Superalloy GH4169 Research Articles

Effect of Temperature on Foreign Object Damage Characteristics and High Cycle Fatigue Performance of Nickel-Based Superalloy GH4169

High-speed ballistic impact tests were conducted at room temperature and 500 °C on nickel-based superalloy GH4169 simulated blade specimens containing leading-edge features. The microscopic characteristics of the impact notch at room temperature versus 500 °C were observed by electron backscatter diffraction (EBSD), and it was found that the grains on the notched subsurface were ruined, while in more distant regions, the impact energy was mainly absorbed by grain boundaries. Internal damage is more concentrated in the notched subsurface region at 500 °C compared to room temperature. The high cycle fatigue strength of the damaged specimens under different conditions was tested. The results showed that the high cycle fatigue strength of the damaged specimens increased with the increase in the notch depth, and the fatigue strength of the damaged specimens at 500 °C was higher than the fatigue strength at room temperature. Both the 48 h post-impact holding time at 500 °C and the preload during impact at 500 °C increased the fatigue strength of the damaged specimens.

Competitive Fracture Mechanism and Microstructure‐Related Life Assessment of GH4169 Superalloy in High and Very High Cycle Fatigue Regimes

ABSTRACTHigh and very high cycle fatigue tests were performed to examine the microstructure and fracture mechanism of GH4169 superalloy in combination with techniques including electron‐backscatter diffraction (EBSD). Fractographic analysis revealed that surface failures are induced by surface flaws, whereas internal failures are caused by pores, facets, and inclusions. The three‐dimensional observation shows that fracture surfaces exhibit an irregular texture due to crystallographic mismatch of grains and plastic deformation at the crack tip. Based on EBSD analysis, Euler angles exhibited a complex geometry of grain orientation at the crack tip area, hindering crack propagation as evidenced by lower values of the Schmid factor and misorientation at the crack tip. Furthermore, the threshold values of small and long cracks decrease, whereas the transformation sizes from small to long crack growth increase from surface to internal failure. Finally, a novel microstructure defect‐based life prediction model is established, and the predicted results demonstrate a close resemblance to experimental outcomes.

High-Temperature Oxidation Behavior of GH4169 superalloy Repair by Wire-Fed Electron Beam Directed Energy Deposition

This study systematically examines the high-temperature oxidation behavior of GH4169 nickel-based superalloy repaired via wire-fed electron beam directed energy deposition (EB-DED). The analysis focuses on two distinct regions: the deposited zone and substrate zone. After exposure to 850 °C for 120 h, the oxidation films consisted of an outer layer of Cr2O3 and an inner layer of Al2O3 and TiO2. The deposition zone exhibits lower oxidation resistance, attributed to more pronounced element segregation resulting from the EB-DED process condition. This investigation establishes a clear correlation between element segregation and oxidation resistance, demonstrating that severe element segregation leads to poor oxidation resistance.

Novel crack hindrance analysis, fracture behavior, and life assessment of forged GH4169 superalloy under high and very high cycle fatigue conditions

The axial loading high- and very-high-cycle fatigue tests with stress ratios of −1 and 0.1 were conducted to investigate the fracture mechanism, crack hindrance behavior, and life assessment of forged GH4169 nickel-based superalloy in combination with techniques including 2D and 3D microscopies, and electron-backscatter diffraction (EBSD). Fractographic observations reveal that surface failures are caused by surface flaws or slipping under both stress ratios, whereas internal failures are attributed to pores or cavities only at a stress ratio of 0.1. Based on the EBSD analysis of the crack hindrance phenomenon, it is observed that high-angle grains and annealing twins form a complex structure that impedes crack growth. This is evidenced by lower values of kernel average misorientation, geometric compatibility factor, and Schmid factors within the crack hindering zone. Under the influence of different stress ratios, the threshold values and transition sizes from small to long cracks are elucidated. Considering the effect of microstructural defects and stress concentration, a crack initiation fatigue life estimation model is developed, demonstrating a good resemblance between predicted and experimental results. Finally, a novel hypothesis is developed to analyze the relationship between loading and energy dissipation, potentially offering valuable insights for further research.

Assessment and Investigation of GH4169 Superalloy: A Frugal Innovative Attempt to Identify Dominant Lubricant Fluid under Dry and Wet Conditions

Assessment and Investigation of GH4169 Superalloy: A Frugal Innovative Attempt to Identify Dominant Lubricant Fluid under Dry and Wet Conditions

Effect of ultrasonic micro-forging on the microstructure and properties of GH4169 superalloy deposited by laser direct energy deposition

Nickel-based superalloys prepared by laser direct energy deposition (DED) still suffer from microstructure, elemental segregation, and unstable strength, which cannot meet the service requirements and severely limit the application and development of DED-prepared superalloy parts. In this paper, GH4169 specimens with high density and free of defects were prepared by ultrasonic micro-forging assisted laser direct energy deposition (UMT-DED) method. The effects of UMT on the dendritic structure, elemental segregation, and precipitation phases of the alloys prepared by UMT-DED, as well as the densities, hardness, and tensile properties at room and high temperatures were investigated. The contribution of the strengthening mechanism to the yield strength was estimated. The grain refinement mechanism and the deformation mechanism of the Laves phase in GH4169 were discussed. The results show that UMT achieves grain refinement by forming fine crystal strips between the layers. The proportion of fine grain areas increased from 5.9 % to 33.3 %. The plastic deformation introduced by UMT provides external work for dislocation movement to break and fracture part of the Laves phase during plastic deformation, with dislocation cutting of the Laves phase being the main deformation mechanism. The residual stresses was transformed into residual compressive stress. The tensile strength, yield strength, and elongation of the specimens at 25 °C were increased by 4.23 %, 6.42 %, and 23.67 % respectively.

Microstructure and Mechanical Properties of GH3535 Superalloy Joints Using Electron Beam Welding

To achieve low‐stress and small‐deformation welding of thin‐walled structures for the fourth‐generation nuclear power plants, GH3535 superalloy is welded to itself using electron beam welding (EBW). The microstructure and mechanical properties of the GH3535 superalloy joints are characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), hardness, and tensile tests. A macro‐defect‐free GH3535 superalloy joint could be obtained using 22 mA welding beam current under 65 kV welding voltage with 300 mm min−1 welding speed. Different sub‐grain solidification morphologies are observed at the weld zone because of the influence of composition undercooling on the solidification process of the weld pool. The M6C type carbides formed in the weld zone and heat‐affected zone (HAZ) take place eutectic transformation under the action of thermal cycles. The eutectic transformation of M6C has no significant effect on the strength of HAZ, whereas this phenomenon is beneficial to hinder the dislocation movement in the weld zone, thereby promoting the tensile strength of the joint. The Vickers hardness of weld zone and HAZ are 250.6 and 252 HV0.5, remarkably lower than that of the base metal (261.2 HV0.5), due to the grain coarsening in those zones. The tensile strength of the GH3535 superalloy joint reached 791 MPa, ≈93.5% that of the base metal, with the fracture occurred in the weld zone.

Single-pass ultra-high-power laser welding of thick nickel-based GH3535 superalloy: Microstructure evolution and microhardness

In comparison to narrow-gap laser welding, the ultra-high-power laser welding (UHPLW) represents an efficient method for single-pass welding of 22 mm thick GH3535 superalloy. This paper explored the microstructure evolution and microhardness distribution along the direction of weld penetration. The results showed that the direction of grain growth changed from horizontal to an inclined downward direction towards the bottom of the joint along the penetration direction. Precipitates distributed in the interdendritic region were identified as M2C and M6C carbides. The rapid cooling rate in the lower zone (LZ) of the joint resulted in slight elemental microsegregation and a lower volume fraction of precipitates than in other zones. The smaller grain size and the higher volume fraction of the precipitates resulted in a higher microhardness in the middle zone (MZ) of the entire joint. The study results will facilitate the application of UHPLW for the efficient welding of GH3535 thick plates.

Creep-fatigue damage level evaluation based on the relationship between microstructural evolution and mechanical property degradation

Creep-fatigue interaction is identified as a primary failure mode for components operating under high temperatures. As operational durations extend, this interaction not only alters the material's microstructures but also initiates a gradual degradation in mechanical properties, significantly impacting its deformation and damage behaviors. In this work, the dynamic microstructural evolution of GH4169 superalloy during creep-fatigue was elucidated via qualitative characterization, and damage level evaluation method was subsequently developed by bridging microstructure degradation to mechanical property degradation. Creep-fatigue tests were performed at 650 °C with various tensile holding times and were interrupted at lifetime fractions of 10 %, 50 % and 80 % for further analysis and tensile evaluations. Results revealed that the prolonged exposure to holding times induced the coarsening of γ″ precipitates alongside an increase in low-angle grain boundaries, culminating a reduction in creep-fatigue strength. The development of voids and cracks exacerbated the degradation of elongation, leading to a hybrid fracture mode encompassing both intergranular and transgranular cracking paths. Synthesizing microstructural evolutions to qualitatively categorize diverse degradation levels imparted a robust physical basis for damage evaluation. A mapping model was established to correlate the average kernel average misorientation (micro-degradation indicator) with the tensile plastic strain energy density (macro-degradation indicator). The damage level evaluation method was endowed with quantitative metrics utilizing this model, and its generality was additionally validated in P92 steel. This work offers an insight into the quantitative damage evaluations of creep-fatigue-induced degradations in materials, thereby providing a theoretical basis for the development of operation management and inspection plans of components.

Entropy‐based method considering nonlinear hardening effect to predict the crack propagation life of superalloy GH4169 at elevated temperature

AbstractThis paper aims to determine the relationship between thermodynamic entropy generation and fatigue crack propagation life of superalloy GH4169 at 300–650°C. The entire specimen was considered as the thermodynamic system. The plastic energy dissipation in the crack tip was obtained by finite element simulation utilizing the Chaboche nonlinear hardening model. Then the cyclic entropy generation rate (CEGR) and the accumulated entropy generation are calculated by combining simulation and experimental methods. Results show that the CEGR is a power function of the stress intensity factor range, and it is almost a constant at fatigue failure. The fatigue fracture entropy (FFE) increases as fatigue cycles at failure increase at constant temperature, but it first decreases and then increases when temperature increases from 300 to 650°C. A fatigue life prediction model based on the thermodynamic damage parameter is established and verified by comparison with experimental results and available data in the literature.

Experimental research on turning nickel-based superalloy GH4169 under cryogenic cooling mixed lubrication jets

Abstract GH4169 nickel-based superalloy is the material of choice in industries such as aerospace due to its exceptionally high strength, corrosion resistance, and stability under high temperatures. However, GH4169 has relatively poor thermal conductivity, limiting the effective heat dissipation during the cutting process. This causes elevated temperature in the machining area, adversely affecting both the quality of machining and the life of cutting tools, and there are no mature processing techniques currently available to address these challenges. This paper explores a machining method with cryogenic cooling mixed lubrication for turning on GH4169, compared to traditional cutting fluids and only liquid nitrogen cooling. The results show that compared to conventional emulsion machining, techniques using liquid nitrogen cooling and a combination of liquid nitrogen and emulsion significantly reduce tool wear rates and temperature, and improve surface quality, thereby enhancing machining efficiency. These findings offer a new perspective and solution for the machining processes of GH4169 nickel-based alloy.

Experimental study of picosecond laser-assisted grinding of GH4169 nickel-based superalloy

The nickel-based superalloy GH4169 exhibits excellent thermal stability and fatigue resistance, making it widely utilized in the aerospace and marine manufacturing industries. However, the high mechanical strength of the nickel-based superalloy GH4169 leads to issues such as high grinding forces during grinding and poor surface morphology of the material after grinding. To improve the processing quality of GH4169, this study employs ultrafast pulse laser texturing to create two distinct biomimetic structures on its surface. The study explores the impact of laser parameters on both the recast layer and surface hardness. Subsequently, grinding experiments are conducted on both structured and non-structured workpieces. The grinding forces and surface roughness during grinding are analyzed, and the surface morphology of the workpiece after grinding and the corrosion resistance of the material are also tested. According to the test results, the grinding forces of the fishbone-like and nacre-like structure workpieces are reduced compared with those of the non-structured workpieces, and the maximum tangential grinding forces are reduced by 38.54 % and 35.98 %, and the maximum normal grinding forces are reduced by 30.24 % and 29.6 %, respectively. In addition, the corrosion resistance of the surface of the structured workpieces after grinding is better compared to the non-structured workpieces, and the best corrosion resistance is obtained for the fishbone-like structure.

Research on hot deformation behavior and microstructure evolution mechanism of GH4169 superalloy

The hot deformation behavior and microstructure evolution of GH4169 superalloy were investigated through hot compression experiments with a temperature range of 900–1100 °C and strain rates ranging from 0.01 to 5 s−1. Concurrently, the flow stress curve of the alloy was obtained and constitutive equations were established. Based on the dynamic material model, a hot working diagram was established and the hot working window was optimized. The findings demonstrate that the high-temperature softening mechanism of this alloy primarily involves dynamic recrystallization (DRX), while both discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) exist. According to the hot processing map, the process parameters corresponding to the unstable areas are low temperatures and medium-high strain rates (900–985 °C, 0.15–5 s−1), and high temperatures and high strain rates (1025–1100 °C, 2.5–5 s−1). The reason is that the appearance of deformation bands and flow localization in the microstructure. The optimal hot working parameters for GH4169 are 1000 °C/0.01 s−1 and 1050–1100 °C/0.01–0.1 s−1, where the microstructure consists of uniformly distributed DRX grains. The volume fraction of DRX in GH4169 alloy rises with higher temperatures or lower strain rates. In addition, the reduction of intergranular dislocations promotes the migration of grain boundaries from low angle grain boundaries (LAGBs) to high angle grain boundaries (HAGBs).

Influence of temperature on hot corrosion behavior of GH4169 superalloy subjected to Na2SO4–NaCl salts attack

This work studies the hot corrosion behavior of GH4169 Ni-based superalloy, deposited with a mixture of salts comprising 95 wt% Na2SO4 and 5 wt% NaCl, across three distinct temperatures (i.e., 650 °C, 800 °C and 950 °C). Corrosion and non-corrosive exposure experiments were compared, yielding data on mass loss and gain, respectively. Material characterization results revealed that the corrosion layer was mainly comprised of Cr2O3, Fe2O3, NiO, Al2O3, TiO2, NbS2 and MoS2. Notably, as the temperature ascended from 650 °C to over 800 °C, the corrosion mechanisms underwent a transition from pitting to uniform corrosion, corresponding to low-temperature hot corrosion and high-temperature hot corrosion, respectively. At 650 °C, a large number of semi-ellipsoidal corrosion pits manifested on the surface. Conversely, at 800 °C and 950 °C, the corrosion layer on the surface exhibited nearly uniform spallation. The pit growth model and spallation dynamics model were, respectively, developed based on the observed microstructure features. The models serve as tools for quantitative examination of the hot corrosion process of the superalloy at different temperatures.

An Optimized Strain-Compensated Arrhenius Constitutive Model of GH4169 Superalloy Based on Hot Compression.

A precise constitutive model is essential for capturing the deformation characteristics of the GH4169 superalloy in numerical simulations of thermal plastic forming processes. Hence, the aim of this study was to develop a precise modified constitutive model to describe the hot deformation behavior exhibited by the GH4169 superalloy. The isothermal cylindrical uniaxial compression tests of the GH4169 superalloy were carried out at temperatures of 950~1100 °C and strain rates of 0.01~10 s-1 using a Thermecmastor-200KN thermal-mechanical simulator. The original strain-stress curves were corrected by minimizing the effects of plastic heat and interfacial friction. Based on the true stress-strain curves, the original strain-compensated Arrhenius constitutive model was constructed using polynomial orders of 3, 5, and 10, respectively. The results showed that once the polynomial order exceeds the 5th, further increasing the order has little contribution to the accuracy of the model. To improve prediction ability, a higher precision Arrhenius constitutive model was established by extending a series of material parameters as functions that depend on temperature, strain, and strain rate, in which the error can be reduced from 4.767% to 0.901% compared with the classic strain-compensated Arrhenius constitutive model.

Size effect and underlying microstructural mechanism in cyclic deformation behavior of nickel-based superalloy sheet

The nickel-based GH4169 superalloy is widely used in the aerospace field, which has desirable oxidation resistance and strength in extreme environments. However, the size effect and underlying microstructural mechanism in the cyclic deformation of the GH4169 sheet are still not fully elucidated, which affects the forming accuracy precision of thin-walled components. To this end, the cyclic mechanical properties and microstructural evolution of the GH4169 sheets with different thicknesses and grain sizes were systematically investigated via cyclic shearing tests. The superalloy sheet exhibits obvious early re-yielding, instantaneous softening and permanent softening during the cyclic deformation and these cyclic deformation behaviors are obviously affected by size effect. To rationalize the cyclic mechanical responses and size effect, transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) tests were conducted. The results indicated that the dislocation slip patterns are principally planar array slip and cross slip in the cyclic shearing deformation. Meanwhile, the annihilation of unstable dislocation and the presence of carbides led to the instantaneous softening. Moreover, the change of loading direction, the reduction of texture strength, the proportion of low-angle grain boundary (LAGB), and geometrically necessary dislocation (GND) density together result in the occurrence of permanent softening. Based on the comparative analysis of the microstructure evolution of superalloy sheets with different size factors, the underlying mechanism of size effect on cyclic deformation was clarified. The findings in the research combine the cyclic mechanical response and microstructure evolution closely in the cyclic deformation of superalloy sheets and deepen the understanding of size effect under complex loading paths.

Difference in hot deformation behavior of a Ni–Fe based superalloy through cast-wrought and additive manufactured processes

Traditional cast-wrought superalloys have been challenging in cogging due to element segregation. However, additive manufacturing technology is anticipated as a novel method for producing low-segregation superalloys. A set of isothermal compression tests were conducted on a Ni–Fe based superalloy GH4169 in various processing conditions, including as-cast and as-homogenized alloy produced by triple melting (Alloy TMC and TMH), as well as additive manufactured alloy (Alloy AM). Flow stresses were examined to develop activation energy maps and processing maps. Additionally, microstructure evolutions were observed to investigate the mechanisms of recrystallization nucleation and grains refinement during hot deformation. Under specific deformation conditions, three alloys have developed to varying refinement stages. As Zener-Hollomon parameter Z decreases, the nucleation mechanism shifts from continuous to discontinuous dynamic recrystallization. Alloy TMH exhibits enhanced hot workability compared to TMC, which is attributed to its lower activation energy Q and more limited instability region. Q value of Alloy AM is slightly higher than that of TMH; however, it demonstrates a wider processing window. Utilizing AMed superalloys for hot deformation not only provides advantages in low segregation and fine grains, but also simplifies the process sequences. This is expected to break through the current technical bottleneck associated with higher performance superalloy turbine disks.

In situ investigation of hydrogen embrittlement induced by δ phase in selective laser-melted GH4169 superalloy

Direct evidence of hydrogen-assisted crack nucleation and propagation associated with the δ phase in the selective laser melted GH4169 superalloy was obtained. The analysis of hydrogen trapping sites using thermal desorption spectroscopy revealed that the δ phase exhibits strong hydrogen capture capability, with a hydrogen desorption activation energy of 35.45 ± 2.51 kJ/mol. In addition, spatially resolved hydrogen mapping conducted by scanning Kelvin probe force microscopy and hydrogen microprint technique provided further evidence for the δ phase as a deep hydrogen trapping site. The atomic-scale characterization sufficiently reveals the deformation mechanism of the δ phase induced by dislocation accumulation. Hydrogen-promoted dislocation slip localization facilitates the formation of microvoid defects in the δ phase, which is the main reason for the δ phase fracture, and induces intergranular and transgranular cracks.

Multiscale microstructural consideration for high strength diffusion bonding of Ti2AlNb alloy to GH4169 superalloy with (TiZrHfNb)95Al5 interlayer

A high entropy interlayer (TiZrHfNb)95Al5 was successfully designed for vacuum diffusion bonding of GH4169 superalloy to Ti2AlNb alloy. The relationships between grain size, grain boundary, lattice mismatch and microhardness, elastic modulus, shear strength and fracture behaviors were revealed. The typical microstructure was Ti2AlNb/B2/Solid solution/(Ti, Zr, Hf)2(Ni, Nb)+(Ti, Zr, Hf)(Ni, Nb) + Solid solution/(Ti, Zr, Hf)(Ni, Nb) + (Cr, Ni, Fe)ss/(Cr, Ni, Fe)ss/Cr-rich(Cr, Ni, Fe)ss/Ni-rich(Cr, Ni, Fe)ss/GH4169. With the holding time increased, the shear strength overall increased and decreased sharply, and the highest shear strength reached 384 MPa at 980 °C for 90 min. The microstructure had anisotropic crystal orientation, and the joints of Zone Ш for 90 min consisted of 92.08 % HAGBs and 7.92 % LAGBs. The residual strains and stresses decreased when the holding time increased. Meanwhile, recrystallisation appeared in Zone Ш, and the increase in the recrystallisation rate led to grain refinement. The lattice mismatch between (Ti, Zr, Hf)(Ni, Nb) and (Cr, Ni, Fe)ss phases was 25.05 %, indicating that the interface was non-coherent, and (Ti, Zr, Hf)(Ni, Nb)+(Cr, Ni, Fe)ss phases were located at an elastic modulus dramatically changed interface. Thus, the cracks easily formed in this interface and led to joint fracture. Moreover, the fracture mechanism was brittle fracture.

Influence of Pre-strain on the Microstructure and Mechanical Properties of GH4169 Superalloy

Abstract In this study, GH4169 superalloy was subjected to pre-straining after aging, with pre-strain deformations ranging from 0.2% to 10%. Subsequently, the tensile performance of the alloy was tested at various deformation levels. The microstructure of several pre-tensile deformed alloys was also examined. The results show that when the pre-strain deformation increases, the strength of the alloy is improved, the elongation is greatly reduced, and the orientation of equiaxed crystals increases. The pre-strain of GH4169 superalloy increases LAGB and dislocation density while decreasing HAGB and annealing twins.