NiCr Layer Research Articles

Achieving high sheet resistance and near-zero temperature coefficient of resistance in NiCr film resistors by Al interlayers

Thin film resistive materials with low temperature coefficients of resistance (TCR) and high sheet resistances are essential for various electronic applications, such as embedded resistors. In this study, Al inserting layers and NiCr resistive layers were sequentially deposited on alumina ceramic substrates via DC magnetron sputtering to fabricate Al/NiCr bilayer resistive materials. The electrical properties of the bilayer films were adjusted by varying the thicknesses of the Al inserting layers and annealing conditions. When the thickness of the Al inserting layer varied from 5 to 7.5 nm, and post-annealing treatments ranging from 200℃ to 400℃ were applied, evident Al-NiCr interdiffusion occurred, forming intermediate layers at the interfaces and oxides on the film surfaces. A mixture of partial crystalline phases and amorphous phases was also observed in the cross-sectional high-resolution transmission electron microscope (HRTEM) images. The formation of intermediate layers and surface oxides and the balance between partial crystalline phases and amorphous phases collectively enhanced the electrical performance of bilayer film resistors, achieving thin film resistors with a remarkably low TCR of −6.61 ppm/K and a sheet resistance of up to 265.95 Ω/sq. By rational design of Al layers, NiCr layers and thermal treatment, thin film resistors with near zero TCRs and extremely wide sheet resistance range of 93.34–1439.01 Ω/sq can be obtained.

Microstructural and electrical behavior of NiCr/Al nanomultilayered films prepared by magnetron sputtering

The NiCr/Al nanomultilayered films with different Al thicknesses (tAl) were prepared by magnetron sputtering. The structural evolution of the Al nanolayer with the increase in tAl was investigated. When the Al layer thickness changed from 1.2 nm to 2.4 nm, the Al layer could keep the co-epitaxial growth with the adjacent NiCr layer. Accordingly, the crystallization degree improved. When the Al layer thickness changed from 2.4 nm to 3.0 nm, the transformation from the coherent to incoherent interfaces took place between the NiCr and Al layers. Meanwhile, the co-epitaxial growth with the adjacent NiCr nanocrystallites was destroyed, the crystallinity and the grain size decreased, leading to the increase of the resistivity under the combined effects of the grain boundary scattering and interface scattering. The interfacial evolution of NiCr/Al nanomultilayered films was closely related to the changes of electrical properties. When the Al layer thickness changed from 3.0 nm to 3.6 nm, the surface quality of the film was improved, which effectively reduced the scattering of defects and vacancies during the electron transport, resulting in the decrease of the resistivity of the NiCr/Al nanomultilayered film.

Metallographic Evaluation of Ni-Cr Cold Spray Layers on the Tube

The article deals with metallographic evaluation of Ni-Cr Cold Spray layers, which were deposited on GOST 22K steel for four layer variants. The sprayed Ni-Cr layer should primarily serve to protect the heterogeneous weld in the nuclear power industry. Metallographic evaluation of the applied layer was focused on the evaluation of spray fillability in the notch.

Comparative Study of HVOF Cr3C2–NiCr Coating with Different Bonding Layer on the Interactive Behavior of Fatigue and Corrosion

In order to improve material service life under a fatigue and corrosion coupling environment, a high-velocity oxygen fuel (HVOF) Cr3C2–NiCr coating with a bonding layer was prepared. The objective was to obtain the optimum bonding layer for the HVOF Cr3C2–NiCr coating, which included a laser cladding (LC) Ni625 layer, extreme high-speed laser material deposition (EHLA) Ni625 layer and HVOF NiCr layer. Fatigue properties of the samples with various bonding layers were investigated by means of a four-point bending fatigue test. Electrochemical impedance spectroscopy (EIS) and the salt spray test were executed after the bending fatigue test to simulate the interactive effect of fatigue and corrosion atmosphere. Failure surfaces were characterized by scanning electron microscopy (SEM) and an energy-dispersive spectrometer (EDS) to indicate the details of corrosion products. Corrosive behaviors of samples were adequately demonstrated according to the results, which included the curves of potentiostatic polarization, impedance magnitude and phase degree, and corrosion products. The result showed that the cycles of perforative cracking for the sample with the EHLA Ni625 bonding layer was almost three times than that of the sample with the HVOF NiCr layer. The magnitude of EIS reduced from ~105 to ~103 for the sample after BFT. Eventually, the main improvement mechanism of the HVOF Cr3C2–NiCr coating with the EHLA Ni625 bonding layer was attributed to the grain refinement of the bonding layer and performed a good level of metallurgical bonding with the substrate.

Digital Process Chain for Processing of Bend-Sensitive Functional Structures on a Flexible Substrate

System-in-foil technology continues to realize relevance in industry and research. In this article, a digital process chain for the fabrication of bend-sensitive sensor structures on a flexible polyimide foil is described. This means that none of the steps in this process chain requires the manufacturing of a structured mask or cliché. Therefore, an arbitrary layout can be manufactured and easily be changed without major effort. Patterning of the sensor layout is realized by direct imaging of a laminated dry film photoresist. The sensor structure is fabricated by a liftoff process using sputtering of a NiCr layer. Finally, the sensor structures are characterized by a static bending test.

Microstructure Characteristics, Tribology and Nano-Hardness of Plasma Sprayed NiCrRe Coating

This paper presents the results of the investigation of NiCrRe coating deposited by plasma spray process at the atmospheric pressure on boiler steel substrate. These coatings were characterized by means of a scanning electron microscopy, and Energy-dispersive X-ray spectroscopy. The wear resistance of plasma sprayed NiCrRe coatings has been investigated under dry sliding conditions at applied load of 10 N in air. The continuous stiffness measurement (CSM) method was used for the investigation of nanohardness using Agilent G200 Nano-indenter in order to determine the mechanical properties of the coatings. Microstructural observations pointed out that the NiCr layer with white isles of rhenium possessed porosity, oxidized, un-melted and semi-melted particles, and inclusions. According to the results the thickness of the layer is 450 µm, the indentation modulus 158 ± 24.4 GPa, hardness 3.74 ± 0.76 GPa and the coefficient of friction is 0.45.

Thermal stability and optical properties of low emissivity multilayer coatings for energy-saving applications

In this study, the deposition and characteristics of Si- and Ti-series multilayer coatings with respective glass/Si3N4/NiCr/Ag/NiCr/Si3N4 and glass/TiO2/ZnSnO3/ZnO/Ag/NiCrOx/ZnSnO3/Si3N4 structures were investigated. Experimental analyses were performed, and the optical performance and thermal stability of the coatings were assessed. The as-deposited Si- and the Ti-series samples exhibited optimal shading coefficient of 0.49 and 0.57, respectively. Thermal annealing in air was performed to analyze the thermal stability and oxidation resistance of the samples. The Si- and Ti-series samples prevented the failure of low-emissivity properties at 700 and 600 °C, respectively. In addition to high transparency, the Si-series samples exhibited improved low-emissivity properties, reduced light pollution, and superior thermal stability compared to the Ti-series samples. The use of Si3N4 and NiCr layers effectively prevented the oxidation and cracking of the Ag layer upon heat treatment. This study presents the characteristics of Si- and Ti-series samples for energy-saving building applications.

Magnetron-Sputtered Ni-Cr and Ti-Si Layers to Protect Ti-46Al-8Nb (at.%) Substrates Against Gas Absorption

Ni-Cr and Ti-Si layers were deposited by magnetron sputtering on Ti-46Al-8Nb (at.%) substrates to suppress penetration of gases, which brings about undesirable changes in mechanical properties. Alloy samples with and without surface protection were subjected to interrupted oxidation at elevated temperature (700 and 800 °C) for up to 300 h. Selected mechanical properties as well as adhesion of surface layers were examined in the as-received and oxidized state. Analytical techniques used to characterize surfaces and cross sections of the samples included scanning electron microscopy and light microscopy, energy-dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy and x-ray diffraction. Both investigated layers were sufficiently adherent and effective in hindering gas absorption at 700 °C; however, only Ni-Cr showed promising properties for higher-temperature applications.

Experimental investigation of alumina coating as tritium permeation barrier for molten salt nuclear reactors

This study experimentally investigates the reduction efficiency of tritium permeation through 316 stainless steel tubing coated with alumina as a tritium permeation barrier (TPB) in support of the development of molten salt nuclear reactors, particularly for fluoride salt-cooled high-temperature nuclear reactors (FHRs). The TPB coatings composed ofan intermediate bond layer of NiCr, a transition layer of NiCr + alumina, and a pure alumina layer were successively added onto the outer surface of commercial 316 stainless steel tubing via plasma thermal spray. In order to generate a continuous gaseous tritium source, 35 g of purified natural-lithium FLiBe salt was irradiated by thermal neutron flux at 620 °C in the Massachusetts Institute of Technology Research Reactor (MITR). The preliminary results suggest that the TPB coatings on tube surfaces significantly reduced the tritium permeation rate at 700 °C. To get a better understanding of the TPB, the microstructure of the coated tubes was characterized with various techniques.

Diffusion bonding of hydrogenated TC4 alloy and GH3128 superalloy using composite interlayers

The Nb and Nb/Ni interlayers were designed for the diffusion bonding of the hydrogenated TC4 alloy and GH3128 superalloy joint. Typical microstructure of the TC4-0.3 H/Nb(Ni/Nb)/GH3128 joints were investigated. The effects of holding temperatures and durations on the microstructure evolution of the hydrogenated TC4/GH3128 joints were investigated. The addition of a Nb interlayer can successfully suppress the brittle Ti-Ni phase formation and the maximum joint strength reached 245 MPa bonded at 860 ℃/60 min under 10 MPa. The design of the Nb/Ni interlayer successfully eliminated the unbonded voids and the Ni-Cr layer formed when bonding with a single Nb interlayer. The maximum shear strength of ˜270 MPa was achieved when bonding at 860 ℃ for 80 min under 10 MPa. Fracture mechanism of the hydrogenated TC4/GH3128 joints bonded with two interlayers were analyzed finally.

Inorganic-metallic bilayer on Mg alloy via wet and dry plasma treatments

The present study investigated the formation of inorganic-metallic bilayer on Mg alloy by combination of wet and dry plasma treatments. For this purpose, Mg alloy subjected to plasma electrolytic oxidation (PEO) in a silicate-based electrolyte was treated subsequently by dry plasma treatment via radio frequency (RF) sputtering to deposit Ni-Cr alloy on the porous inorganic layer. From microstructural observation, Ni-Cr layer modified the morphologies of the porous inorganic layer owing to the conformal coverage. Per electrochemical assessments, sample with bilayer exhibited superior corrosion protection due to the less defective microstructures and the presence of stable oxides. The electrochemical mechanism underlying the superior corrosion resistance of bilayer coating was discussed in the context of an equivalent circuit model by taking the surface morphologies into account.

Nanostructure, structural stability, and diffusion characteristics of layered coatings for heat-assisted magnetic recording head media

The intense laser heating in heat-assisted magnetic recording (HAMR) has been a major hindrance to HAMR technology from becoming commercially viable. Thermal damage of the near-field transducer (NFT) and write pole (WP) embedded in the trailing edge of the magnetic head due to failure of the protective carbon overcoat after prolonged heating at an elevated temperature are major obstacles. Therefore, the main objective of this study was to develop an effective coating method for HAMR heads. This was accomplished by introducing a new class of layered coatings consisting of ultrathin amorphous carbon (a-C) overcoat, adhesion (SiN) layer, and buffer (NiCr or TaOx) layer sequentially deposited onto Au and FeCo base layers to mimic the layer stacking of NFT and WP elements, respectively. The structural stability of the a-C overcoats and diffusion characteristics of each comprising layer under conditions of heating at 350 °C for 30 min in an Ar atmosphere were investigated by high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM), and electron energy loss spectroscopy (EELS). For most stacking configurations the HRTEM/STEM and EELS results generally revealed some layer intermixing and minute carbon atom rehybridization in the heated a-C overcoats. The findings of this investigation suggest that further optimization of the developed layered coatings can provide a viable solution to thermal damage of HAMR heads.

FORMATION AND STUDY OF PLASMA SPRAYING DOUBLE-LAYER COMPOSITE COATINGS (VISCOUS METALLIC NiCr AND SOLID ZrO2 LAYER)

. The paper presents results pertaining to investigations on influence of plasma jet parameters and fractional composition of initial powder on characteristics of two-layer composite coatings on the basis of nickel-chromium, and zirconium dioxide in the shielding elements. Optimization has been carried out on the basis of obtaining maximum powder use factor. A comparative analysis for dependence of the powder use factor in viscous metal layers of nickel-chrome and nickelaluminum on spraying distance shows that while having similar character of curves for the presented dependencies an absolute value of powder use factor is higher for nickel-chromium powder. It can be explained by a higher ductility of the latter and correspondingly smaller rebound of particles which are colliding with substrate. The investigation results for cross section microstructure in the formed coatings while using scanning electron microscopy are given in the paper. The paper considers cross section microstructures for ZrO2-coating and intermediate Ni–Cr layer. The submitted data reveal that an initial stage of the coating is characterized by porosity and an average pore size is of several micrometers, and in some areas its size reaches 20 mm. The microstructure of a Ni–Cr layer is characterized by lower porosity. Impact of compression plasma flows on sprayed coating leads toformation of fused oxide layer with thickness of 12–15 mm and contributes to smoothing of surface relief and formation of cracks on the surface which are preferably propagating into coating depth. Processing of oxide coatings by compression plasma also results in reduction of their porosity.

Microstructure Effect of Intermediate Coat Layer on Corrosion Behavior of HVAF-Sprayed Bi-Layer Coatings

The inherent pores and carbides of Cr3C2-NiCr coatings significantly reduce the corrosion resistance, the former by providing preferential paths for ion diffusion and the latter by forming cathodic sites in galvanic couples (between NiCr and Cr3C2). Adding a dense intermediate layer (intermediate coat layer) between the Cr3C2-NiCr coating (top coat) and substrate increases the corrosion protection of the coating if the layer acts as cathode in connection to the top coat. In the present work, NiCr, NiAl, and NiCoCrAlY layers were deposited by high-velocity air-fuel process as intermediate coat layers for the Cr3C2-NiCr top coat. Effects of coating microstructure on corrosion behavior of single- and bi-layer coatings were studied by open-circuit potential and polarization tests in 3.5 wt.% NaCl at room temperature. A zero resistance ammeter technique was used to study the galvanic corrosion of the coupled top and intermediate coat layers. Methods such as SEM and XRD were employed to characterize the as-sprayed and corroded coatings and to investigate the corrosion mechanisms. The results showed that the NiCoCrAlY coating not only presented a more positive corrosion potential (Ecorr) than the Cr3C2-NiCr coating, but also provided a better passive layer than the single-phase NiCr and NiAl coatings.

Modelling of the interdiffusion and oxidation of a multilayered chromia forming thermal barrier coating

The stability of multilayered coatings is important in long‐term use and thus accurate predictions of the effects of exposure at temperature are extremely important. In this paper, the prediction and validation of a multilayered thermal barrier coating with a bond coat based on the MCrAlY system is presented. The coating was a three layered bond coat consisting of a NiCrAlY layer with an aluminised outer region onto which a NiCr layer with 2 wt% Si had been deposited. Onto this an yttria partially stabilised zirconia topcoat was applied. The coating system was exposed to 800 °C for times up to 3000 h. The specimens were sectioned and scanning electron micrographs obtained. Energy dispersive spectroscopy, EDS, was used to provide compositional data on each of the layers in the starting condition and also to produce elemental profiles through the sections with increasing time at temperature. The oxidation kinetics were determined from oxide growth measurements over time. The variation of these elemental profiles with exposure time were compared with the ODIN finite‐difference code, which also allowed for chromium depletion due to its selective oxidation. Generally, satisfactory agreement was found.

The behavior of ZrO2/20%Y2O3 and Al2O3 coatings deposited on aluminum alloys at high temperature regime

Aluminum alloy present numerous advantages like lightness, high specific strength and diversity which recommend them to a high number of applications from different fields. In extreme environments the protection of aluminum alloys is difficult and requires a high number of requirements like high temperature resistance, thermal fatigue resistance, corrosion fatigue resistance and galvanic corrosion resistance. To obtain these characteristics coatings can be applied to the surfaces so they can enhance the mechanical and chemical properties of the parts. In this paper two coatings were considered for deposition on an AA2024 aluminum alloy, ZrO2/20%Y2O3 and Al2O3. To obtain a better adherence of the coating to the base material an additional bond layer of NiCr is used. Both the coatings and bond layer were deposited by atmospheric plasma spraying on the samples. The samples were subjected to a temperature of 500°C and after that slowly cooled to room temperature. The samples were analyzed by electron microscopy and X-ray diffraction to determine the morphological and phase changes that occurred during the temperature exposure. To determine the stress level in the parts due to thermal expansion a finite element analysis was performed in the same conditions as the tests.

Stainless steel to titanium bimetallic structure using LENS™

Laser Engineered Net Shaping (LENS™) is a commercially available additive manufacturing technique that was used for one step manufacturing of bimetallic structures of stainless steel and Ti6Al4V (Ti64) alloy. Two approaches were adopted for manufacturing these bimetallic structures. In the first approach, direct deposition of Ti64 on SS410 substrate and compositionally graded bimetallic structures were attempted without any intermediate bond layer. In the second approach, an intermediate NiCr bond layer (of thickness ∼750μm) was deposited to minimize thermal and residual stresses for these bimetallic structures. Direct deposition of Ti64 was successful only for a couple of layers before the structures were delaminated. Compositionally graded bonding was unsuccessful with the formation of brittle intermetallics and related residual stresses causing delamination. Using an intermediate NiCr layer, bimetallic structures were successfully fabricated. Our work is focused on LENS™ based processing approach and related microstructural evolution towards bimetallic structures.

X-ray Absorption Study of Structural Coupling in Photomagnetic Prussian Blue Analogue Core@Shell Particles

X-ray absorption spectroscopy experiments of core@shell, photomagnetic, and Prussian Blue analogue heterostructures obtain the local structure around the magnetic transition-metal ions before and after illumination. Two samples, containing nickel hexacyanochromate (Ni–Cr) and cobalt hexacyanoferrate (Co–Fe) in Ni–Cr@Co–Fe and Co–Fe@Ni–Cr geometries, were studied. Both materials display the well-known photoinduced valence tautomerism for Co–Fe, accompanied by a large change in cobalt to nitrogen distances. Furthermore, these experimental results show a structural coupling of the photoactive Co–Fe layer to the passive Ni–Cr layer. Finally, the strain across the heterostructured interface in Co–Fe and Ni–Cr containing core@shell models is investigated with simulations that use custom potentials derived from density functional theory calculations.

Formation and oxidation resistance of Al/Ni coatings on low carbon steel by flame spray

In this work the effect of heat treatment on the structure and the durability of double layer Ni/Al coatings was investigated. An initial Ni–Cr layer was primarily deposited by thermal spray, followed by a successive Al metallic layer in a second stage. The specimens were then heat treated in inert atmosphere. Nickel aluminide compounds were formed as a result of the diffusion between the two layers upon annealing. Indeed, scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy examinations of the coated samples revealed that the as sprayed coatings contain two distinct Al and Ni–Cr layers while the heat treated coatings were gradually transformed to Al3Ni depending on the heat treatment parameters. The as sprayed and annealed specimens were tested by subjecting them in an air environment at 700°C and 800°C, for the evaluation of their durability and resistance. It was found that the annealed samples have superior high temperature resistance compared with the as sprayed coatings and bare steel, which is attributed to the presence of Ni–Al compounds, to the low coating porosity and to the formation of dense oxides on the coating surface.

Friction and Wear Characteristics of Plasma-Sprayed Self-Lubrication Coating with Clad Powder at Elevated Temperatures up to 800 °C

NiCr/(Cr3C2-BaF2·CaF2) coating was fabricated by atmospheric plasma spray technology using clad powder. The coating shows low porosity, high microhardness and bonding strength, and it also exhibits good friction reduction and wear resistance at elevated temperatures up to 800 °C which is due to the formation of a kind of continuous BaF2·CaF2 eutectic lubricating film. The excellent mechanical and tribological properties of the coating are partially attributed to the protection of NiCr layer of the composite powders which can decrease oxidation, decarburization of Cr3C2, and ablation of BaF2·CaF2 eutectic during spray and deposition process.