Nickel-based Superalloy Research Articles

Achieving ultra-high efficiency in directed energy deposition of pure copper on Inconel 718 substrate with a 3500 W blue laser

High efficiency deposition of highly reflective copper on a nickel-based superalloy substrate presents a significant challenge. This study first used a 3500 W high-power and 7.5 mm2 large-spot blue laser in Directed Energy Deposition, and successfully deposited copper on an Inconel 718 substrate. The process exhibited stability, with no significant cracks or pores observed. To the best of our knowledge, we have achieved the highest cladding efficiency of 62.84 mm2/s in the current cladding of copper. The interface between copper and Inconel 718 displayed a smooth composition transition at 3500 W, and the width reached 418 μm. The cladding layer displayed a columnar dendritic morphology at the bottom, gradually transitioning to equiaxed dendrites at the top. Dendrites enriched in elements found in Inconel 718 solidified, while Cu from the powder mainly solidified in the interdendritic region. The utilization of a high-power, large-spot blue laser offers a promising process for the efficient fabrication of large Cu/Ni dissimilar structural components.

Parameter automatic optimization strategy for laser powder bed fusion using neural network infrared radiation intensity prediction model

Conventional scanning approaches with fixed laser parameters are prone to causing localized defects and in-homogeneous performance when forming parts with complicated geometries using the laser powder bed fusion (LPBF) process. While online monitoring of the forming process using thermal cameras allows the identification of abnormal infrared radiation intensity values of the scanning line to pinpoint regions of potential defects, it fails to proactively prevent defects from occurring. To solve this problem, this study constructed a back propagation (BP) neural network to predict the infrared radiation intensity of the current layer before scanning. In the meantime, this study designed a parameter optimization algorithm to adjust the local scanning parameters with a view to avoiding defects and thus enhancing the performance consistency of the formed parts. This study drew on the idea of the divide-and-conquer method to divide the parts into multiple units for data acquisition by thermal camera, and has collected 500,000 pieces of experimental data through 15 experiments. By utilizing these data, this study trained a BP neural network to predict the infrared radiation intensity, and its mean absolute error (MAE) of the prediction results was 25, the coefficient of determination (R2) was 0.708, and the F1 score (abnormal radiation intensity identification and classification) was 0.802. Subsequently, the study optimized the scanning parameters of the unit by using particle swarm optimization (PSO), and performed practical application and validation on spherical gear parts of 316 L stainless steel and blade parts of DZ125 nickel-based superalloy. Findings indicated that the automatic optimization strategy can effectively prevent abnormal infrared radiation intensity values during the scanning process and enhance the performance consistency of the LPBF process for complicated parts in both different materials and structures.

Effects of sub-solvus ageing on the tensile and creep properties of a new cast nickel-based superalloy

For nickel-based superalloys with medium volume-fraction γʹ phase (20 %–40 %), dual or multi-stage aging treatments are usually conducted to generate a microstructure containing the multimodal distribution of γʹ for a balance of strength and plasticity. In the present study, the microstructure and high-temperature properties of a novel cast nickel-based superalloy K4800 were investigated after being subjected to three heat treatments (HT) procedures, namely HT1: 1180 °C/4 h + 1090 °C/2 h + 800 °C/16 h, HT2: 1180 °C/4 h + 1060 °C/2 h + 800 °C/16 h and HT3: 1180 °C/4 h + 800 °C/16 h. It was found that the sub-solvus aging treatments at 1090 and 1060 °C precipitated sub-micron-sized (∼300 nm) primary γʹ phase which enhanced the ductility during 800 °C tensile (the total elongation of T1, T2, and T3 samples were 6.75 %, 7.3 %, and 3.25 %, respectively) without evidently impairing the strength. After careful microstructure observation and deformation mechanism analysis, the enhancement of elongation was rationalized that the precipitation of the sub-micron-sized primary γʹ phase decreased the volume-fraction and size of the nanometer-sized γʹ phase which was precipitated at 800 °C, and simultaneously, promoted the dislocation movement by suppressing the non-planar slip. However, an excessive amount of the sub-micron-sized primary γʹ phase led to a faster ripening process of the nanometer-sized γʹ during creep, which decreased the creep life at 800 °C/430 MPa (T1: 125 h, T2: 199 h, and T3: 198 h). Based on this, we monitored the number density of nanometer-sized γʹ phase coexisting with different amounts of large γʹ during creep. An area fraction less than 7 % of the sub-micron-sized γʹ phase was considered to have little detrimental effect on the creep life of K4800 alloy, which corresponded to a sub-solvus temperature range about 1080–1090 °C.

Damage critical transformation mechanisms in milling nickel-based superalloy honeycomb composites using different tool structures

Nickel-based superalloy honeycomb composite (NBSHC) has been developed into an indispensable material for aerospace and defense industries due to light weight, high temperature resistance and extremely high specific strength. Nevertheless, NBSHC is particularly difficult to machine, combing superalloy with thin-walled structure properties, and is prone to damage such as burr, tearing and core deformation. To realize the efficient and low-damage processing of NBSHC, the different tool structures were used during the milling NBSHC experiments under ice-freeing conditions. The material removal mechanisms of different cutters were revealed based on the micro and macro view, and verified by the experiment results. Then, the cutting force and damage behavior of different tools under different parameters during milling NBSHC process were analyzed. For the first time, the damages critical transformation mechanisms during milling NBSHC process were summarized based on above investigations. Results showed that: Since the contact area between saw blade or disc cutters and NBSHC workpiece was a surface, and the in-plane force was small. The qualities of NBSHC machined by saw blade and disc cutters were excellent. Due to the large in-plane force, discontinuity cutting and tearing from removed material, the quality of NBSHC machined by end-milling cutter was extremely terrible. Large cutting force, large contact volume, frequent impacts induced by discontinuity cutting and tearing from the removed material sharply increased the plastic deformation, thus deteriorating the quality of NBSHC and contributing to the transformation of slight damages into severe damages. This work provided significant theories and guidelines for efficient and low-damage machining of NBSHC in aerospace and defense fields.

Effect of heat treatment on the microstructural evolution and mechanical property of nickel-based superalloy K447A manufactured by Powder Bed Fusion Laser Beam (PBF-LB)

Nickel-based superalloy is an indispensable material in the aerospace industry. With the development of metal additive manufacturing theory, the additive manufacturing technology will further expand and accelerate the application of nickel-based superalloy in the aerospace industry. In this study, nickel-base superalloy K447A with high volume fraction γ′ strengthening phase was formed by Powder Bed Fusion Laser Beam (PBF-LB), and the effect of different heat treatments on the microstructure and mechanical properties of K447A alloy was analyzed. In the as-built sample, cellular structures consisting of dense dislocation tangles were formed. Elongated columnar grains grew preferentially along <001> direction. Fine MC precipitates segregated at the boundary of cellular structure. The process of grains recovery (1185 °C), grains recrystallization (1260 °C), and grains rapid growth (1300 °C) of K447A alloy during heat treatment could be observed. Many stable and homogeneous cubic γ′ phases precipitated from the K447A alloy after high-temperature heat treatment. When the heat treatment was increased to 1300 °C, MC precipitates dissolved and the number of carbides in the ST-1300 sample was significantly reduced. The average microhardness and ultimate tensile strength of the as-built sample were 407 HV and 527 MPa, respectively. When the heat temperature reached 1260 °C, the microhardness and ultimate tensile strength reached the maximum. When the heat temperature was raised to 1300 °C, the ultimate tensile strength decreased sharply, but the elongation and the toughness increased significantly. Based on the above results, the relationship between microstructure, mechanical properties, and deformation mechanism was discussed.

Increased long-term stress-rupture life of a nickel-based superalloy with relatively homogeneous duplex grain size distributions

Effect of duplex grain size distributions on long-term stress-rupture life of Nimonic 80A had been investigated. Non-homogeneous duplex grain size distributions greatly reduce stress-rupture life. Regional distribution of coarse grains is not good for acquiring high stress-rupture life, the formation of micro-void and propagation of cracking can easily occur at coarse grain boundary especially when plate-like Cr23C6 precipitates at grain boundary. But relatively homogeneous duplex grain size distributions are of great significance in improving stress-rupture life, the samples even possess the life value up to more than 13000 h especially when hardly any plate-like Cr23C6 precipitates at grain boundaries. Slightly increased Ti/Al ratio from 1.65 to 1.80 is also beneficial to obtain a significantly longer stress-rupture life value. The γ′ phase is very stable and always exhibits a coherent orientation relationship with γ on {100} and {111} atomic planes. The grain boundary cracking will not easily appear at the early stage of stress-rupture test in the samples with relatively homogeneous grain size distribution, the coarse and adjacent fine grains possess better deformation adjustability, and the grain boundary cracking is apparently wider and the number of cracking is also getting more after fracture for the sample with longer stress-rupture life.

An Experiment Study on Surface Topography of GH4169 Assisted by Ultrasonic Elliptical Vibration Ultra-Precision Turning

Nickel-based superalloys (GH4169) are a typical difficult-to-machine material with poor thermal conductivity and severe work hardening. They are also prone to poor surface quality, severe tool wear, and poor machinability, which affect their performance. In this paper, an experimental study of GH4169 ultrasonic elliptical vibratory ultra-precision cutting was carried out. The experimental results show that ultrasonic elliptical vibratory cutting (UEVC) significantly reduces surface roughness and improves surface quality compared to conventional cutting (CC). The effects of cutting parameters such as cutting speed, feed rate, cutting depth, ultrasonic amplitude, and tool nose radius on the surface roughness of GH4169 workpieces were further investigated in UEVC. Based on the analysis of the experimental data, the optimal combination of parameters for GH4169 ultrasonic elliptical vibration ultra-precision cutting was determined: cutting speed of 3 m/min, feed rate of 16 μm/rev, cutting depth of 2 μm, ultrasonic amplitude of Ay = 3.0 μm, Az = 0.8 μm, and a tool nose radius of 0.8 mm. This parameter combination improves the machining quality of GH4169 and provides a valuable reference for the subsequent development of ultrasonic elliptical vibratory cutting for other difficult-to-machine materials.

Mechanical behavior and underlying mechanism of nickel-based superalloy during coupling electrical pulse and ultrasonic treatment

Coupling electric pulse and ultrasonic treatment (CEPUT) is a multi-energy field-assisted forming technology that can improve the forming efficiency of materials. The current research focused on the surface modification of materials by CEPUT, lacking the explanation of its coupling mechanism. In this study, Inconel 718 was adopted as the research object to observe the mechanical behavior and microstructure after CEPUT uniaxial tension experiment. The deformation tendency of grain under coupling multi-energy field was described by analyzing the texture evolution and dislocation morphology. The coupling mechanism of ultrasonic vibration and pulsed current was revealed in CEPUT. The experimental results revealed that there was a nonlinear relationship between the increase of flow stress softening efficiency and the increase of ultrasonic energy density and current density. This phenomenon was the macroscopic manifestation of interference between initial ultrasonic vibration and vibration after energy attenuation, which was related to dislocation slip and recrystallization under coupled multi-field. In addition, more efficient path of dislocation slip was demonstrated through the CEPUT. Among them, ultrasonic vibration caused local resistance to rise at the dislocation source and dislocation pile-up, which strengthened the local Joule heating effect; while the pulsed current reduced the activation energy required for dislocation slip near the waning points. This effectively reduced the resistance of dislocation motion near the pinning point, promoting the chance of dislocation crossing and annihilation. Meanwhile, the high temperature caused by pulsed current and local high strain caused by ultrasonic vibration were more favorable to dynamic recrystallization, and the change of grain orientation was more active. The texture strength and grain orientation of the matrix can be effectively controlled by adjusting the input power of ultrasonic vibration and pulsed current.

Effects of Co and Nb on the Crack of Additive Manufacturing Nickel-Based Superalloys

Effects of Co and Nb on the Crack of Additive Manufacturing Nickel-Based Superalloys

Flame-retardant mechanism for platinum coating of nickel-based superalloy

This study presents a novel approach for enhancing combustion resistance of a nickel-based superalloy by the application of platinum coating. The combustion behaviors of Pt-coated samples were studied using the promoted-ignition combustion standard test at 7–25 MPa (≥ 99.5 % oxygen). In contrast to uncoated samples, the Pt-coated samples exhibit notable improvements in resistance to burning, as demonstrated by reduced combustion length and rate. The underlying mechanism can be ascribed to two factors. One notable effect of the Pt coating is the influence on diffusion and distribution of combustion elements. In particular, it impedes the oxidation and combustion of Al with the highest combustion heat. The second one is the comparatively lower heat released by the Pt-coated samples throughout the combustion process, as well as the substantial capacity to reduce the temperature at which combustion ceases. The aforementioned discoveries offer new perspectives on enhancing the compatibility of metal materials with oxygen.

Creep cavities and carbide evolution in interrupted creep conditions along P91 steel of dissimilar weld joint

The creep behaviour of dissimilar weld joint of 316LN SS-P91 steel when subjected to lower applied stresses (below 100 MPa) generally fails in a Type-IV pattern. The dissimilar weld joint was welded through shielded metal arc welding (SMAW) process with INCONEL as electrode, a nickel-based superalloy. An interrupted creep test was carried out at creep condition of 80 MPa −600 °C temperature. Interruption was done at two stages of creep, i.e. (a) mid of secondary and (b) start of tertiary. Microstructural evolution with respect to the hardness variation along various regions of P91 steel at interrupted and the failed specimen was done. A coarsening of hierarchical boundaries and M23C6 carbides was observed along HAZ region that has resulted with respect to time and temperature.

Comparative study on microstructure, mechanical and high temperature oxidation resistant behaviors of SLM IN718 superalloy before and after heat treatment

The microstructure, phase transformation behavior, heat treatment effects, and their impacts on the mechanical properties and high-temperature oxidation resistance of IN718 nickel-based superalloy processed by selective laser melting (SLM) both before and after heat treatment was systematically investigated. The heat treatment process involved a two-step aging at 720 °C for 8 h plus 620 °C for 10 h with a controlled slow cooling rate of 10 °C/min. Through the comprehensive use of scanning electron microscopy (SEM), X-ray diffraction (XRD), electron backscattering diffraction (EBSD), and transmission electron microscopy (TEM), the evolution of the microstructure and its mechanism of influence on material properties were revealed. The study identified the formation of γ phase, γ′ phase, γ'' phase, δ phase, and Laves phase during the SLM forming process. Heat treatment played a key role in improving the microstructure and properties of the SLM-processed alloy, with experimental results showing that the mechanical performance and high-temperature oxidation resistance were significantly enhanced after heat treatment. Specifically, the material after heat treatment exhibited a yield strength of 1472 MPa, a tensile strength of 1608 MPa, and an elongation of 9.2%, which represented increases of 76.5%, 38.4%, and 16.5% respectively, compared to the as-printed alloy. Moreover, the oxidation resistance at 1000 °C of the heat-treated samples improved significantly, with weight loss reduced from −0.17 mg/cm2 before heat treatment to −0.15 mg/cm2. Microstructural analysis further indicated that heat treatment optimized the crystal orientation, promoted the formation of more precipitated phases and reduced defects, thereby enhancing the overall performance of the material. This work provides significant scientific insights into understanding and optimizing the IN718 nickel-based superalloy processed by SLM, demonstrating the crucial role of heat treatment in improving its microstructure and properties.

Effect of power density on microstructure characterization and fatigue behavior of laser shock peened Rene-80 Ni-based superalloy

The microstructure plays a crucial role in determining the mechanical properties and performance of materials, particularly in high-strength alloys such as Rene-80. This study focuses on the microstructure characterization of Rene-80 nickel-based superalloy after undergoing Laser Shock Peening (LSP), an advanced surface treatment technique imparting beneficial residual stresses and improving fatigue life. The primary objective of this research is to investigate how varying power densities during the LSP process affect the microstructure of the Rene-80 superalloy. The power density in LSP is a critical parameter that influences the intensity of shock waves imparted onto the material’s surface, consequently impacting the microstructure. Through advanced microscopy techniques and analysis, the study explores the resulting microstructural changes, including surface roughness, dislocation density, and the presence of defects like dislocations and dislocation cells. These alterations are vital indicators of the material’s mechanical properties, such as tensile and fatigue strength. LSP samples were characterized using various techniques, including field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and X-ray diffraction (XRD) analysis. Additionally, the mechanical performance of the samples was assessed through low-cycle fatigue tests and tensile tests, both conducted before and after LSP treatment. The optimal power density for Laser Shock Peening is determined to be 2.5 HEL. At this power density, the shock wave generated does not create a molten layer on the surface but accumulates defects, resulting in maximum compressive residual stress at the surface. LSP induces intense plastic deformation in the sample, distorting γ’ precipitates. Higher power densities lead to the formation of cross-linked sets of slip bands, highlighting defect slip as the main mechanism of plastic deformation in the LSP process. Understanding these effects is essential for optimizing the LSP process parameters to achieve desired mechanical properties and enhance the performance and longevity of components made from Rene-80 nickel-based superalloy in high-stress applications. It was found that the fatigue life of the samples increased by 500% and optimizing the effect of power density on the LSP process led to an improvement in the fatigue life of the Rene 80 samples.

Molecular dynamics simulation of tensile properties of Nickel-based superalloy with temperature and Co

Ni(Nickel)-based superalloys are used as indispensable materials for turbine blades in aero-engines because of their excellent creep, fatigue and corrosion resistance. Co(Cobalt), as one of the new key elements in Ni-based superalloys, has attracted extensive attention in Ni-based superalloys field. However, the effect mechanism of Co on Ni-based superalloys is still controversial. To solve this problem, tensile properties and microstructure of Ni-based superalloys doped with or without Co (5 %) have been investigated through molecular dynamics simulation, and the joint impact of temperature and Co on the superalloy mechanical properties has also been analyzed. The findings indicate that 5 % Co doping reduces the yield stress, yield strain, and elastic modulus of the structure, while increasing the flow stress at 300 K–600 K; however, the advantage decreases at 900 K and disappears completely at 1200 K. This can be explained that Co doping leads to more slippage of stacking faults in the elastic stage and hinders the loop formation of dislocations at 300 K–600 K, while more Stair-rod dislocations occur in the plastic stage. These effects disappear at 900 K–1200 K.

Plastic deformation delocalization at cryogenic temperatures in a nickel-based superalloy

A nickel-based superalloy is examined during monotonic deformation from ambient to cryogenic temperatures, reaching as low as liquid helium temperature. A detailed multimodal analysis of the microstructure and plasticity is conducted to discern changes in deformation mechanisms and plastic deformation localization under cryogenic conditions. This study employs high-resolution digital image correlation and transmission electron microscopy to identify the deformation mechanisms and understand their influence on plastic deformation localization as the temperature varies. At cryogenic temperatures, unusual plastic deformation localization processes are observed, attributed to the competing activation of a range of deformation processes. Furthermore, a mechanism of slip delocalization, i.e., local plastic deformation homogenization through closely spaced slip, is noted at these extreme temperatures. Ultimately, the impact of the microstructure is identified across the temperature range, from room to cryogenic temperatures.

Additive manufacturing Hastelloy X with enhanced properties by optimizing strategies

Optimizing laser additive manufacturing (LAM) scanning strategies is crucial for improving the quality and performance of metallic parts formed by laser powder bed fusion (LPBF), particularly for alloys with high susceptibility to cracking. However, there is limited research on the effects of unidirectional and unidirectional-remelting strategies on the temperature field and forming quality of LPBF-manufactured Hastelloy X (HX), a nickel-based superalloy highly susceptible to cracking. This study focused on the temperature field, surface roughness, crack occurrence, and mechanical and thermal properties of LPBF-manufactured HX, employing four different laser scanning strategies: chessboard, bidirectional, unidirectional, and unidirectional-remelting. Specimens manufactured using the unidirectional-remelting strategy showed the lowest surface roughness (4.12 μm), highest density (99.64 %), superior tensile properties (tensile strength of 1068.29 MPa and elongation of 16.82 %), lowest coefficient of friction (0.65), highest thermal conductivity (9.77 W/m·K), and lowest specific heat capacity (0.38 J/g/K) compared to other strategies. This can be attributed to the unidirectional-remelting strategy resulting in specimens with equiaxed grains, the most uniform elemental and residual stress distributions, as well as the strongest grain boundary and dislocation strengthening. Moreover, it exhibited compressive residual stress in HX specimens. Interestingly, the tensile properties of the unidirectional-formed HX parts ranked second only to the unidirectional-remelting formed parts, owing to the efficacy of texture strengthening. These findings provide insights into the underlying mechanisms of optimizing laser scanning strategies for LPBF fabrication of HX, offering essential references for the LAM of crack-sensitive alloys, especially nickel-based superalloys.

Study of Serrated Boundary Micromechanics During Micropillar Compression in Nickel-Based Superalloy

Study of Serrated Boundary Micromechanics During Micropillar Compression in Nickel-Based Superalloy

Surface morphology and integrity research of ultrasonic-assisted milling of cast superalloy K4169

The nickel-based casting superalloy K4169 is extensively utilized in aerospace engines for its extraordinary mechanical and thermal properties. However, achieving high surface integrity of the superalloy remains challenging. Ultrasonic-assisted machining (UAM) is an advantageous technology, while the influence on cast superalloy is imperative to be revealed. The study on surface morphology and integrity of K4169 was carried out using ultrasonic-assisted end milling. The results showed that the ultrasonic vibration effectively suppresses surface defects and facilitates a regular surface texture. A more significant deformed layer of 7.3 μm was induced in UAM, representing a 97% enhancement relative to CM. Additionally, surface microhardness and compressive residual stress show a tendency to increase with ultrasonic amplitude. Specifically, the surface compressive residual stress in UAM reached 822 MPa, signifying a 69.6% increase over CM.

Simultaneous enhancement of elevated temperature strength and ductility in additive-manufactured nickel-based superalloy via doping Y2O3 nanoparticles

In this work, we coated a layer of Y2O3 particles in Hastelloy X (HX) nickel-based superalloy powder by in situ chemical method and combined with laser powder bed fusion (LPBF) technology to develop a high-performance Y2O3-doping alloy, designated as Y-HX. The results show that the doping of Y2O3 particles prevents crack formation during the printing process and reduces solute segregation at cell and grain boundaries by increasing the viscosity of the molten pool. The doping of Y2O3 particles to the printed Y-HX alloy enhances grain boundary characteristics, transforming coarse sheet-like carbides into finely dispersed granular carbides at the boundaries during subsequent heat treatment. Additionally, doping with Y2O3 particles increases the recrystallization activation energy of the Y-HX alloy from 149.4 to 278.8 kJ mol–1. At 750 °C, the Y-HX alloy exhibits an ultimate tensile strength of 619 ± 2 MPa and an elongation of 52 % ± 2 %, along with an ultimate tensile strength of 325 ± 3 MPa and an elongation of 47 % ± 2 % at 900 °C. Our work provides a promising way to develop additive-manufactured superalloys with exceptional thermal stability and remarkable high-temperature mechanical properties.

Influence of GH4169 addition on cracking control, microstructure and mechanical properties of GH4169/K465 composite material manufactured by selective laser melting

In the process of additive manufacturing, K465 nickel-based superalloy tends to form a eutectic structure with a low melting point. Subsequently, rapid cooling leads to the formation of significant residual tensile stress. This tensile stress makes the prepared sample susceptible to cracking. The research explored the susceptibility to cracking of the alloy material and analyzed the microstructure and properties of GH4169/K465 alloy obtained. The generation of cracks can be managed by decreasing the concentration of Al and Ti elements. The microstructure of GH4169/K465 alloy consists of a matrix phase γ, a white Laves precipitated phase, and spherical particle precipitated phase NbTi4. The mechanical properties of samples 1GH1K, 7GH5K, and 3GH1K were analyzed. The results indicated an elongation exceeding 20 %, a tensile strength exceeding 1000 MPa, and a reduction in hardness from 329 HV to 285 HV. The powder mixing process has been demonstrated to effectively address the shortcomings of individual materials by combining the strengths of different alloy materials to produce a hybrid material with excellent comprehensive performance.