Effect of γ′ phase coarsening on tensile properties during long-term aging of NiCoCrFeAlTiMoW alloy

Abstract

A γ′ phase strengthened NiCoCrFeAlTiMoW alloy was prepared in a vacuum arc melting furnace, and X-ray diffractometer (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and tensile testing machine were used to investigate the coarsening behavior and the evolution law and mechanism of mechanical properties of the γ′ phase after 200 h long-term aging at 750, 850 ℃ and 950 ℃.The results show that γ′ phase remains spherical during the aging process when the aging time is extended, γ′ phase size gradually increases and the solidification phenomenon occurs at 750, 850 ℃ and 950 ℃. The alloy has a high diffusion activation energy with a value of 357 kJ/mol.This is mainly due to the fact that the matrix is a high entropy solid solution with complex composition, and the diffusion of Al and Ti atoms in the matrix becomes difficult due to the hysteresis diffusion effect. The yield strength of the alloy gradually increases after aging at 750 ℃, the yield strength after aging at 850 ℃ first increases and then decreases, and gradually decreases after aging at 950 ℃. The change in the yield strength of the alloy is caused by the increase in the size of the γ′ phase, which leads to a shift in the precipitation strengthening mechanism of the alloy.

Keywords

• γ′ phase coarsening
• high-entropy alloy
• mechanical property
• strengthening mechanism