Stability of γ′ precipitates revealed by in-situ heating and tension TEM in selective laser melted IN718Plus superalloy

Stability of γ′ precipitates has been systematically investigated by in-situ heating & tension TEM in selective laser melted (SLM) IN718Plus superalloy. With optimized heat-treatment strategies, a bimodal distribution with primary γ' (with size around 90 nm) and secondary γ' (with size around 27 nm) formed and enhanced the 704 °C tensile property 17% to 1.18 GPa compared to the AMS 5442A standard. In-situ TEM experiments demonstrated that bimodal γ′ precipitates adopted high stability during heating to 950 °C, enhanced the 704 °C tensile resistance by superior pinning for dislocations. The higher stability and excellent reinforcing properties were achieved with Nb enrichment (10.1 at. %), which enhanced ordering arrangement of primary γ′ superlattice, as investigated at Angstrom scale by iDPC-STEM and HAADF-STEM. This study offers valuable insights into the mechanisms of microstructural stability and reinforcement principles of precipitation strengthened nickel-based superalloy.