Influence of Post-deposition Heat Treatments on the Microstructure and Mechanical Properties of Wire–Arc Additively Manufactured ATI 718Plus

To maximize the benefits of additive manufacturing (AM) processes, optimizing the as-processed microstructure and its associated mechanical properties through post-deposition heat treatment is important. The present study investigates the influence of post-deposition heat treatments on the microstructure and mechanical properties of wire–arc additively manufactured (WAAM) ATI 718Plus. The application of the standard heat treatment recommended for the wrought ATI 718Plus led to the formation of excessive eta (η) phase particles along the interdendritic spaces. This microstructure degrades the tensile properties of the WAAM condition and exhibits a profound anisotropic effect. To enhance the microstructure for improved properties, the nature of the submicron-sized particles that formed within the microstructure is identified. Experimental and thermodynamic simulation tools are utilized to develop time–temperature-transformation (TTT) diagrams, and the growth kinetics of η phase in the WAAM ATI 718Plus is determined. Based on the analyses, appropriate heat treatments capable of precipitating a moderate amount of η phase are designed and evaluated. The newly developed heat treatment significantly improves the mechanical properties of the AM alloy and reduces the anisotropic effect.