Ni-based Superalloy Research Articles

Behavior of YSZ (High Y2O3 Content) Layer on Inconel to Electro-Chemical Corrosion

The high yttria content of a stabilized zirconia (YSZ) (38 wt% Y2O3) coating was deposited by atmospheric plasma spraying (APS) from Metco 207 powders on an Inconel 718 (Ni-based superalloy) substrate. As a metal coating connection, a layer of cermet powder (Ni-20% Al—410NS) was used before the ceramic layer deposition. The electro-chemical corrosion resistance of these materials was tested using Inconel cylinders with a diameter of 10 mm and a thickness of 1 mm, with and without the ceramic layer. Linear and cyclic measurements were obtained in H2SO4 electrolyte media at pH = 2. Electro-impedance spectroscopy (EIS) experiments were performed on the sample covered with the ceramic layer to evaluate the interface behavior. Scanning electron microscopy (SEM), along with equipment to determine chemical composition, and an energy dispersive spectrometry (EDS) detector were used to characterize the material surface before and after corrosion tests. It was observed that the corrosion resistance of Inconel was influenced by the bonding layer and the ceramic coating.

Effect of Zr on creep deformation behaviors of PM Ni-based superalloys

Effect of Zr on creep deformation behaviors of PM Ni-based superalloys

Precipitation-controlled grain boundary engineering in a cast & wrought Ni-based superalloy

Grain boundary engineering (GBE) describes the various approaches to control the fraction and composition of special boundaries in designing engineering materials. For example, complex thermo-mechanical processing routes are harnessed to increase the fraction of Σ3 twin boundaries, bringing about improvements to strength, toughness, and corrosion properties in austenitic stainless steels. However, high-temperature gas turbine engine components designed for the most demanding applications must be manufactured from Ni-based superalloys. To provide the required high-temperature strength, their microstructures are highly complex and consist of an austenitic γ-matrix, γ' precipitates, and grain boundary (GB) carbides, and/or borides. GBE approaches for Ni-based superalloys have been reported to reduce in-service GB cracking via targeted engineering of the GB microstructure. However, the same complex microstructures severely limit the processability of the most advanced Ni-based superalloys required to develop the next generation gas turbine engines.To tackle this challenge, we propose precipitation-controlled GBE for Ni-based superalloys with limited formability, via formation of GB serrations and precipitation upon slow cooling. We showcase our approach by achieving controlled GB precipitation of GB-γ' and M6C carbides in the cast & wrought Ni-based superalloy René 41 via a simple heat treatment. Ductility improvements are predicted via crystal plasticity modeling due to increased slip transmission compatibility. Instead of generating additional Σ3 twin boundaries only, these interfaces are directly incorporated into the GB network. It is shown that precipitation-controlled GBE is enabled by GB-γ' nucleating heterogeneously on M6C whereby competitive coarsening of GB-γ' provides the driving force. The fundamental mechanisms of our GBE approach are discussed and summarized in a qualitative microstructural model.

Stability of high energy superlattice faults in Ni-based superalloys from atomistic simulations

High energy stacking faults generated by lattice dislocations entering the strengthening precipitates of Ni-based superalloys are responsible for the unique mechanical properties of these structural materials. However, the question about stability of these faults has not received the attention it deserves. Using atomistic simulations, we show that the anti-phase boundary (APB) can spontaneously transform into super intrinsic stacking fault (SISF) and the complex stacking fault (CSF) can spontaneously transform into L12 lattice structure. The former transformation explains the experimentally observed presence of isolated SISFs and super extrinsic stacking faults (SESFs) in the precipitates. Finally, multiple studies were focused on finding alloying additions which increase the APB and CSF energies. We demonstrate therefore that alloying additions which increase stacking fault energies may conversely decrease their stabilities.

Oxidation behavior of a low-cost second-generation Ni-based single crystal superalloy at 900 °C and 1000 °C

Oxidation behavior of a low-cost second-generation Ni-based single crystal superalloy at 900 °C and 1000 °C

Local plastic deformation in the vicinity of topologically close-packed phases in a Ni-based single crystal superalloy

Local plastic deformation in the vicinity of topologically close-packed phases in a Ni-based single crystal superalloy

Carbide precipitation in a Ni-based superalloy fabricated by DED and cast after long-term thermal exposure

Carbide precipitation in a Ni-based superalloy fabricated by DED and cast after long-term thermal exposure

Influence of hydrogen on the γ-matrix lattice parameters of a Ni-based superalloy - a synchrotron diffraction study

Influence of hydrogen on the γ-matrix lattice parameters of a Ni-based superalloy - a synchrotron diffraction study

Single-crystalline Ni-based superalloy builds using laser-directed energy deposition (L-DED): A multi-scale modeling and experimental approach

Single-crystalline Ni-based superalloy builds using laser-directed energy deposition (L-DED): A multi-scale modeling and experimental approach

Investigation of Microstructure and Hot Crack Formation Mechanisms in the Heat-Affected Zone of GTAW-Repaired Cast K4002 Nickel-Based Superalloy with HGH3113 Filler Metal

Surface forming employing the gas tungsten arc welding (GTAW) with the HGH3113 filler metal was developed to repair gas-turbine investment castings composed of the non-weldable cast Ni-based superalloy K4002. This study mainly investigated the microstructure evolutions, fracture modes of the as-cast and repaired specimen, as well as the formation mechanisms of hot cracks. The results showed that as-cast K4002 alloy had millimeter-sized grains and various phases and solidified as follows: L → L1+γ1 → L2+γ1+(γ2+MC(1))eut →γ1+(γ2+MC(1))eut+(γ3+γ'1)eut+MC(2) → γ1+(γ2+MC(1))eut+(γ3+γ'1)eut+MC(2)+γ'2. The phase transformations of repaired specimens were intricate. The cladding layer (CL) was constituted of columnar dendrites of varying dimensions, as well as the precipitated carbide particles and flocculent structures within the interdendrites. In the heat-affected zone (HAZ), the reprecipitated granular carbides coexisted with the initial blocky carbides, and the sizes and morphologies of the γ' phase were also significantly different. Compared with the as-cast condition, the volume fractions of the γ/γ' eutectic, MC carbide, and initial γ' exhibited a decrease from 14.7% to 9.7%, 2.5% to 2.0%, and 62.1% to 43.1%, respectively. The tensile strength after repair reduced slightly, but the ductility improved significantly. What’s more, liquation cracking, strain-age cracking (SAC), and ductility-dip cracking (DDC) all occurred in the HAZ. There was a partially melted zone (PMZ) between the CL and HAZ. The PMZ contained reprecipitated γ/γ' eutectics and fine carbides, and both liquation cracks and SAC arose from this region. The intergranular liquid film solidified through two modes (liquid film migration and normal solidification), which led to insufficient wetting of the grain boundaries, forming the liquation crack. Both SAC and DDC eventuated under great stress due to the reduction of grain boundary ductility. These two kinds of cracks were identified by the type of precipitated phases around the cracks. Moreover, high-angle grain boundaries decreased the susceptibility of liquation crack but intensified the DDC sensitivity.

Effect of scan strategy and substrate preheating on crack formation in IN738LC Ni-based superalloy during laser powder bed fusion

Effect of scan strategy and substrate preheating on crack formation in IN738LC Ni-based superalloy during laser powder bed fusion

Cutting performance and surface integrity during rotary ultrasonic elliptical milling of cast Ni-based superalloy

Cutting performance and surface integrity during rotary ultrasonic elliptical milling of cast Ni-based superalloy

Influence of Aging Treatment and Volume Fraction on Nano-Indentation Behavior of Ni-Based Single Crystal Superalloys.

The effects of aging treatment and the volume fraction of precipitation particles on the nano-hardness and nano-indentation morphology of Ni-based single crystal superalloys are systematically investigated. Using nano-indentation tests and atomic force microscopy (AFM), this study examined the mechanical properties and related physical mechanisms of Ni-based superalloys that have two volume fractions of precipitation particles and four aging treatment times. Results analyzed using the Oliver-Pharr method indicate that prolonging the aging time or increasing the volume fraction of particles enhances the nano-hardness and creep resistance of Ni-based single crystal superalloys and reduces the indentation-affected area. Additionally, the nano-hardness and elastic modulus decrease gradually with increasing applied force, revealing an obvious indentation size effect. These variations are closely linked to the size and density of particles and work hardening rate, as well as to the topologically close-packed (TCP) phases, which influence dislocation movement and accumulation within the material and lead to various nano-indentation behavior in Ni-based single crystal superalloys. The related study provides theoretical guidance and experimental data to support the design and application of superalloys.

Dislocation dynamics in Ni: Parameterizing dislocation trajectories from atomistic simulations

We present a methodology using Differential Evolution Monte Carlo (DE-MC) to fit the parameters of an equation of motion to molecular dynamics (MD) trajectories of an a2〈110〉{111} edge dislocation in pure face-centered cubic (FCC) Ni, which is used as a model system. The motion of the edge dislocation under shear was observed using MD simulations with a classical effective potential, and the dislocation position was extracted. The parameters of interest were the effective mass, drag coefficient, and force experienced by the dislocation. Using DE-MC within a Bayesian framework, we estimated the joint posterior distribution of the parameters from the accepted samples produced by the DE-MC algorithm. The obtained distribution was then used to propagate the parameter uncertainties through the model, the equation of motion, which was used to predict the dislocation positions and velocities at the simulation timesteps as well as the uncertainty in the predictions. The mean fit was found to match the MD dislocation position data with a root mean square error (RMSE) of 0.2nm. We demonstrate how parameter distributions determined using the proposed methodology can be applied to obtain a mobility law for the class of dislocations studied with quantified uncertainties. This work is part of a longer-term study aiming to develop a surrogate model for precipitation strengthening, specifically dislocation-precipitate interactions, in Ni-based superalloys with uncertainty quantification. Accordingly, we also discuss the limitations of the selected model within this context and the necessary model extensions to overcome them. Published by the American Physical Society 2024

Hardness Degradation Behaviors of Ni-Base Superalloys after Phase Coarsening

Ni-based superalloys are commonly utilized in the production of hot-end components in the aerospace, energy, and other sectors. Due to the extreme environment, phase coarsening is prone to occur within the alloys, leading to degradation in the mechanical properties and thus posing a risk to equipment safety. To investigate the influences of volume fraction of precipitation particles and phase coarsening on hardness of materials, and explore the relationship between their microstructure and macroscopic hardness, based on the finite element method simulations, a two-dimensional Vickers hardness model is constructed for testing. Results show that hardness is closely linked to the particle shape, size, and distribution features; with the increase of the volume fraction of particles or the degree of phase coarsening, the hardness of alloys gradually weakens; and when the volume fraction of particles is larger, the decrease in the hardness is more obvious along with the degree of phase coarsening. Related research makes a good reference for the design of Ni-base superalloy structures as well as the evaluation or prediction of their mechanical properties during the service.

A phase-field study to explore the nature of the morphological instability of Kirkendall voids in complex alloys

The present research explores theoretical and computational aspects of the morphological instability of Kirkendall voids induced by a directed flux of vacancies. A quantitative phase-field model is coupled with a multi-component diffusion model and CALPHAD-type thermodynamic and kinetic databases to obtain a meso-scale description of Kirkendall void morphologies under isothermal annealing. The material under investigation is a diffusion couple consisting of a multi-phase multi-component single-crystal Ni-based superalloy on one side and pure Ni on the other side. The flux of the fastest diffuser in the superalloy, Al, towards the pure Ni causes a strong flux of vacancies in the opposite direction. This directed flux of vacancies leads to morphologically instable growth of voids. Phase-field simulations are performed in two (2D) and three dimensions (3D) to understand these instabilities, and the results are compared with experimental observations obtained by synchrotron X-ray tomography. Finally, the simulation results are analyzed with respect to the Mullins–Sekerka linear stability criterion.

Enhancing sulfur embrittlement resistance in Ni-based superalloys through synergistic effects of boron and carbon co-doping

Enhancing sulfur embrittlement resistance in Ni-based superalloys through synergistic effects of boron and carbon co-doping

Microstructure Analysis of the Alloy 625-nTiC Metal-Matrix-Composites Produced by Suction Casting

Alloy 625 is a Ni-based superalloy with the main alloying elements being Nb, Cr, and Mo. It is known for its excellent corrosion resistance, good weldability, both high heat and creep resistance, and good strength. The current work presents the microstructure of Alloy 625-nTiC metal matrix composites (MMC) fabricated through suction casting. The microstructure and chemical composition of strengthening phases were investigated by light microscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results showed that fabricated MMC composites are characterized by a dendritic microstructure with irregular distribution of the strengthening precipitates. Based on chemical composition analysis, the strong enrichment in Nb and Ti was revealed.

Investigating Elastic Deformation of Ordered Precipitates by Ab Initio-Informed Phase-Field Crystal Modeling

Ni-based superalloys, essential for high-temperature applications, derive strength from coherent second-order precipitates that impede dislocation motion through coherency misfit and elastic mismatch. This study employs multi-component phase-field crystal (PFC) simulations to explore the elastic deformation of such precipitates. Using a binary ordered square structure for the precipitate and a single species square structure for the matrix, elastic properties and lattice parameters are fitted to data from ab initio density functional theory calculations for Ni and Ni3Ti systems. Simulations reveal a smooth strain gradient across the matrix–precipitate interface with coherency misfit influenced by precipitate size and strain state. These findings highlight the utility of PFC simulations for understanding strain distribution and deformation in precipitate–matrix systems with the potential to offer insights for both experimental and computational studies.

Radiation Shielding and Spectroscopic Investigations of Newly Produced Co and Ni Based Super Alloys

Radiation Shielding and Spectroscopic Investigations of Newly Produced Co and Ni Based Super Alloys