addition of intermittent 600 degrees C (0.55T(m)) heat treatments designed to impart thermally-stable microstructural modifications in additively manufactured (AM) Inconel 718 (In718). Instrumented microindentation uncovered significant surface and sub-surface hardness enhancements exceeding 600 HV following LP + TME, a 20% increase over the as-built material. High magnitude compressive residual stresses exceeding -310 MPa were also measured following a 350-h 600 degrees C thermal exposure; a 25% increase compared to the material subjected to only a single laser shot. Thermal stabilization and overall material enhancement were determined to be the result of the formation of thermally-stable subgrains, subgrain and grain growth regulation through pinning effects, and dislocation-precipitate interactions.

Automated summary

A novel LP scheme, LP + TME, was demonstrated to achieve thermal stabilization and material enhancement in high temperature systems through the formation of thermally-stable subgrains and interactions between dislocations and precipitates.