Ni-Cr Alloy Research Articles

Additively Manufactured Stainless Steel Wind Tunnel Model Support Featuring Honeycomb Structures for Vibration Attenuation

Wind tunnel model support (WTMS) is an indispensable component of wind tunnel testing. However, the presence of vibrations within the model‐support system can compromise the accuracy of data and give rise to significant safety hazards. In this study, an approach for vibration attenuation by incorporating honeycomb structures into the design of the WTMS is proposed. To this end, stainless steel WTMSs with integrated honeycomb structures are fabricated by selective laser melting (SLM). Results showed that stainless steels prepared under optimized SLM processing parameters exhibit high crystallinity and consist of single‐phase Fe–Cr–Ni alloy. The stainless steels exhibited robust mechanical properties, including a tensile strength of ≈1 GPa, an elongation of ≈8%, and a compressive strength of ≈1.4 GPa. These exceptional mechanical properties can be attributed to the formation of a cellular structure and tangled dislocations. The first‐order and the third‐order resonant response of WTMS honeycomb structures can be effectively reduced. The vibration reduction mechanism can be attributed to the occurrence of local resonance when the natural frequency of the internal periodic unit of the WTMS closely matched the vibration frequency of the model. The utilization of honeycomb structures holds significant potential for achieving vibration attenuation in WTMS.

Sealing Ni-Cr/Ni-Al alloys with borosilicate glass: Bonding strength, sealing interface, and fracture behavior

Encapsulation of the cold junction of sheathed thermocouples by incorporating glass-to-metal seal, which substitutes for the conventionally used organic sealants, is expected to improve the reliability of thermocouples. In this study, the sealing of borosilicate glass with thermocouple wire materials, i.e., Ni-Cr and Ni-Al alloys, was investigated. Three types of specimens were prepared for both alloys: nonoxidized, mildly preoxidized, and deeply preoxidized. High-temperature sealing with borosilicate glass was conducted for each specimen. The results revealed that grain boundaries were preferentially oxidized in both alloys and that preoxidation significantly increased the bonding strength between the alloys and borosilicate glass. However, the preoxidation conditions corresponding to the optimal bonding strength differed between the two alloys, which necessitates tailored pretreatment of the metal surface. For the Ni-Cr alloy, the sealing interfaces indicated that the deeply preoxidized specimens achieved the optimal bonding strength because of the synergistic effect of the glass saturation mechanism and mechanical interlocking mechanism, whereas the mildly preoxidized specimens were affected by unexpected chemical reactions and the consequent microscopic defects at the sealing interface. For the Ni-Al alloy, the deeply preoxidized specimens exhibited inferior bonding strengths compared with the mildly preoxidized specimens, which was attributed to their overmature intergranular oxidation, in which the grain boundaries were eroded by molten glass during sealing and trapped the glass after cooling. The glass in the grain boundaries was stressed by the cooling contraction of the metals and became prone to cracking. This study reveals the microscopic bonding mechanisms for the sealing of glass to Ni-based alloys and the causes of failure, providing a new perspective on the regulation and optimization of the sealing interface.

Multi-dimensional analysis of Ni Cr alloy nanofilms based on Ps-LIBS technology

Multi-dimensional analysis of Ni Cr alloy nanofilms based on Ps-LIBS technology

Microstructure and Characteristics of the Welded Joint between Ni-Cr Alloys and Copper

Microstructure and Characteristics of the Welded Joint between Ni-Cr Alloys and Copper

Phase-field modeling of interdiffusion between dissimilar Fe-Cr-Ni alloys during non-isothermal hot isostatic pressing

Powder metallurgy hot isostatic pressing (PM-HIP) has emerged as a promising alternative to welding for joining dissimilar metals. During HIP, interfacial bonding is mediated by solid state diffusion. The interdiffusion zone across the interface depends on processing conditions, calling for the need for accurate numerical tools capable of simulating interdiffusion and possible phase transformation in order to optimize processing parameters. Here, a phase-field (PF) model based on CALPHAD-based free energy functionals is developed to simulate the interdiffusion and phase evolution between dissimilar Fe–Cr–Ni based steels undergoing HIP and is demonstrated using the interface between 316L and SA508 steels. To overcome the numerical challenges caused by the singular magnetic and entropy terms in the CALPHAD free energy models in the Fe–Cr-Ni system, polynomial functions are fitted with temperature dependent coefficients represented by Fourier series to accurately describe the phase stability of both fcc and bcc phases in the composition and temperature space. This enables simulations of non-isothermal HIP cycles. Diffusivity data from commercial software and literature are taken to parameterize the kinetic parameters. A discrete nucleation model is incorporated for possible phase transformation. The modified thermodynamic models are validated against previous experiments at 923 K and 1273 K. The interdiffusion kinetics are benchmarked against new HIP experiments joining powder and bulk 316L to bulk SA508 with three different HIP cycles. The good agreement between simulations and experiments on both phase stability and interdiffusion indicate that the model is suitable for simulating interdiffusion between Fe–Cr–Ni alloys during HIP cycles. It is also found that using powder and bulk 316L gives similar interdiffusion profiles at elevated temperature when a dense interface forms during HIP.

Centimeter-scale single-crystal hexagonal boron nitride freestanding thick films as high-performance VUV photodetectors

Large-scale hexagonal boron nitride (h-BN) single crystals are highly desirable not only as the substrate or dielectric for van der Waals heterostructures, but also the promising candidates in optoelectronics, electronics, detectors, as well as recently boomed room-temperature single-photon sources. Here, we report the synthesis of centimeter-scale single-crystal h-BN films with hundreds of micrometer thickness via the metal flux method. The growth control along the out-of-plane and in-plane directions of h-BN crystals is realized by the adjustment of NiCr alloy composition, from which the limited solubility of N atoms can be promoted by high diffusion in molten reactants. This also benefits to forming a distinct interface between the synthesized h-BN crystals and the metal ingot, giving rise to an easy exfoliation of the large area high-quality thick films. Such h-BN crystals have been demonstrated as both self-powered flexible and rigid vacuum-ultraviolet photodetectors, allowing for efficient photodetection in terms of high responsivity, rapid response speed, and high operational temperature. A maximum photoresponsivity of 3.35 mA/W is achieved at a wavelength of 185 nm with an operational temperature spanning to 500 °C (and possibly beyond). The large-area freestanding h-BN single crystal described herein reveals great potential as a high-performance photodetector, and versatile platform for other superb electronic and optoelectronic devices.

Atomistic analysis of the mechanisms underlying irradiation-hardening in Fe–Ni–Cr alloys

This work presents a comprehensive examination of the physical mechanisms driving hardening in irradiated face-centered cubic FeNiCr alloys. The evolution of irradiation-induced defects during shear deformation is modeled by atomistic simulations through overlapping cascade simulations, where the nucleation and evolution of dislocation loops is validated by transmission electron microscopy images obtained from irradiated FeNiCr alloys using tandem accelerator. The effect of different shear rates on the microstructure of irradiated materials with a specific focus on the changes in the density of voids and dislocation loops induced by irradiation was analyzed. Additionally, the fundamental interaction processes between single irradiation-induced defects contributing to irradiation hardening, such as voids and dislocation loops in the alloy are explained. The analysis at atomic level indicates that both the dislocation loops and the voids exhibit strengthening effects. Furthermore, the nanometric voids are much stronger obstacles than dislocation loops of comparable size. The mechanism of cutting the voids leads to an increase of voids density and thus contributes to an increase in irradiation hardening. The mechanism of collapse of small voids into dislocation loops leads to decrease of voids density and at the same time increase of loops density. The coupling effect between the density of voids and dislocation loops is determined. Finally, the novel, physical mechanisms-based model of irradiation hardening and dislocation-radiation defect reaction kinetics are developed, which consider the mechanisms of void cutting, void shrink and void collapse to dislocation loop.

Technical assessment of shear bond strength at ceramo-alloy interface after various surface treatment combinations and application of metal bonding agent.

Bonding between metal and ceramic is one of the most important aspects of a successful prosthesis. Various methods have been recommended for preparing the metal surface to enhance the bond between metal and ceramic including the use of a metal bonding agent. This study aims to evaluate and compare the shear bond strength of the metal-ceramic (M-C) interface after combinations of various surface treatments including the application of a metal bonding agent. 40 Ni-Cr alloy specimens were made and divided into 4 groups of 10 each based on the combination of surface treatments. Sandblasting, surface grinding, and Oxidation heat treatment (OHT) were performed on specimens from Group 1 (Control). In addition, Group 2 specimens received ultrasonic cleaning, Group 3 steam cleaning, and Group 4 metal bonding agent application. Following surface treatments on all specimens, porcelain build-up was performed, and shear bond strength was tested in a Digital Universal testing machine. The statistical tests used were independent t-test and ANOVA. Results revealed that Group 4 specimens had the highest mean value of shear bond strength of 39.087 MPa while Group 3 specimens showed the least mean shear bond strength of 18.154 MPa with highly statistically significant results (p< 0.001). The surface treatments and application of bonding agent to metal prior to porcelain application resulted in increased shear bond strength of the metal-ceramic interface.

Pulsed electroplating of ZrO2-reinforced Ni-Cr alloy coatings from the duplex complexing agents-containing bath for engineering applications: Importance of operating conditions

The progress in tribocorrosion performance of the engineering parts is in dire need of improving their surface properties. In the present contribution, Ni-Cr-ZrO2 layers were electrodeposited on St37 steel. The stress was put on optimizing the process factors, including the parameters involved in pulsed current electrodeposition and level of the ZrO2 reinforcing nanoparticles (0–20 g/L) in the bath. The surface characteristics of the electrodeposits were evaluated using FESEM, EDS, AFM, and XRD. The tribomechanical characteristics of the films were determined using a Vickers microhardness tester and pin-on-disk apparatus. The electrochemical behavior of the samples was studied using OCP, EIS, PDP, and immersion techniques. The results demonstrated that the included ZrO2 nanoparticles led to more homogenous, rougher, and defect-free surfaces, while they did not change the phase composition of the alloy electrodeposits. The polarization resistance of the Ni-Cr alloy coating increases by 6.7 times when 10 g/L of the reinforcing nanoparticles is added to the electrolyte. A decrease of ≈42 % in the mean COF value was obtained by the incorporation of 10 g/L ZrO2 nanoparticles into the plating bath. The coating system developed holds the promise to address both technical requirements and health concerns.

Effects of Ta Addition on the Microstructure, Compression Properties and Oxidation Resistance of NiAl-Cr(Mo) Alloy

Effects of Ta Addition on the Microstructure, Compression Properties and Oxidation Resistance of NiAl-Cr(Mo) Alloy

Development of Nickel-Chromium Alloy Electroplating and Its Surface Morphology Studies for Automobile Industries

In the electroplating industry, alloy plating is typically one of the most difficult processes. We are showcasing the Ni-Cr (Nickel Chromium) alloy electroplating in our work. Trivalent chromium bath is made in order to resist the hazardous hexavalent chromium, and co-deposition of chromium and nickel is accomplished. Our work is appropriate for industrial electroplating in the automotive industry because Ni-Cr alloy exhibits good corrosion resistance along with features including wear resistance, ductility, and thermal stability. Through the use of SEM (Scanning Electron Microscopy), EDAX (Energy Dispersive X-Ray Analysis), and XRD (X-Ray Diffraction) studies, we are able to clearly observe the surface morphology in this project. These research allow us to observe the Porous behavior surfaces. Figure 1

First-Principles Kinetic Monte Carlo Modeling of Passivation in Ni-Based Alloys

Corrosion by metal oxidation is a major problem for many structural materials, including Ni-based alloys in high-temperature applications. Passivation can be achieved through various alloying strategies, but common theoretical approaches to understanding key factors such as the critical concentration of the minor element are limited in their predictive capability. In particular, existing models often do not explicitly capture competing metal cation migration mechanisms in the oxide. In this study, we examine passivation kinetics of Ni-Cr and Ni-Al alloys by modeling the evolution of initial NiO oxide films as Cr/Al are incorporated. Surrogate models for the energies of various oxide configurations and the migration barriers of metal cations are parameterized from density functional theory calculations. These inputs are used to drive kinetic Monte Carlo simulations over long time scales. By tracking the time-dependent oxidation behavior across alloy composition, we predict critical concentrations of Cr/Al to form continuous passivation layers. Compositional and structural analyses of the simulated oxides are used to quantify fractions of different phases and provide insight into the nature of passivation in each alloy system. The effect of increasing or decreasing the exchange rate of metal atoms near the alloy-oxide interface, which can be related to alloy processing, is also explored. We discuss the applicability of our method to other systems and its incorporation into an existing open-source software package.This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Oxidation Kinetics in Ni-Cr Alloys Through Comprehensive Analysis of Parabolic and Cubic Grain Growth Dynamics and Their Implications on High-Temperature Oxidative Stability

Oxidation Kinetics in Ni-Cr Alloys Through Comprehensive Analysis of Parabolic and Cubic Grain Growth Dynamics and Their Implications on High-Temperature Oxidative Stability

Effect of powder composition, PTAW parameters on dilution, microstructure and hardness of Ni–Cr–Si–B alloy deposition: Experimental investigation and prediction using machine learning technique

The implementation of hard-facing alloy on the existing materials caters the need for high-performance surfaces in terms of wear and high temperatures. The present research explore the effect of Plasma Transferred Arc Welding (PTAW) parameters and powder composition on dilution, microstructure and hardness of the commonly used hard-facing alloy Ni–Cr–Si–B powder. The hard-facing alloy was deposited with three weight proportions of boron (2.5 %, 3 % and 3.5 %). The statistical-based Grey Relational Analysis (GRA) followed by a Machine Learning Algorithm (MLA) was implemented to identify the ideal parameters and degree of significance of each parameter and for the prediction of the responses. The dilution percentage, microstructure analysis, and phase detection were estimated through elemental analysis, Scanning electron Microscopy (SEM) and X-ray Diffraction Analysis (XRD) respectively. The experimental and modelling results revealed that 400 mm/min of scanning speed, 8 gm/min of powder delivery, 14 mm of stand-off distance, and 120 A of current were the optimal parameters along with 3.5 wt% of boron powder composition to yield a better dilution, microstructure and hardness.

Oxidation of additive manufactured 699XA Ni-based alloy under different atmospheres

The oxidation behaviour of an additively manufactured (AM) NiCrAl alloy (VDM® Powder 699XA) was compared with the hot rolled counterpart in different atmospheres (dry air, Ar-10 %H2 and Ar-10 %H2-10 %H2O) for 48 h at 950 and 1100°C. Internal oxidation occurred through the twin boundaries and dislocations in the AM material. Such defects promoted the outward diffusion of Al and the growth of a protective Al2O3 scale at reduced PO2 (Ar-10 %H2 and Ar-10 %H2-H2O), hence restraining the internal oxidation. It is thus demonstrated that this high Cr-containing alloy is a marginal alumina former under controlled conditions like the hot rolled alloy.

Oxidation of Ni–30Cr Alloy at Low Temperature and Low Oxygen Partial Pressure: Experimental Methods to Improve Kinetics Constants Determination

Ni–30Cr model alloy was used to study chromia-scale formation behaviour. During its formation the mass variation signal is weak and it is important to take specific care to measure oxidation kinetics by thermogravimetric analysis. Symmetrical design allows the determination of very small mass changes in compensating buoyancy effects and limiting measurement drift. The mass variation measurement comprises noise coming from different sources that affects the electronic signal. It must be minimised to improve accuracy. This involves keeping the room-temperature constant, strictly balancing the beam and minimising buoyancy effects. By this way it was possible to acquire kinetics and to measured rate constants, kp, in a range from 3.10–5 to 3.10–10 mg2.cm−4.s−1 equivalent to 10–12 down to 10–17 cm2.s−1. Oxygen partial pressure (PO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${P}_{{O}_{2}}$$\\end{document}) was monitor and revealed an abnormal consumption of oxygen at the beginning of the thermal exposure. Experiments with an inert material showed parasitic reactions identified by mass spectrometry as combustion of impurities. As oxygen consumption is not only due to oxidation of the sample, corrosion kinetics can’t be deduced from it. Hence, to determine whether the oxygen supply from the gas is a limiting parameter, a model, which quantifies oxygen consumption by sample oxidation within the thermobalance, is proposed.

Effect of Calefaction and Stress Relaxation on Grain Boundaries/Textures of Cu–Cr–Ni Alloy

The Cu–Cr–Ni alloy is a key material for the manufacturing of connectors, which requires excellent resistance to stress relaxation. However, the inherent correlation among microstructure, texture, and properties is still unclear. In this study, we investigated the influence of calefaction and stress relaxation on the grain boundaries (GBs), textures, and properties of the Cu–Cr–Ni alloy. The results showed that calefaction and stress relaxation had opposite effects on GBs and textures. Calefaction led to a decrease in the proportion of low-angle grain boundaries (LAGBs), an increase in the Schmidt factor (SF) value of the grains, and a transition of texture from &lt;111&gt; to &lt;113&gt;. The grains with higher SF values were more susceptible to plastic deformation, which deteriorated the stress relaxation resistance. By comparison, stress relaxation led to an increase in the proportion of LAGBs, a decrease in SF values of the grains, and a transition of texture from &lt;113&gt; to &lt;111&gt; and &lt;001&gt;. After stress relaxation, the variation trends of the GBs and textures were consistent with those of other plastic deformations, indicating that stress relaxation can be verified by the variations in GBs and textures. Our findings provide a theoretical basis for improvements in stress relaxation resistance of the Cu-based alloys used in connector industry.

Elucidating the role of Cr migration in Ni-Cr exposed to molten FLiNaK via multiscale characterization

Structural materials used in nuclear reactor environments are subjected to coupled extremes such as high temperature, irradiation, and corrosion which act in concert to degrade their functional performance. Connecting alloy microstructure such as grain boundaries, and accumulating point defects with corrosion attack and pore morphology is critical to understanding underlying mechanisms. We uncover the compositional variations and morphology at multiple length scales in corrosion-damaged Ni-Cr alloy after exposure to oxidants in molten fluoride salts. A complex network of dense corrosion pores is detected by surface-level SEM observations. The corrosion pores take on a 1-dimensional morphology and are enriched with Ni and depleted of Cr 1–5 µm from the pore surface. STEM-EDS and 4D-STEM strain maps acquired simultaneously highlight the local variations in composition and structure of a ≤ 200 nm Cr-rich layer identified from a cross-section taken at the bottom of an isolated corrosion pore between the Ni-Cr alloy matrix and the embedded salt. However, the absence of an observed interface between the Ni-Cr alloy matrix and the FCC-structured Cr-rich layer suggests that Cr plating from the salt did not transpire. These findings support a proposed Cr lattice diffusion mechanism rather than Cr-precipitation from the salt to accommodate temperature transient conditions during sample cooling. Through the development of a 1D phase field model, these results are rationalized by formation energies for the Ni- and Cr-oxidation into the molten salt. This study reveals the locally altered microstructure caused by high temperature corrosion in non-steady-state molten salt nuclear reactor environments.

Propane steam reforming over La0.8Sr0.2Ni1-yMyO3 (M = Cr, Mn, Fe, Co) perovskite-type oxides

Perovskite-type oxides have attracted significant attention in recent years as potential catalysts for hydrocarbon reforming reactions. Herein, a series of oxides with the formula La0.8Sr0.2Ni1-yMyO3 (LSNi1-yMy; M=Cr, Mn, Fe, Co) have been synthesized and tested for the propane steam reforming (PSR) reaction. Materials were characterized employing BET, XRD, H2-TPR, SEM/EDX, TEM/SAED and TPO techniques. Optimal results were obtained for LSNi0.5Cr0.5, which exhibited high propane conversion (78 %), H2-selectivity (98 %), and excellent stability with time-on-stream (40 hours) at 600 °C. This has been attributed to the exceptional ability of LSNi0.5Cr0.5 to maintain its perovskite structure under reaction conditions, the in situ formation of finely dispersed Ni-Cr alloy crystallites, and the suppression of reactions that lead to graphitic carbon deposition. This study provides deeper insight into the effects of structural properties and reducibility of perovskite-type oxides on their catalytic properties and can be used to design catalysts with improved performance.

First-principles and cluster expansion study of the effect of magnetism on short-range order in Fe–Ni–Cr austenitic stainless steels

Short-range order (SRO), the regular and predictable arrangement of atoms over short distances, alters the mechanical properties of technologically relevant structural materials such as medium/high entropy alloys and austenitic stainless steels. In this study, we present a generalized spin cluster expansion (CE) model and show that magnetism is a primary factor influencing the level of SRO present in austenitic Fe–Ni–Cr alloys. The spin CE consists of a chemical cluster expansion combined with an Ising model for Fe–Ni–Cr austenitic alloys. It explicitly accounts for local magnetic exchange interactions, thereby capturing the effects of finite temperature magnetism on SRO. Model parameters are obtained by fitting to a first-principles data set comprising both chemically and magnetically diverse face-centered cubic configurations. The magnitude of the magnetic exchange interactions are found to be comparable to the chemical interactions. Compared to a conventional implicit magnetism CE built from only magnetic ground state configurations, the spin CE shows improved performance on several experimental benchmarks over a broad spectrum of compositions, particularly at higher temperatures due to the explicit treatment of magnetic disorder. We find that SRO is strongly influenced by alloy Cr content, since Cr atoms prefer to align antiferromagnetically with nearest neighbors but become magnetically frustrated with increasing Cr concentration. Using the spin CE, we predict that increasing the Cr concentration in typical austenitic stainless steels promotes the formation of SRO and increases order–disorder transition temperatures. This study underscores the significance of considering magnetic interactions explicitly when exploring the thermodynamic properties of complex transition metal alloys. It also highlights guidelines for customizing SRO through adjustments of alloy composition.