Effect of temperature on the creep behavior and mechanism of GH4169 alloy

GH4169, a precipitation-strengthened nickel-based superalloy, has been extensively used in structural applications in temperatures up to 650 ℃ because of its high-temperature strength, long-term stability, thermal fatigue, creep resistance, corrosion resistance, weldability, oxidation resistance, and easiness to forging. Although GH4169 has been introduced for many years, it is still widely used in many applications, especially under a high-temperature environment such as the turbine engine and the turbine disk part of advanced aero-engines, spacecraft, and gas turbines. Its microstructure mainly contains five phases: γ, γ″ (Ni₃Nb), γ′ (Ni₃AlTi), δ (Ni₃Nb), and MC carbides. The main strengthening phase of the GH4169 alloy is the γ″ phase, which is metastable, and its phase transformation to the δ phase occurs when exposed at temperatures above 650 ℃. This paper studied the effect of temperature on the creep behavior and mechanism of the nickel-based superalloy GH4169 and analyzed its fracture morphology and creep rupture mechanism. Experimental results showed that the steady creep rate of the GH4169 alloy increased, and the creep life of the GH4169 alloy decreased significantly with the increase of the creep temperature, i.e., the alloy had strong temperature sensitivity. During the creep process, the γ" phase grew, aggregated, and transformed to the δ phase. With the increase of the creep temperature, the transition of the γ″ phase to the δ phase was faster, the amount of γ″ phases in the crystal decreased, the size and volume of the δ phase increased, and the number and size of secondary cracks decreased. When the creep temperature was 650 ℃, more bright white tearing edges in the fracture appeared, the dimple size was different, and there were a small amount of precipitates and carbonization. When the temperature increased to 670 ℃, the dimple size decreased, with mainly shallow dimples and cleavage surfaces appearing. When the temperature increased to 690 ℃, there were only a few dimples and cleavage steps, and the number of δ phases increased significantly, which meant that the fracture mode was cleavage fracture or quasi-cleavage fracture.