Ni-Cr Alloy Research Articles

Investigation on the effect of nickel and nickel-chromium alloy pulse current plating on copper substrate

ABSTRACT In the present study, nanocrystalline nickel (Ni) and nickel-chromium (Ni-Cr) alloy coatings were developed on copper (Cu) substrate using pulse current. The pulse current parameters include a cycle time of 240 milliseconds at a duty cycle of 0.5 and 4.17 Hz frequency. The surface morphology, texture, hardness, scratch resistance and porosity were investigated for different coatings developed by pulse plating. Energy Dispersive Spectroscopy (EDS) analysis revealed good quality Ni and Ni-Cr alloy coatings developed on the copper substrate. The peak current of the pulse has been observed to have an impact on the coating weight and thickness. The micrographs of the coatings explored under Field Emission Scanning Electron Microscopy (FESEM), depict uniform coatings consisting of fine primary and coarse secondary granules of Ni and Cr. The hard primary and secondary Ni granules deposited on the surface of Cu increase its hardness, corrosion and wear resistance. Further, it was observed that the Ni-Cr alloy plated samples are harder and less porous in nature compared to Ni plated samples.

Development and Mechanical Characterization of Ni-Cr Alloy Foam Using Ultrasonic-Assisted Electroplating Coating Technique

Metal foams and alloy foams are a novel class of engineering materials and have numerous applications because of their properties such as high energy absorption, light weight and high compressive strength. In the present study, the methodology adopted to develop a Ni-Cr alloy foam is discussed. Polyurethane (PU) foam of 40PPI (parts per inch) pore density was used as the precursor and coating techniques such as electroless nickel plating (ELN), ultrasonic-assisted electroplating of nickel (UAEPN), and pack cementation or chromizing were used to develop the Ni-Cr alloy foam. The surface morphology, strut thickness and minimum weight gain after each coating stage were evaluated. It was observed from the results that the adopted coating techniques did not damage the original ligament cross-section of the PU precursor. The minimum weight gain and the coating thickness after the UAEPN process were observed to be 42 g and 40–60 μm, respectively. The properties such as porosity percentage, permeability and compressive strength were evaluated. Finally, the pressure drop through the developed foam was estimated and verified to determine whether the developed foam can be used for filtering applications.

Quality of the Ceramic and Ni-Cr Alloy Joint after Al2O3 Abrasive Blasting.

The purpose of this in vitro study was to determine the effect of airborne-particle abrasion process parameters on the strength of the Ni-Cr alloy-ceramic bond. One hundred and forty-four Ni-Cr disks were airborne-particle abraded with 50, 110 and 250 µm Al2O3 at a pressure of 400 and 600 kPa. After treatment, the specimens were bonded to dental ceramics by firing. The strength of the metal-ceramic bond was determined using the shear strength test. The results were analyzed with three-way analysis of variance (ANOVA) and the Tukey honest significant difference (HSD) test (α = 0.05). The examination also considered the thermal loads (5000 cycles, 5-55 °C) to which the metal-ceramic joint is subjected during exploitation. There is a close correlation between the strength of the Ni-Cr alloy-dental ceramic joint and the alloy roughness parameters after abrasive blasting: Rpk (reduced peak height), Rsm (the mean spacing of irregularities), Rsk (skewness of the profile) and RPc (peak density). The highest strength of the Ni-Cr alloy surface bonding with dental ceramics under operating conditions is provided by abrasive blasting under 600 kPa pressure with 110 µm Al2O3 particles (p < 0.05). Both the abrasive blasting pressure and the particle size of the Al2O3 abrasive significantly affect the joint's strength (p < 0.05). The most optimal blasting parameters are 600 kPa pressure with 110 µm Al2O3 particles (p < 0.05). They allow the highest bond strength between the Ni-Cr alloy and dental ceramics to be achieved.

Role of Fe in long-range ordered Ni2Cr precipitates in Ni-Cr-Fe model alloys during isothermal aging

The precipitation of new phases during long-term service at elevated temperatures is a concern for the thermal stability of engineering alloys. In Ni-Cr-based alloys, e.g., Alloy 690, the formation of long-range ordered Ni2Cr causes embrittlement and may impact the lifetime of nuclear power plant components. In this work, we quantify the formation and evolution of Ni2Cr precipitation in eleven Ni-Cr-Fe model alloys with 0, 5, 7, and 10 wt % Fe contents, and with Ni/Cr atomic ratios of 1.8, 2.0, 2.2, 2.4. These alloys were isothermally aged up to 10,000 h at temperatures between 330 and 475 °C. The alloys were characterized by synchrotron-based x-ray diffraction and Vickers hardness testing to quantify Ni2Cr precipitate size, and the impact of precipitate size on the mechanical properties as a function of Fe content. After 10,000 h of aging at 475 °C and 418 °C, the formation of Ni2Cr was observed in all alloys with 0 and 5 wt % Fe. After 10,000 h of aging at 418 °C, Ni2Cr precipitates were also observed in the 7 wt % Fe containing Ni/Cr=2.0 sample. No clear evidence of Ni2Cr was observed in any of the 10 wt % Fe samples at any time and temperature combination. We find that the face-centered cubic matrix lattice contraction and Vickers hardness are correlated with the Ni2Cr formation. The greatest change in hardness and lattice contraction occurs in stoichiometric alloys (Ni/Cr=2.0) with 0 wt % Fe at 475 °C. The rate of change in the material properties for the 5 wt % Fe alloys is reduced, however the magnitude of changes is similar to 0 wt % Fe alloys. A precipitation hardening model developed for Ni-Cr alloys based on critical resolved shear stress with weakly coupled dislocations shows a clear link between Ni2Cr precipitate size and hardness. This trend held across all alloys with Ni2Cr formation regardless of Fe concentration. This important structure-property relationship can potentially help define Ni-Cr-Fe-based component lifetimes directly through an understanding of how Ni2Cr formation impacts mechanical properties as a function of Fe content.

Characterization and High-Temperature Oxidation Behavior of Ni–20Cr Deposits Fabricated by Cold Spray-Based Additive Manufacturing

Hot corrosion is a critical problem in a wide range of high-temperature applications. Ni–20Cr alloy is frequently used in such applications owing to its good hot-corrosion resistance. In the current work, thick Ni–20Cr plates in a thickness range of 6–10 mm were fabricated using cold spray-based additive manufacturing (CSAM). High-pressure cold spraying was used with nitrogen as the propellant gas. Pre- (substrate heating, SH) and post-heat treatments (hot isostatic pressing, HIP) were also performed to comprehend the changes in the deposit properties. The deposits were subjected to microstructural and mechanical characterization to explore the potential of cold spraying for CSAM of Ni–20Cr standalone products. The cold-sprayed plates were successfully developed without any oxide formation. HIP treatment was found to be useful to reduce porosity. The cold-sprayed substrate-heated Ni–20Cr deposits exhibited excellent oxidation resistance at a high temperature of 900 °C.

Development of Rotor Core with High Magnetic Flux by Partial Non-Magnetic Improvement of Silicon Steel

Flux leakage in the rotor core bridges is a problem specific to interior permanent magnet motors and has been unsolved till date. It is widely known that if the bridges are partially non-magnetically improved with low magnetic polarization, the leakage flux will be smaller, and the rotor will have a higher magnetic flux. We proposed that the portion of the silicon steel sheets that becomes the bridge after pressing can be non-magnetized and laminated to fabricate the rotor core. Partially non-magnetic material with a polarization of almost zero was obtained by melting and mixing Ni–Cr alloy powder with the silicon steel sheets. This non-magnetic improvement treatment was applied to the bridge in the rotor core sheet, in which the non-magnetic area width was 1.45 mm, and the prototype rotor core was fabricated by laminating 60 rotor core sheets. Upon measurement, the rotor core showed approximately 35% higher magnetic flux than a conventional one, with the actual value nearly identical to that obtained from the magnetic field analysis.

Comparing the intergranular oxidation of Ni-Cr and Ni-Al model alloys in 480 °C hydrogenated steam

The intergranular oxidation of binary Ni-xAl (x = 4, 7 at.%) and Ni-yCr (y = 11, 15 at.%) model alloys was studied in a 480 °C hydrogenated steam environment. It was observed that the intergranular oxidation susceptibility in Ni-Al and Ni-Cr alloys is different. In Ni-Al alloys, HAGBs are very susceptible to intergranular oxidation, while low energy grain boundaries behave similar to bulk material. In Ni-Cr alloys, LAGBs and CSLBs are susceptible to intergranular oxidation, while HAGBs are protected by an external oxide. The structure of the intergranular oxide was also different between Ni-Cr and Ni-Al alloys; the intergranular oxide formed in Ni-Al alloys was sharper and penetrated to greater depth compared with Ni- Cr alloys. Comparisons are made to previous testing of alloy 600 (Ni-16Cr-Fe) in similar environments, highlighting the potential effect of residual Al and Ti on the intergranular oxidation of the alloy.

On the origin of the strain hardening mechanisms of Ni20Cr alloy manufactured by laser powder bed fusion

Additively Manufactured (AM) metallic alloys differ from their conventionally produced counterparts by complex multi-scaled microstructures leading to deeply modified mechanical behavior. The characterization of these new links between microstructure and mechanical properties is of first importance. Nevertheless, many alloys produced by Laser Powder Bed Fusion (LPBF) process exhibit multi-phase microstructures which makes difficult the understanding of these links. In this article, we aimed at simplifying this complexity by investigating the basic strain hardening mechanisms of AM (LPBF) alloys of a theoretically monophasic Ni20Cr alloy manufactured by laser powder bed fusion. Based on the analysis of the microstructure and the tensile mechanical behavior including loading-unloading-relaxation tests, a comparison with conventionally manufactured Ni20Cr alloy is performed. First, an increase in yield stress for the LPBF samples is observed due to both effective stress and backstress modification. Second, the strain hardening mechanisms are modified for LPBF manufactured samples compared to cast ones. Kocks-Mecking model is then employed to reproduce the tensile curves and better analyze the strain hardening mechanisms. Results are discussed in terms of specific LPBF microstructure feature contributions to stress and strain hardening. We reveal that dislocation cells associated to dendrites are proved to be responsible for about 50% of the improved yield stress of LPBF material and seem to control the dislocation production, forest interactions being inoperative for those materials.

Synthesis of biocompatible coating on Ni-Cr alloy by cathodic cage plasma processing technique as anti-pathogenic bacteria for medicinal applications

The current research work reports the deposition of titanium-based multilayer coating (TiO/TiN) on Ni-Cr metallic alloy by a cathodic cage plasma processing technique using a titanium cage along with various combinations of gas mixtures i.e., N2-H2-Ar-O2 at 400 °C. The samples were characterized using x-ray photoelectron spectroscopy (XPS), which revealed the surface coating of TiO/TiN with Ti 2p at 462 eV, N 1s at 406 eV and O 1s at 530.09 eV. The x-ray diffraction (XRD) analysis confirmed the polycrystalline structure in the titanium-based coating with (111) for TiO/TiN and a crystallite size of 32 nm. Scanning electron microscopy (SEM) and x-ray dispersive spectroscopy (EDX) analysis of titanium-based TiO/TiN coatings was well correlated with the above mentioned findings. Corrosion analysis using polarization potentio-dynamic plots (PDP) and electrochemical impedance spectroscopy (EIS) revealed a significant improvement in various corrosion parameters like corrosion resistance, corrosion rate, surface porosity, corrosion protection efficiency, impedance, and charge transfer resistance. A spectrophotometer was used to measure the leaching of toxic ions (Ni, Cr) from untreated and treated specimens in NaCl electrolyte. Findings revealed efficient antibacterial activity of TiO/TiN-coated specimens against E. coli and S. aureus as compared to untreated samples. This work will be helpful for understanding the biological features of metallic materials for medicinal applications.

Experimental studies on carbon nanotube strain sensors

Conventional metal foil strain sensors only measure strain on the structural surface in predetermined directions and locations. These are made of Nichrome (Ni-Cr alloy) and Constantan (Cu-Ni alloy) and have gauge factor of 2. A carbon nanotube (CNT) as a strain sensing material is gaining research interest due to its outstanding electrical and mechanical properties. These sensors apart from multidirectional sensing are capable of making additional contributions such as structure strengthening or structure damping. Bucky paper (BP) alternatively called CNT film or CNT network made from single-walled carbon nanotube or multiwalled carbon nanotubes (SWCNT or MWCNT) has been used by some researchers in the past as strain sensor. However, they have observed nonlinear relationship between strain and change in resistance, and lower gauge factor. Literature review in the field indicates that there is scope for improvement in the performance of Bucky paper-based strain sensors. The objective of this experimental work is to investigate effect of CNT film constituents (MWCNT, SWCNT and mix of both), purification of CNTs and effect of preparation method on sensitivity. The work involves preparation of film from CNTs by vacuum filtration method and preparing the strain sensors from the same. These sensors are loaded along with conventional foil strain gauges on opposite side. The change in resistance of sensor due to applied load is measured to evaluate sensitivity or gauge factor of sensor for various cases. It was observed that the sensitivity of CNT strain sensor is dependent on the preparation and purification methods as well as on the aspect ratio.

Contact fatigue properties of NiCrCr3C2 and AlSi coatings for sealing performance of the Wankel engine

NiCrCr3C2 and AlSi coatings were prepared using supersonic plasma equipment. The contact fatigue properties of the coatings were evaluated under dry friction, fuel oil, and lubricating oil conditions. The fatigue life of the NiCrCr3C2 coating was much longer than that of the AlSi coating at the same pressure. Under the same conditions, the NiCrCr3C2 coating had better contact fatigue performance than the AlSi coating, and due to the wettability of Cr3C2 and NiCr alloys, the Cr3C2 hard phase was firmly embedded in the NiCr alloy to ensure hardness and wear resistance at high temperatures.

Evaluation of Bond Strength of Resin and Non-resin Cements to Different Alloys.

A strong metal-cement bond is one of the many factors that contribute to the clinical success of a fixed prosthesis. Even though it is crucial to create ideal resistance and retention forms during tooth preparation, dental cement must be strong enough to hold the restoration in place in the mouth.The present study set out to evaluate and compare the binding strength of resin modified glass ionomer cement, resin cement, and glass ionomer cement to four different metal alloys: titanium alloy, cobalt-chromium (Co-Cr) alloy, nickel-chromium (Ni-Cr) alloy, and noble metal alloys (silver palladium based). Two hundred and forty metal alloy specimenswere created; these were fashioned from (i) a noble metal alloy (silver-palladium based), (ii) a titanium alloy, (iii) a cobalt-chromium alloy, and (iv) a nickel-chromium alloy. A universal testing machine was used to perform the shear test, and statistical analysis of the result was done using a two-way analysis of variance (ANOVA) test and Bonferroni test. Results:The Co-Cr alloy among the cement under investigation had the highest mean value of shear bond strength of 8.06 MPa, whereas a noble metal alloy had the lowest shear strength with a mean value of 5.36 MPa. The resin cement demonstrated the highest shear strength with a mean value that was higher than the other two types of cement. The shear bond strength of the examined samples was significantly affected by the interaction of the alloy and cement, according to the two-way ANOVA test (p=0.001). The results demonstrate that resin cement offers a stronger bond, followed by resin-modified GIC and GIC. The Co-Cr alloy had the highest shear bond strength, followed by Ni-Cr, titanium, and noble metal alloy which showed significantly lower shear strength than the other three alloys.

Rheological Characteristics of Fe–C–Cr(Ni) Alloys

The principal objective of this project was to investigate the rheological properties of Fe-C-Cr and Fe-C-Ni-based low-alloy steels using an Anton Paar high-temperature rotational viscometer up to 1550 °C. The emphasis was placed on determining the liquidus temperatures and evaluating the flow and viscosity curves and the temperature dependence of dynamic viscosity. All were studied depending on the change in the content of chromium (0.010-4.863 wt%), nickel (0.001-4.495 wt%), and carbon (0.043-1.563 wt%). It was shown that the dynamic viscosity decreases with increasing nickel content and increases with increasing carbon and chromium content. The experimental data of the flow curves were fitted using the Herschel-Bulkley model with a good agreement between the measured and calculated values. Characterization of the internal structure was performed by SEM and EDX analyses, confirming non-significant changes in the microstructure of the original and remelted samples. The phase composition of the selected samples was also determined using JMatPro 12.0 simulation software (Sente Software Ltd., Guildford, UK).

Short-range ordering plays a determining role in the low-cycle fatigue life improvement of fcc metals: A conclusive study on low solid-solution hardening Ni-Cr alloys

The effect of short-range ordering (SRO) on the low-cycle fatigue (LCF) behavior of low solid-solution hardening Ni-Cr alloys with high stacking fault energies (SFEs) was systematically studied under cycling at constant total strain amplitude (Δεt/2) in the range of 0.1%–0.7%. The results show that an inducement of SRO structures can notably improve the fatigue life of the alloy regardless of Δεt/2, and several unique fatigue characteristics have been detected, including the transition of fatigue cracking mode from intergranular cracking to slip band cracking, the non-negligible evolution from non-Masing behavior in pure Ni to Masing behavior in the Ni-40Cr alloy, and the secondary cyclic hardening behavior in the Ni-10Cr and Ni-20Cr alloys. All these experimental phenomena are tightly associated with the transformation in cyclic deformation mechanisms that is induced by SRO based on the “glide plane softening” effect. Furthermore, a comprehensive fatigue life prediction model based on total hysteresis energy has been reasonably proposed, focusing on the analyses of the macroscopic model parameters (namely the fatigue cracking resistance exponent β and the crack propagation resistance parameter W0) and microscopic damage mechanisms. In brief, on the premise that the effects of SFE and friction stress can be nearly ignored, as in the case of the present low solid-solution hardening Ni-Cr alloys with high SFEs, an enhancement of SRO in face-centered cubic metals has been convincingly confirmed to be an effective strategy to improve their LCF performance.

Temperature-Dependent Morphological Evolution during Corrosion of the Ni-20Cr Alloy in Molten Salt Revealed by Multiscale Imaging

Understanding the mechanisms leading to the degradation of alloys in molten salts at elevated temperatures is significant for developing several key energy generation and storage technologies, including concentrated solar and next-generation nuclear power plants. Specifically, the fundamental mechanisms of different types of corrosion leading to various morphological evolution characteristics for changing reaction conditions between the molten salt and alloy remain unclear. In this work, the three-dimensional (3D) morphological evolution of Ni-20Cr in KCl-MgCl2 is studied at 600 °C by combining in situ synchrotron X-ray and electron microscopy techniques. By further comparing different morphology evolution characteristics in the temperature range of 500-800 °C, the relative rates between diffusion and reaction at the salt-metal interface lead to different morphological evolution pathways, including intergranular corrosion and percolation dealloying. In this work, the temperature-dependent mechanisms of the interactions between metals and molten salts are discussed, providing insights for predicting molten salt corrosion in real-world applications.

Black Phosphorus Nanosheets in Field Effect Transistors with Ni and NiCr Contacts

Herein, the fabrication and electrical characterization of multilayer black phosphorus (BP)‐based field effect transistors with Ni or NiCr alloy contacts are reported. The devices show p‐type conduction and hysteresis in the transfer characteristics that enable their use as nonvolatile memories. The differences between Ni and NiCr contacts are investigated and the Y‐function method is applied to extract the channel mobility up to 112 cm2 V−1 s−1 and the contact resistances. Ni contacts present specific contact resistance of 6.3 k Ω μm that increases to 18.1 k Ω μm for NiCr. These findings are important for the technological exploitation of multilayer BP in a new class of electronic and optoelectronic devices.

One dimensional wormhole corrosion in metals

Corrosion is a ubiquitous failure mode of materials. Often, the progression of localized corrosion is accompanied by the evolution of porosity in materials previously reported to be either three-dimensional or two-dimensional. However, using new tools and analysis techniques, we have realized that a more localized form of corrosion, which we call 1D wormhole corrosion, has previously been miscategorized in some situations. Using electron tomography, we show multiple examples of this 1D and percolating morphology. To understand the origin of this mechanism in a Ni-Cr alloy corroded by molten salt, we combined energy-filtered four-dimensional scanning transmission electron microscopy and ab initio density functional theory calculations to develop a vacancy mapping method with nanometer-resolution, identifying a remarkably high vacancy concentration in the diffusion-induced grain boundary migration zone, up to 100 times the equilibrium value at the melting point. Deciphering the origins of 1D corrosion is an important step towards designing structural materials with enhanced corrosion resistance.

Carburization of High-Temperature Alloys during Steam Cracking: The Impact of Alloy Composition and Temperature

Prior studies found that the carburization tendency is negligible for technically developed materials at temperatures below 900 °C, especially for Al-containing alloys compared to non-Al-containing alloys applied in steam cracking reactors. However, it is unclear whether this benefit remains at higher temperatures. This work compared coke deposition tendencies of recently developed alloys to each other and to a conventional material when cracking ethane at a higher temperature (950 °C) than previously reported. Under the studied experimental conditions, coking rates vary in the range of 1.22 × 10–6 to 20.5 × 10–6 kg/(m2·s) for Al-containing alloys, while for non-Al-containing alloys, coke deposition rates fall in a range of 4.95 × 10–6 to 33 × 10–6 kg/(m2·s). In general, aluminum-containing alloys showed less coke formation and improved stability against aging after five cracking cycles compared to the non-aluminum-containing materials. The results also showed that substantially less, if any, carburization could be detected in developed alloys even at high temperatures, in contrast to the results from a reference conventional alloy of 27/34 Cr–Ni. At higher temperatures, the protective oxide surface layer of the Al-containing alloys remained noticeably durable and integrated with negligible spallation compared to the ones of non-Al-containing alloys. In fact, the 27/34 Cr–Ni alloy showed the highest coking rate and carburization, implying the most vulnerable oxide surface layer relative to the other alloys. However, energy-dispersive X-ray (EDX) results showed no signs of carburization or deterioration of the surface of 27/34 Cr–Ni after experiments at 880 °C, indicating that both the temperature and matrix composition can play significant roles in determining the suitability of an alloy for application in steam crackers.

Synthesis and Properties of Octet NiCr Alloy Lattices Obtained by the Pack Cementation Process

NiCr alloys with different components were obtained by pack chromation and homogenization heat treatment of octet Ni lattice. The microstructure, alloy composition, microhardness and quasi-static compression properties of the NiCr lattice were tested. The results showed that after homogenization heat treatment, the NiCr alloy lattice had an austenitic structure with uniform composition. Compared with the pure nickel lattice, the microhardness, compressive strength, elastic modulus and energy absorption of the NiCr lattice increased with the increase of chromium content. The microhardness, specific strength, specific modulus and specific energy absorption of the Ni-45Cr alloy were 363 HV, 11.1 MP/(g/cm3), 1169.1 MP/(g/cm3) and 10 J/g, respectively, which were attributed to the solid solution strengthening provided by chromium and the increase in density. NiCr alloy lattices have high strength and toughness and may have potential applications in high-temperature filters or heat exchangers.

Comparative assessment of TiN thin films created by plasma deposition technique on the surface features of NiCr alloys for dental applications

Introduction: Surface treatment is an important technique to increase adhesion between implants and bones, improving its mechanical characteristics and consequently the patient’s comfort. Objectives: Ni-Cr alloys were the object of study in this work, with the purpose of analyzing and evaluating the effect of thin films deposition of titanium nitride via plasma, on its surface and comparing with cathodic cage (CC) and hollow cathode (HC) methods, for dental applications. Methods: Eighteen samples were prepared and the experiment was conducted in two steps: the pre-sputtering (1h, 350 °C, gases: Ar and H) and sputtering (4h, 450 °C, gases: Ar, Ni, and H). To characterize and compare the samples with those of reference, the Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Vickers Microhardness and wettability tests were used. Results: The results presented by SEM showed that during the surface treatment using CC, voids were formed, and using HC, the samples showed a more homogenous behavior. In microhardness tests, using a 25gf load, it was possible to observe that the HC method allowed an increase of 87% when compared to the reference and treated samples. Significance: Lastly, it can be concluded that both methods are suitable for Ni-Cr alloy surface treatment, and the HC technique, a method already used by dental professionals, presents better results due to the formation of a thicker film layer.