Study On Microstructure Evolution And Fatigue Creep Life Prediction Of Nickel-based Superalloy

Aero-engine is known as the "heart" of an aircraft.It is a modern high-tech product that integrates a variety of disciplines and technologies.It represents the highest scientific and technological level and comprehensive strength of a country.As the core rotor component,turbine blades are of self-evident importance to aero-engines,and their mechanical properties play a decisive role in the overall performance of aero-engines.Compared with other materials,nickel-based superalloys have better high-temperature mechanical properties,and will be used as the main material of turbine blades for a long time from the past to the future.In this thesis,the nickel-based superalloy is taken as the research object,and the influence of its microstructure on the mechanical properties is analyzed.On this basis,the life of the nickel-based superalloy is evaluated,and its microstructure is optimized.The specific work of the thesis mainly includes the following parts:(1)Establish a unit cell model to characterize the microstructure of nickel-based superalloys,and analyze their mechanical properties.Firstly,the microstructure of nickelbased superalloy is analyzed,and the unit cell model of nickel-based superalloy is established by finite element simulation analysis method,and the stress and strain of the unit cell model under uniaxial tensile load are analyzed.On this basis,the content and size of the strengthening phase were changed,and the yield strength of the nickel-based superalloy was analyzed.The results showed that the increase of the content of the strengthening phase and the refinement of the size were beneficial to improve the yield strength of the nickel-based superalloy.The optimization design of the microstructure of nickel-based superalloy based on genetic algorithm.(2)Analyze the yield strength performance degradation law and evaluate the residual fatigue life of nickel-based superalloys.This chapter first analyzes the change of the size of the strengthening phase in the nickel-based superalloy under loading,and calculates the degradation model of the yield strength with the loading time combined with the stress/strain curve of the unit cell model.Then,combined with the energy method model and the Walker mean stress correction criterion,a A residual fatigue life evaluation model considering yield strength degradation.Finally,the prediction accuracy of the model is verified by the fatigue experimental data of DD3 nickel-based superalloy.(3)Fatigue-creep life evaluation of nickel-based superalloy high-pressure turbine blades considering strength degradation.In this chapter,the multi-field coupling simulation of nickel-based superalloy high-pressure turbine blades is firstly performed,and the stress/strain analysis results at critical points are obtained;secondly,the fatigue life of high-pressure turbine blades is calculated based on the low-cycle fatigue life model considering the degradation of yield strength;The creep life model of the plasticity theory is used to evaluate its creep life;finally,the linear cumulative damage rule is used to calculate the fatigue and creep total damage of the high-pressure turbine blade and evaluate its life,and then further evaluate the probability damage of the high-pressure turbine blade according to the load uncertainty.