Formation mechanism and thermal stability of γ' and γ" compact co-precipitated nanostructure in directed energy deposited Ni-based alloy

In order to understand the formation mechanism of a special nanostructure of γ' and γ" co-precipitated phase which present an important potential in the improvement of high thermal stability, strength and ductility in the superalloy, the influence of the atomic ratio of (Al+Ti)/Nb on the microstructures of the Ni-Cr-Al-Ti-Nb alloys has been investigated using laser directed energy deposition (DED). As the ratio of (Al+Ti)/Nb increases in the as-deposited and heat-treated alloy, the precipitation ability of γ' phase in the alloy is improved, accompanied with a reduction in the precipitation of γ" phase. When this ratio reaches 1.5 with the alloy composition of Ni-13.5Cr-5.26Al-1.95Ti-4.8Nb (at.%), the γ' and γ" co-precipitated nanostructure with the pattern of γ" phase attaching to six surfaces of the cubic γ' phase is generally produced in the as-deposited and heat-treated alloy. Furthermore, it was revealed that Ti element has the critical effect on the formation of this compact co-precipitated nanostructure.