Ni Cr System Research Articles

Thermodynamics and kinetics of long-range ordering in FCC Ni-33at.%Cr alloys: Insights from atomic scale modeling

This study investigates the thermodynamics and kinetics of the Ni-Cr system, focusing specifically on the kinetics of the order–disorder phase transformation in the Ni-33at.%Cr alloy. Combining density functional theory, CALPHAD-type models, and experimental diffusion data, we introduce and validate an efficient pair interaction model (PIM) and use it in Monte Carlo simulations. Our results include a detailed phase diagram of Ni-Cr in face-centered cubic structure and kinetic models that delineate the behavior of solid solutions at high temperatures and ordered structures at low temperatures. The simulations shed light on tracer diffusion and ordering kinetics within Ni-33at.%Cr, demonstrating good agreement with existing experimental data. Furthermore, our simulation-driven insights prompt a reevaluation of certain aspects of related experimental studies concerning the apparent ordering activation enthalpies and growth kinetics. We also provide a thorough discussion on the strengths of our models and features for future improvement.

Accelerating the development of Fe–Co–Ni–Cr system HEAs with high hardness by deep learning based on Bayesian optimization

Accelerating the development of Fe–Co–Ni–Cr system HEAs with high hardness by deep learning based on Bayesian optimization

Structure and tribological properties of detonation coatings based on Cr3C2-NiCr after pulse-plasmaine treatment

Cr3C2-NiCr metal-ceramic coatings have found wide application in the protection of machine parts and equipment operating under extreme conditions. In this study, Cr3C2-NiCr based detonation coatings which have been subjected to pulse-plasma treatment were studied. The study showed that IPO reduced the surface roughness by 48 %, reduced the coating friction coefficient by about 2 times, increased the hardness of the coatings from the original 12 GPa to 16.2 GPa and improved their wear resistance by 2 times compared to untreated coatings. Pulse-plasma treatment provides qualitative formation of coatings from metal-ceramic material of Cr3C2-NiCr system with complex heterogeneous structure-phase state, where the layered structure of areas of carbide particles and matrix metal in immediate proximity from “carbide-matrix” border with selections in matrix of dispersed secondary carbides is revealed.

On the use of nanometer-scale multilayers to determine interdiffusion coefficients: Comprehensive characterization of interdiffusion at low temperature in the Ni–Cr system

Nanoscale multilayers offer a convenient way to determine interdiffusion coefficients at low temperatures. However, knowledge regarding the impact of the microstructure on measurements is limited. In the present study, we measure the interdiffusion coefficient in the face-centered cubic (fcc) solid solution of the Ni–Cr system at 440 °C using multilayers composed of alternating layers of pure Ni and Ni78Cr22 (at.%), with a nominal wavelength of 4.5 nm. Three techniques were used to characterize the evolution of the multilayers with annealing time: atom probe tomography (APT), energy-dispersive X-ray spectroscopy (STEM-EDX) and X-ray reflectivity (XRR). Each technique allowed to determine an interdiffusion coefficient. The results evidence that the interdiffusion coefficient is dependent from the technique used to measure it. The primary cause is a very complex microstructure resulting from the elaboration method used to obtain the fine concentration modulation. The analysis of atom probe tomography volumes reveals a high density of columnar grain boundaries (GB) with extended chemical widths. The segregation at GB was measured and a model was derived, allowing to dissociate the contribution of lattice interdiffusion between layers from that of diffusion along and perpendicularly to GBs. The present results could serve as guides for future diffusion investigations involving multilayers.

Effect of Cr on a Ni-Catalyst Supported on Sibunite in Bicyclohexyl Dehydrogenation in Hydrogen Storage Application

A comparison of the activity of mono- and bimetallic Ni-Cr/C catalysts deposited on a carbon carrier (sibunite) in the bicyclohexyl dehydrogenation reaction as a stage of hydrogen evolution in hydrogen storage systems is carried out. The interaction of Ni and Cr supported onto the carbon carrier—sibunite in bimetallic NiCr systems affects the change in the parameters of the crystal lattice of nickel, compared with the FCC lattice of Ni, as shown by the methods of XPS, TPR, XRD, high-resolution TEM and electron diffraction.

Effect of chemical disorder on Griffiths phase in weak itinerant ferromagnetic Ni92−xCuxCr8 alloy

We report magnetic and thermal properties of Cu substituted Ni92−xCuxCr8 polycrystalline alloys close to their critical concentration (xc~18%), where ferromagnetic order disappears. From the detailed analysis of field and temperature dependent magnetization data weak itinerant ferromagnetic character has been identified for the compositions below xc. Spin-fluctuations theory using the Ginzburg–Landau formalism further revealed the contributions of spin fluctuations, which increase near xc. Specific heat data shows unusual low-temperature variation with an enhanced Sommerfeld coefficient and non Fermi-liquid behavior due to strong magnetic fluctuations near xc. The magnetization data and the linear term of the specific heat follow the theoretical predictions of a ferromagnetic quantum critical point within the experimental uncertainties. The exponent of the power-law M(H) ∝Hλ fits to low-temperature magnetic isotherms and its variation with composition indeed suggests a possibility of quantum Griffiths phase in these alloy compositions. Finally, this study shows that the Cu substituted Ni-Cr system shows Griffiths phase at critical point even after the reduction of disorder.

Investigation of the Nature of the Interaction of Me-MeN-(Me,Mo,Al)N Coatings (Where Me = Zr, Ti, or Cr) with a Contact Medium Based on the Ni-Cr System

This paper discusses the results of a study focused on the nature of the interaction of Me-MeN-(Me,Mo,Al)N coatings (where Me = zirconium (Zr), titanium (Ti), or chromium (Cr)) with a contact medium based on the Ni-Cr system. The studies were carried out during the turning of nickel–chromium alloy at different cutting speeds. The hardness of the coatings was found, and their nanostructure and phase composition were studied. The experiments were conducted using transmission electron microscopy (TEM), X-ray diffraction (XRD), and selected area electron diffraction (SAED). According to the studies, at elevated cutting speeds, the highest wear resistance is demonstrated by the tools with the ZrN-based coating, while at lower cutting speeds, the tools with the TiN- and CrN-based coatings had higher wear resistance. At elevated cutting speeds, the experiments detected the active formation of oxides in the ZrN-based coating and less active formation of oxides in the CrN-based coating. No formation of oxides was detected in the TiN-based coating. The patterns of cracking in the coatings were also studied.

Wagner interaction coefficient between nitrogen and chromium in liquid nickel-based alloys

The authors propose a simple theory of thermodynamic properties of nitrogen solutions in liquid Ni–Cr alloys. This theory is completely analogous to the theory for liquid nitrogen solutions in alloys of the Fe–Cr and Fe –Mn systems proposed previously by the authors in 2019 and 2020. The theory is based on lattice model of the Ni–Cr solutions. The model assumes FCC lattice. In the sites of this lattice are the atoms of Ni and Cr. Nitrogen atoms are located in octahedral interstices. The nitrogen atom interacts only with the metal atoms located in the lattice sites neighboring to it. This interaction is pairwise. It is assumed that the energy of this interaction depends neither on the composition nor on the temperature. It is supposed that the solutions in the Ni–Cr system are perfect. Within the framework of the proposed theory, a relation is obtained that expresses the Wagner interaction coefficient between nitrogen and chromium in liquid nickel-based alloys. The right-hand part of the appropriate formula is a function of ratio of the Sieverts law constants for solubility of nitrogen in liquid chromium and nickel. The values of these constants for the temperature of 1873 K are assumed to be K′(Cr) = 15,2; K′(Ni) = 0,0015 wt. %. An estimate is obtained for the Wagner interaction coefficient in nickel-based alloys = 21,4. This corresponds to the value of the Langenberg interaction coefficient = –0,105, wich is very close to the experimental estimates = –0,108 for the temperature of 1873 K (Surovoi et al., 1971) and = –0,11 for the temperature of 1823 K (Stomakhin at al., 1965).

Quantitative description of the role of Cr on the ordering characteristics of a single phase Ni-16 wt.% Mo- 7wt.% Cr alloy

Binary and ternary Ni-Mo based alloys under the service conditions of high temperature show precipitation and chemical ordering which influence their microstructure, mechanical and corrosion properties. In the present work, the phase transformation behaviour of Ni-Mo and Ni-Mo-Cr alloys is studied to identify the role of Cr in altering the stability of brittle ordered intermetallic phases. TEM characterization demonstrates that the addition of Cr destabilizes not only the long-range ordered D1a phase but also the short-range order represented by <1 ½ 0> ordering wave vectors. EXAFS studies on Ni-Mo and Ni-Mo-Cr alloys establish preferential bonding of Cr with Ni as the first nearest neighbour in the fcc lattice replacing Mo. The cluster-expansion based calculations on Ni-Mo, Ni-Cr and Cr-Mo systems show that the nearest neighbour pair and multisite interaction energies are changed in magnitude as well as in sign for Ni-Mo and Ni-Cr systems signifying that the D1a type ordering tendency is reduced with Cr addition and the disordered fcc phase is stabilised. A combination of experimental and theoretical studies unequivocally establishes the stability of the disordered fcc structure, which is crucial for the long-term use of the selected Ni-Mo-Cr alloy at elevated temperatures.

Surface and Size Effects on the Behaviors of Point Defects in Irradiated Crystalline Solids

We present an elaborate study of the surface and size effects on the transient and steady-state behaviors of point defects in irradiated solids. In this investigation, both pure Ni and binary Ni-Cr were utilized as model systems. We utilize the spatially-resolved rate-theory (SRRT) modeling approach, and directly account for the effects of dose rate, production bias, and defects recombination, reactions with volumetric sinks, and diffusion to surface sinks. Several simulations were conducted to investigate the effects of these parameters in both coupled and decoupled manners. In the presence of production bias, the effects of surface and size persist even as the surface to volume ratio decreases. This was associated with a surface-induced and size-regulated instability. This instability is only triggered above a critical size between 100 and 500 nm. The critical size decreases with increasing dose rate, increasing production bias, or lowering the temperature. Moreover, this instability results in a pattern that favors the separation of vacancies and interstitials. Once this pattern develops, anomalies in the dependence on size for the transient and steady-state concentrations of point defects and the surface/boundary sink strength are observed. These anomalies tend to render irradiation damage more severe. For pure Ni, it was shown that vacancy supersaturation increases with size, and the rate of increase also rises with size. For the binary Ni-Cr system, it was shown that the magnitude of enrichment/depletion of Ni/Cr at the boundary increases with size, and the width of the enrichment/depletion layer also increases with size. The results obtained here agree well with experimental observations in irradiated materials such as the formation of void denuded zones adjacent to grain boundaries and the size and temperature dependence of the radiation resistance of nanomaterials. The size-dependent behaviors reported here also shed new light on the radiation tolerance of nanomaterials, i.e., the irradiation-induced instabilities are suppressed in such materials. Lastly, the implications of the results obtained here on the development of efficient reduced order models or the utilization of ion irradiation as a surrogate to neutron irradiation are discussed.

Characterization, growth kinetics and formation mechanism of aluminide coating by plasma paste aluminizing on IN738

In this research, with the single-step plasma paste aluminizing technique which has been considered in recent years, aluminizing of a Ni-base superalloy (IN738) was performed at 600, 700 and 800 °C for 0.5, 1, 2 and 4 h. The paste was composed of pure Al powder and ethanol. FE-SEM analysis showed that a multi-layer aluminide coating was formed on the IN738 samples. The outer layer of the coatings consisted of Al3Ni2, ζ-phase in Al–Ni–Cr system and Ni0.35Al0.3Ti0.35 in the sample aluminized at 600 and 700 °C for 2 h, and Al0.96Ni1.04, Al3Ni2, Al8Cr5 and Ni0.35Al0.3Ti0.35 in the sample aluminized at 800 °C for 2 h. Moreover, in the outer layer in addition to enriching each of the aluminide phases, morphological evolution from an interconnected structure to an island-like structure and eventually to an equiaxed grain structure happened with the increase of aluminizing temperature. The growth kinetic of aluminide coating in plasma paste aluminizing obeyed a parabolic law and the growth activation energy was calculated as low as about 83 kJ/mol. Enhanced diffusion in this aluminizing process can be related to the presence of liquid-state diffusion in early stages and the effect of plasma radiation on solid-state diffusion in later stages.

The diffusion controlled growth rate of solid-solid interphase boundaries containing ledges

In this work the velocity of an isolated growth ledge located on an interphase boundary is solved by the method of matched asymptotic expansion where the “inner” solution is obtained by a conformal mapping procedure. In contrast to previous work, both a constant flux and local equilibrium is maintained at all points along the step face when formulating the solution. The matching procedure leads to a solvability condition for the problem, which in turn yields an analytic solution for the Peclet number as a function of supersaturation. The theoretical treatment is extended, in an approximate way, to the case of multiple steps. Predictions from the matched asymptotic expansion formulation are compared to experimental results for BCC precipitate growth in the Ni–Cr system.

Cermet Plasma TiC–Cr3C2–NiCr–Mo–C Coatings

To determine the possibility of maintaining the maximum possible carbon content in TiC carbide, a powder additionally doped with chromium carbide, molybdenum, and carbon was produced by plasma spraying of the cermets of the TiC–NiCr system. To reduce the effect of gases from the air atmosphere, plasma spraying was carried out using a standard plasmatron, supplemented with a special nozzle. The analysis of the oxygen, nitrogen, and carbon content in the powder manufacturing stages and in the coatings was carried out. The content of O and N is reduced in the sintering step for spraying a powder with respect to the content in the starting components, but increases again during spraying. In the coating, the quantitative distribution of the carbide phases was determined by their size. A change in the phase composition and dimensions of the crystal lattices of the phases in the powder for deposition and coatings was determined. The share of the main hardening TiC phase in the coating decreased by 9.7% with respect to the initial mixture, but taking into account the newly formed carbide phases with the participation of chromium and molybdenum, the proportion of all the carbide phases in the coating increased by 12.7%. The microhardness of the plasma coating at loads of 200 and 20 g on the indenter was 14.9 and 28.7 GPa, respectively. The reasons for the decrease in the actual microhardness of the cermet coating in relation to the theoretically possible one based on the volume fraction of the strengthening phases are analyzed.

Angular-dependent interatomic potential for the binary Ni–Cr system

A new interatomic potential has been developed for the Ni–Cr system in the angular-dependent potential (ADP) format by fitting the potential parameters to a set of experimental and first-principles data. The ADP potential reproduces a wide range of properties of both elements as well as binary alloys with reasonable accuracy, including thermal and mechanical properties, defects, melting points of Ni and Cr, and the Ni–Cr phase diagram. The potential can be used for atomistic simulations of solidification, mechanical behavior and microstructure of the Ni-based and Cr-based phases as well as two-phase alloys.

Computational Design of Gradient Paths in Additively Manufactured Functionally Graded Materials

Additive manufacturing (AM) has enabled the creation of a near infinite set of functionally graded materials (FGMs). One limitation on the manufacturability and usefulness of these materials is the presence of undesirable phases along the gradient path. For example, such phases may increase brittleness, diminish corrosion resistance, or severely compromise the printability of the part altogether. In the current work, a design methodology is proposed to plan an FGM gradient path for any number of elements that avoids undesirable phases at a range of temperatures. Gradient paths can also be optimized for a cost function. A case study is shown to demonstrate the effectiveness of the methodology in the Fe–Ni–Cr system. Paths were successfully planned from 316 L Stainless Steel (316 L SS) to pure Cr that either minimize path length or maximize separation from undesirable phases. Examinations on the stochastic variability, parameter dependency, and computational efficiency of the method are also presented. Several avenues of future research are proposed that could improve the manufacturability, utility, and performance of FGMs through gradient path design.

Classical interatomic potential for quaternary Ni–Fe–Cr–Pd solid solution alloys

In this paper, we present a new quaternary interatomic potential for the NiFeCrPd system, which is an extension on the previous NiFeCr potential. Density functional theory is used to calculate the quantities to be fitted, with particular focus on the energetics of point defects with solutes, for the potential to be used towards understanding radiation damage properties. The potential thus will enable the modeling of multi-elemental solid solution alloys consisting of up to four elements. To test the potential, we have performed atomistic kinetic Monte Carlo simulations to investigate the effect of configurational entropy on the self-diffusion coefficients. The self-diffusion coefficients are found to increase with chemical complexity, contrary to the common postulation of sluggish diffusion in high entropy alloys (HEAs). In addition, we have performed molecular dynamics simulations to elucidate the effect of Pd on vacancy diffusion and clustering in pure Ni and binary alloys. In agreement with recent irradiation experiments, our simulations show that while large vacancy clusters, such as stacking fault tetrahedra, are formed in pure Ni, Ni–Fe and Ni–Cr systems, negligible vacancy clustering is observed in Ni–Pd systems, indicating a possible effect of Pd in reducing cluster sizes. We suggest that this potential will be useful for studying the defect evolution in multi-component HEAs.

Effect of boron on enhancing infrared emissivity of Ni-Cr system coating

High infrared emissivity coating possesses great value in practical application, whether in the military or civilian areas. In this study, B-NiCr precursor powder containing NiO, Cr2O3 and ZrB2 was calcined at 1300 °C and then used to prepare a high infrared emissivity B-NiCr coating via atmospheric plasma spraying. A large number of test methods were employed to analyze the powder and coating, including TG-DSC, XRD, FE-SEM, infrared spectrometer and so on. The result of infrared emissivity measurement indicates that the coating possesses maximum infrared emissivity of 0.908 at 1000 °C while the infrared emissivity is 0.901 after thermal shock test. Comparing with NiCr coating, Ni2CrO2(BO3) formed during calcination may be the main factor to improve the infrared emissivity of B-NiCr coating. The B-NiCr coating possesses good thermal shock resistance and can withstand 50 times thermal shock at least without falling off, from 800 °C to room temperature.

Dry reforming of methane on nickel-chrome, nickel-cobalt and nickel-manganese catalysts

Dry reforming of methane was investigated over Ni-based catalysts containing Cr, Mn and Co metals. The materials were synthesized via co-precipitation method and they were calcined at 800 °C in order to obtain the spinel structure NiM2O4. The structural and textural properties were characterized using: XRD, Raman and XPS spectroscopies, BET and SEM-EDX techniques. The reducibility was studied by TPR and HT-XRD techniques under H2 atmosphere. The spinel structure NiM2O4 was confirmed for Ni-Cr and Ni-Mn catalysts by XRD and Raman spectroscopy. In the case of Ni-Co, the results revealed the presence of cobalt oxide Co3O4 with spinel structure and NiO; the NiCo2O4 spinel was not observed. All catalysts were very active in dry reforming of methane with a good H2 selectivity. The best catalytic performance was observed for Ni-Cr system with high CH4 and CO2 conversions (up to 90%), high H2 selectivity (reaching 99%) and with low coke formation (4% of converted CH4).

Internal Oxidation in Dry and Wet Conditions for Oxygen Permeability of Fe–Ni Alloys at 1150 and 1100 °C

The design of new austenitic alloys based on the Fe–Ni–Cr system requires knowledge of their oxygen permeability. Data are available for pure Fe and Ni but not for Fe–Ni alloys. Wagner’s model for internal oxidation is used to evaluate the oxygen permeability in Fe–Ni alloys. Internal oxidation of Fe–Ni–Cr alloys carried out at 1150 and 1100 °C in Rhines packs and H2/H2O mixtures is described. Internal oxidation produces zones of FeCr2O4 and Cr2O3 precipitates, according to parabolic kinetics. Permeabilities are deduced taking into account interfacial diffusion contributions. Oxygen permeability decreases with nickel addition in a non-ideal way, and oxygen permeability in nickel-rich alloys is independent of the studied environments. However, the oxygen permeability in iron at the highest temperature studied is increased in H2/H2O.

Analysis of the Passivation and Local Dissolution of Ni-Cr-Based Alloys Using the Cabrera-Mott and Point Defect Models

ABSTRACT In Fe-Cr based steels, the effects of low concentrations of alloying elements such as N, Mo, and W are somewhat understood with respect to corrosion and passivation. Such alloying often achieves significant improvements in corrosion resistance [1]. However, the roles of alloying elements in a Ni-Cr system are much less well understood. Upon adding small to intermediate concentrations of Mo to Ni-Cr, the corrosion resistance improves dramatically [2]. The Pitting Resistance Equivalent Number can forecast corrosion resistance based on major and minor alloying element concentrations but is empirical and does not provide predictive capabilities nor scientific insights [4]. The goal of this study is to identify the mechanism(s) by which alloying elements improve aqueous passivation in the Ni-Cr-Mo system at the atomic scale and to investigate the oxide properties of the protective passive film. The alloys under study are Ni-11Cr, Ni-11Cr-6Mo, Ni-22Cr, Ni-22Cr-6Mo, and Ni-22Cr-6Mo-3W, wt%, polycrystalline solid solutions. Previous studies have postulated the influence of different elements on passivity in acidic and high [Cl-] environments [3,5]. Cr has been shown to provide passivity during repassivation and enhance resistance to corrosion in oxidizing acids while Mo enables repassivation during oxide film breakdown and increases the resistance to reducing acids [3]. Electrochemical impedance spectroscopy (EIS) studies have been used to analyze the passive film for a Ni-22Cr-13Mo-3W-3Fe-2.5Co, wt%, alloy in varying environments [4]. This presentation explores DC and AC electrochemical techniques for exploring controlled growth of passive oxide films on Ni-Cr alloys. Potentiostatic and galvanostatic holds were used in aqueous chloride and chloride-free solutions of increasing acidity. The data was analyzed using the Cabrera-Mott (C-M) and Point Defect (PDM) models in order to investigate their applicability to the case of Ni-Cr oxide growth with varying concentrations of minor alloying elements [6,7]. A major challenge to the application of either C-M or PDM is that the film thickening rate must be assessed independently from the total oxidation rate. Inductively Coupled Plasma-Optical Emission Spectroscopy indicates that a significant portion of the applied anodic charge during oxidation is associated with direct cation ejection and/or dissolution of the oxide into solution rather than thickening of the film. Therefore, the oxide growth rate and charge must be extracted from the total current for C-M and PDM analysis. EIS techniques were used to characterize and model the electrochemically grown oxides, represented as a constant phase element, to enable the calculation of oxide thickness. The impedance data following potentiostatic oxide growth was compared to the data produced from single frequency EIS where the impedance was continuously recorded in order to extract the variation of oxide charge and thickness over time. The oxide thicknesses calculated using these methods was related to the charge that goes toward oxide film growth. By comparing these values to the potentiostatic or galvanostatic total charge, the portion involved in dissolution was removed for C-M and PDM analysis. Subsequently, diagnostics were used to test the applicability of C-M and PDM models. Results are reported herein. Ex situ Raman and X-ray Photoelectron Spectroscopy were utilized to characterize the chemical and molecular identities of the oxide film, accurately calculate the thickness, and test the accuracy of the EIS-dependent oxide calculations. These ex situ methods corroborated the determination of the potentiostatic and galvanostatic charges associated with the growth of the oxide. ACKNOWLEDGEMENTS This work was funded by the U.S. Office of Naval Research Multi-University Research Initiative under a subcontract from Northwestern University SP0028970-PROJ0007990 with Dr. David A. Shifler. REFERENCES [1] Sedriks, A.J. (1996). Corrosion of stainless steels (2nd ed.). New York: Wiley [2] Bocher, F., Huang, R., & Scully, J. R. (2010). Prediction of critical crevice potentials for Ni-Cr-Mo alloys in simulated crevice solutions as a function of molybdenum content. Corrosion, 66(5). [3] Lloyd, A. C.; Noel, J. J., McIntyre, S.; & Shoesmith, D. W. (2004). Cr, Mo, and W alloying additions in Ni and their effect on passivity. Electrochimica Acta, 49, 3015-3027. [4] Combrade, P. (2001). Corrosion mechanisms in theory and practice (2nd ed.). CRC Press: Marcus. 349-397. [5] Jakupi, P.; Zagidulin, D.; Noel, J.J.; & Shoesmith, D.W. (2011). The impedance properties of the oxide film on the Ni-Cr-Mo Alloy-22 in neutral concentrated sodium chloride solution. 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