Ni-Cr Alloy Research Articles

Effects of in situ composite ceramics on the mechanical properties and microstructure of Fe–Cr–Ni alloys

Fe–Cr–Ni composites reinforced with Al2O3–MgO composite ceramics were prepared via reactive hot pressing at 800 °C for 2 h under 30 MPa. The composites primarily comprised Cr0.19Fe0.7Ni0.11, Fe–Cr, magnesium aluminate spinel, Al2O3, and MgO phases. The mechanical properties and microstructure of the metal matrix composites changed with the changing in situ Al2O3–MgO content. The composite ceramic exhibited excellent mechanical properties (Vickers hardness = 5.59 GPa, bending strength = 244.59 MPa, and fracture toughness = 11.66 MPa·m1/2) when Al2O3/(MgO + Al2O3) (mol/mol) was 0.6371 owing to the difference in the residual stress at the interface between the ceramic particles and metal matrix.

Effect of heating temperature on the behavior of reinforced zinc-rich coating with nanoparticles

An experimental study has been conducted to develop unique zinc-rich coatings for the protection of low carbon steel reinforcements. These coatings are applied to low carbon steel substrates and subjected to various temperatures (100 °C, 150 °C, 200 °C, and 250 °C) to assess their mechanical integrity, corrosion resistance, and durability, replicating extreme service environments. The study integrates different nanoparticle concentrations into the zinc matrix (including Zn only, 50% Zn + 50% TiO2, 50% Zn + 30% WC + 20% TiO2, 40% Zn + 40% Ni-Cr Alloy + 20% TiO2, 70% Zn + 30% WC, and 50% Zn + 50% Ni-Cr Alloy) to assess their reinforcement effectiveness and contribution to thermal stability. The performance properties are assessed using adhesion tests, coating ratings, hardness assessments, electrochemical analysis, and field emission scanning electron microscopy (FESEM). The findings reveal that zinc coatings with a composition of 50% Zn, 30% WC, and 20% TiO2 provide excellent adhesion, particularly beneficial for high-temperature applications. Coatings containing Ni-Cr alloy display outstanding thermal stability, a vital characteristic for withstanding high-temperature conditions. At 250 °C, evaluating the compositions for the most favorable potential at the highest current densities is imperative. Microstructural analysis from room temperature to 250 °C shows a significant improvement in the integration and refinement of WC and Ni-Cr within the Zn matrix, resulting in the coatings’ optimal performance.

A metallurgical approach for separation and recovery of Cu, Cr, and Ni from electroplating sludge

Electroplating sludge is extensively produced in chemical precipitation–based treatment of electroplating wastewater. It poses a huge threat to environmental safety if not properly disposed, ascribed to its high contents of heavy metals. An innovative metallurgical approach was proposed a to recycle Cu, Cr, and Ni from it. Ammonia leaching was firstly performed to selectively leach Cu from Cr, in which the Cu oxide and sulfide were leached into the leachate while the Cr oxide and Ni carbide (NiCx) retained in the residue. (NH4)2SO4 increased the Cu leaching rate via increasing the dissolved oxygen amount in the ammonia leachate and converting CuS to Cu2+. Under the optimal conditions, the leaching efficiency of Cu achieved 96.5 % while that of Cr was only 0.1 %. In the followed aluminothermic reduction, C in the leaching residue could be effectively removed via a thermal oxidation, which in turn decreased the formation of a C-containing compound of high melting point and benefited the Cr and Ni recovery. Cr and Ni from the residue were reduced and recovered in a Cr-Ni alloy, and the reductant of Al first changed to a refractory Al2O3 and then transformed to a low melting point 12CaO·7Al2O3 with the additive of CaO. This transformation increased the molten slag fluidity and promoted the separation of Cr-Ni alloy from slag. Moreover, the excessive Al increased the Cr and Ni yields and concentrated all of them to be together. Partial Al was used as reductant, and the other Al transferred into Cr-Ni alloy to decrease its melting point. Cr and Ni contents in the smelting slag could be decreased to 0.11 wt% and 0.12 wt% respectively, showing an efficient recovery. This work provided a high efficiency method to recover Cu, Cr, and Ni from waste electroplating sludge.

Biomechanical Analysis of Mandibular Premolar Restored with Different Custom Post Core

Abstract Objective This study investigated biomechanical behavior of custom post core made of six different materials on the tooth with and without the ferrule under different occlusal load. Materials and Methods Three-dimensional models of mandibular first premolar, with and without ferrule, reconstructed from micro-computed tomography image are restored with different custom post core and zirconia crowns. By using the finite element analysis, von Mises stress shown in MPa was measured under simulated axial and oblique load of 200 [N]. To compare the stress distribution, six different custom post core materials were chosen: zirconia, Ni-Cr alloy, gold alloy, glass fiber-polyether ether ketone, polyether ether ketone, and carbon fiber-polyether ether ketone. Results Custom post cores with a higher modulus of elasticity showed higher measured stress in the posts, but less stress in dentin. Measured stress in custom post core under oblique loading was approximately three times higher compared with axial loading. Stress in custom post core and in dentin under both types of loads was slightly higher in teeth without ferrule effect. Conclusion The use of custom cast post cores made of different alloys is recommended in restoration of endodontically treated teeth, with extensive loss of tooth structure especially in teeth without ferrule effect.

Improved corrosion resistance and cytotoxicity of nickel‐based alloy using novel plasma processing technique

AbstractIn this study, we address challenges in the biocompatibility of nickel‐based (NiCr) alloys, prevalent in the dental industry, due to toxic metal ion release impacting corrosion resistance and cytotoxicity. Employing magnetron sputtering and cathodic cage plasma nitriding (CCPN), a duplex plasma treatment (DPT) is introduced to the NiCr alloy. The novel approach enhances surface morphology, notably reducing ion leakage compared with untreated samples. Specifically, the CCPN‐TiN‐treated sample significantly improves corrosion resistance and minimizes metal ion leakage. This transformative DPT emerges as a promising solution for surface modification, particularly mitigating toxic ion leaching in aggressive electrolytes. This research demonstrates a major stride in enhancing NiCr alloy biocompatibility, emphasizing the vital role of innovative surface modification techniques for biomedical applications and challenges.

The Impact of Recasting on the Bond Strength of Metal Ceramic Restorations

Objective The objective of this study is to evaluate the effect of recasting of Nickel Chromium (Ni-Cr) alloy on the bond strength of metal-ceramic restoration. Materials and Methods Forty-five samples fabricated from one Ni-Cr alloy were divided into three groups. Group 1 consisted of 100% fresh alloy; Group 2 consisted of 50% fresh alloy mixed with 50% alloy taken from sprue and button remnants of group 1 and group 3 consisted of 50% new alloy mixed with 50% alloy taken from sprue and button remnants of group 2. All samples were then bonded to a ceramic material. The bond strength of the Metal-Ceramic was then assessed using a 3-point bending test. The failure mode was investigated under a stereomicroscope and confirmed under scanning electron microscopy (SEM). Results Group 1 (100% fresh alloy) showed the highest bond strength amongst the other groups, while the lowest was recorded for group 3 (50% fresh alloy with 50% cast twice alloy). According to the International Organization for Standardization (ISO), the bond strength of fresh alloy and the group casted once attained the required level. Conclusion The outcome of this study indicates that the use of 100% fresh Ni-Cr base metal alloy yields the highest bond strength of metal ceramic restoration.

Mechanically Durable and Fluorine‐Free Ni–Cr Alloy‐Based Highly Hard Superhydrophobic Coating on Al Alloy

Superhydrophobic coatings, known for their water‐repelling properties, play an important role in corrosion resistance and self‐cleaning applications. This study addresses the pressing need for eco‐friendly and durable fabrication methods for metal surfaces, particularly Al alloys, recognized for their inherent low mechanical properties. The innovative electroplating technique successfully fabricates superhydrophobic coatings on Al alloy surfaces, incorporating a high‐hardness Ni–Cr alloys layer and a low‐surface‐energy stearic acid layer. The resulting coatings exhibit outstanding mechanical durability, corrosion resistance, and self‐cleaning capabilities. With a water contact angle of 165° and a corrosion protection efficiency of 98.6%, these coatings offer a substantial improvement over traditional methods. Moreover, the Leeb hardness of the coated alloy experiences an impressive 83% increase compared to pristine Al alloy. This universally applicable approach opens avenues for developing mechanically robust superhydrophobic coatings on various metallic substrates, with broad implications for engineering applications.

A reactive force field approach to modeling corrosion of NiCr alloys in molten FLiNaK salts

The interface between NiCr alloys and FLiNaK molten salt exhibits complex corrosion behavior, mainly driven by intricate chemical interactions involving Cr and F−ions. Understanding these dynamic reactions is crucial for developing effective corrosion mitigation strategies to ensure the long-term durability of Ni-based alloy components in molten salt technologies. However, obtaining molecular-level understanding through experiments is challenging. To address this, we utilize reactive molecular dynamics simulations enabled by a reactive force field, ReaxFF, to investigate detailed reaction dynamics at the atomic level. We first present the development of the ReaxFF parameter set for Ni/Cr/F/Li/Na/K based on extensive first-principles calculations. With this force field, we achieve a strong agreement for the structure of FLiNaK molten salt by comparing the pair distribution functions with experimental and simulation results. Furthermore, our simulations successfully reproduce the experimental phenomenon of Cr dissolution in fluoride salt, with the corrosion rate depending on the alloy and salt compositions. Particularly, our simulations reveal that increasing the concentration of Li can enhance the formation of a compact double layer, mitigating Cr dissolution. This work enables a fundamental understanding of the interfacial behavior between fluoride salt and NiCr alloys.

Frictional ignition of dispersion-strengthened Ni-Cr alloys

Frictional heating of metals at reciprocating or sliding contacts in high-pressure oxygen environments poses a risk of catastrophic metal fires. This phenomenon, known as frictional ignition, has been implicated in several high-profile failures of oxidizer-rich turbopumps, presenting an ongoing challenge in the development of next-generation reusable rocket engines. Early NASA investigations on frictional ignition of candidate turbine materials identified oxide dispersion-strengthened Ni-base superalloys as exceptionally resistant to ignition. In this study, we performed high-speed sliding, frictional ignition experiments on binary Ni-Cr alloys and two oxide dispersion-strengthened Ni-Cr alloys – MA754 and MA758. Analysis of recovered non-ignited samples revealed the in situ growth of oxide tribolayers on rubbing surfaces during sliding. An order of magnitude reduction in friction coefficient during the initial stages of sliding was attributed to the formation of these tribolayers. An abrupt increase in friction coefficient preceding ignition was linked to tribolayer breakdown, exposing the hot underlying metal to high-pressure oxygen. The oxide dispersion-strengthened alloy MA754 was the only material that did not ignite under any test conditions. Its specific content of Cr and Y2O3 dispersoids synergistically promote rapid growth of a thick, adherent oxide tribolayer strengthened by refractory Ni2CrO4 precipitates. These features collectively mitigate tribolayer breakdown, suppressing ignition. The present results highlight the importance of tribolayer stability in achieving frictional ignition resistance and suggest alloy design strategies for tailoring oxidational wear behaviors to develop intrinsically ignition-resistant materials.

Corrosion analysis of orthodontic brackets and arch wires – An <em>in vitro</em> study

Orthodontic plates are fixed onto the teeth in a dynamic environment in the oral cavity. The Orthodontic appliances, which includes both the brackets and the arch wires, are exposed to different pH fluctuations in the mouth. These appliances are manufactured using metal alloys that made out from nickel, iron, cadmium and titanium. These are commercially available in Sri Lanka and in the international market in different prices covering a large price range. Recent studies are investigating on the biocompatibility of these materials with the aim of determining the upper limit of the biological tolerance and to find methods to maintain ion release within acceptable limits. According to the previous studies there are evidences that the Ni and Cr ions release from Ni-Cr alloy in the presence of different acidity of artificial saliva. In this research in vitro corrosion process of selected orthodontic wires in artificial saliva solutions were evaluated with the aim of identifying a relationship between the quality and the price of selected orthodontic appliances available in Sri Lankan market. Eighteen specimens from different brands were selected and immersed in each of different types of artificial saliva at different pH, for different storage periods. All the sample tubes were incubated at 37°C. The release of metal ions from specimens with time were studied by conductivity, Atomic Absorption Spectroscopic (AAS) and mass loss measurements. According to the results, all specimens prepared using Ni -Ti wires release Ni²⁺ in the range between 9 ppm – 20 ppm during one year study period. Ni²⁺ concentration in all saliva solutions has increased with time and in specimens B, D, E, F the Ni²⁺ releasing rates were decreased with time. According to this study, all brands of brackets which were used in this study may lead to develop nickel hypersensitivity with time.

Cooperative enhancement of strength and corrosion resistance through architecture of nanotwins and low angle grain boundary in Ni20Cr alloy

Effects of ultrasonic shot peening (USSP) on microstructure, strength and corrosion performances of Ni20Cr alloy were investigated. A gradient nanotwinned structure consisting of high densities of nanotwins, low angle grain boundaries and dislocations was formed. Hardness, strength-ductility synergy and corrosion resistance was enhanced simultaneously. Deformation mechanism varying with strain level was discussed. X-ray photoelectron spectroscopy (XPS) showed that thinner passive film with higher Cr3+ content formed after USSP, which might be accounted for the improvement in corrosion resistance. This work develops a simple method to enhance mechanical properties and corrosion resistance simultaneously in industrial Ni-Cr alloys.

Fe–Ni–Cr alloy matrix composite reinforced by superhard in-situ TiB2 produced through casting

ABSTRACT Fe–7.2Ni–16.2Cr–7Ti–3B (wt-%) composition was melted and cast into strips producing an in-situ TiB2 reinforcement within a stainless-steel matrix. The composite was characterised for microstructure and nanoindentation hardness. The microstructure consisted of in-situ formed particles of TiB2 and fine eutectic of austenite–borides. Superhigh nanoindentation hardness of 47.2 GPa was measured on TiB2 particles with 590.2 GPa elastic modulus while these values for the matrix were 6.95 and 277 GPa respectively.

ZTA/high Ni–Cr alloy steel composites prepared by liquid phase sintering

The interfacial bonding, wear resistance, corrosion resistance and high temperature oxidation resistance of ZTA/high Ni–Cr alloy steel composites prepared by liquid phase sintering were investigated. The results showed that the ZTA particles bonded well with high Ni–Cr alloy steel matrix and produced transition new phases, including (Al, Cr)2O3, Al60Mn11Ni4, Mn2SiO4, MnCr2O4, (Mn, Fe)2SiO4 and MnSiO3. With the addition of ZTA particles, the wear resistance of the composites was reduced substantially. When the ZTA content is 40 vol%, the wear resistance is two times of the matrix, which is better than that of the Cr16 material. The small content of ZTA particles added can enhance the corrosion resistance of the composites. When ZTA was in small amounts, there was passivation of the samples and the corrosion resistance increased. When the content of ZTA reaches 30 vol%, the passivation phenomenon disappears. The corrosion resistance of the composites is much higher than that of the Cr16 material. The composites have good resistance to high temperature oxidation at temperatures below 700 °C. Industrial testing of plate hammers was carried out on a corrosive slag machine at a high temperature of 700 °C. The results show that the ZTA/high Ni–Cr alloy steel composite has twice the service life of the Cr26 material.

Structural phase transformation in single-crystal Fe–Cr–Ni alloy during creep deformation using molecular dynamics simulation and regression-based machine learning methodology

Structural phase transformation in single-crystal Fe–Cr–Ni alloy during creep deformation using molecular dynamics simulation and regression-based machine learning methodology

Corrosion Behavior of Binary Ni-Cr Alloys in Molten FLiNaK Salts at Different Electrochemical Potentials

The development of molten salt reactors (MSRs) is a collaborative effort among academia, government laboratories, and industry, with the aim of realizing the potential of clean nuclear energy. However, the corrosion of structural alloys presents a significant engineering challenge in this application. Addressing this issue requires investment not only in testing and characterizing candidate alloys, but also in developing a scientific framework to understand the fundamental mechanisms governing the corrosion of metallic materials in molten fluorides which can then guide alloy design [1].In this work, the corrosion behavior of binary Ni-Cr alloys (5-20 wt.% Cr) in molten LiF-NaF-KF (or FLiNaK) salts between 550oC and 750oC was interrogated using electrochemical methods coupled with thermo-kinetic analysis. Electrochemical techniques, including linear sweep voltammetry, electrochemical impedance spectroscopy (EIS) and chronoamperometry, were utilized to elucidate the rate-limiting kinetic factors and to identify the dependence of corrosion morphology on applied potential. Additionally, Ni-Cr alloys were also immersed 99.9% pure FLiNaK salts with a known oxidizer concentration (e.g., 0.1-5 wt.% EuF3) coupled with open-circuit potential measurement to provide a time-based description of morphological evolution in the case of a dynamically changing electrode potential. These results are corroborated by examination of the post-corrosion morphology using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron backscatter diffraction (EBSD) techniques as well as salt composition analysis using inductively coupled plasma mass spectrometry (ICP-MS), X-ray diffraction (XRD) and in situ cyclic voltammetry.The systematic choice of potential revealed multiple potential regimes in which Ni-Cr alloys exhibit distinctly different corrosion morphologies. At intermediate potentials, a porous bicontinuous structure is formed by dealloying of the less noble element (Cr) and percolation into the Ni-rich alloy within grains and along grain boundaries. At other potentials, charge transfer control dissolution of both Cr and Ni leads to the formation of a crystallographic faceted structure. The morphological differences suggest the presence of multiple corrosion processes in Ni-Cr in FLiNaK controlled by either transport or interfacial reaction. These findings can be explained through electrochemical processes at the alloy-salt interface, as well as the roles of surface, grain boundary and bulk diffusion kinetics involving the alloying constituents. Furthermore, the effect of radiation damage on Ni20Cr alloys on these rate-limiting corrosion regimes will be investigated. Acknowledgment Research is primarily supported as part of the fundamental understanding of transport under reactor extremes (FUTURE), an Energy Frontier Research Center (EFRC) funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES).[1] Chan, H.L., et al. Npj Materials Degradation 6(1), 46 (2022).

An investigation on nitrogen uptake and microstructure of equimolar quaternary FeCoNiCr high entropy alloy after active-screen plasma nitriding

Under nitrogen diffusion treatments, N-expanded austenite (γN) can form at the surface of self-passivating Fe-Cr, Ni-Cr, and Co-Cr alloys at low temperatures, which provides beneficial hardening and enhancements in wear resistance without reducing corrosion resistance. Given the wide research interests in multicomponent equimolar alloys, an equimolar quaternary FeCoNiCr high entropy alloy (HEA) was investigated after active-screen plasma nitriding at 430–480 °C in this study. Firstly, the formation of γN-FeCoNiCr case at 430 °C was demonstrated with the bright case appearance after metallographic etching, the lattice expansion under XRD, the FCC electron diffraction patterns and the shear bands under TEM. Secondly, the thick treatment cases at ∼9–16 μm first indicated that N interstitial diffusion was not sluggish in the FeCoNiCr surface. Thirdly, analogous to stainless steels, the onset of dark regions in the etched γN-FeCoNiCr case was owing to the formation of a cellular mixture of CrN + γ-(Fe, Co, Ni) nano-lamellae at elevated treatment temperatures. The residual bright regions in γN-FeCoNiCr at 480 °C showed ∼1–3 nm CrN nanoprecipitates with no substantial Cr segregation. Additionally, a significant nanocrystalline layer was seen at the topmost surface at 480 °C, which is most likely associated with the high substrate Cr content.

Effect of Cerium Addition on the Microstructure and Shape Memory Properties of Austenitic Fe–Mn–Si–Cr–Ni Alloys

The addition of rare earth elements, such as cerium, to austenitic Fe–Mn–Si‐based shape memory alloys has been shown to improve both corrosion resistance and shape recovery. However, the mechanisms underlying the effect of Ce on shape recovery are still unclear. This study investigates the influence of the addition of small amounts of Ce (0.18, 0.42, and 0.96 wt%) on the microstructure and shape recovery of an austenitic Fe–13.50Mn–3.98Si–9.54Cr–4.51Ni alloy. Ce additions induce the formation of a large number of Ce‐rich particles, which act as austenitic grain refiners. Both grain refinement and the formation of Ce‐rich particles contribute to the strengthening of the matrix at 0.42 wt% Ce addition. In addition, Ce additions alter the MS temperature, which increases with Ce additions. Total shape recovery improves with 0.18 and 0.42 wt% Ce additions, but decreases with 0.96 wt% Ce addition. The beneficial effect of Ce addition in improving the shape recovery of the austenitic Fe–Mn–Si–Cr–Ni alloy is related to the enhancement of the elastic shape recovery component of the total shape recovery. However, the shape memory recovery due to the shape memory effect always decreases with the increase of the Ce content.

Elemental partitioning and corrosion resistance of Ni–Cr alloys revealed by accurate ab-initio thermodynamic and electrochemical calculations

Elemental partitioning during thermal processing can significantly affect the corrosion resistance of bulk alloys operating in aggressive electrochemical environments, for which, despite decades of experimental and theoretical studies, the thermodynamic and electrochemical mechanisms still lack accurate quantitative descriptions. Here, we formulate an ab initio thermodynamic model to obtain the composition- and temperature-dependent free energies of formation (ΔfG) for Ni–Cr alloys, a prototypical group of corrosion-resistant metals, and discover two equilibrium states that produce the driving forces for the elemental partitioning in Ni–Cr. The results are in quantitative agreement with the experimental studies on the thermodynamic stability of Ni–Cr. We further construct electrochemical (potential–pH) diagrams by obtaining the required ΔfG values of native oxides and (oxy)hydroxides using high-fidelity ab-initio calculations that include exact electronic exchange and phononic contributions. We then analyze the passivation and electrochemical trends of Ni–Cr alloys, which closely explain various oxide-film growth and corrosion behaviors observed on alloy surfaces. We finally determine the optimal Cr content range of 14–34 at%, which provides the Ni–Cr alloys with both the preferred heat-treatment stability and superior corrosion resistance. We conclude by discussing the consequences of these findings on other Ni–Cr alloys with more complex additives, which can guide the further optimization of industrial Ni–Cr-based alloys.

Atomic Investigation of Corrosion Mechanism and Surface Degradation of Fe–Cr–Ni Alloy in Presence of Water: Advance Reactive Molecular Dynamics Simulation

Atomic Investigation of Corrosion Mechanism and Surface Degradation of Fe–Cr–Ni Alloy in Presence of Water: Advance Reactive Molecular Dynamics Simulation

Tin Oxide Modification of Indium Oxide Gas Sensitive Layers to Increase Efficiency of Gas Sensors

Monitoring of air pollutions is one of actual trends in the development of industrial and domestic instrumentation. There are sets of tasks for improving gas analytical instruments because of increasing demand for control of a concentration of explosive and toxic gases on a level with maximum allowable concentration. The aim of the paper was to investigate the methods of formation and elemental composition of indium oxide films modified with tin oxide on the surface of gas sensor elements as one of the promising compounds for improving the detection efficiency of explosive and toxic gases in the environment. The processes of formation of gas-sensitive films deposited on the surface of nichrome alloy information electrodes were studied in this article. Substrates of anodic aluminum oxide with area of 10 × 10 mm2 and a thickness of 45 ± 0,5 μm were chosen for research. Two layers on the surface of the samples were formed. The first layer was formed from NiCr alloy (Ni – 80 %, Cr – 20 %) with a thickness of ≈ 0.3 μm by ion-plasma sputtering. The second layer was based on indium oxide with addition of tin oxide with thicknesses from ≈ 0.3 μm to ≈ 1.0 µm and coated with sol-gel technology. Five samples of gas-sensitive films were formed with different methods of deposition and heat treatment. Scanning electron microscopy was used for study of films’ morphology and elemental compositions of samples. The most perfect continuous semiconductor films were obtained by multilayer applying of a sol-gel paste. When semiconductor films were processed at annealing temperatures of 700 °C and higher in vacuum so there was observed cracking of semiconductor films up to a layer of NiCr alloy. The developed surface of gas-sensitive films allows to reach high sensitivity and affectivity of semiconductor sensors for control of air gas composition.