Effect of long-term aging on microstructure stability of a novel nickel base powder superalloy

Abstract

The microstructure stability, evolution law and identification of carbide and harmful phase TCP of nickel-base powder superalloy aged at 800 ℃ for 100 h —10000 h were studied by means of field emission scanning electron microscope, atomic force microscope and electron backscatter diffraction. The results show that with the increase of aging time, the grain size changed little, the grain boundary coarsened and the twin boundary Σ3 increased first and then decreased. γ' phase coarsened obviously from 500 h aging, and the coarsening rate increased first and then decreased The coarsening mechanism is mainly the combination of adjacent γ' phase by AFM analysis. Lath-like σ phase CrCo precipitated at the grain boundary first after aging for 1000 h. When the aging time was up to 2000 h, the needle-like μ phase Co7(W, Mo)6 was observed in the crystal. With the further increase of aging time, the total content of TCP phase at grain boundary and in crystal increased obviously. However, at 10000 h, the TCP phase in the crystal and at the grain boundary almost disappeared, mainly because the atoms in the TCP phase diffused into the γ' phase to form a new solid solution and deposited on the grain boundary, which further coarsened the grain boundary.