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.

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.

Machine learning study on time-temperature-transformation diagram of carbon and low-alloy steel

Time-temperature-transformation(TTT)diagram plays a critical role in designing appropriate heat treatment process of steels by describing the relationship among holding time,temperature,and quantities of phase transformation.Making predictions for TTT diagrams of new steel rapidly and accurately is therefore of much practical importance,especially for costly and time-consuming experimental determination.Here,TTT diagrams for carbon and low-alloy steels were predicted using machine learning methods.Five commonly used machine learning(ML)algorithms,backpropagation artificial neural network(BP network),LibSVM,k-nearest neighbor,Bagging,and Random tree,were adopted to select appropriate models for the prediction.The results illustrate that Bagging is the optimal model for the prediction of pearlite transformation and bainite transformation,and BP network is the optimal model for martensite transformation.Finally,the ML framework composed of Bagging and BP network models was applied to predict the entire TTT diagram.Additionally,the ML models show superior performance on the prediction of testing samples than the commercial software JMatPro.

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.