Properties Of Nickel-based Superalloys Research Articles

Evolution of microstructure and properties of IN738 alloy under thermal exposure with different post-processing states

The microstructure and properties of nickel-based superalloys under thermal exposure are the key basis for evaluating the high-temperature stability and proposing process optimization strategies. This study investigated the microstructural evolution and the corresponding tensile properties of IN738 alloy with different post-processing states under thermal exposure at 700 °C. The results show that the microstructures of IN738 alloys with different post-processing states (i.e., hot isostatic pressing (HIP) and standard heat treatment (SHT)) are significantly different. For the HIPed sample, large cuboidal γ′ and a small number of ultra-fine spheroidal γ′ precipitates are present in the γ matrix. Under thermal exposure, the size and volume fraction of ultra-fine spheroidal γ′ increase with prolonged thermal exposure time. In comparison, the SHTed sample is characterized as a bimodal distribution of γ′, with large primary cuboidal γ′ and small secondary spherical γ′. The size and volume fraction of primary γ′ increase first and then remain steady under thermal exposure. In particular, the tensile properties under exposure depend highly on the post-processing states. The increase of tensile strength after the thermal exposure in the HIPed sample is attributed to the rising fine spherical γ′ volume fraction. The rising size and volume fraction of primary γ′ in the SHTed sample improve the tensile strength during thermal exposure.

Sustainable EDM of Inconel 600 in Cu-mixed biodegradable dielectrics: Modelling and optimizing the process by artificial neural network for supporting net-zero from industry

The properties of Nickel-based superalloy(s) like stability at extreme conditions, greater strength, etc., complicate its cutting through conventional operations. Therefore, electric discharge machining (EDM) is preferred for its accurate cutting. However, the conventional dielectric i.e., kerosene used in EDM is hydrocarbon based which generates toxic fumes and contribute to the CO2 emissions during the discharging process in EDM. This affects the operator's health and the environment. Therefore, the potentiality of five biodegradable dielectrics has been deeply examined herein to address the said issues. Nano copper powder is also employed for uplifting the cutting proficiency of these dielectrics. A set of 15 experiments was performed via full factorial design. An artificial neural network (ANN) is constructed to model and optimize the material removal rate (MRR), surface roughness (SR), and specific energy consumption (SEC). The highest MRR (5.527 mm3/min) was achieved in coconut oil whereas for obtaining the lowest SR, the sunflower oil at powder concentration (Cp) of 1.0 g/100 ml is the best choice. Sunflower oil also gave a 17.05% better surface finish compared to other dielectrics. Amongst the biodegradable dielectrics, olive oil consumes lowest specific energy (SEC) i.e., 264.16 J/mm3 which is 28.8% less than the SEC of other oils. Furthermore, the maximum CO2 reduction of 72.8 ± 1.4% is achieved with Olive oil in comparison to that found with kerosene in EDM. The multi-objective optimization is conducted and sunflower oil with Cp of 0.667 g/100 ml is termed out to be optimal solution. The biodegradable dielectrics have demonstrated excellent performance for EDM to support net-zero goals from the industrial sector.

Optimizing the Thermomechanical Process of Nickel-Based ODS Superalloys by an Efficient Method.

Thermo-mechanical process of nickel-based oxide dispersion strengthened (ODS) superalloys is critical to produce desired components. In this study, an efficient method of consolidating powder is introduced to optimize the preparation process, microstructure and properties of nickel-based ODS superalloys. The influences of consolidation temperature, strain rate and ball milling time on the hardness of nickel-based superalloys were studied. The relationship among process, microstructure and hardness was established, the nanoparticles strengthening and grain boundary strengthening in nickel-based ODS superalloys were discussed. The results indicate that long ball milling time, moderately low consolidation temperature and high strain rates are beneficial to improving properties of nickel-based superalloys. Moreover, dispersion strengthening of nanoparticles and grain boundary strengthening play important roles in enhancing nickel-based ODS superalloys.

Radiation and Fast Neutron Shielding Properties of Nickel-Based Superalloys: Inconel 600, 718 and 725 Superalloys

This study focuses on simulation of the radiation shielding parameters for nickel-based superalloys: Inconel 600, 718 and 725 superalloys. The partial interactions, mass attenuation coefficient value (µ m), effective atomic number value (Z eff), effective electron density value (N el) and half value layer (HVL) at photon energy ranging of 1 keV–100 GeV, were estimated theoretically by WinXCom software program. Moreover, buildup factors (energy absorption buildup factor and exposure buildup factor) were determined using geometrical progression (G-P) fitting method for energy ranging 0.015–15 MeV at deep penetration 1–40 mfp (mean free path).Also, fast neutron removal cross sections (ΣR) were simulated by partial density method at energy ranging from 2 to 12 MeV. The results found that nickel-based superalloy Inconel 725 had excellent radiation shielding property. The study also brings the significance of these samples by comparing with standard commercial concrete.

Properties of nickel-based superalloys of equiaxial crystallization

Purpose. The aim of the work is to obtain predictive regression models, with the help of which, it is possible to adequately calculate the mechanical properties of nickel-based superalloys of equiaxial crystallization, without carrying out preliminary experiments.
 Research methods. To find regularities and calculate the latest CALPHAD method was chosen, and modeling of thermodynamic processes of phase crystallization was performed.
 Results. As a result of experimental data processing, the ratio of alloying elements Kg¢ was proposed for the first time, which can be used to assess the mechanical properties, taking into account the complex effect of the main alloy components. The regularities of the influence of the composition on the properties of heat-resistant nickel alloys of equiaxial crystallization are established. The analysis of the received dependences in comparison with practical results is carried out. The relations well correlated with heat resistance, mismatch and strength of alloys are obtained.
 Scientific novelty. It is shown that for multicomponent nickel systems it is possible with a high probability to predict a mismatch, which significantly affects the strength characteristics of alloys of this class. The regularities of the influence of the chemical composition on the structure and properties of alloys are established. A promising and effective direction in solving the problem of predicting the main characteristics of heat-resistant materials based on nickel is shown
 Practical value. On the basis of an integrated approach for multicomponent heat-resistant nickel-based alloys, new regression models have been obtained that make it possible to adequately predict the properties of the chemical composition of the alloy, which made it possible to solve the problem of computational prediction of properties from the chemical composition of the alloy. This allows not only to design new nickel-based alloys, but also to optimize the composition of existing brands.

High Temperature Oxidation and Thermal Shock Properties of La2Zr2O7 Thermal Barrier Coatings Deposited on Nickel-Based Superalloy by Laser-Cladding

In order to reduce the difficulty and cost of manufacturing and improve the high temperature oxidation and thermal shock properties of nickel-based superalloy, a thin La2Zr2O7 thermal barrier coating without bond coat was successfully prepared by laser-cladding using La2Zr2O7 powders on a nickel-based superalloy substrate. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods were used to characterize the microstructure of the coating. The high temperature oxidation and thermal shock properties of the coating were evaluated by the air isothermal oxidation method at 1100 °C for 110 h and thermal cycling method at 25~1100 °C, respectively. The results show that the coating is mainly composed of La2Zr2O7 phase. The oxidation weight gain rate of the coating is about two-thirds of that of the substrate, and the first crack thermal shock lifetime of the coating is about 1.67 times of that of the substrate. The oxidation products of the coating are mainly Fe2O3, Cr2O3, NiCr2O4, Nb2O5 and La2Zr2O7. The existence of La2Zr2O7 phase in the coating is the main reason for the improvement of its oxidation resistance at 1100 °C and its thermal shock resistance at 25~1100 °C.

Effect of sintering temperature and heat treatment on microstructure and properties of nickel-based superalloy

A nickel-based superalloy was prepared through powder metallurgy (P/M). In order to balance their microstructure and properties, heat treatments were carried on the alloys. The microstructures of the alloys were characterized by optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The solidification process in the alloys during the sintering process was calculated using Thermo-Calc software. A good quality nickel-based superalloy with a homogeneous microstructure and fine grain size can be obtained at the sintering temperature of 1140 °C. The alloys mainly consist of irregular polygon CrB particles, irregular morphology Ni3B particles, hexagonal M7C3 particles, (γ-Ni + Ni3B) eutectics and bright γ-Ni solid solution matrix. The calculated results show that the solidification process in the alloys during the sintering process is liquid → liquid+γ-Ni → liquid+γ-Ni + M7C3 → liquid+ γ-Ni + M7C3+CrB → γ-Ni + M7C3+CrB+(γ-Ni + Ni3B). The calculation results are helpful to understand the microstructure evolution in the nickel-based superalloy and agree well with the experimental data. The microstructure of the alloys after solution treatment is mainly composed of supersaturated γ-Ni solid solution and M7C3. During the aging treatment, the supersaturated γ-Ni solid solution decomposed and many small particles were uniformly precipitated in the γ-Ni solid solution. As the aging temperature increased, the decomposition process of supersaturated γ-Ni solid solution was accelerated and the precipitated particles became coarsen according to Ostwald ripening theory. The hardness of the alloys increased when aging treated at 300 °C and 500 °C due to the second phase strengthening effect, and then the hardness decreased when aging treated at 700 °C due to the coarsening of precipitated particles.

Tensile Deformation and Fracture Behaviors of a Nickel-Based Superalloy via In Situ Digital Image Correlation and Synchrotron Radiation X-ray Tomography.

Nickel-based superalloys have become key materials for turbine disks and other aerospace components due to their excellent mechanical properties at high temperatures. Mechanical properties of nickel-based superalloys are closely related to their microstructures. Various heat treatment processes were conducted to obtain the desired microstructures of a nickel-based superalloy in this study. The effect of the initial microstructures on the tensile deformation and fracture behaviors was investigated via in situ digital image correlation (DIC) and synchrotron radiation X-ray tomography (SRXT). The results showed that the size and volume fraction of γ″ and γ′ phases increased with the aging time. The yield strength and the ultimate tensile strength increased due to the precipitation strengthening at the expense of ductility. The surface strain analysis showed severely inhomogeneous deformation. The local strains at the edge of specimens were corresponded to higher void densities. The fracture of carbides occurred owing to the stress concentration, which was caused by the dislocation accumulation. The fracture mode was dimple coalescence ductile fracture.

Improvement of the technology of melting ingots of nickel based alloys by vacuum arc remelting (VAR)

Purpose. Improvement of the technological modes for the melting of nickel-based cathodes of composition Ni−Cr−Al−Y in order to improve their quality, namely, reducing the total number of defects in the form of discontinuities, pores, non-melts and increasing the homogeneity of the structure and chemical composition. Methods. To prepare the smelting charge for melting, the raw materials were chopped to the required size and mixed, which made it possible to ensure uniform distribution of the alloying elements in the entire volume of the smelting charge. To obtain experimental ingots, a vacuum-arc furnace was used. The mass of smelting-charge loading per melting was 4 000…6 000 g. Testing of melting modes was carried out by experimental implementation of the process. The range of modes is as follows: I = 450...1 800A, U = 30...45 V, t = 25...35 min, preliminary creation of a vacuum of 1∙10-4 mbar. The operating fluid is Ag/He gas mixture (70/30), pressure 0.5 bar, temperature of chill mold heating − 250…800 °С, melt temperature before pouring − 1 400…1 700 °С. For a comprehensive assessment of the chemical composition, a study was conducted in two zones of ingot fragment, in the central part of the sample and on its surface. The chemical composition studies were performed using a multipurpose scanning electron microscope REM 106І equipped with a microanalysis system. Metallographic studies of the obtained structure of the ingot were carried out using optical and electronic microscopes. Results. It has been established that the use of vacuum-arc remelting process to produce nickel-based alloys using preparation methods of smelting-charge with various size and refining the melting process parameters allows to produce ingots with a minimum number of proper defects, with the formation of a uniform structure and uniform distribution of alloying elements in the entire alloy. Scientific novelty. The regularities of the influence of the technological parameters of the charge preparation and the melting process on the structure and properties of nickel-based superalloys are established. Practical significance. Practical use of the obtained results will significantly improve the homogeneity of ingots in the production of cathodes for coating, which in turn will have a positive effect on the quality of applied coatings and the total resource of parts.

Creep deformation micro-mechanisms of CM 247 DS LC Ni-base superalloy under relevant service condition

In order to meet the 21st century challenges, the need to improve the high temperature load bearing capabilities or creep properties of nickel base superalloys is more important than ever. Thorough understandings of creep deformation micro-mechanisms are essential for improving high temperature performance of these alloys. Therefore, in the present study, creep deformation micro-mechanisms of CM 247 DS LC alloy used for fabricating turbine blades and vanes under relevant service conditions have been explored. The creep deformation behaviour at the investigated temperatures has been divided into three temperature regimes. In the lower temperature regime, a classical three stage creep curve is observed, i.e., primary creep followed by steady-state creep and then an accelerating creep stage leading to failure. While, in the intermediate temperature creep regime a relatively shorter secondary creep region is seen, in contrast, secondary creep stage is almost missing in the high temperature regime. Transmission electron microscopic (TEM) studies revealed that the deformation micro-mechanisms in the low temperature regime are dominated by γ′-precipitates shearing of anti phase boundary (APB) coupled dislocations pair. In the high temperature regime, the deformation is dominated by the extensive dislocation networks formation and severe γ′-rafting. In the intermediate temperature regime, the deformation micro-mechanisms are basically mixture of both low and high temperature deformation micro-mechanisms. The facts revealed by TEM observations were well supported by scanning electron based factographic and microstructural analysis.

High-temperature site preference and atomic short-range ordering characteristics of ternary alloying elements in γ’-Ni3Al intermetallics

Remarkable high-temperature mechanical properties of nickel-based superalloys are correlated with the arrangement of ternary alloying elements in L12-type-ordered γ′-Ni3Al intermetallics. In the current study, therefore, high-temperature site occupancy preference and energetic-structural characteristics of atomic short-range ordering (SRO) of ternary alloying X elements (X = Mo, W, Ta, Hf, Re, Ru, Pt or Co) in Ni75Al21.875X3.125 alloy systems have been studied by combining the statistico-thermodynamical theory of ordering and electronic theory of alloys in the pseudopotential approximation. Temperature dependence of site occupancy tendencies of alloying X element atoms has been predicted by calculating partial ordering energies and SRO parameters of Ni-Al, Ni-X and Al-X atomic pairs. It is shown that, all ternary alloying element atoms (except Pt) tend to occupy Al, whereas Pt atoms prefer to substitute for Ni sub-lattice sites of Ni3Al intermetallics. However, in contrast to other X elements, sub-lattice site occupancy characteristics of Re atoms appear to be both temperature- and composition-dependent. Theoretical calculations reveal that site occupancy preference of Re atoms switches from Al to both Ni and Al sites at critical temperatures, Tc, for Re > 2.35 at%. Distribution of Re atoms at both Ni and Al sub-lattice sites above Tc may lead to localised supersaturation of the parent Ni3Al phase and makes possible the formation of topologically close-packed (TCP) phases. The results of the current theoretical and simulation study are consistent with other theoretical and experimental investigations published in the literature.

Low-Cycle Fatigue Properties of Nickel-Based Superalloys Processed by High-Gradient Directional Solidification

The low-cycle fatigue (LCF) properties of DD10 (single-crystal) and DZ53 (columnar-grained) superalloys solidified by liquid–metal cooling (LMC) and high-rate solidification (HRS) processes have been systematically investigated. It was found that the LCF life of DZ53 solidified by LMC was obviously better than that solidified by HRS. In contrast, for DD10, LMC showed no remarkable influences on LCF properties at high temperature and only improved LCF properties at intermediate temperature. Microstructure examination showed that the cracks generally initiated at micropores in the subsurface at intermediate temperature. However, the cracks occurred on the surface due to oxidation, or persistent slip bands near script-MC at high temperature. Therefore, the benefits of LMC technique can be attributed to both of the reduced casting defects which significantly affect the LCF properties at intermediate temperature and the improved microstructural homogeneity which was strongly correlated to the LCF properties of alloys at high temperature.

The Effect of Multi-inclined Holes on the Creep Properties of Nickel-Based Superalloy

AbstractThe creep properties of GH3536 nickel-based superalloy plate specimens without/with multi-inclined holes were studied under applied stress 80/90/100 MPa at 850 ℃, respectively. Interesting finding is focused on the inflection point, that is, both the fraction elongation and creep strain achieve the maximum value under 90 MPa. Further study is carried out by two methods: the finite element analysis (FEA) calculation and scanning electron microscope (SEM). The FEA results show that the dangerous areas appear in the regions near the end of ellipse axis along the inclined angle orientation, which is similar to the actual fracture appearances. What is more, the tiny holes and dimples are the main characters of creep fracture for multi-inclined hole specimens, whereas the creep fracture of specimens without holes is the result of growth and coalescence of voids. In addition, based on creep performance, laser drilling is better than that of the electric spark drilling, which provides a proof that the creep performance of specimens with multi-inclined holes will be better with the improvement of the drilling process.

Review and Analysis of Powder Prior Boundary (PPB) Formation in Powder Metallurgy Processes for Nickel-based Super Alloys

Powder metallurgy of nickel-based super alloys have been developed and used for a wide range of products, owing to their excellent high temperature rupture life, creep strength and fatigue crack growth resistance. Typical processes for high performance PM super alloys include hot isostatic pressing (HIPing), hot extrusion and hot isothermal forging. Hot isostatic pressing is normally conducted at a high temperature by using metal forming standards at low pressure for a long time. However an intrinsic problem, i. e. powder prior boundary (PPB) precipitate networks, can occur in the HIPing process. In this paper, a comprehensive review of PPB formation in the powder metallurgy of super alloys is presented. Research on PPB formation process from room temperature to high temperature and during HIPing, has been reviewed and PPB formation mechanisms are discussed. Methods to reduce PPB effects on the mechanical properties of nickel-based super alloys, including heat treatment, changing the proportions of composition elements, and plastic deformation to break up the PPB networks, are reviewed.

Microstructural Stability and Hot Deformation of γ–γ′–δ Ni-Base Superalloys

Nickel-base superalloys exhibit excellent high-temperature mechanical and physical properties and remain the first choice for structural components in advanced gas turbine engines for the aerospace propulsion and power generation applications. In response to the increasing demand for more efficient solutions and tighter requirements linked to gas turbine technologies, the properties of nickel-base superalloys can be improved by modification of their thermo-mechanical and/or compositional attributes. Recent investigations have revealed the potential use of ternary eutectic γ–γ′–δ Ni-base superalloys in advanced gas turbines due to high temperature mechanical properties that are comparable to state-of-the-art polycrystalline Ni-base superalloys. With properties largely dependent on microstructural strengthening mechanisms, both the composition and thermo-mechanical processing parameters of this novel class of alloys need to be optimized concurrently. The hot deformation characteristics of four γ–γ′–δ Ni-base superalloys with varying levels of Nb were evaluated at temperatures and strain rates between 1353 K and 1433 K (1080 °C and 1160 °C) and 0.01 to 0.001/s, respectively. Evidence of dislocation-based plasticity was observed following deformation at low temperatures and high strain rates, while high temperatures and low strain rates promoted superplasticity in these alloys. The extent of the microstructural changes and the magnitude of the cavitation damage which occurred during deformation was found to vary as a function of the alloy composition.

NICKEL BASE SUPERALLOYS USED FOR AERO ENGINE TURBINE BLADES

ABSTRACTNickel base Superalloys service at high temperatures, particularly in the hot zones ofgas turbine engine. These materials allow the turbine to operate more efficiently bywithstanding higher temperatures. Turbine Inlet Temperature (TIT) depends on thetemperature capability of first stage high-pressure turbine blade made of nickel basesuperalloys exclusively.Single crystal Nickel base turbine blade is free from g/ g¢ grain boundaries;boundaries are easy diffusion paths and therefore reduce the resistance of thematerial to creep deformation.Experimental investigation carried out by using Different scrap of turbine blades withdifferent chemical compositions were melted aiming to control the chemicalcomposition of the product alloy, leading to a steel alloy called iron base superalloywith nickel content (24.3%) and chromium content (13.2%) this new alloy has almostthe same mechanical properties of nickel base superalloy of higher price. This newalloy can be used for production of turbine blades for small gas turbine engines lessthan 200 KW. Solidification behavior of stepped cast specimen of nickel basesuperalloy was studded by using three different cast thicknesses size. The resultsand conclusion of this work show that the higher the cooling rate is the better themechanical properties. The results also show that the increase of cobalt and titaniumcontents of nickel base alloy from 1.08 & 9.31 and 2.68 & 10.78 respectively leads toan increase in ultimate tensile strength, yield strength and hardness. Microstructureinvestigation of nickel base superalloys was conducted on all samples, the resultsshow the continuous matrix (g) and the primary strengthening phase (g¢), themicrostructure change from dendrite structure to a fine cellular one by increasingtitanium percent content.

Evaluation of Creep Deformation and Mechanical Properties of Nickel-based Superalloys through FE Analysis Based on Crystal Plasticity Models

Abstract The shape and the size of the γ ′ phase s are the controlling factors for the mechanical and creep properties of nickel-based super-alloys. In order to take into account of the effect of these underlying microstructures on the deformation behavior of these alloys, a multi-scale approach is essential. In this work, a homogenized dislocation density based crystal p asticity model has been developed from a detailed model containing γ − γ ′ phase s exclusively at the lower length scale. The mechanisms like anti-phase boundary shearing and micro-twinning etc. have been incorporated. The model has been used to simulate the creep deformation behavior of single crystal experiments. The results of simulation were compared to those of experiment and were found to be satisfactory.

Chemical and Structural Characterization of γ/γ′ Interfaces

More attention has been paid to the interfaces since mechanical properties of nickel-base superalloys are determined to some degree by them. The compositional transition across γ/γ′ interfaces and atomic structure of the interfaces was investigated using three-dimensional atom probe tomography and scanning transmission electron microscope equipped with high-resolution Energy Dispersive X-ray Spectrometry. Results show that no obvious segregation to the interfaces or ledges of the precipitates in the present experimental alloys has been observed. Also, adsorption of a solute to the interface was not observed. The interfaces are not flat as usually thought at an atomic scale. The interfacial thickness is about two atomic layers, i.e. 0.7 nm.

Effect of temperature on motion of misfit dislocation in γ/γ'interface of a Ni-based single-crystal superalloy:molecular dynamic simulations

The effect of temperature on motion of misfit dislocation in the γ/γ' interface of a Ni-based superalloy is studied in periodic simulation cells subjected to an applied shear stress. The simulation results show that no matter what temperature is, the motion of misfit dislocation occurs through the nucleation and the propagation of the double kink; at low temperature, the interaction of the misfit dislocation facilitates the motion of the misfit dislocation; on the contrary, at higher temperature, it can obstruct the motion of the misfit dislocation, and improves the mechanical properties of nickel-base superalloys.

The thermodynamic modeling of precious-metal-modified nickel-based superalloys

Thermodynamic modeling of precious-metal-modified Ni-based super-alloys (PMMS) was performed in this study using the CALPHAD approach. With this approach, the effects of platinum-group metals (PGMs) such as platinum, iridium, and ruthenium on the properties of nickel-based superalloys and their interplay with other alloying elements were understood from a thermodynamic and phase equilibrium point of view. Thermodynamic database containing PGMs was developed on the basis of the PanNi1 database for multi-component nickel alloys. The database was first validated with available experimental data. It was then used to understand phase stability and phase transformation temperatures, such as liquidus, solidus, and γ′ precipitation temperature, of PGM modified nickel-based superalloys. The effects of alloying elements on the formation of strengthening γ′ precipitate and their partitioning in γ and γ′ were also discussed.