Study On Thermal Stability Of Ni-Cr-Mo And Ni-Co-Cr Based Alloys

In order to achieve energy saving and emission reduction,and to alleviate the increasingly serious environmental problems and energy crisis,it is particularly important to study 700? ultra-supercritical coal-fired generating units with higher efficiency.At present,major countries in the world have carried out relevant research.K325 and M985 are nickel-based superalloys developed by the Institute of Metal Research of the Chinese Academy of Sciences.They have good corrosion resistance and oxidation resistance.They are candidate materials for 700? advanced ultra-supercritical generator sets in my country.Due to the particularity of the use environment,good thermal stability and durability are the key to ensuring long-term service of materials.This paper studies the thermal stability behavior of K325 and M985 alloys.This paper studies the structure evolution of K325 alloy during long-term aging at650?,675?,700?,725? and 750?.During the long-term aging process,the alloy precipitates a strengthening phase ?".The average size of the ?" phase grows with the extension of the aging time.When the temperature is 700? and below,the growth of the ?" phase satisfies the LSW theory.During the alloy aging process,as the aging time increases,the alloy precipitates ? phase at the grain boundary and around the MC carbides.The generation of ? phase is greatly affected by temperature.The higher the temperature,the shorter the time required for precipitation and coarsening.The higher the rate.The effect of K325 alloy on the mechanical properties of the alloy during the long-term aging process was studied.With the increase of the alloy aging time,the yield strength and tensile strength of the alloy showed an increasing trend,while the reduction of area and elongation showed a decreasing trend,and with The precipitation of ? phase increases,and the downward trend is more obvious.Tensile fracture is dominated by mixed fracture,with cracks distributed along the grain boundary.The impact performance is significantly affected by the precipitation of the ? phase.With the precipitation of the ? phase,the impact absorption energy of the alloy decreases significantly,and the ? phase can reduce the toughness of the alloy.Cause a decrease in mechanical properties.The structure degradation behavior of K325 alloy after persistence was studied.When the alloy is subjected to external force,the ?? phase will accelerate to the ? phase,resulting in a decrease in the mechanical properties of the alloy.The carbides at the grain boundaries are preempted by the precipitation and growth of the ? phase.The growth space of grain boundary carbides inhibits the growth of grain boundary carbides.The structure degradation behavior of M985 alloy after persistence was studied.During the persistence process,the sample structure of M985 was stable,and the grain size and grain boundary carbides did not change significantly.The ?'phase in the matrix grows up,and with the increase of the endurance life,the morphology of the ?'phase also changes from spherical to cubic.The average size of the ?'phase does not satisfy the LSW theory due to the applied stress.