Effects of pre-treatments on mechanical properties and fracture mechanism of a nickel-based superalloy

The effects of pre-treatments (interrupted and direct water-cooled methods) on the microstructural evolution, mechanical properties and fracture mechanism of a nickel-based superalloy are studied. It is found that the mechanical properties and fracture mechanism of the studied superalloy are sensitive to pre-treatment. The number and size of gamma ''(Ni3Nb) and gamma'(Ni3Al) phases rapidly decrease with the increase of interrupted temperature. For the interrupted water-cooled superalloy, when the interrupted temperature is below 705 degrees C, the microhardness is relatively high due to the precipitation of the gamma '' and gamma' phases. However, when the interrupted temperature is increased from 705 degrees C to 780 degrees C, the microhardness dramatically decreases. Meanwhile, the yield strength and ultimate tensile strength also rapidly decrease, while the elongation to fracture sharply increases. Additionally, the fracture mechanism of the studied superalloy transforms from brittle intergranular fracture to ductile transgranular fracture with the increase of interrupted temperature. Compared with the direct water-cooled superalloy, the microhardness, yield strength and ultimate tensile strength of the interrupted water-cooled superalloy are greatly improved when the interrupted temperature is below 780 degrees C.