Solute atom migration in GH4169 superalloy under electrostatic fields

Electric field treatment （EFT） was applied on GH4169 alloy during aging at 500-800℃ to investigate the microstructure and property variation of the alloy under the action of EFT. The results demonstrate that the shortdistance diffusion of Al, Ti, and Nb atoms can be accelerated by EFT, which results in the coarsening of γ′and γ＂ phases. Meanwhile, lattice distortion can be caused by the segregation of Fe and Cr atoms, owing to the vacancy flows migrating toward the charged surfaces of the alloy. Therefore, the alloy is hardened by the application of EFT, even if the strength of the alloy is partly reduced, which is caused by precipitation coarsening.

Interaction between γ'precipitate distribution and microstructure homogeneity during hot deformation in a Ni-based superalloy

The inhomogeneous microstructure of the Ni-based superalloys used for turbine disks was an intolerable defect for the mechanical performance.The effects of the distribution ofγ'precipitate,forging temperature,and strain level on the microstructure evolution of GH4730 alloy were investigated by EBSD during hot deformation.The results showed that the heterogeneous factor peaked at the transition temperature from the single-phase to the double-phase region.The coupling effect of heat and stress led to the heterogeneous precipitation and distribution ofγ'phase during the transition region,which was the main reason for the formation of inhomogeneous microstructures.The coherentγ'phases of approximately 0.3μm were diffusely distributed inside the large grains,increasing the grain strength,making recrystallization refinement difficult,and thus forming large unrecrystallized grains.The incoherentγ'phases with a size of approximately 1.1μm located at the grain boundaries and pinned the grain boundaries,and thus the accumulated strain at the grain boundaries caused the occurrence of discontinuous dynamic recrystallization and promoted continuous refinement of the grains.The microstructure evolution of new Ni-based superalloys during hot forging was focused,and the formation mechanism of inhomogeneous microstructure and control measures was explained.A theoretical basis for improving the microstructure homogeneity of the new cast and wrought superalloys was provided.

Solidification behaviour and hot cracking susceptibility of a novel Ni-based superalloy

A novel Ni-based superalloy GH4151,with a γ′ volume fraction of about 55%and a service temperature capability up to 8oo oC,was investigated.Due to the different cooling conditions of various regions during the solidification of ingots,significant cooling rate variations may lead to the occurrence of hot cracking.Conventional scanning laser microscope was utilised to investigate the solidification process and phase precipitation behaviour of the GH4151 under wide range cooling rates.The characteristics of L→γ transformation were analysed,and the growth rates of at each stage were calculated.The segregation behaviour was predicted using the Scheil equation,and the predicted results match well with the experimental results.The sensitivity coefficient for hot cracking was modified,and cracking sensitivity coefficient values for the alloy under different cooling rates were computed,revealing that the alloy is most susceptible to hot cracking at 10℃/min cooling rate.Therefore,controlling the cooling rate can reduce the possibility of hot cracking in ingot.

Microstructure evolution characterization of Ni-based GH4720Li superalloy during strain-controlled fatigue at 550℃

High-temperature fatigue property of Ni-based GH4720Li superalloy at 550℃has been investigated at maximum strain from 0.8%to 1.1%.Microstructural characterization and oxidation behavior of superalloy during high-temperature fatigue have been analyzed by transmission electron microscopy and scanning transmission electron microscopy.The results show that a stable response following a slight cyclic hardening during initial cycles was revealed at the maximum strain from 0.8%to 1.0%.The stable response decreased with an increase in maximum strain.Continuous cyclic hardening was observed at the maximum strain of 1.1%.There is difference in dislocation substructures between primary γ'precipitates and γ grains.Dislocation cell and mechanical twin were formed in the interior of primary γ'precipitates and γ grains.The primary γ'precipitate interface would migrate toward the interior of primary γ'precipitates along twin boundaries,leading to instability of primary γ'precipitates.The secondary γ'depleted zone was distinctly generated near the surface due to the decomposi-tion of secondary γ'precipitates.The crack initiation and propagation during high-temperature fatigue were found inside the secondary γ'depleted zone.The primary γ'precipitates could effectively hinder the crack propagation.Al-rich oxide films(Al_(2)O_(3))were initially produced at crack tips,because the rate of diffusion of Al was relatively higher than that of other elements at crack tips.

Oxidation damage zone formed in creep fatigue crack growth of GH4169 alloy at 650℃

In the creep fatigue crack growth of GH4169 alloy,oxidation is a prominent damage source,which is mainly manifested as the oxidation damage zone in front of crack tip.In order to investigate the property of the oxidation damage zone formed in the creep fatigue crack growth,crack growth tests of directly aged GH4169 alloy were conducted at 650℃ in air under various load conditions.Interrupted tests were performed to observe the damage characteristics at crack tip.Block tests were systematically executed to quantify the dependency of oxidation damage zone size on load and holding time.The crack propagation of the GH4169 alloy has a close relationship with grain boundary oxidation at 650℃.An oxidation damage zone in front of crack tip includes intergranular microcracks and oxidised but uncracked grain boundaries.Its size has been calculated from transient crack growth rate and described as a function of maximum stress intensity factor and holding time.Based on oxidation damage zone size,a novel model has been developed to predict the creep fatigue crack growth rate of the GH4169 alloy at 650℃.

Progress in the Research and Manufacture of GH4169 Alloy

GH4169 alloy has been widely used in fields such as aviation, aerospace, and petrochemical, because of its excellent combination of mechanical and processing properties. These properties include good high-temperature strength, excellent creep and fatigue resistance, and good processing and welding performance. The requirement for high performance, high reliability, and long service life of modem engines has led to the incentive to develop GH4169 alloys with improved performance, such as increased temperature-bearing capacity, improved creep endurance, and better fatigue resistance. Advances during the past thirty years in ba- sic research and industrial technology related to GH4169 alloy were systematically summarized, including advances in alloy modi- fication, melting process optimization, and hot deformation technology.

Inclusions in wrought superalloys:a review

Inclusions in wrought superalloys significantly affect the stability of the alloy properties and limit their use and devel-opment in aeroengines and other applications.The types and sources of inclusions in wrought superalloys were reviewed with analysis of the conditions of inclusion formation from the viewpoints of thermodynamics and kinetics.The ther-modynamic data for inclusion formation in nickel-based and cobalt-based alloys were summarized and improved.The damage of inclusions to the fatigue and tensile properties and workability of these alloys and the mechanisms of crack initiation and propagation caused by inclusions were also discussed,and the effects of inclusions with different charac-teristics on crack propagation were reviewed.In addition,the control methods and mechanisms of inclusions in the triple smelting process(vacuum induction melting+protective electroslag remelting+vacuum arc remelting)were covered,providing a reference for improving the control technology of inclusions in wrought superalloys.Finally,the difficulties and development trends for inclusion control in wrought superalloys were discussed.