Laser directed energy deposition of thin-walled GH4099 superalloy with gradient microstructure and mechanical properties

The present study used laser-directed energy deposition(L-DED) to manufacture a GH4099 superalloy thin-walled structure with a gradient microstructure and mechanical properties. A systematic analysis examined the heat-driven changes in microstructure and both microscopic and macroscopic mechanical properties along the build direction. Columnar crystal epitaxial growth increased from bottom to top, while heat flow transformed intergranular impurities into tiny columnar crystals. Non-equilibrium solidification dendrites introduced fluctuations in elastic modulus and hardness. The substantial increase in microscopic mechanical properties observed with height primarily stemmed from variations in γ' characteristics with respect to height. The increase in grain size and precipitate size leads to a gradual decrease in the gradient of macroscopic mechanical properties from bottom to top. Intragranular carbides are primarily attributed to the γ/γ' interface and regions near dislocations, whereas intergranular carbides grow along specific orientations and are pinned at grain boundaries.