Neutron Diffraction Stress Analysis Of Nickel-based Polycrystalline Superalloys

GH4169(Inconel 718)alloy is a kind of Fe-Ni-Cr based deformed superalloy,which is strengthened by y"(Ni3Nb)phase with some ?"(Ni3(Al,Ti,Nb))phase separating out embedding in fcc austenitic y matrix phase.It shows excellent mechanical properties,such as strength of extension,yield strength,endurance strength under the working temperature between-253 ? to 650 ?.Meanwhile,it has good abilities of corrosion prevention,anti-radiation,hot working and welding.Due to the outstanding properties and the alloy free of Co,GH4169 superalloy is wildly used in the fields of aeronautics,astronautics,petrochemical industry and nuclear energy.The quenching rate after solid solution directly influences the service performance of GH4169 superalloy.The high rate quenching process avoids the excessive precipitation phase separating out and its abnormal grain growth.However,high residual stress is inevitably induced by the large thermal gradient,which influences the mechanical properties of the alloy.Owing to the low stacking fault energy of GH4169 superalloy,the residual stress inside the material easily piles up and is hard to relax.The residual stress originated by quenching process will remain in the planks,resulting in the abnormal deformation in the machining of parts.The insufficient size precision affects the normal assembly.Additionally,in service,the residual stress inside the alloy will pile up with the external loading stress,resulting in the distribution of the stress nonuniform,which causes the structural instability.Therefore,to improve the service life and its security,accurately controlling the residual stress in the superalloy is important.Therefore,building the method of the residual stress measurement and establishing association with some parameters are helpful to understand and control the distribution of the residual stress inside the GH4169 superalloy.From the perspective of the evolution of internal residual stress in GH4169 alloy,using the measurement of neutron diffraction and finite element simulation,the distribution of residual stress and its correlation to macro performance are reasonably analyzed in this article.The research content is mainly divided into three parts as shown in following.(I)Study of the features of GH4169 alloy by neutron diffraction measurement.This part searches the parameters of neutron diffraction measurement and builds a series of the experimental methods,which lays the foundation for the neutron diffraction experiment of GH4169 alloy.(II)Study of residual stress distribution of GH4169 alloy after quenching process by neutron diffraction.This part measures the residual stress in GH4169 superalloy and builds a model of finite element simulation.The experimental measurement results are used to compare and verify the reliability of the simulation calculations.Then the formation and evolution of the residual stress in the quenching process are understood according to the simulation process.(?)Study of the evolution of the stress under the condition of superposition of residual stress and external stress at the elastic deformation stage.According to the static uniaxial tensile loading method and the basic requirements of the neutron diffraction experiment,the design of the sample fixture and the basic parameters of the loading equipment are determined.Uniaxial tensile neutron diffraction measurement is performed on the samples in two different stress states.Through the neutron diffraction result of the stress free sample,a method for measuring Young's modulus of GH4169 alloy is established.By the use of the measured Young's modulus,we find that in the.initial stage of tensile loading,the stress in GH4169 alloy varies different with the external load.However,when the external load stress reaches a certain level,the stress response at different positions tends to be consistent.It shows that when the external loading stress is applied,the original self-balancing stress inside the sample will be broken,and the stress in the sample will be redistributed to maintain the balance with the external stress.When the new equilibrium is reached,the stress at different internal positions will keep synchronized as the external load increases.