Superalloy GH4169 Research Articles

Fretting fatigue life improvement of nickel-based superalloy GH4169 dovetail slots by deflecting abrasive waterjet peening process

The proposed deflecting abrasive waterjet peening (DAWJP) process can be used for surface strengthening of metallic parts with confined space features, which has great potential to improve the surface integrity and fretting fatigue (FF) life of dovetail slots in turbine discs. In this paper, the nickel-based superalloy GH4169 dovetail slot is strengthened by DAWJP and shot peening (SP), and the effects of DAWJP and SP on surface integrity and FF performance of the dovetail slot are investigated. First, the DAWJP with three different processes (water pressure of 205 MPa, traverse speed of 5 mm/s, standoff distance of 2 mm, and path interval of 0.05, 0.1, and 0.15 mm) and the SP with one process (peening intensity of 0.25 mmA with coverage of 100%) were conducted on the contour surface of the dovetail slot. The surface integrity of the dovetail slot before and after the DAWJP and SP treatment was investigated, including microstructure, surface roughness and microscopic morphology, microhardness, and residual stress. Results showed that the dovetail slot treated by the DAWJP with different path intervals formed a plastic deformation layer with a thickness of 22–43 μm and surface roughness Ra and Sa of 0.391–0.501 μm and 0.763–0.907 μm. The surface microhardness and CRS of the DAWJP-treated dovetail slot were approximately 541–591 HV and 1005–1169 MPa, 16%–27% and 178%–224% times higher than the as-received dovetail slot. The SP-treated dovetail slot produced relatively large surface roughness, slight plastic deformation, and low microhardness and CRS compared with the DAWJP-treated dovetail slot. Finally, FF tests were carried out to study the FF behavior of the dovetail slot before and after DAWJP and SP treatment. The FF lives of the dovetail slot treated by DAWJP were 4.82 and 3.91 times that of the as-received dovetail slot at room temperature and a high temperature of 650 °C. In contrast, the FF lives of the SP-treated dovetail slot were 2.96 and 1.96 times that of the as-received specimen at room temperature and a high temperature of 650 °C, which verified that DAWJP has a more significant effect on improving the FF life of dovetail slots than the SP treatment used for comparison. The FF fracture and fretting contact surface and its cross-sectional microstructure were examined, and the results showed that the extreme grain refinement, large CRS, and high work-hardening induced by DAWJP could be the key to greatly improving the FF life of dovetail slots. This work takes the lead in the surface treatment of dovetail slots through the proposed DAWJP process, which provides a feasible reference plan for effectively and economically improving the FF resistance of dovetail slots in turbine discs.

The influence of electron beam welding technology on mechanical properties of GH4169 welded joints

Super-alloy GH4169 and related welded structures were widely used in the aero-engine industry region. Vacuum electron beam welding is one of the most advanced welding technologies, and the influence of the mechanical property caused by the welding technology still needs further research. Firstly, the hardness, microstructure, and tensile properties of the GH4169 electron beam welded joint were tested. After electron beam welding and two-stage aging treatment, the weld zone was strengthened and its hardness is higher than that of the base metal zone. The microstructure characterization results showed that the grain size of the weld and heat-affected zone was larger than that of the base metal. The tensile results show that the static properties of the welded joint are similar to that of the base metal, and the residual height has no obvious effect on the static strength of the welded joint. The high-temperature creep properties of GH4169 electron beam welded joints with residual height were tested. The results show that residual height will lead to a transient fracture of welded joints under relatively safe service conditions. The fatigue performance of GH4169 welded joints with and without residual height was tested respectively. The results show that the fatigue life of the welded joints without residual height was about 10 times longer than that of the welded joints with residual height under the same stress level, and for the welded joint with residual height, the residual height position will become the main fatigue crack source.

Determination of relationship between high-temperature low cycle fatigue damage and mechanical property degradation: Experimental and theoretical analyses

Mechanical properties of metallic materials gradually degrade under high-temperature low cycle fatigue (HTLCF) loading, which is a manifestation of fatigue damage accumulation. In this study, a mapping modeling is developed to determine the relationship between micro-scale HTLCF damage and macro-scale mechanical property degradation. Strain-controlled HTLCF tests in GH4169 superalloy are carried out at 650 °C and interrupted at various lifetime fractions for subsequent microscopic characterizations and high-temperature tensile tests. Quantitative analysis of electron backscatter diffraction indicates a three-stage increase in kernel average misorientation and geometrically necessary dislocation throughout the cyclic process, along with variations in the fraction of different grain boundaries. Simultaneously, the evolutions of shearing precipitate and de-twinning are characterized using transmission electron microscope. Furthermore, the mechanical properties of GH4169 superalloy, such as yield strength, ultimate tensile strength, elongation and work-hardening rate, demonstrate different degradation characteristics after exposure to HTLCF damage. Based on these results, the mechanism of HTLCF-induced mechanical property degradation is clarified and the mapping modeling is established using tensile plastic strain energy density and kernel average misorientation. Finally, a damage level evaluation method for engineering components is developed after the generality and flexibility of model is verified in different high-temperature materials.

Comparative study of the effects of conventional shot peening and ultrasonic shot peening on very high cycle fatigue properties of GH4169 superalloy

This study investigates the effects of two different shot peening techniques, conventional shot peening (CSP) and ultrasonic shot peening (USP), on the very high cycle fatigue (VHCF) properties of the GH4169 superalloy. The study evaluates and compares surface roughness, X-ray diffraction patterns, microhardness, and residual stress in specimens treated with CSP and USP. The VHCF tests reveal that both CSP and USP treatments improve the VHCF properties of the GH4169 superalloy. However, while the USP-treated specimens have deeper work hardening and compress residual stress layers, their VHCF lives are significantly shorter than those of the CSP-treated specimens. Additionally, the study finds that the stress triaxiality, which inhibits dislocations at the crack tip, is higher closer to the center of the specimen. The transmission electron microscopy (TEM) results further confirm that the reduced dislocation density and increased stress concentration in the plastic zone of the high stress triaxiality region promote fatigue short crack propagation and reduce the fatigue properties of the material.

Effect of Aging Temperature on Precipitates Evolution and Mechanical Properties of GH4169 Superalloy

GH4169 is primarily strengthened through precipitation, with heat treatment serving as a crucial method for regulating the precipitates of the alloy. However, the impact of aging temperature on the microstructure and properties of GH4169 has not been thoroughly studied, hindering effective regulation of its microstructure and properties. This study systematically investigated the effects of aging temperature on the evolution of precipitates and mechanical properties of GH4169 alloy using various techniques such as OM, SEM, XRD and TEM. The results indicate that raising the aging temperature leads to an increase in the sizes of both the γ″ and γ′ phases in the alloy, as well as promoting the precipitation of δ phase at grain boundaries. Notably, the increase in γ″ phase size enhances the strength of the alloy, while the presence of δ phase is detrimental to its strength but greatly enhances its elongation. The yield strength of the alloy aged at 750 ℃ exhibits the highest yield strength, with values of 1135 MPa and 1050 MPa at room temperature and elevated temperature, respectively. As the aging temperature increases, the Portevin-Le Châtelier (PLC) effect during elevated temperature tensile tests at 650 ℃ gradually weakens. The PLC effect disappears almost completely when the aging temperature reaches 780 ℃.

Preparation and mechanical properties of ultra-high strength superalloy fibers

GH4169 superalloy fibers with ultra-high strength and ultra-fine grain (UFG) were fabricated by cold deformation and low temperature annealing, which provides a simple and effective method for preparation of UFG materials. In this study, the fibers were cold-drawn for 13 times and then cold-rolled 25 passes. Finally the annealing experiment is carried out on the cold-rolled samples. The fiber area was reduced by 97% and the grain size reaches 66 nm after cold deformation. In the subsequent annealing 450 ℃ for 30 min, the grain size was further reduced to 42 nm and the tensile strength of the fiber increases to about 2.05 GPa. The increase of the superalloy fiber energy storage and decrease of the curvature of the grain boundary lead to the low-temperature phase transformation. By controlling the annealing condition, these precipitation nanoparticles keep stable, the superalloy fibers are further refined and thus obtain higher strengthening superalloy fibers.

Evolution mechanism for a surface gradient nanostructure in GH4169 superalloy induced by an ultrasonic surface rolling process

In this study, the evolution mechanism of surface gradient nanostructure induced by the ultrasonic surface rolling process (USRP) in GH4169 superalloy was investigated. The gradient nanostructure, which was characterized using transmission electron microscopy, revealed that the repeated impacts induced by USRP produced a gradient nanostructure with a thickness of ∼330 μm at the surface of the material. Equiaxed nanograins with an average grain size of ∼30 nm were observed on the topmost surface, and the grain size gradually increased with depth. In the nanocrystallization mechanism, dislocations first formed as a result of the initial plastic strain introduced by USRP. Next, dislocation tangles and dislocation walls were formed and gave rise to the formation of low-angle and high-angle grain boundaries, which resulted in grain refinement. As plastic strain accumulated, nanoscale deformation twins were formed. The interaction between dislocations and deformation twins further refined the parent grains to produce equiaxed nanograins with high-angle grain boundaries. In addition, stacking faults were generated when the interaction between dislocations and deformation twins was initiated. A 9R structure was observed inside the nanograins at the topmost surface that significantly improved the work-hardening capacity of the superalloy by acting both as dislocation blockers and dislocation storage sites. The microhardness of the nanostructured GH4169 superalloy was improved by 67% as compared to the untreated material.

Research on Cutting Temperature of GH4169 Turning with Micro-Textured Tools

The GH4169 superalloy has the characteristics of high strength, strong thermal stability, large specific heat capacity, small thermal conductivity, etc., but it is also a typical hard-to-cut material. When cutting this material with ordinary cutting tools, the cutting force is large, and the cutting temperature is high, which leads to severe tool wear and short service life. In order to improve the performance of tools when cutting GH4169, reduce the cutting temperature, and extend the service life of the tool, micro-textured tools were used to cut GH4169 in spray cooling. The effects of micro-texture morphology and dimensional parameters on cutting temperature were analyzed. Firstly, tools with micro-textures of five different morphologies were designed near the nose on the rake face of the cemented carbide tools. The three-dimensional cutting models of the micro-textured tools with different morphologies were established by using ABAQUS, and a simulation analysis was carried out. Compared with the non-textured tools, the micro-texture morphology with the lowest cutting temperature was selected according to the simulation results of the cutting temperature. Secondly, based on the optimized morphology, tools with micro-textures of different size parameters were designed. When cutting GH4169, the cutting temperature of the tools was simulated and analyzed, and the size parameters of the micro-textured tools with the lowest cutting temperature were selected as well. Finally, the designed micro-textured tools were processed and applied in cutting experiments. The simulation model was verified in the experiments, and the influence of size parameters of micro-textures on the cutting temperature was analyzed. This paper provides a theoretical reference and basis for cutting GH4169 and the design and application of micro-textured tools.

Analysis of Tool Wear in GH4169 Material Milling Process

Nickel-based superalloy GH4169 is a material with strong mechanical properties and is difficult to process. In order to reduce tool wear during material processing and improve the workpiece surface processing quality, based on the finite element simulation software DEFORM, the influence of n, ap, and fz parameters on tool wear during carbide tool milling GH4169 was studied, and a simulation of an orthogonal experimental model was established. The prediction model of tool wear was obtained. The ultrasonic vibration milling was compared with ordinary milling, and the improvement degree of different coating materials on carbide tool wear was explored. The results showed that the ultrasonic vibration signal is helpful to reduce tool wear, improve the surface quality of the workpiece, and improve the stability of the milling process. TiAlN/TiN (WC)-composite-coated tools have good cutting performance, help to reduce tool temperature, reduce tool wear, and improve tool life.

Wear behavior of SiAlON ceramic tool and its effects during high-speed cutting

Nickel-based superalloys are widely employed in aerospace and other fields on account of excellent performance. However, the tool is easily worn out in cutting of superalloys, which will deteriorate the surface quality and lower the service life of the components. In this paper, the effect of ceramic tool wear on surface integrity during high-speed turning of superalloy GH4169 was studied. The results demonstrate that tool wear raises cutting temperature and cutting force. The wear mechanisms of the rake face of the ceramic tool are adhesive wear and oxidation wear, and the wear mechanisms of the flank face are adhesive wear, oxidation wear and abrasive wear. The enhancement effect of tool wear on thermal effect is greater than that on mechanical effect, which forms a larger tensile residual stress on the machined surface. In addition, tool wear increases the thickness of the plastic deformation layer, raising the KAM value from 0.43° to 0.63° at a cutting speed of 200 m/min.

Molecular dynamics study of the effect of rolling process on subsurface strengthening of nickel-based superalloy GH4169 plastic deformation

In this paper, the molecular dynamics (MD) method is used to establish a rolling model at the nanoscale, the same depth of rolling is rolled, and three rolling methods are used, namely, one time, two times and three times respectively. The effects of three rolling methods on the workpiece are studied, and the evolution of dislocation and defect atoms, subsurface damage, surface quality and subsurface micro-strengthening mechanism of the rolled workpiece are mainly analyzed. The results show that the dislocation density increases most significantly by one rolling, and the difficulty of material deformation is reduced by multiple rolling, with the increase of rolling times, the surface roughness increases. We found that the rolling process has a directional effect on the micro-strengthening of nickel-based single crystal alloys, and the strengthening effect is most significant in the normal direction. The subsurface strengthening effect of rolled workpiece is positively correlated with dislocation density and rolling force. Compared with the previous macro rolling test research, we observed the strengthening effect of dislocation density on rolling plastic deformation of nickel-based single crystal alloy from the microscopic level, which can provide a reference for understanding the strengthening mechanism of rolling process on nickel-based single crystal alloy and the optimization of rolling parameters.

Study on Electrolyte Dissolution Characteristics of GH4169 Super Alloy

GH4169 super alloy has a wide application in the field of aeronautics and astronautics, in order to realize the high quality and fast processing of the complex workpieces with electrochemical machining (ECM), we have studied the electrochemical dissolution characteristics of GH4169 super alloy in composite electrolyte, and explored the rule of influence on machining voltage, feed speed, electrolyte pressure for the machining gap (SG), material removal rate (MRR) and surface roughness (Ra). The results showed that under the composite electrolyte of 10%NaCl+16%NaNO3+4%NaClO3, 17.5V machining voltage and the electrolyte pressure 0.8MPa; temperature 30°C, with 1.0mm/min cathode feed speed, achieved high efficiency and high surface quality machining, surface roughness reached to 0.8μm.

Investigation of microstructure and mechanical properties of GH4169 superalloy joint produced by linear friction welding

Linear friction welding (LFW) method is a solid-state manufacturing process. In the present study, GH4169 superalloy was welded using LFW method. Macro morphology and shortening of LFW GH4169 joints were investigated to understand the effect of welding variables on the geometric parameters such as joint shape and size. Detailed microstructural and mechanical property of the welded GH4169 material were investigated to understand the effect of welding variables on the microstructure as well as mechanical properties. Compared with the GH4169 raw material, the grains of the welded joints are refined, and the tensile strength of the joints under two sets of parameters is greater than that of the raw material.

An Al2O3/Ni–Al tritium permeation barrier coating for the potential application in thorium-based molten salt reactor

The Al2O3/Ni–Al composite coating was formed on the outside surface of GH3535 superalloy by pack aluminizing and subsequent in-situ oxidation, and deuterium permeation tests were carried out to assess the tritium permeation barrier performance of the coating. Scanning Electron Microscopy (SEM) showed that the surface of Al2O3 films was dense, homogeneous, and crack-free. Transmission Electron Microscopy (TEM) photos manifested that the interface between γ-Al2O3 film and Ni–Al interlayer was distinct without micropores, and the thickness of Al2O3 film with the structure of γ-phase is approximately 80 nm. The Arrhenius equation for permeability of GH3535 was obtained as Φ=1.37·10−7·exp(−57.92(KJ mol−1)/RT) by deuterium permeation tests. The deuterium permeation reduction factor of Al2O3/Ni–Al coating kept 2–3 orders of magnitudes at a temperature from 400°C to 700°C. The D-permeation resistant performance of this coating still has the potential to be further improved.

Microstructure, texture and mechanical properties of Inconel GH4169 superalloy fabricated by wire arc additive manufacturing with arc oscillation

Arc oscillation is an important process parameter that can significantly improve the quality of the deposition. However, the mechanism and characteristics of arc oscillation on the microstructure and mechanical properties are unclear during wire arc additive manufacturing (WAAM) process. In this study, the microstructure evolution and mechanical properties of GH4169 superalloy fabricated by WAAM with arc oscillation were investigated and compared with the corresponding as deposited samples. Results showed that the tensile properties (ultimate tensile strength and yield strength) of the deposition with arc oscillation were improved with retention in elongation above 45%. With the arc oscillation, Laves phase was significantly suppressed and the content of Laves phase decreased. Further, arc oscillation induced texture randomization with lower texture intensity (10.15 mud), achieving a prominent reduction by 36.7%. From the present study, it is evident that arc oscillation during WAAM is a potential manufacturing route that can effectively tailor the microstructure.

Microstructure evolution characterization of GH4169 superalloy under ultrasonic high-frequency vibration energy

Microstructure evolution characterization of GH4169 superalloy under ultrasonic high-frequency vibration energy

Investigation on White Layer Formation in Dry High-Speed Milling of Nickel-Based Superalloy GH4169

To investigate the formation mechanism of the white layer on the machined surface during high-speed milling of nickel-based superalloy GH4169, several cutting parameters were selected for milling experiments. Energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and electron backscattered diffraction (EBSD) were employed to characterize element distribution, phase transformation, and microstructure changes in the machined surface of the superalloy and then reveal the formation mechanism of the white layer on the machined surface. The results show that the white layer appears on the machined surface of GH4169, which is dense and has no obvious structural features. The total amount of elements in the white layer remains unchanged, but the distribution of elements such as C, N, O, Fe, and Ni changes due to phase change. The formation mechanism of the white layer is due to the dynamic recovery and dynamic recrystallization caused by the heat–force coupling effect, which leads to the grain refinement of the material and thus forms the white layer. This investigation can provide theoretical support to improve the service life of the parts in actual machining.

Particle-scale computational fluid dynamics study on surface morphology of GH4169 superalloy during multi-laser powder bed fusion with low energy density

Multi-laser powder bed fusion (ML_PBF) can improve the efficiency of traditional single-laser process, but the study on the potential defects causing by the introduction of multiple lasers is still open. In this paper, the particle-scale computational fluid dynamics (CFD) method is used to simulate the molten pool behavior of nickel-based superalloy in triple-laser PBF (TL_PBF) process with low energy density. The processing parameters on the flow and temperature fields and balling phenomenon in the TL_PBF process are mainly studied. The comparison between the simulation and the experimental results shows that the proposed model is reliable and can reproduce the balling phenomenon. The simulation results show that in the competition of three melt flows, the molten track of the main laser is randomly deviated to one of the molten tracks of the auxiliary lasers due to the uneven distribution of the powder bed. In the TL_PBF process, the larger the vertical offset is, the more serious the balling phenomenon is. When the parallel offset is larger than the sum of the radii of the two adjacent lasers, the larger the parallel offset is, the more the pits generated on the surface of the molten tracks are, leading to the extreme degradation of surface quality. It can be concluded that the synchronous TL_PBF with low energy density can obtain better surface quality when the parallel offset is about the sum of the radii of two adjacent lasers. This work can be used to guide multi-laser additive manufacturing to improve products with better surface quality.

High temperature wear behavior of NiCoCrAlY-Cr2O3-AgMo coating on GH4169 superalloy

In order to determine the possible application of NiCoCrAlY-Cr2O3-AgMo (NCA) coating for the finger seal used in aeroengine, the microstructure and wear behavior against GH605 counterbody of NCA coating at 400 ℃, 500 ℃ and 600 ℃ were studied. The experimental results indicate that NCA coating exhibited low coefficient of friction (COF) and good wear resistance at high temperatures. The COF of NCA coating decreased with raising temperature and the average COF was 0.268 at 600 ℃. Wear rates of both GH605 pin and NCA coating at 600 ℃ were much lower compared to those at 400 ℃ and 500 ℃. It was found that NiMoO4 and MoO3 as effective lubricants formed a lubricant film on the worn surface of the coating at 600 ℃, which improved the tribological properties of NCA coating. In view of the excellent tribological properties of NCA coating at high temperatures, especially at 600 ℃ which is the most common operating temperature of the finger seal used in aeroengine, it is preliminarily determined that NCA coating has a possible application for the finger seal of aeroengine.

Molecular dynamics study on the effects of nanorolling processes on the properties of nickel-based superalloy GH4169

Rolling is a process that can improve the performance and roughness of machined parts and has a special economic value; therefore, the optimization of rolling process parameters is crucial to workpiece performance. In this paper, three rolling methods are used in molecular dynamics (MD) rolling simulations to study their effects on the surface of nickel-based superalloy GH4169 at the nanoscale. The surface and subsurface of the workpiece after rolling with the three different rolling methods are studied separately; in particular, a comparative analysis of the dislocation generation and movement on the subsurface, crystal defect evolution, and surface roughness was performed. The results show that the increase in subsurface dislocation density by average rolling has a significant influence on the work hardening effect, and the average roughness of the rolled groove surface is the lowest. This is an important reference for the optimization of the parameters of actual rolling processes.