Strengthening behavior of Nb in the modified Nimonic 80A

The microstructures and mechanical properties of Nb modified Nimonic 80A were investigated. Nb increases the precipitate temperature and weight fraction of γ′ phase. The substitution of Ti by Nb and the precipitate of (Nb, Ti)C lead to the decrease of Ti composition in γ′ phase after full heat treatment. The diffusion of Nb from γ to γ′ phase makes part of the fine γ′2 particles coexist with the coarse γ′1 particles. The δ-Ni3Nb phase precipitates in γ matrix channel and exhibits an orientation relationship with the blocky (Nb, Ti)C at 845 °C: (100)δ ‖ (100)MC and [010]δ ‖ [010]MC. Precipitate of (Nb, Ti)C in γ matrix channel and at grain boundaries suppresses γ′ coarsening and grain boundary sliding, respectively. The (Nb, Ti)C precipitated at grain boundary also suppresses the coalescence of cavities at high temperature. The stress-rupture life of the 1.5 wt% Nb modified Nimonic 80A increases by about 25.4% at 750 °C/310 MPa and the creep life increases from less than 500 h to more than 1300 h at 750 °C/240 MPa. The diffusion of Nb element into γ′ phase and the precipitates of carbides significantly improve the mechanical properties of Nimonic 80A.