A new Ni-base superalloy: production-microstructure-properties correlation

The new nickel-base super alloy AF955 (R) (UNS N09955) was developed by Foroni S.p.A. in response to the industrial need for a material that preserves the excellent properties of the precipitation hardened nickel-based superalloys, while also providing adequate resistance to hydrogen embrittlement. A wide mechanical and microstructure characterization of the new superalloy was carried out to rationalize the effects of the production route and different heat treatments of alloy AF955 (R). Mechanical properties were evaluated by Rockwell hardness and tensile tests. The microstructure was investigated by conventional Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) with micro-chemical measurements with Energy Dispersion Spectroscopy (EDS) for a general and phase precipitation assessment, and by Transmission Electron Microscopy (TEM) for a quantitative characterization of the nanometric precipitation strengthening phases, namely gamma prime (gamma') phase and gamma double prime (gamma '') phase. Quantitative relationships between mechanical properties and strengthening precipitation phases, were obtained by using the Weakly Coupled Dislocation (WCD) model and the Strongly Coupled Dislocation (SCD) model. The WCD model for deformable particles resulted successful to correlate the quantitative microstructure results obtained through TEM with the yield strength of the new superalloy after two different heat treatments.