NiCr Research Articles

Erosion Response of High-Velocity Oxy-Fuel Sprayed Marble Dust-NiCr Coatings

In the present research, raw marble dust (an ornamental stone waste) with and without pre-mixing of nickel chrome (NiCr) powder are used as the feedstock material to deposit overlay coatings on the mild steel substrates through HVOF spraying technique. The physical as well as mechanical characterizations of the deposited coatings in terms of deposition efficiency, adhesion strength, coating thickness and micro-hardness are done at controlled laboratory conditions. To get an insight to the erosion behavior of the deposited coatings, high temperature solid particle erosion trials on them are carried out as per ASTM G76 considering the test parameter combinations obtained from Taguchi’s L16 orthogonal array. On analyzing the experimental outcomes, impact velocity, NiCr content in the feedstock, erodent temperature and impingement angle are found to be sequentially significant in terms of affecting the wear loss of the coatings. Based on the findings from the analysis, further experimentations are conducted at different levels of the significant control factors to ascertain their effects on the wear rate more precisely. The micrographs of the worn surfaces taken using a scanning electron microscope are studied to identify the possible damage mechanisms causing the erosion loss.

The importance of plasma paste boriding parameters for thickness, nanomechanical properties, residual stress distribution and fracture toughness of layers produced on Nimonic 80A-alloy

Borided layers of different thickness were produced on Nimonic 80A-alloy using plasma paste boriding method. The process was carried out at the temperature of 750 °C, 800 °C and 850 °C for 3 h and 6 h. All produced layers consisted of a fine-grained mixture of nickel borides and chromium borides. Higher boriding temperature and time resulted in the obtaining of boron-rich CrB phase in the microstructure of the borided layer. Simultaneously, this layer was characterized by higher hardness and Young’s modulus. Compressive residual stresses were generated in all produced layers. However, the most advantage course of the curve is characteristic of the borided layer produced at the highest temperature and time. The increase in layer thickness was accompanied by a decrease in the crack’s length (from 33.8 to 7.7 µm), as well as an increase in the fracture toughness (from 0.4439 to 2.4087 MPa·m1/2).

Phase Transformations in a Metastable Fe–18Cr–10Ni Alloy during Megaplastic Deformation

Phase Transformations in a Metastable Fe–18Cr–10Ni Alloy during Megaplastic Deformation

Microstructures and Properties of Ni–Cr–P Filler Metals and Brazed Joints Bearing CNTs

Microstructures and Properties of Ni–Cr–P Filler Metals and Brazed Joints Bearing CNTs

Accelerated Life Test and Life Model Development of Ni-Cr-Based Quartz Tube Heater for Home Appliances

Purpose: This study identified the potential failure mechanisms of a quartz tube heater and established an accelerated life test (ALT) method through the two-stage quality function deployment (QFD) method.BRMethods: The equipment for the ALT was developed independently. The Weibull distribution was used as life distribution and the inverse power model was employed as the accelerated model. An optical microscope, field effect scanning electron microscope, and an energy dispersive spectrometer were used to analyze the failure of the failed quartz tube heater.BRResults: The acceleration model was confirmed as an inverse power model with a material constant of 15.7. From the failure analysis, the failure mechanism was identified to be the moisture penetrated by the breathing of the quartz tube heater corroded the Ni–Cr stranded wire.BRConclusion: Since the quartz tube heater continues to be widely used for industrial and home applications, it can be used as a helpful device in establishing reliability test methods for quartz tube heaters in the future. The established acceleration model can be applied not only to the quartz tube heater but also to the heater with a metal heating wire.

Effect of diffusion brazing time on microstructure, isothermal solidification completion and microhardness distribution during joining of Nicrofer 5520 superalloy using a liquated Ni–Cr–B interlayer

In the present study, the effect of time on the microstructural evolution, distribution of elements, type of precipitated phases, and microhardness of diffusion brazed Nicrofer 5520 superalloy using a BNi-9 (Ni–15%Cr–3.7%B) interlayer was investigated. The diffusion brazing was carried out at 1120 °C for seven different holding times by using a 38 μm thick interlayer. The results indicated that the holding time of 30 min was sufficient for complete isothermal solidification. The eutectic gamma solid solution, Ni-rich borides, and Cr–Mo-rich borides were identified near the bond center before the completion of isothermal solidification, (Ni, Mo, Cr)-rich borides and Cr–Ni–Mo–Fe carbides with different morphologies were found in the diffusion affected zone (DAZ). In the holding time longer than 30 min and, the volume fraction of the precipitated phases in the DAZ decreased, and they transformed into rounder particles. Accordingly, the chemical composition of the interlayer became more homogeneous, resulting in a lower DAZ phases’ density that is happened over the higher brazing times. As the holding time was increased, the chemical composition in the interlayer became more similar to the base metal, and the microhardness in the bond zone and its surrounding became more uniform.

Ni–Cr alloys for effectively enhancing hydrogen evolution processes in phosphate-buffered neutral electrolytes

Significant efforts have been made to develop highly active non-noble metal-based, affordable metallic and stable electro-catalysts for hydrogen evolution reaction (HER). Strong acid and bases are now used in HER operations to achieve large-scale, sustained H2 fuel production. However, few studies have utilized phosphate-buffered neutral electrolytes (PBS) in the field of neutral electrolyte technology. In this work, a certain alloys with a Ni–Cr basis have been produced as favorable components for the HER under neutral conditions. Additionally, the current investigations are emphasizing on the concentration of buffer phosphate species in the HER activity of various materials. By employing polarization and electrochemical impedance spectroscopy (EIS) in neutral solutions, the electro-catalytic activity of new alloys on HER was evaluated. According to the preliminary findings, the examined Ni–Cr-based alloys show superior HER catalytic activity in neutral electrolytes. Additionally, the Ni–Cr alloy matrix with Fe and Mo added enhances HER electrocatalytic efficiency while lowering interfacial charge transfer resistance. Due to its low overpotential of −297 mV @ 10 mA cm−2 and Tafel slope of 94 mV dec−1 in 1.0 M PBS media, the Ni–Cr–Mo–Fe alloy exhibits an efficient HER, suggesting that the Ni–Cr–Mo–Fe electrode will be a potential noble metal-free electro-catalyst for HER. The Ni–Cr–Mo–Fe cathode is a readily available and affordable material for the production of HER in neutral medium.

Effect of WC content on ultrasonic properties, thermal and electrical conductivity of WC–Co–Ni–Cr composites

Abstract This study focused on the effect of WC on the ultrasonic properties, thermal and electrical conductivity of WC–Co–Ni–Cr composites. The samples were produced by powder metallurgy method for microstructural, physical, and ultrasonic characterization. Pulse-echo, hot disk, and four probe methods were used to evaluate the ultrasonic properties, thermal and electrical conductivity of WC–Co–Ni–Cr composites with different WC contents, respectively. Experimental results show that thermal conductivity and electrical conductivity of WC–Co–Ni–Cr composites increase linearly with increasing WC content and then decrease rapidly. The reason for this rapid decrease is expressed in the fact that the structure becomes more ceramic as the WC additive ratio increases. The same situation was observed in ultrasonic measurements. As the amount of WC particles in the sample increased, longitudinal and shear wave velocity, attenuation values, and elastic modulus increased.

Degradation of metronidazole in water using dielectric barrier discharge synergistic with sodium persulfate

A series of water pollution problems caused by antibiotic wastewater need to be solved urgently. Dielectric barrier discharge (DBD) is one of the advanced oxidation processes (AOPs) with the advantages of rapid reaction, stable discharge. Sodium persulfate (PS) is a reagent with strong oxidation and good water solubility, but need to be activated in order to effectively used in wastewater treatment. DBD can activate PS. The effects of technological parameters (input power, air velocity, Metronidazole (MTZ) initial concentration, discharge gap), material of external electrode and sodium persulfate addition amount on the degradation rate and energy efficiency were investigated for MTZ in simulate antibiotic wastewater and a self-made immersed DBD reactor alone or in synergy with PS. Under the optimized conditions of input power of 12 W, air velocity of 150 mL·min−1, MTZ initial concentration of 50 mg·L-1 and discharge gap of 2.0 mm, the maximum degradation rate of MTZ was 60.71 % and 58.68 % for copper wire and nickel–chromium wire as external electrode, respectively. The maximum synergistic degradation rate was 96.48 % and 90.30 % with copper or nickel–chromium external electrode, respectively, when the molar ratio of PS to MTZ was 50. The contributions of O3, ·OH and SO4-· free radicals in the process of DBD synergistic degradation of MTZ with PS were explored via Indigo sodium disulfonate spectrophotometry and free radical scavenger methanol, tert-butyl alcohol. The ozone concentration in the solution can reach 2.965 × 10-2 mmol·L-1. The contributions of ·OH and SO4-· free radicals were 46.73 % and 29.69 %, respectively. The probable degradation paths of MTZ were also proposed based on intermediate product analysis with LC-MS.

Occupational exposure to nickel and hexavalent chromium and the risk of lung cancer in a pooled analysis of case-control studies (SYNERGY).

There is limited evidence regarding the exposure-effect relationship between lung-cancer risk and hexavalent chromium (Cr(VI)) or nickel. We estimated lung-cancer risks in relation to quantitative indices of occupational exposure to Cr(VI) and nickel and their interaction with smoking habits. We pooled 14 case-control studies from Europe and Canada, including 16 901 lung-cancer cases and 20 965 control subjects. A measurement-based job-exposure-matrix estimated job-year-region specific exposure levels to Cr(VI) and nickel, which were linked to the subjects' occupational histories. Odds ratios (OR) and associated 95% confidence intervals (CI) were calculated by unconditional logistic regression, adjusting for study, age group, smoking habits and exposure to other occupational lung carcinogens. Due to their high correlation, we refrained from mutually adjusting for Cr(VI) and nickel independently. In men, ORs for the highest quartile of cumulative exposure to CR(VI) were 1.32 (95% CI 1.19-1.47) and 1.29 (95% CI 1.15-1.45) in relation to nickel. Analogous results among women were: 1.04 (95% CI 0.48-2.24) and 1.29 (95% CI 0.60-2.86), respectively. In men, excess lung-cancer risks due to occupational Cr(VI) and nickel exposure were also observed in each stratum of never, former and current smokers. Joint effects of Cr(VI) and nickel with smoking were in general greater than additive, but not different from multiplicative. In summary, relatively low cumulative levels of occupational exposure to Cr(VI) and nickel were associated with increased ORs for lung cancer, particularly in men. However, we cannot rule out a combined classical measurement and Berkson-type of error structure, which may cause differential bias of risk estimates.

Effect of coping materials and designs to the marginal adaptation of metal porcelain crowns

The Metal porcelain crowns are still widely used because of the clinically satisfactory mechanical, esthetic, marginal and internal adaptation properties and affordable, but metal collars on the marginal labial are not aesthetically acceptable because of dark shadows in the cervical region which can be overcome by marginal porcelain butt joint coping design on the marginal labial. Recent clinical studies have introduced a type of cobalt chromium coping material that is biologically more biocompatible than nickel chromium which can cause allergic reactions. In this study, Ni-Cr and Co-Cr coping materials were used with full metal collarless and modified metal collarless coping designs. The purpose of this study was to determine the effect of material and coping design on the marginal adaptation of metal porcelain crowns. This type of research is experimental laboratory. The typodontic central incisor teeth were prepared and duplicated using CAD/CAM to become zirconia and implanted in acrylic resin blocks for the manufacture of 24 porcelain metal samples. The application of an opaque layer on both coping designs was burned at 975˚C followed by the application of dentin, enamel and glazing.

Kinetics and Mechanical Characterization of Hard Layers Obtained by Boron Diffusion in 80/20 Nickel–Chromium Alloy

This study examines the formation of hard layers containing Ni-B and Cr-B on the surface of 80/20 nickel–chromium alloy. The work evaluates the mechanical properties of the boride layers using instrumented nanoindentation. In addition, the growth kinetics of the coatings were assessed by applying a kinetic model that relates the layer thickness with the experimental parameters of temperature and treatment time. First, the boride layers were achieved using the powder-pack boriding process in a conventional furnace. The treatment time was set at 2, 4, and 6 h at temperatures of 900, 950, and 975 °C, respectively. The microstructure of the layers was analyzed by X-ray diffraction. The thickness of the layers showed a closed correlation with the experimental parameters of time and temperature, and was established between 38.97 and 156.49 µm for 2 h to 900 °C and for 6 h to 975 °C, respectively. The hardness and Young’s modulus values agree with those presented in the literature for boriding nickel alloys, being in the range of 1.3 GPa on average and 240 to 270 GPa, respectively. The resulting layers exhibited a characteristic diffusion zone where the hardness values decrease gradually without the typical high hardness gradient observed on borided steels.

Investigation of the deformation behavior and mechanical characteristics of polycrystalline chromium-nickel alloys using molecular dynamics.

In this study, the mechanical properties and plastic deformation responses of nanocrystalline Cr-Ni alloy were investigated via tensile tests by molecular dynamics (MD) simulation. The effect of various compositions, various grain sizes (GSs) from 4.7 to 11.0nm, and various temperatures from 300 to 1500K is analyzed. The results indicate that the yield strength of the polycrystalline Cr-Ni alloy decreases as decreasing GS, which shows the inverse Hall-Petch relation in the metal softening as reducing GS. Young's modulus (E) increases in the order of the increasing GSs and single crystalline. E rises as raising the percent of Ni from 5 to 15% and then decreases as increasing %Ni to 20%. Besides, E is the linear decrease function with increasing temperature. The maximum stress decreases as increasing temperature and increasing %Ni from 5 to 15%. But that decreases as increasing %Ni from 15 to 20%. The maximum stress value of single crystalline is smaller than that of polycrystalline. The high shear strain zones depend on the GS and alloy composition. The shear strain zones focus on the grain boundary at a low temperature and disperse over the entire specimen when the specimen works at a high temperature. The reason is that the grain boundary helps release stresses to prolong the plastic deformation period to prevent rapid specimen destruction.

The Influence of Metal Coping Design on Fracture Resistance of Porcelain-Fused-to-Metal Crown

The porcelain-fused-to-metal crown is the most popular indirect restoration in dentistry due to its high fracture resistance and low cost. However, unaesthetic labial margin is unacceptable to patients. Metal collar causes dark discoloration, which is worsened by gingival recession. Modification in metal collar coping has been developed to combine high fracture resistance of metal and high aesthetic of porcelain. Modification in crown fabrication including structure and composition of both nickel chromium alloy and feldspathic porcelain; application of self-cured resin cement and digital method; is meant to improve aesthetics without compromising fracture resistance. This study was an experimental laboratory research to evaluate fracture resistance of porcelain-fused-to-metal crowns with different metal coping designs. A total of 20 samples were used and divided into 4 groups according to different coping designs: (1). full metal collar; (2). full metal collarless; (3). modified metal collarless with 1.5 mm reduction; (4). modified metal collarless with 2 mm reduction. Universal Testing Machine (LRXPlus, Lloyd) was used to measure fracture resistance of all crowns. Average fracture resistance value for group 1 was 988.42 N; Group 2 was 1180.15 N; Group 3 was 1089.47 N; Group 4 was 1202.61 N. The results of statistical analysis showed that there was a difference in fracture resistance among porcelain-fused-to-metal crowns with different coping designs, although the value was not statistically significant. The higher coping reduction at labial margin, the higher the fracture resistance and standard deviation.

Impact of HVOF-Sprayed Ni–Cr and (Co,Ni)O Coatings on the Corrosion Behavior of Cu–Ni–Fe Anodes for Green Aluminum Production

Impact of HVOF-Sprayed Ni–Cr and (Co,Ni)O Coatings on the Corrosion Behavior of Cu–Ni–Fe Anodes for Green Aluminum Production

Nanomechanical and tribological properties of nickel–chromium multilayer coating on Inconel 617

Multilayer coatings of Ni and Cr were deposited onto Inconel 617, and multi-scale physical properties were characterized using high temperature tribological experiments, nanoindentation, and microscratch. The effect of high temperature aging (950 °C under helium environment) on two different Ni/Cr multilayer coatings with individual layer thicknesses of 50 and 200 nm denoted by Ni/Cr(50) and Ni/Cr(200) was investigated. Nanoindentation of original coatings showed a hardness of 6 GPa that increases to 14 GPa for both samples once aged. Microscratch results support the macro-tribology results where Ni/Cr(50) (without aging) was the only delaminated coating with significant wear. Additionally, aging in both cases reduced the in situ coefficient of friction and wear. Cross-section energy dispersive spectrometry confirmed that the aged oxide layer was two to three times thicker than the original coating. An abundance of chromium oxide was found in the main body of the coatings, which led to higher hardness and better wear resistance.

Kiln-fired clay bricks synergizing nickel–chromium plating sludge and fly ash: mechanical characteristics and cradle-to-gate life cycle assessment

Kiln-fired clay bricks synergizing nickel–chromium plating sludge and fly ash: mechanical characteristics and cradle-to-gate life cycle assessment

The formation and evolution of Ni2Cr precipitates in Ni–Cr model alloys as a function of stoichiometry characterized by synchrotron x-ray diffraction

Ni-based alloys containing significant amounts of Cr, may precipitate new phases during long-term service at elevated temperatures. In Ni–Cr model alloys, the formation of Ni2Cr has been found to impact the material properties, including the strength and ductility after isothermal aging below the critical temperature of 590 °C. In this work, we quantify the formation and evolution of long-range ordering in four Ni–Cr binary model alloys (Ni/Cr = 1.8, 2.0, 2.2, 2.4) after isothermal aging up to 10,000 h at temperatures between 373 and 475 °C. The alloys were characterized by hardness testing and synchrotron-based x-ray diffraction to quantify the impact of Ni2Cr phase fraction and precipitate size on mechanical properties. After 500 h of isothermal aging, the formation of Ni2Cr was detected in all four alloys at 475 °C. In the stochiometric alloy samples (Ni/Cr = 2.0), the formation of Ni2Cr was found after 500 and 3000 h aging at 418 and 373 °C, respectively. We found that the matrix lattice contraction and Ni2Cr phase fraction both saturate after early aging times. This is in stark contrast to the hardness and Ni2Cr precipitate size that both continue to increase with increasing aging time. Our results highlight that changes in hardness correlate linearly with Ni2Cr precipitate size rather than phase fraction. This important structure-property relationship can potentially help define Ni–Cr-based component lifetimes directly through an understanding of how Ni2Cr formation impacts strength and ductility. We find that a precipitation hardening model for critical resolved shear stress with weakly coupled dislocations shows good agreement with the material property changes quantified from experimental measurements.

Role of diffusion-induced grain boundary migration in the oxidation response of a Ni-30 Cr alloy

Surface deformation of Ni and Fe alloys often contributes to improved oxidation resistance at low and intermediate temperatures. While this beneficial effect has been attributed to fast diffusion mediated by high densities of dislocations and grain boundaries, their contributions ought to be limited due to the very rapid recovery and recrystallization at these temperatures. To elucidate the mechanisms responsible for the beneficial effect of deformation, a Ni-30 at.% Cr alloy in electropolished and ground conditions was oxidized in air at 600 °C for times up to 50 h. The electropolished surface produced a duplex scale with nodules consisting of external NiO and internal Cr2O3 oxides. Limited bulk Cr diffusion sustained Cr2O3 thickening, leading to a continuous thin Cr-depletion zone (<50 nm at 50 h) beneath the scale away from nodules. Alternatively, the ground surface generated a single oxide Cr2O3 layer. Since recovery and recrystallization took place within less than 10 min, the contribution of dislocations remained limited. Instead, the significantly faster Cr transport to the surface yielding exclusive selective Cr oxidation was enabled by diffusion-induced grain boundary migration (DIGM). Rather than diffusion along stationary grain boundaries as previously reported, DIGM and consequently grain growth of the sub-surface recrystallized region resulted in the originally deformed region to become uniformly Cr depleted over several micrometers. DIGM also plays a dominant role in the electropolished sample with the formation of a near Cr2O3 single layer and limited external NiO above grain boundaries.

Shape recovery performance of a (V, C)-containing Fe–Mn–Si–Ni–Cr shape memory alloy fabricated by laser powder bed fusion

In the present work, a Fe–Mn–Si shape memory alloy containing V and C has been fabricated by laser powder bed fusion for the first time. A pronounced pseudo-elasticity compared to a similar alloy but conventionally manufactured is achieved after aging treatment, as a result of the fine microstructure developed during the process and of the evaporation of Mn. The formation of high precipitate densities is also responsible for the improved thermo-mechanical properties. The size and density of precipitates significantly vary with aging conditions and account for important variation in material's performance. A maximum pseudo-elasticity is observed in samples aged at 750 °C for 6 h. The recovery strain upon unloading exceeds the values achieved in the conventionally manufactured alloy by more than 50%.