Microstructure Eveolution During Aging Process And The Effect On Creep Rupture Property Of GH3625 Superalloy

The first high-temperature gas-cooled reactor nuclear power plants(HTR-PM)in the world is being built in China and this Chinese self-developed technology is also taking a lead.The material used as key components of controlling rod system is solid solution strengthened 625 nickel-based superalloy containing niobium.It will serve under the high temperature(550°C-950°C)long-term ageing working condition for 40 years,which leads to the microstructure degradation and the bottleneck problem of creep performance unstable and uneven.The paper systematically studys the precipitates evolution of 625 alloy under long-term service conditions by means of microstructural analysis and creep test,especially focusing on the effects of precipitation type,morphology and content on high temperature creep rupture properties.Implementing with advanced analytical methods such as SEM,TEM and XRD etc.modern analytical means,the paper systematically investigate the precipitates precipitation,evolution and growth of intragranular and grain boundary precipitates during long-term aging of 625 alloy at 650 °C,700°C and 780 °C.The results show that the precipitation and growth of 625 alloy precipitates at different temperatures are controlled by diffusion process.The coarsening process of ?? phase in 650°C and 700°C aging process conforms to LSW theory.The content of ? phase increases with aging time prolonging at 780°C.Meanwhile,the study gets the time index n of Avrami precipitation kinetics equation and the precipitation rate ? of ? phase.On this basis of above all,the effect of precipitates on creep rupture properties is further studied.Under the same creep condition,the microstructure obtained by different aging treatment parameters has significant difference and shows different creep properties.625 alloy aged at 700°C×120h has the best high temperature creep rupture properties.The above research enriches the research results of precipitation and evolution of aging precipitates and investigates the relationship between aging precipitates precipitation,evolution and creep behavior of 625 alloy,which has theoretical value of material science.It also can provide basic experimental support for dimension accuracy and running stability of controlling rod components at service temperature.It is convenient to apply research results to the production of HTR controlling rod components and meet the requirement of the nation.