Tailoring the strength of inconel 718: Insights into LPBF parameters and heat treatment synergy

Abstract

• Achieving target properties of LPBF Inconel 718 while optimizing process parameters and minimizing residual porosity. • Tuning strength and ductility through thermomechanical treatments to minimize harmful phases and refine microstructures. • Analysis of texture and its changes after heat treatment and correlation to mechanical behavior. • Assessment of recrystallisation and grain growth linked to texture and strength. The enhancement of mechanical performance in Inconel 718 fabricated via Laser Powder Bed Fusion by optimizing process parameters and various post-processing heat treatments, such as double aging and high-temperature isostatic pressing, are explored. Phase and texture evolution were characterized by high-energy diffraction electron backscatter diffraction analysis, showing a weak Goss-type texture in the as-built condition. Carrying out a homogenization annealing above δ solvus, e.g. at 1155 °C, suppresses its transformation into δ phase and enables an aging treatment to achieve a controlled precipitation of γ’/γ’’ instead. MC-type carbides were detected in different morphologies at grain boundaries and in the matrix. Linking the microstructural changes with trends in the tensile properties along three build orientations, i.e. horizontal, diagonal and vertical to the build platform, we show that texture and anisotropy in the as-built condition can largely be eliminated by an annealing at 1155 °C. The mechanical properties can be adjusted further by adding double-aging or varying the cooling rate after the solvus treatment. The findings reveal a clear correlation between optimized LPBF parameters, heat treatment strategies, microstructural evolution, phase distribution, and the resultant mechanical properties, which contributes to the development of tailored process chains for specific application requirements.

Topics & Concepts