Influence of Unimodal and Bimodal γ' Precipitate Size Distributions on the deformation Mechanisms in ATI 718Plus

This study combined novel modeling and transmission electron microscopy (TEM) characterization to understand how γ' precipitate size distribution affects the deformation of ATI 718Plus. 720 ℃ to 900 ℃ aging was applied to solution-treated samples, resulting in unimodal and bimodal γ' size distributions. The microstructures were tensile tested to failure to assess their yield strength, ultimate tensile strength, and elongation-to-failure. Some samples were removed after 3-4% plastic strain and TEM was used to study the precipitate-dislocation interactions. For the unimodal samples with ~7 nm diameter γ' precipitates, dislocations sheared through the precipitates. Samples with ~24 nm diameter γ' precipitates exhibited dislocation loops and paired dislocations. The bimodal distribution, with ~6 nm and ~28 nm diameter γ' precipitates, showed shearing as the dominant deformation mechanism and exhibited the highest strength. The findings aligned with theoretical calculations of critical resolved shear stress for shearing and looping.