Search

Co‐based superalloys with the advantages of high melting point, high‐temperature mechanical properties, and large resistance under hot corrosion environment are potential candidates for turbine engine components. The isothermal oxidation behavior of Co–Ni–Al‐based superalloy with the addition of Mo and Cr in dry air at 1073 and 1173 K was investigated. The results showed that similar three‐layer oxides structures were composed of Co‐containing oxides, complex oxides rich in Co and Al, and Al2O3 layer formed on both 2Mo and 2Cr Co–Ni–Al‐based superalloys, and Mo‐containing oxides also existed in the subsurface. The oxides in the outer layer transferred from Co3O4 to denser CoO with the increase in temperature. The γ'‐free zone formed under the Al2O3 layer due to the depletion of Al. Co–Ni–Al‐based superalloys need to conquer a large energy barrier at an earlier stage of oxidation and exhibit good oxidation resistance at 1073 K. [ABSTRACT FROM AUTHOR]

High temperature tensile behaviors of two W-free Co-Ni-Al-based γ'-strengthened superalloys at 773 K ~ 1073 K were investigated. The tensile strength and elongation of two superalloys decrease with increasing temperature. The fracture mechanism changes from dimple fracture to brittle fracture. A detailed observation of the fracture shows that the intermediate temperature embrittlement caused by decohesion of slip plane plays a significant role in reducing high temperature performance. Both superalloys reach to peak yield strength at 923 K. Occurance of yield strength anomaly (YSA) is derived from the synergistic effects of dislocation locking strengthening and dynamic strain aging strengthening. Dislocation cross-slipping hinders the dislocation migration. Dislocations' unpinning to the moving solutes increases the yield strength at 723 K ~ 973 K. A rapid weakening of grain boundaries strength decreases the yield strength at 1073 K. • Yield strength anomaly was synergistically affected by dislocation locking and dynamic strain aging. • Intergranular fracture was caused by the decrease of grain / twin boundaries strength and decohesion of slip plane. • The yield strength increased with increasing dislocation locks' densities while the ductility decreased due to ITB effect. [ABSTRACT FROM AUTHOR]