Study On Creep And Stress Rupture Of Hot Rolled GH4169 Alloy

GH4169 alloy has high strength,heat resistance,oxidation resistance,corrosion resistance,good thermal stability and thermal fatigue resistance in high temperature environment,which is widely used in complex working conditions,and is used to manufacture aviation jet engines,combustion turbines,turbine blades,turbine discs,etc.The creep fracture is one of the main forms for the failure of GH4169 alloy in service.The main precipitations of GH4169 alloy are γ′ phase,γ′′ phase and δ phase,and these precipitated phases change during creep,which affects the properties of the alloy.In addition,it is unclear that the effects of temperature,stress and grain size on the creep properties and the effects of trace Co elements on the persistence properties.Based on the above problems,a series of experiments are designed in this paper to investigate the creep and stress rupture properties of GH4169 alloy.The creep performances of GH4169 alloy under different temperatures and stresses were investigated,and the results show that the γ′′ phase coarsens and reduces the free energy of the system during the creep process,and the coarsening process of γ″ phase is mainly controlled by the diffusion of Nb in the matrix.As creep,the γ′′ phase loses its tissue stability and transforms into the δ phase.With the increase of temperature/stress,the transformation rate of γ′′ phase to δ phase accelerates,which makes the δ phase increase,the number of strengthened phase γ′′ phase decreases,and the creep life decreases.During creep,grain boundary slippage leads to stress concentration near the δ phase,leading to the formation of cavities.As creep,the cavities expand and connect to form cracks.The formation of δphase within the grain leads to the increased tendency to transgranular fracture.Cracks around the δ phase and MC carbides are the main cause of failure.The creep properties of GH4169 alloy with different rolling deformation by rolling to control the grain size were tested to study the effect of grain size on creep properties.The findings indicate that when rolling deformation increases,grain size reduces and that the presence of additional grain boundaries increases the likelihood of stress concentration and crack development.Additionally,when rolling deformation increases,the rate of conversion of the phase also rises,making the most δ phase and the least γ′′ phase of the alloy with 70%rolling deformation.As the grain size decreases,the GND density and KAM values at grain boundaries increase,leading to microstructure instability and larger deformation during creep,and the number of dimples on the fracture decreases and the creep properties decrease.The stress rupture tests of GH4169 alloy with different Co contents was conducted and the results show that the Co element can effectively reduce the stacking fault energy,which makes the number of twins in Co-containing alloy significantly more than that in Co-free alloy.In addition,the number and size of δ phase and MC carbides in Co-free alloy are significantly more than those in Co-containing alloy,and dislocation movement is hindered by them,and dislocations accumulate along δ phase under stress,leading to stress concentration,higher GND density and increased possibility of crack initiation,resulting in poor stress rupture performance of Co-free alloy.The mismatch between the plastic deformation of the second phase particles and the matrix and the formation of cracks by the merger of voids are the causes of alloy failure.