GH4169 Alloy Research Articles

Evidence of microstructural evolution linked to non-monotonic distribution of micromechanical properties induced by shot peening

The residual stress field induced by surface strengthening processes such as mechanical shot peening and other forms of plastic deformation does not generally exhibit a simple “monotonic” distribution trend. Some researchers have analyzed this fact from a mechanical perspective based on Hertz theory. However, the micro/nano-scale microstructural changes corresponding to the distribution of residual stress fields still appear to be lacking. In this study, we focused on a widely used material in aviation manufacturing, namely nickel-based superalloy GH4169, as our experimental material. We subjected GH4169 alloy to mechanical strengthening treatment using a shot peening intensity of 0.25 mmA, followed by quantitative testing of micromechanical performance indicators such as microhardness and residual stress. To thoroughly investigate the relationship between micromechanical properties and microstructure changes, we utilized transmission electron microscopy (TEM) to observe and analyze shot-peened materials at different depths. Our findings revealed that the most severe microstructural distortion induced by mechanical shot peening in GH4169 alloy was likely to occur within a depth range of 25 to 75 µm. This observation aligns with the actual phenomenon that the maximum microhardness and maximum residual compressive stress did not manifest on the outermost surface of the material. By presenting a detailed analysis of deformation defects such as dislocations, stacking faults, and twinning in different depths of mechanically strengthened layers, our study contributes to a deeper understanding and practical application of post-processing technologies based on plastic deformation.

Direct observation and characterization of a novel long period stacking ordered phase in GH4169 alloy

As is widely recognized, the Long Period Stacking Ordered (LPSO) phase is an important strengthening phase in the rare earth magnesium alloys. The LPSO phase not only enhances the strength of the alloy, but also improves its plasticity, thereby effectively addressing the strength-ductility trade-off phenomenon. Therefore, the preparation of metallic materials containing LPSO phase provides a new idea for designing a new generation of high-strength and high-toughness alloys. In present study, A novel nano-sized LPSO phase is observed and characterized for the first time in GH4169 nickel-based alloy. The results show that the stacking sequence of the LPSO phase is ABCBCBA, which indicates that this LPSO phase has a 6H structure. Meanwhile, the orientation relationships between LPSO phase and the Ni matrix are (11–1)γ//(0006)LPSO and [011]γ//[2-1-10]LPSO.

Corrosion Behavior of Pre-oxidized GH4169 Alloy with Solid NaCl Deposited in a Wet Oxygen Flow at 600 °C

Corrosion Behavior of Pre-oxidized GH4169 Alloy with Solid NaCl Deposited in a Wet Oxygen Flow at 600 °C

A novel two-scale nonlinear damage accumulation model for vibration fatigue life prediction

Vibration is the main factor causing high cycle fatigue. The macro-response stress and strain of the structure under the excitation of vibration load are generally in the elastic stage. However, fatigue failure still occurs due to long-term cyclic load, which is unexplainable by the macro-plastic accumulation method. Therefore, a two-scale nonlinear damage accumulation model is proposed for vibration fatigue based on the physical characteristics of multi-scale fatigue damage evolution. In this model, two-scale elastic-plastic constitutive equations based on the equivalent inclusion theory are built, and a two-stage damage accumulation strategy with two critical damages is designed. A resonance fatigue life prediction algorithm is established based on the proposed model, and a validation test is carried out using the cantilever beam made of GH4169 alloy. The results show that the deviation between the vibration fatigue life prediction and test results is within a scatter band of factor 2, indicating that the two-scale nonlinear damage accumulation model is effective in the vibration fatigue region.

Quality control of NiCr-Cr3C2-hBN@Ni coating on thin-walled GH4169 alloy surface prepared by plasma spraying

As equipment lightweight trends progress, thin-walled structures have seen extensive application in critical aerospace components. Nevertheless, the aero-engine tail nozzle flaps are exposed to the harsh operating conditions of high-temperature friction, so there is an urgent requirement to prepare wear-resistant, self-lubricating coatings with a wide range of temperatures for their protection. Due to the poor rigidity and weak strength of thin-walled workpieces and complex forms of structural stresses, the processing is extremely difficult. In order to solve the thermal deformation problem of coating workpieces prepared by spraying on the surface of thin-walled workpieces, the effects of spraying path, cooling airflow, and spraying interval on the thermal force field of thin-walled workpieces to prepare NiCr-Cr3C2-hBN@Ni coating are investigated in this study using finite element simulation. As a result, the deformation and stress of thin-walled workpieces can be minimized by adding back-side cooling air during the spraying process and moving the cooling air with the gun in a set interval, with the maximum warpage and maximum stress being less than 2.366 mm and 0.177 GPa, respectively. During the spraying process by simulating the optimum spraying process, no significant warpage of the substrate occurred and the coating was sprayed with uniform thickness. Typically, the thickness error rate is 16.7 %, and the coating hardness reaches 15–20 GPa, with excellent tribological properties in a wear rate of 10−5 mm3·N−1·m−1 and 10−6 mm3·N−1·m−1, which protects the workpiece effectively.

Effect of annealing temperature on microstructure and properties of the microtubes for GH4169 alloy

The effects of annealing temperature on the recrystallization and grain boundary distribution characteristic for the drawn microtube of GH4169 alloy were studied by scanning electron microscope (SEM) equipped with an electron backscatter diffraction (EBSD) analysis system and transmission electron microscopy (TEM). The results demonstrated that at an annealing temperature of 850 °C, only a small proportion of recrystallization for the microtube underwent. As the annealing temperature increased, the proportion of recrystallization also increased. Specifically, at 900 °C, the proportion reached 95.8%, indicating complete recrystallization. Fine recrystallization grains were obtained with an average grain size of 4.73 μm. As the annealing temperature is above 900 °C, the microtube also undergo complete recrystallization, and the grains grow up gradually. At 1000 °C, the average grain size grows to 7.42 μm. The results also revealed that with the annealing temperature increasing, the proportion of Σ 3 grain boundary of the microtube was rising. The proportion of Σ 3 grain boundary increased from 30.1% to 34.2% with the annealing temperature increased from 900 °C to 1000 °C. Moreover, as the annealing temperature increased from 850 °C to 1000 °C, the room temperature tensile strength of the tube decreased from 1323 MPa to 965 MPa, the yield strength decreased from 1054 MPa to 523 MPa, and the fracture elongation increased from 10.2% to 31.2%.

Probabilistic notch fatigue assessment under size effect using micromechanics-based critical distance theory

Geometrical discontinuities are inevitable in engineering structures due to various functional requirements, which often yield complex stress–strain state and thereby significantly impact their fatigue performances. In this study, crystal plasticity theory is coupled with traditional critical distance theory for notch effect modelling considering microstructural heterogeneity. Specifically, microstructural and geometrical size effects on critical distance and fatigue performance are studied based on Sub-modelling approach. In addition, critical distance theory is coupled with Weibull distribution for probabilistic fatigue life evaluation of notched components. The developed method is verified and compared by using experimental data of GH4169 alloy. The findings demonstrate that the evaluated P-S-N curves exhibit strong agreement with tested data and geometrical size effect poses larger influence than the grain size effect on critical distance and fatigue life.

Strengthening mechanism and forming control of linear friction welded GH4169 alloy joints

Numerical simulation and experimental research on Linear Friction Welding (LFW) for GH4169 superalloy were carried out. Based on the joint microstructure and mechanical properties, a suitable welding process was determined, which provided an important theoretical basis for the manufacture and repair of aeroengine components such as the superalloy blisk. The results show that the joint strain rate gradually increases with the increase of welding frequency, and the deformation resistance of the thermoplastic metal increases in the welding process, resulting in the interface thermoplastic metal not being extruded in time to form a flash, so the joint shortening amount gradually decreases. The thermoplastic metal in the center of the welding surface is kept at high welding temperature for a long time, resulting in the decrease of the joint strength. The microhardness of the joint shows a “W” distribution perpendicular to the weld, and most of the joints break in the Thermo-Mechanically Affected Zone (TMAZ) with high tensile strength and low elongation. When the welding area is increased without changing the aspect ratio of the welding surface, the interface peak temperature increases gradually, and the joint shortening amount decreases with the increase of the welding interface size.

Constraints-related microscopic fatigue crack propagation behaviour of polycrystalline alloys

Based on the microscopic polycrystalline fatigue crack propagation (MPFCP) model, the MPFCP behaviours of GH4169 alloy under different micro-notch depths and lengths (constraints) were studied from aspects of MPFCP path, MPFCP rate and stress distribution. The influences of the initial crack angle on MPFCP behaviour were further explored. It was observed that the grain boundary, the grain size and the stress state were different during crack propagation under different constraints, resulting in different MPFCP paths. The MPFCP path was straighter under high constraints, and the MPFCP rate was related to the micro-notch size and the loading direction. The crack tip needed more stress accumulation at low constraints than under high constraints to ensure smooth MPFCP behaviour. The influence of the initial crack angle on the MPFCP path was mainly reflected in the grain interior where the initial crack was located. The initial crack angle had a greater influence on the MPFCP rate than on the MPFCP path.

Comparative investigation on microstructure and mechanical properties of GH4169 superalloy after laser shock peening with and without coating

To cater to the diverse requirements of industrial applications, it is crucial to conduct a comprehensive investigation into the influence of laser shock peening (LSP) with and without coating (LSPwC) on the microstructure and mechanical properties of materials. This study employs various methods to compare and analyze the effects of LSP and LSPwC on the microstructure and mechanical properties of GH4169 alloy. One notable contrast between LSP and LSPwC lies in the formation of oxide layers and microcracks on the surface of LSPwC-treated samples. Tensile tests subsequently reveal that LSP enhances the tensile strength, whereas LSPwC diminishes it. The reduced strength in LSPwC-treated samples can mostly be attributed to the oxide layer and microcracks resulting from laser-induced heat, as determined through failure analysis. After the removal of the oxide layer, the strength undergoes a significant improvement with LSPwC treatment, surpassing both the strength and ductility levels observed in GH4169 treated with LSP alone. These improvements can be attributed to a combined effect involving the removal of the oxide layer and microcracks, the formation of a gradient hardened layer, and the presence of dense slip bands.

Difference of properties after heat treatment between GH4169 and GH3536 alloys fabricated by direct energy deposition

In this study, thin-walled parts of GH4169 and GH3536 superalloys were prepared using the direct energy deposition (DED) method, respectively. The results revealed that solution aging treatment was effective in eliminating the boundary of the molten pool and refining the grain structure to some extent. Subsequently, the Laves phase redissolved in the γ matrix, releasing Nb element. This was followed by the formation of γ′, γ″, and δ phases, which effectively improved the yield strength and tensile strength of the GH4169 alloy after high temperature heat treatment. In the case of the GH3536 alloy, heat treatment caused a change in microstructure from columnar crystals to larger equiaxed crystals. Additionally, chain carbides precipitated at the grain boundaries, which increased the elongation after fracture but decreased the yield strength and tensile strength to some extent. Following solid solution aging treatment, the ultimate tensile strength of GH4169 deposited parts exhibited a 27.7% increase in the deposition direction and a 15.6% increase in the laser scanning direction. Conversely, the tensile strength of GH3536 showed minimal variations, but the elongation in both directions experienced notable improvements, rising by 22% and 20.7%, respectively. Solution aging treatment further eliminated the mechanical anisotropy of the two superalloys due to the inhomogeneity of microstructure and grains, as well as the existence of molten pool boundaries and grain boundary segregation. Furthermore, the microstructure and mechanical properties of GH3536 alloy were found to be better than those of GH4169 alloy, both before and after aging.

Test Data Evaluation of Very High Cycle Fatigue Based on Maximum Likelihood Method

The very high cycle fatigue tests of TC4 alloy were accomplished through ultrasonic fatigue experiment which were conducted on the ultrasonic fatigue testing system at frequency range of 20000 ±1000 Hz. In contrast to the commonly used Basquin model, a Maximum Likelihood Method to fit the three-parameter nonlinear model was used to verify the adaptability in very high cycle fatigue regime. These two methods were used to estimate S-N curves of three types of materials which were TC4 alloy, GH4169 alloy and TC17 alloy in the very high cycle fatigue regime and the results were compared with test data. The evaluation result of the MLM model based on the three-parameter nonlinear model shows a good agreement with test data. The mean and variance of relative error of the MLM model are less than those of the Basquin model, providing a suitable evaluation method for predicting very high cycle fatigue limit which often has higher scatter.

Effect of Powder Recycling on Microstructure and Tensile Behavior of GH4169 Alloy Fabricated by Selective Laser Melting (Invited)

Effect of Powder Recycling on Microstructure and Tensile Behavior of GH4169 Alloy Fabricated by Selective Laser Melting (Invited)

The hydrogen embrittlement mechanisms and hydrogen induced cracking process of selective laser-melted GH4169

This study investigates the hydrogen embrittlement sensitivity and brittle failure mechanism of selective laser-melted GH4169 alloy under hydrogen precharged conditions. Fractographic analysis reveals that a high concentration of hydrogen facilitates the formation of small quasi-cleavage steps near the fracture edge. Additionally, hydrogen promotes the migration of {111} planar dislocations, resulting in shear failure of the δ phases and the nucleation of microvoids. These microvoids then propagate, leading to the development of hydrogen-assisted transgranular cracks along the dislocation slip bands. The deformation behaviors of the δ and γ" phases were characterized using high-resolution transmission electron microscopy.

Temperature dependence in tensile properties and deformation behavior of GH4169 alloy

Temperature dependence in tensile properties and deformation behavior of GH4169 alloy

Study on Microstructure of Pack-Borided GH4169 Alloy

The structure of the solid pack-boriding layer of nickel-based alloy is studied in this paper. The nickel-based alloy GH4169 was subjected to pack-boriding treatment at 850 °C and 950 °C, and the structure of the alloy boriding layer was studied. After the boriding treatment, a relatively continuous and uniform boriding layer was formed on the surface, which was mainly composed of nickel borides and chromium borides. The sample formed a layered structure of a boriding layer, diffusion zone, and substrate. After boriding treatment, Cr migrated to the surface to form CrB, Cr5B3, and Cr2B chromium borides, while Ni migrated to the lower part of the boriding layer to form Ni2B and Ni3B nickel borides.

Improving the tribological properties of ZrO2(Y2O3)-graphite composites at high temperature through three-dimensional continuous structure

ZrO2(Y2O3)-graphite composites with a three-dimensional (3D) continuous structure were prepared by using a core-shell design of graphite and ZrO2(Y2O3). The effect of structure on the friction-reducing and anti-wear mechanisms from room temperature to 700 °C was investigated. During high-temperature friction, abrasive wear and brittle fracture are the main wear mechanisms for ZrO2(Y2O3)-graphite composites with homogeneous composition. For the composites with 3D structure, the continuous ZrO2 matrix with high load-carrying capacity and the formation of a dense friction layer with self-lubricating and thermal oxidation resistance improve the tribological properties significantly, reducing the coefficient of friction by about 10% and the wear rate by nearly two orders of magnitude when coupled with GH4169 alloys at 600 °C.

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

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

Laser directed energy deposition/milling hybrid additive manufacturing of thin-walled GH4169 alloy: Effect of processing strategy on its microstructure and mechanical properties

Laser directed energy deposition (LDED)/milling hybrid manufacturing process was utilized to produce thin-walled GH4169 parts for the first time. The impact of processing strategy, including varied milling rounds and building heights, on the printability, microstructure, and mechanical properties of the GH4169 parts were investigated. Increasing the number of milling rounds within a certain height along the build direction reduced the distance between adjacent hybrid-processed interfaces. Base on a comparative study of the thermal histories of LDED and LDED/milling processes, it was found that the microstructure at the hybrid-processed interfaces experienced less heat accumulation and fewer heating/cooling cycles. Therefore, GH4169 parts after milling exhibited a lower proportion of the Laves phase area with refined sizes and greater interdendritic Nb segregation than those produced by LDED alone. With increased milling rounds, the ultimate tensile strength and yield strength of the thin-walled GH4169 part fabricated using the hybrid process increased from 777.0 MPa to 823.0 MPa and from 506.0 MPa to 538.0 MPa, respectively, while the elongation decreased from 35.1% to 27.2%. These effects can be attributed to an increase in milling round within a constant forming distance, resulting in higher stiffness of the fabricated thin-walled GH4169 part. Finally, a thin-walled GH4169 blade with excellent dimensional accuracy and surface finish was successfully produced using the LDED/milling hybrid process, demonstrating the potential applicability of this process to nickel-based alloys.

Crystallization Behavior of a Ti-Zr Alloy with GH4169 Alloy Powder as an Additive Prepared via Low-Temperature Liquid-Phase Spark Plasma Sintering

Crystallization Behavior of a Ti-Zr Alloy with GH4169 Alloy Powder as an Additive Prepared via Low-Temperature Liquid-Phase Spark Plasma Sintering