Significant Improvement of Strength in Wrought 945A Ni-Based Superalloy by Aging Treatment

Abstract

Ni-based superalloys have attracted much attention due to their good resistance to high-temperature and -pressure environments. Compared with the traditional 718 Ni-based superalloy, 945A Ni-based superalloy with a lower Ni content showed better performance in terms of precipitated hardening and corrosion resistance. In this study, the aging behavior and the evolution of mechanical properties of the wrought 945A Ni-based superalloy were investigated. Microstructures were analyzed by scanning electron microscopy (SEM), bright field transmission electron microscopy (TEM), high-resolution TEM and high-angle annular dark field scanning TEM. Mechanical properties were measured by tensile and compressive tests. The results illustrated that the compressive yield stress was significantly improved by increasing aging time from 229 to 809 MPa. The increase was greater than 220%. This improvement was mainly attributed to the precipitates of the γ′ phase and carbides during the aging treatment. The residual dislocations generated by the plastic processes stimulated the formation of these precipitates. The precipitation behavior and the strengthening mechanism are discussed in detail.

Excellent Double-Aging Strengthening Effect with the High Density γ’ Phase of 945A Nickel-Based Alloy

“…Compared with the original state, the compressive yield stress of all the double-aging processed samples is much higher than that of the original sample. From the data comparison, the stress of the double-aging processed samples increases by 778 MPa compared to the original state, whereas the improvement in the compressive yield stress by the double-aging process in this study exceeds that of the previous directed-aging at 725 °C [21], even at the same aging time. The 5# sample presents the best compressive yield stress of 1007 MPa, which is 778 MPa higher than that of the original state.…”

“…Combining Figures 1 and 2, only the carbides can be observed in the matrix, indicating that there was no precipitation behavior before aging treatment. Figure 4 shows the engineering stress-strain curves and the comparison diagram of compressive yield stress between the presented double-aging samples and previously directed aging samples [21]. From the engineering stress-strain curves in Figure 4a, the compressive yield stress increases with the increment of the double-aging time.…”

“…With the increment of the aging time, the compressive yield stress is significantly enhanced. Compared with the previous direct-aging treatment [21], the volume fraction of the γ' phase is improved, and the interspace between each precipitate is reduced. This enhances the Orowan strengthening effect, which results in higher yield stress.…”

“…direct-aging treatment [21], the volume fraction of the γ' phase is improved, and the interspace between each precipitate is reduced. This enhances the Orowan strengthening effect, which results in higher yield stress.…”