Mechanism And Simulation Of Microstructure Repair Of Creep Defect In Nickel-based Superalloy Under Hot Isostatic Pressing

Nickel-based superalloys are widely used in the production of engine turbine blades because of their good high-temperature resistance,corrosion resistance and oxidation resistance.Due to the long-term working of the blades under high temperature and high pressure and high corrosion environment,various damages will be produced,and creep cavity is one of the most typical damages.In order to get the creep cavity repair solution,this paper takes K465 nickel-based cast superalloy as the research object to study the creep repair behavior under the action of hot isostatic pressure,reveal the organizational changes of the alloy during the healing process,elucidate the relationship between microstructure transformation,alloy element diffusion,etc.and creep cavity repair.This paper provides key experimental data for the creep damage mechanism of nickel-based superalloys.This paper uses three-dimensional video microscope,scanning electron microscope(SEM)with energy spectrum(EDS)and other equipment.The γ’-phases are characterized though quantitative metallographic analysis by Image Pro Plus software for the original tissue of nickel-based superalloy,pre-creep treatment damage tissue and the hot isostatic pressing tissue.This paper will study the effect of hot isostatic pressing technique on the creep cavities and the structure combined with the alloy tissue composition and microstructure morphology characteristics.The analysis result shows that hot isostatic pressing technique can make the creep cavities heal.The ANSYS finite element analysis software is used to simulate spherical and ellipsoidal creep cavities.Three different loading methods are adopted for the model,including no force in any direction,Y-direction pressure and isostatic pressure.Though comparing the Von Mises stress distribution and elastic strain energy density changes in the vicinity of the cavity,the analysis obtains that:(1)Regardless of the spherical cavity or the ellipsoidal cavity,the obvious stress concentration phenomenon only occurs near the cavity under the action of isostatic pressure.(2)At the same under the condition of different isostatic pressure at HIP temperature or different HIP temperature at the same isostatic pressure,the maximum elastic strain energy density near the cavity shows a linear growth trend with the increase of pressure(or temperature).(3)Take points on the boundary of the creep cavity,the analysis shows that there is a tendency to preferentially heal at the end points of the long and short axis of the cavity.According to the creep cavity healing mechanism,combined with the theory of grain boundary diffusion,intracrystalline diffusion,and surface diffusion,considering the presence or absence of internal pressure,derive the healing dynamics equation of the grain boundary cavity and intragranular cavity,and use Matlab software performs numerical analysis on the healing dynamics equation,draws the relationship between HIP temperature,isostatic pressure and cavity healing time,and the repair parameter scheme is constructed,which provides a key theoretical basis for actual experiments.