The Study On High Temperature Low Cycle Fatigue Properties And High Temperature Creep Properties Of GH4169 Alloy

In this paper, the high temperature tensile as well as the high temperature low cycle fatigue and high temperature creep behavior have been studied for the GH4169 alloy with four different heat-treated states. The effect of heat treatment on high temperature properties of the GH4169 alloy was obtained. And then, the influence of grain size, the fraction ofδphase and the size ofγ″phase in the GH4169 alloy on the fracture mechanisms of the high temperature low cycle fatigue and high temperature creep behavior were analyzed by optical microscope, scanning electron microscope (SEM) and transmission electron microscope (TEM) observations. The slip features of the high temperature low cycle fatigue for the GH4169 alloy with different heat-treated states were also discussed.Results of the high temperature tensile tests for the GH4169 alloy with different heat-treated states show that the tensile strength and the yield strength of the GH4169 alloy with smaller grain size are higher than that of the GH4169 alloy with larger grain size. The high temperature tensile strength is decreased due to the existence of the needle-shapedδphase. When the grain size and the fraction ofδphase are invariable, the yield strength of the GH4169 alloy with larger size ofγ″phase is higher than that of the GH4169 alloy with smaller size ofγ″phase, but the tensile strength is close to each other. The fracture morphology observations indicate that the fracture mechanism of the high temperature tensile belongs to the micropore-gathering ductile fracture, and the characteristics of intergranular fracture are also observed in the GH4169 alloy with larger size ofγ″phase.Results of the high temperature low cycle fatigue tests at 600 ?C with different strain amplitudes show that the smaller grain size and larger size ofγ″phase are beneficial to the high temperature low cycle fatigue properties of the GH4169 alloy, while the existence ofδphase does harm to the low cycle fatigue life. Cyclic softening is the main feature of the GH4169 alloy during the high temperature low cycle fatigue, which can be attributed to the dislocation cutting acrossγ″phases. Additionally, TEM observations show that the dislocation slip is the mechanism of high temperature low cycle fatigue for the GH4169 alloy. The spacings between the slip bands become narrow and the densities of the slip bands increase when the grain size is smaller or there are needle-shapedδphases in the GH4169 alloy. Meanwhile, the tendency of multiple slip can be increased because of the decrease in the size ofγ″phase.Results of the high temperature creep tests at a temperature of 600 ?C and a stress of 825 MPa show that the creep rupture time of the GH4169 alloy with smaller grain size are longer than that of the GH4169 alloy with larger grain size. The creep rupture time are increased as a result of the existence ofδphase. The mechanisms of creep rupture vary with the microstructures of the GH4169 alloy. The initiation mechanisms of the creep cracks for the GH4169 alloy without apparentδphase and with the needle-shapedδphase are wedge-type and void-type, respectively. The propagation mechanisms of the creep cracks for the GH4169 alloy with different heat-treated states all belong to the combination of intergranular and transgranular type. The creep elongation is improved for the existence of needle-shapedδphase.