Superalloy Inconel Research Articles

Incremental Feeding High-Pressure Sliding (IF-HPS) Process for Upscaling Highly Strained Areas in Metallic Materials with Enhanced Mechanical Properties

This paper presents an overview of the recent development of incremental feeding high-pressure sliding (IF-HPS) process for grain refinement of metallic sheets with enlarged areas. The IF-HPS process is a method of severe plastic deformation (SPD) under high pressure without increasing the machine capacity. The IF-HPS process combines an incremental feeding technique with the high-pressure sliding (HPS) process so that a severely deformed area can be extended. Development of the IF-HPS process includes the use of flat-type anvils instead of groove-type anvils, which makes it easier to enlarge the SPD-processed areas. The development is also described in terms of the sliding mode and the feeding pattern, where the former is determined by the sliding distance and the numbers of the reciprocation of the sliding and the latter by the feeding distance and the feeding direction. The application of the IF-HPS process is made to metallic materials such as a Ni-based superalloy (Inconel 718), a Ti-6Al-7Nb alloy (F1295) and commercially available Al alloys (A1050, A3105, A5052 and A5182). It is shown that the grain refinement is successfully achieved so that superplastic elongation more than 400% is attained in the Ni- and Ti-based alloys, and the room-temperature tensile strength is well enhanced in the Al alloys. It is then demonstrated that the IF-HPS process is promising to extend the SPD-processed area without increasing the machine capacity. Furthermore, a new approach is suggested for material design, such as the hybrid materials composed of conventional and fine-grained materials and functionally graded materials.

Ductile failure of Inconel 718 during flow forming process and its numerical investigation

Understanding the fracture mechanisms and predicting failure in forming processes is of great interest to increase formability and numerical methods have been proven effective. Incremental forming processes such as flow forming possess challenges due to material experiencing complex stress states and highly non-linear deformation histories during forming. Although some of the ductile failure criteria integrated into finite element (FE) simulations are found to be in better correspondence with the experimental findings, they mostly lack sufficient accuracy in predicting formability limits for flow forming and spinning processes. In this context, this work is concerned with the analysis and prediction of ductile failure of nickel-based super alloy Inconel 718 (IN718) in the flow forming process through FE analysis. Failure is modeled with three different models, namely Cockcroft–Latham (CL), Johnson–Cook (JC) and modified Mohr–Coulomb (MMC), implemented as a user subroutine in explicit FE solver Abaqus. Tensile tests are conducted with four different specimen geometries in order to identify parameters of the plasticity and damage models. Then, the developed framework is applied to a FE simulation of the flow forming process to predict formability limits and perform process parameter optimization to improve formability. Flow forming tests conducted at three thickness reduction values reveal that the forming limit of the material is at about 50% thickness reduction where radial cracks are observed on the outer surface. It is found that the CL model is able to predict formability limits and crack initiation locations while the MMC and JC models failed in both with significant over prediction of damage. Furthermore, the effect of temperature and process parameters such as the ratio of feed rate to revolution speed and roller axial and radial offsets are further examined with the developed FE frameworks. It has been shown that process parameter optimization requires accurate modeling of ductile damage since the behavior of different models is diverse.

Possibilities of Using Impedance Spectroscopy for Indirect Measurements of Thin Layers of Al & Cr-Al Coatings on Ni-based Superalloy Inconel 713LC Applied by the "Out-of-pack" Diffusion Method

Possibilities of Using Impedance Spectroscopy for Indirect Measurements of Thin Layers of Al & Cr-Al Coatings on Ni-based Superalloy Inconel 713LC Applied by the "Out-of-pack" Diffusion Method

Three-dimensional modeling of solidification grain structures generated by laser powder bed fusion

Grain structures generated by laser powder bed fusion (L-PBF) of the Ni-based superalloy Inconel 718 (IN718) are studied using Cellular Automaton modeling. A hybrid methodology is developed to benefit from a full thermohydraulic simulation that predicts the shape of the consolidated track and the temperature field. The advantage is to reach a large size of the simulation domain while still taking advantage of a thermohydraulic numerical solution of the L-PBF process at the scale of the melt pool. The computed grain structure becomes available in a Representative Elementary Volume (REV) of an Additively Manufactured (AMed) specimen and can be studied statistically considering the distribution of crystallographic orientations and the grain density. It is also possible to vary process and material parameters to approach industrial practice. The strategy consisting in opposite bidirectional scanning of the powder with an additional 67° rotation at each new layer is demonstrated. It is compared with the standard opposite bidirectional monoaxial scanning strategy and the opposite bidirectional orthogonal biaxial scanning strategies with two perpendicular axes, all reproducing trends reported in experimental literature. The generation of virtual REVs of AMed microstructures by L-PBF for IN718 opens the way to study new processing parameters and coupling with models for the prediction of metallurgical properties.

Study on the Effect of Inter-Layer Cooling Time on Porosity and Melt Pool in Inconel 718 Components Processed by Laser Powder Bed Fusion.

This paper investigates the effects on the material microstructure of varying the Inter-Layer Cooling Time (ILCT) during the printing process in laser powder bed fusion (L-PBF) multi-laser machines. Despite these machines allowing higher productivity rates compared to single laser machines, they are affected by lower ILCT values, which could be critical for material printability and microstructure. The ILCT values depend both on the process parameter sets and design choices for the parts and play an important role in the Design for Additive Manufacturing approach in L-PBF process. In order to identify the critical range of ILCT for this working condition, an experimental campaign is presented on the nickel-based superalloy Inconel 718, which is widely used for the printing of turbomachinery components. The effect of ILCT on the microstructure of the material is evaluated in terms of porosity and melt pool analysis on printed cylinder specimens, considering ILCT decreasing and increasing in the range of 22 to 2 s. The experimental campaign shows that an ILCT of less than 6 s introduces criticality in the material microstructure. In particular, at an ILCT value of 2 s, widespread keyhole porosity (close to 1‱) and critical and deeper melt pool (about 200 microns depth) are measured. This variation in melt pool shape indicates a change in the powder melting regime and, consequently, modifications of the printability window promoting the expansion of the keyhole region. In addition, specimens with geometry obstructing the heat flow have been studied using the critical ILCT value (2 s) to evaluate the effect of the surface-to-volume ratio. The results show an enhancement of the porosity value (about 3‱), while this effect is limited for the depth of the melt pool.

Investigation of the tensile deformation behaviour in Ni-based superalloy inconel alloy 617 using EBSD-based finite element simulations and optical flow method

To improve component design, the fundamental understanding of the fatigue behaviour of gas turbine materials is essential. Since Ni-alloys exhibit pronounced elastic anisotropy, the local grain orientation strongly affects the stress and strain distribution in the material under mechanical loadings. This work addresses the characterisation of anisotropic elastic–plastic deformation and its consequences for crack initiation of nickel-base superalloy IN617 under tensile loading. Samples were loaded in situ in a scanning electron microscope (SEM) to correlate the deformation behaviour with the grain structure and the grain orientation determined by electron backscatter diffraction (EBSD) measurements. To calculate the resulting stresses and strains, the EBSD data were used to develop a model by finite element method (FEM) considering the grain structure and orientation. The results of the elastic–plastic finite element (FE) simulation were compared with the theories of the E⋅m model based on the Schmidt factor (m) and anisotropic Young’s modulus (E). A mathematical image registration method called “optical flow method” (OFM), which is capable to calculate the transformation of EBSD measuring points during deformation, was applied to the EBSD data. The strains calculated by the optical flow method and by FE simulation were compared for two samples. The findings revealed large strains in the later crack initiation area found in both the OFM and FEM. The developed FEM model was verified by the successful correlation of hypotheses of the E·m model with the simulated mechanical behaviour. Furthermore, the impact of the microstructural neighbourhood on the mechanical behaviour was emphasised.Graphical

Creep–Fatigue Interaction of Inconel 718 Manufactured by Electron Beam Melting

Electron beam melting of Ni‐base superalloy Inconel 718 allows producing a columnar‐grained microstructure with a pronounced texture, which offers exceptional resistance against high‐temperature loading with severe creep–fatigue interaction arising in components of aircraft jet engines. This study considers the deformation, damage, and lifetime behavior of electron‐beam‐melted Inconel 718 under in‐phase thermomechanical fatigue loading with varying amounts of creep–fatigue interaction. Strain‐controlled thermomechanical fatigue tests with equal‐ramp cycles, slow–fast cycles, and dwell time cycles are conducted in the temperature range from 300 to 650 °C. Results show that both dwell time and slow–fast cycles promote intergranular cracking, gradual tensile stress relaxation, as well as precipitate dissolution and coarsening giving rise to cyclic softening. The interplay of these mechanisms leads to increased lifetimes in both dwell time and slow–fast tests compared to equal ramp tests at higher strain amplitudes. Conversely, at lower mechanical strain amplitudes, the opposite is observed. A comparison with results of conventional Inconel 718 indicates that the electron‐beam‐melted material exhibits superior resistance against strain‐controlled loading at elevated temperatures such as thermomechanical fatigue.

Comprehensive investigations into the force and thermal characteristics of belt grinding Inconel 718 under constant normal forces

Belt grinding is an efficient and widely used method for machining precise high-strength components made from the superalloy Inconel 718. By integrating robots with a force sensor, normal forces can be kept to achieve high-accuracy grinding under varying processing conditions. However, the force and thermal characteristics of belt grinding Inconel 718 under constant normal forces, which significantly affect the quality of ground workpieces, are still unclear. In this study, four characteristics including grinding effects, dynamic grinding forces and force ratios, specific grinding energy as well as dynamic grinding temperature distributions, are comprehensively investigated. The grinding effects are determined by the single-grain scratch test, and the material springback mechanisms are revealed. The influences of grinding parameters on grinding forces, specific grinding energies and grinding temperatures are analyzed in detail. Additionally, a new finite element model is established to obtain the dynamic temperature distributions of grinding surfaces. This study aims to improve understanding of the process of constant-force belt grinding Inconel 718 and lays foundations for further research on grinding mechanisms and modeling.

Episodes of single-crystal material removal mode and machinability in the micro-cutting process of superalloy Inconel-718

The development tendency of miniaturization gives birth to the demand for Inconel-718 miniature parts, and micro-cutting is a promising technique to produce crystalline material miniature parts. Unfortunately, due to the non-negligible edge radius and property anisotropy, the material deformation behaviour and removal mode vary with cutting conditions, resulting in volatile machinability and inferior quality, which hinders the widespread application of Inconel-718 miniature parts. Therefore, it is urgent to clarify the evolution of material removal mode and machinability of Inconel-718 micro-cutting. Existing researches fail to consider the property anisotropy, strain-rate sensitivity and strain-rate inhomogeneity. This paper establishes strain rate-considered single-crystal micro-cutting models and performs simulations under varying cutting conditions, aiming to depict the episodes of material removal mode and machinability of Inconel-718 micro-cutting. Results show that, uncut chip thickness and cutter rake angle influence the material removal mode, and in turn influence machinability. For Inconel-718 single-crystal with [0° 0° 0°] orientation, the transition from the scratching mode to the ploughing mode is in the uncut chip thickness range of 0.2Re∼0.4Re, and the transition from the ploughing mode to the cutting mode is in the uncut chip thickness range of 0.6Re∼0.8Re or the rake angle range of −30°∼-15°. In comparison, cutting speed and clearance angle have little effect on material removal mode. Cutting speed influences the strain rate of the cutting-affected zone, and in turn influences machinability. The maximum strain rate of the cutting-affected zone is respectively around 0.45 s−1 and 10,960 s−1 under the cutting speeds of 2Re/s and 20000Re/s.

Angular distribution of sputtered particles from Inconel718, a Simulation Study

The angular distribution of sputtered particles is an effective tool for obtaining information on the composition and structure of the target and even on the beam energies. The particles of Inconel718 super alloy sputtered at full angle corresponding to each of the probes were calculated. The SRIM program associated with a new ANGULARE simulation program was used to obtain the sputtering yields and angular distribution of sputtered Fe, Al, Cr, Mo, Nb, Ni and Ti particles from Inconel718. The simulation was performed for a large number of incident ions (5 keV, Kr+) and allows the computer to count the number of particles emitted at the solid angle. Angular distributions of pulverized Inconel718 particles and pulverized yields were compared to the literature. Furthermore, the angular distribution of Inconel718 for the differential sputtering yields shows an under-cosine tendency.

Rotary friction welding of Inconel 718 – AISI 304 stainless steel dissimilar joint

Nickel-based superalloy Inconel 718 and austenitic stainless steel AISI 304 are joined by rotary friction welding. The changes in microstructure and mechanical properties of the dissimilar joint for solutionising, solutionising + aging, and post-weld aging treatment, with a prior solution heat treatment, are studied. Two distinct microstructural zones, the FDZ (fully deformed zone) and the TMAZ (thermo-mechanically affected zone) are observed in all weldments. The post-weld aged joint sample shows the highest tensile strength and hardness due to the precipitation of γ′ (Ni3(Ti, Al)) and γ″ (Ni3Nb) strengthening precipitates. The solution-treated sample shows the highest yield strength, while the solutionising + aging treatment is found to deteriorate the mechanical properties of the dissimilar joint. The observed changes in the mechanical properties are investigated based on microstructure and electron dispersive spectroscopy.

Multi-response optimisation and performance evaluation of Inconel 625 superalloy machining under cryogenic cooling environment

ABSTRACT The conventional machining of the widely used nickel-based superalloy Inconel 625 is challenging since it exhibits high strength at elevated temperatures. Cryogenic machining is an effective cooling technique to extract the heat developed during machining and enhance the machining performance of superalloys by eliminating the high-temperature related machining obstacles. The maximum machining performance of cryogenic machining can be achieved by optimising the input parameters considered for the study. This work attempts to improve the cryogenic machining performance of Inconel 625 using grey relational analysis. Multiple responses that are having the most significance on the performance of the machining such as main cutting force, tool wear and surface roughness were considered to optimise the process. The experiments were designed on the basis of the orthogonal array. Taguchi’s L9 design with three levels of cutting speed, feed and depth of cut was considered for conducting the experiments. A cutting speed of 60 m/min, feed of 0.05 mm/rev and depth of cut of 0.2 mm were obtained as the optimal parameters. The analysis of modes of wear and morphology of chips was also conducted using SEM imaging to understand the wear mechanisms and machining performance at the optimal level under cryogenic cooling.

Intuitive graphical presentation of cluster-plus-glue-atom model to obtain composition formulas of industrial alloys

The composition of a solid-solution alloy resides in its chemical unit, consisting of a nearest-neighbor cluster and a few next-neighbor glue atoms according to the cluster-plus-glue-atom model. However, the identification of the glue atoms in the chemical unit requires complex calculations. The present work simplifies this process into an intuitive graphical representation for binary face-centered-cubic solid solutions. By presenting graphically the relationship between the number of glue atoms and the solute-over-solvent atomic radius ratio, in combination with the alloy composition, the specific form of the chemical unit for any given alloy can be directly read from the graph. Two types of cluster formulas are distinguished. One is to idealize the chemical unit with the nearest neighbor completely occupied by solvent atoms, such as the [Zn-Cu12] cluster for α Cu-Zn brass that leads to a chemical unit [Zn-Cu12]Zn4. The second one, more general, is to consider the chemical unit with mixed nearest-neighbor occupations in accordance with Cowley’s short-range-order parameter α1, as exemplified by the presence of a [Zn-Cu9.4Zn2.6] cluster in Cu68.9Zn31.1 alloy that gives [Zn-Cu9.4Zn2.6]Zn1.4Cu2.6. The two formulas are actually identical in chemistry, for both units share the same chemical formula Cu12Zn5, which corresponds to the most widely used brass grade C26000 (70Cu-30Zn). This graphical presentation can also be extended to multi-component alloys through the classification of similar elements as exemplified in superalloy Inconel 718, thus providing a universal means for understanding the compositions of industrial alloys.

Non-conventional machining of nickel based superalloys: A review

Nickel, the 24th most abundant element, is found in 0.016 % of the earth's crust. Addition of Nickel is used as an alloying element in hardenable steels, stainless steels, high-temperature alloys,corrosion-resistant and“nickel-silver,” and aluminium-nickel alloys. Nickel improves the toughness and ductility of cast iron. Nickel-base super alloys (Inconel) are widely regarded as one of the most difficult materials to machine because of their extreme hardness, high strength at high temperatures, tendencyto react with tool materials, and low thermal diffusivity. Because of various issues that arise during the machining process, nickel-based superalloys are regarded as difficult to machine materials; heat will advance into the tool material, causing tool wear tear and premature tool failure. To overcome these challenges, a non-conventional machine process is beneficial for super alloy machining. The present study is review of various nickel-based super alloys and their types, introduction to the non-conventional machining techniques applied to superalloys over the past few decades. Machining with non-conventional methods concludes with some key findings and gaps regarding nickel-based superalloys.

Machining of nickel-based super alloy inconel 718 using alumina nanofluid in powder mixed electric discharge machining

Inconel 718 is a nickel-based superalloy with exceptional mechanical qualities, including high tensile and impact strength, as well as good oxidation and corrosion resistance. EDM is widely used to cut hard materials of this type by common parameters affecting spark, current, duty cycle etc, whereas MRR, SR can be greatly improved by using sufficient fluid properties of the dielectric. Incorporation of alumina nanoparticles with deionized water may improve machining performance, with no prior research on machining characteristics of Inconel 718 using alumina nanofluid in EDM. The machinability of Inconel 718 via the electrical discharge machining process, as well as the performance of alumina nanofluid as a dielectric medium, have been evaluated using deionized water with a concentration of 0.5%. In this study, based on the effect of various input parameters such as and on the MRR, TWR and SR, and the RSM has been used to conduct the experiments. A maximum MRR of 0.048 g min−1, a TWR of 0.00632 g min−1 and an SR of 3.271 μm are achieved. Overall, the use of alumina nanofluid can improve machining performance in EDM, due to the reduction of abnormalities such as crack formation and molten metal debris in the machined surface of Inconel 718.

Stored energy density research on the fatigue crack initiation at twin boundary and life prediction of Inconel718 superalloy

The fatigue crack initiation at twin boundary (TB) and the life prediction of IN718 alloys in the high cycle fatigue (HCF) regime and very high cycle fatigue (VHCF) regime were investigated through crystal plasticity finite element (CPFE) simulations and experiments. The fatigue damage parameter, considering the evolution of geometrically necessary dislocation (GND) density, slip and back stress, known as the back-stress-based stored energy density in this study, Gba, was proposed to precisely characterize the plastic strain distribution and localization, which in turn was engaged in locating fatigue crack initiation site and predicting the fatigue life. The element analysis around TB and the CPFE simulations indicated the coupling of slip activation parallel to the TB and the absence of primarily strengthening phase (γ'') on the both side near the TB was responsible for crack initiation. To predict fatigue life, the varying pattern of the Gba at fracture with fatigue life was studied based on the experimental results in the HCF and VHCF regimes, and the life prediction method was obtained accordingly. Finally, the fatigue life evaluations of the IN718 alloy at three load ratios (R = −0.1, 0.1, and 0.5) were conducted and results showed that the life estimates were basically within ±3 scatted bands.

Nickel-Based Superalloy Inconel 718, Relation between Non-Linear Ultrasonic and Microstructure Changes under the Creep Damages.

Nickel-based superalloy, Inconel 718, has high temperature strength effected by γ"(Ni3Nb) phase at approximately 973 K. It has been found that the creep damage of Inconel 718 was induced by γ"phase disappearance. In the study, we applied the nonlinear ultrasonic method, nonlinear three-wave interaction, for evaluation of the creep damages and the microstructural degradation in γ" phase for Inconel 718 at 973 K, 310MPa. In the nonlinear three-wave interaction method, two intersecting ultrasonic waves produced a scattered wave when the resonance condition was satisfied. The amplitude in resonant scattering wave was measured. We analyzed the relation between the microstructural change and nonlinear acoustic characterizations by the electromagnetic acoustic resonance (EMAR) throughout the creep life, and the nonlinearity corresponded to change of the dislocation density. This was supported with X-ray diffraction, EBSD and SEM observation.

Study on wear morphology of uncoated and MT-CVD TiCN-Al2O3 coated carbide inserts during dry machining of Inconel 825 superalloy

The adoption of the High Speed Machining (HSM) approach by industries to enhance productivity is crucial in order to fulfill the growing demand of the global market. Understanding superalloys' machining behavior is also necessary since they play a significant role in a variety of industries, including the aerospace industry, marine engine parts, biomedical applications, chemical and petrochemical industries, and nuclear fuel processing plants. Hence, dry machining performance of ‘difficult-to-cut’ aerospace superalloy Inconel 825 is studied herein. With uncoated and MT-CVD TiCN-Al2O3 coated carbide inserts, machining experiments are performed at various cutting speeds. Detailed tool wear mechanisms are discussed for each of the cutting inserts with regard to different cutting speeds and hence the performance gain with coated carbide tools is understood as compared to its uncoated counterpart for dry machining of Inconel 825 superalloy.

High temperature corrosion of two superalloys in the impure helium environment

ABSTRACT The helium coolant of a very high temperature gas-cooled reactor contains traces of impurities, which have an adverse effect on the structural metallic materials at elevated temperatures. The chromium-containing superalloys Inconel 617 and Incoloy 800 H have been the representative materials with outstanding performance, and, in this study, their corrosion behaviors were investigated under the impure helium, which was the typical HTGR operating environment. A continuous chromia-based surface scale can be developed in the impure helium, but after being above a critical temperature this oxide layer may be destroyed. This destructive phenomenon may be general for the high-temperature alloys such as Inconel 617 and Haynes 230, however, Incoloy 800 H can spontaneously resist this damage by the silica layer. This study was focused on the critical temperature calculations and measurements for Alloy 617 and 800 H, and the different corrosion behavior has been discussed.

Effect of process parameters on mechanical properties of Inconel718 superalloy fabricated by directional energy deposition

Effect of process parameters on mechanical properties of Inconel718 superalloy fabricated by directional energy deposition