Tailoring of nanoscale γ' precipitates and unveiling their strengthening mechanisms in multimodal nickel-based superalloy GH4720Li

The nickel-based superalloy GH4720Li samples with bimodal and trimodal γ' precipitates distributions were separately modulated by dedicated heat treatments, and their associated tensile properties were investigated. The characteristics of the precipitates were quantified by scanning electron microscopy and deformation microstructures after the tensile test was characterized by transmission electron microscopy. The results indicate that tertiary γ', which acted as the main strengthening source of superalloy GH4720Li, contributes 364–393 MPa to the critical resolved shear stress by pairs of a/2<110> dislocations. The strengthening contribution from secondary γ' precipitates depends on the particle size and the competition between stacking fault shearing and anti-phase boundary shearing. Finally, based on these experimental results, the correlations between yield strength, deformation mechanism, and particle size are discussed in detail. The contribution of each strengthening factor was analyzed quantitatively. This provides new knowledge for the quantitative strength optimization of multimodal-particle-containing alloys.