Microstructural stability and tensile properties of a new γ'-hardened Ni-Fe-base superalloy

The microstructure and tensile properties of a new gamma'-hardened Ni-Fe-base superalloy HT700T in solutionized state are investigated after thermal exposure at 800 degrees C for different durations. Within the grain interior, the average size of gamma' precipitates increases from 28.3 to 274.1 nm with increasing aging time from 8 to 10,033 h, but its volume fraction and morphology remain unchanged with time. At grain boundaries, MC carbide and M23C6 carbide also coarsen with time, but the distribution of these carbides is always discontinuous in the most region of the alloy. Tensile tests on the experimental alloy at 650 degrees C reveal that its yield strength and ultimate tensile strength decrease with aging time, whereas the elongation to fracture increases after thermal exposure for 3053 h and then remains unchanged with increasing time. Transmission electron microscope observations on the slightly deformed specimens disclose that the dominant deformation mechanism in the experimental alloy transits from strongly-coupled dislocation pairs shearing through gamma' precipitates to Orowan looping with time. Based on these experimental observations, it is deemed that the microstructural evolution during thermal aging accounts for the evolution of the operative deformation and fracture mechanisms and therefore the tensile properties of the experimental alloy.

Automated summary

The microstructure and tensile properties of a new gamma'-hardened Ni-Fe-base superalloy HT700T in solutionized state were investigated after thermal exposure at 800 degrees C for different durations. It was found that with increasing aging time, the alloy's yield strength and ultimate tensile strength decreased, while the elongation to fracture increased. The evolution of the microstructural during thermal aging was found to affect the deformation and fracture mechanisms, and consequently the tensile properties of the experimental alloy.