An investigation of the effect of high-temperature cyclic straining and creep loading on tensile mechanical properties of GH4145/SQ alloy

The effect of the reverse cyclic straining and the creep loading on the resultant tensile mechanical properties, such as the strength parameter (σ0.2 and σb ), the ductile parameter (δ and ϕf ) and the composite parameter of the strength and ductility, the static toughness (Ut ), for the precipitation-strengthened nickel-based superalloy GH4145/SQ used for high-temperature turbine and valve studs/bolts in power plant was investigated systematically at a temperature of 538◦C. The experimental results show that in the case of the reverse cyclic straining both σ0.2 and σb increases at early stages of cyclic straining and, after reaching their saturated values, σ0.2 remains relatively constant until about 90% of fatigue life, while σb exhibits continuous reduction up to a level equal to the maximum applied stress amplitude. With the increasing number of straining cycles, both δ and ϕf as well as Ut decrease significantly until final fracture. In the case of creep loading the strength parameters (σ0.2 and σb ) tend to increase, as a whole, while the ductile parameters (δ and ϕf ) and the static toughness (Ut ) exhibit continuous decrease characterization as the amount of the creep deformation increases. The variation of the aforementioned various tensile mechanical properties during cyclic straining and creep loading of the alloy was further discussed by means of the observations of the deformation microstructures as well as the examinations of the fracture features of the specimens. C 2005 Springer Science + Business Media, Inc.