Effects of Post-processing Heat Treatment on Tensile Properties and Strain Hardening Ability of Inconel718 Alloy Components Fabricated by Laser-Directed Energy Deposition

The tensile properties and strain hardening ability of Inconel718 high-temperature alloy components are the key factors affecting their service life. Laser-directed energy deposition (L-DED) is an important method for fabricating Inconel718 components. However, it is difficult to accurately control the material microstructure by adjusting the L-DED process parameters directly to meet the service performance requirements of the components. In this paper, the microstructure of Inconel718 components fabricated by L-DED was regulated by the post-processing heat treatment (PHT) to improve the tensile properties and strain hardening ability of the components. The tensile properties of the specimens in the scanning direction (XY plane, transverse to build direction) and stacking height direction (XZ plane, parallel to build direction) were tested at room temperature, and the effects of different microstructures on tensile properties and strain hardening ability were studied. The results showed that most of the Laves phases in L-DED Inconel718 alloy treated by PHT were dissolved, and precipitated δ stabilized phase and γ′/γ′′ strengthening phase improved the tensile properties of L-DED Inconel718 alloy. All the tensile specimens showed typical microporous coalescence failure mechanism, and the fracture mode exhibited intergranular fracture. The shear-resistant acicular δ phase precipitated by PHT interacted with the dislocation to form Orowan loops, leading to a significant increase in dislocation storage rate during plastic deformation, thereby significantly enhancing the strain hardening ability of the L-DED Inconel718 alloy.