Nickel-chromium Alloy Research Articles

Effect of a lower oxygen level in chromium-nickel alloy doped with refractory metals on the mechanical properties and the microstructure

VKh4Sh (Kh65NVFT) stands for a chromium-nickel alloy that is currently used to make combustion chambers for smaller spacecrafts. Due to a high level of oxygen, this alloy has low plasticity at room temperature, which affects its processability. At the same time, the alloy demonstrated high plasticity at a test temperature of 1,100 oC, which constrains its use as a refractory material. Some researchers attempted to make the alloy more heat-resistant by doping it with such refractory metals as Ta, Nb, Hf, Zr. But the chemical analysis showed no presence of Hf or Zr or they were found at minimum detectable concentration. Later, a process was described when different deoxidizers had been used for a VKh4Sh type alloy, and there are data that show that the concentration of oxygen decreased from 300–500 to 40–50 ppm while hafnium and zirconium were successfully absorbed. Therefore, the aim of this research is to understand how a lower level of oxygen and doping with refractory metals (Ta, Nb, Hf, Zr) change the mechanical properties and the microstructure of this heatresistant chromium-nickel alloy. The structure of the following chromiumnickel alloys was studied with the help of a scanning electron microscope and an attachment designed for energy dispersive microanalysis: Alloy I (base) produced using the conventional process without doping; Alloy II doped with refractory metals: 0.15 Ta – 0.15 Nb – 0.05 Hf – 0.05 Zr; Alloy III produced using a process that involves double vacuum remelting with magnesium deoxidation and doping with 0.15 Ta – 0.15 Nb – 0.1 Hf – 0.1 Zr. A series of mechanical tests was carried out with the alloys at the temperatures of 20, 900 and 1,100 oC. Through experiments, it was established that at 1,100 oC the tensile strength of Alloy III increased by 42% compared with Alloy I and by 20% compared with Alloy II, while the elongation of Alloy III dropped by 86% compared with Alloy I and by 25% compared with Alloy II. A microstructural study of the specimens after the tests showed an enhanced structural stability of Alloy III, which is associated with a lower coagulation rate of the phase particles.

THE MACHINABILITY OF INC 718 BY CERAMIC INSERTS

The work deals with a machinability of Inconel® 718 construction material (hereafter referred to as “INC 718”). This chromium-nickel alloy has an austenitic structure, which in conjunction with its low thermal conductivity is one of the causes of a worse machinability. The aim of the work was to increase the productivity of the roughing turning process. There are more ways to improve the machinability of the INC 718, starting from the heat treatment of the material and ending with the application of process fluids. This work is based on real requirements of a company and therefore the possibilities of elimination of the worse machinability were limited by economic and technological aspects. For this reason, the main tool for increasing the productivity of the machining process was changing the material of the cutting tool and fine-tuning of the cutting conditions. In another part of the work, an evaluation of the experimentally determined force ratios of the reference and newly designed technology, which is the basis for the stress-strain analysis, have been made. The conclusion of the research highlights the newly designed process in terms of machining times and the volume of material achieved per unit of the cutting edge durability.

Investigation on the effect of temperature, pressure and grain size on the creep behavior of nickel-chromium binary alloy through molecular dynamics simulation

The microstructure of a polycrystalline binary alloys has offers a critical effect over the creep behavior and its characteristics, due to its vital role over the diffusion behavior of various atoms through the grain boundaries which leads to alter its mechanical and creep characteristics. In this study, the creep behavior of nickel-chromium binary alloy has been computed under compression mode under varying grain size (4.5 nm, 3.7 nm and 2.9 nm), pressure (1 GPa, 2 GPa and 3GPa) and the temperature (600 K and 900 K) to examine its influence over the creep characteristics of nickel-chromium binary alloy. Through this examination, it is found that the temperature has offer greater influence over the creep characteristics followed by the grain size and the pressure, owing to its superior influence over the diffusion behavior of nickel-chromium binary alloy. Additionally, the analysis of vacancy formation and the displacement of nickel and aluminum atoms have confirmed that the diffusion characteristic plays a vibrant role on the creep mechanism of nickel-chromium polycrystalline alloy.

Development of photometric analysis of structural images in relation to the study of nickel-chromium alloy

This work presents preliminary results of the study of a new nickel-chromium corrosion-resistant alloy “Solution-N” intended to replace the imported G-35 alloy, which is currently used for the manufacture of chemical reactor vessels. In view of the limited amount of smelted material, photometric analysis of structural images is widely used to study its structure and properties. Based on the results of the studies carried out, it is proposed to choose the optimal structural state of the alloy, which has the highest corrosion resistance in the temperature range 600-650°C. Corrosion tests are currently being carried out in the laboratory of the prospective customer.

Production of TiC – Co and TiC – NiCr Composite Powders and Study of Their Interaction with a Target under Cold Spray Conditions

In the first part of the paper, the effect of mechanical treatment of particles of reacting Ti + C + Me (Me = NiCr or Co) mixtures on the process of self-propagating high-temperature synthesis (SHS) is investigated. It is shown that as a result of SH-synthesis in the free burning mode, a metal-ceramic sinter of high porosity is formed, which is easily destroyed by mechanical action. An increase in the volume fraction of the metal binder (NiCr or Co) leads to a redistribution of the sizes of carbides towards smaller values.In the second part of the paper, the results of cold spraying nickel-chromium alloy particles and cermet particles of the TiC – NiCr composition on an aluminum substrate are presented. Produced NiCr coatings have a high porosity (up to 10 %) and a layered structure with clearly defined contours of individual deformed particles (splats). Due to the high hardness and low plasticity of metal – ceramic particles of the TiC – NiCr composition, during their interaction with the surface of aluminum substrate, continuous coating cannot be produced, only individual adhered particles are observed. With prolonged exposure to the flow of such particles, erosion of the substrate takes place.

Vacancy surface migration mechanisms in dilute nickel-chromium alloys

We investigate the unitary mechanisms related to the surface migration of vacancies in dilute Ni-Cr alloys via first-principle calculations. We survey a complete set of surface and sub-surface migration paths for vacancies near the (100) free surface and calculate the corresponding migration barriers. Our results show that a vacancy migrating towards the free surface will face lower energy barriers to migrate via atomic exchange with a neighboring Cr atom rather than with a Ni atom. Once a vacancy reaches the free surface, it will be trapped there. Our results also reveal that, when a Cr atom sits in the atomic plane just below the free surface, any in-plane vacancy hopping jump that would result in the vacancy sitting on top a subsurface Cr atom is energetically unfavorable. Taken together, these fundamental unitary surface migration mechanisms offer insights into the complex interactions between surface segregation and vacancy migration phenomena in Ni-Cr-based alloys.

The Effect of Toothbrushing Duration on Nickel Chromium Alloy Wear

Nickel-chromium alloy is a preferred material for fixed partial denture due to its low cost as well as good physical and mechanical properties. Tooth brushing using toothpaste produces abrasion on restoration, especially in a long period. This study aimed to observe the effect of toothbrushing duration on the wear of nickel-chromium alloy. Twenty four specimens of nickel-chromium alloy (Metal 4all, Ivoclar, USA) in 30X15X1mm3 dimension were treated using tooth brushing simulation machine (wear test machine, pin on plate unidirectional movement type) and toothpaste (modification of Balsam formula). The brushing durations were 30.9, 77.25, 123.6, and 154.5 hours as the simulation of 2, 5, 8, and 10 years tooth brushing. Surface roughness and weight difference as abrasion indicator were measured and analyzed using one-way ANOVA followed by LSD test. Tooth brushing duration of 2, 5, 8, and 10 years increased nickel-chromium alloy surface roughness (Ra) by 0.16, 0.39, 0.43, and 0.56µm with weight loss of 8%, 15%, 23%, and 32 %, respectively. These differences were statistically significant (p <0.05). The result of LSD test showed a significant effect (p <0.05) between groups of toothbrushing duration. The increase of surface roughness affects the increase of wear volume of nickel-chromium alloy indicated by R = 0.11 for brushing duration of 2, 5, 8, and 10 years. The conclusion of this study was 10 years tooth brushing promoted wear on nickelchromium alloy, which was indicated by the increase in surface roughness and weight loss.

Study of the Impact of Protective Process Agents with Carbon Nanopowder Additives on Chip Forming Processes

The present study describes the impact of various protective process agents on chip forming processes. The research was conducted on NiCr20TiAl and 34NiCrMoV14-5 nickel-chromium alloys. New lubricant-cooling process agents with carbon nanopowder additives are studied. The optimal composition of the nanopowder additive and its effect during alloy cutting is examined. Experiments reveal the dependence of shrinkage ratio on cutting speed and various protective process agents. The values of H50 microhardness are also defined when cutting these alloys using protective process agents. Experimental studies found the positive effect of developed agents with nanopowder additives on the processes of NiCr20TiAl and 34NiCrMoV14-5 alloys chip formation.

Prospects for using Chromium-Nickel Alloy 42KhNM in Different Types of Reactors

Prospects for using Chromium-Nickel Alloy 42KhNM in Different Types of Reactors

Enhancing sludge conditioning and dewatering characteristics by active surfaces modified with fast recombining immobilized nanoparticles

Nichrome is a composite of nickel chromium alloys and commonly used as resistance wire for heating equipment. In this study, ability of multilayered heterojunctions between Cr+3-TiO2 and Ni2+-TiO2 nanoparticles to disintegrate acidified slurry sludge was investigated experimentally. Recombination and photoactivity of the Cr3+ and Ni2+ nanoparticles were optimized alternating their atomic mass fractions in the nanocomposites by their heating ability, using a central composite statistical design approach. Effects of the applied method on sludge conditioning, stabilization, and drying behaviors were systematically investigated. Temperature increase (ΔT) at the highest volatile suspended solids (VSS) oxidation level in the treated sludge samples were 2 ± 1 °C, 5 ± 1 °C, and 20 ± 1 °C for “UV C + H2O2-no catalyst,” pure and Cr-Ni-TiO2 thin films (TFs), respectively. Obtained results also indicated that the modified TiO2 nanoparticles were able to decrease sludge bound water content by 45 ± 1% efficiency. Cr3+ and Ni+2 co-doped TF functioned to decrease the unit drying energy from 236 ± 10 kJ kg−1 H2Oevaporated to 140 ± 10 kJ kg−1 H2Oevaporated. Drying profiles of raw and treated the sludge samples were fitted to Henderson and Pabis Model. Drying constants (k) for raw and treated sludge samples by pure TiO2 and Cr-Ni-TiO2 TFs were found to be 0.11 ± 0.01 min−1, 0.12 ± 0.01 min−1, and 0.19 ± 0.01 min−1, respectively. VSS degradation followed pseudo-first-order reaction kinetics in the all assayed conditions and pseudo-first-order reaction rates (k obs) for pure and the modified TFs were determined as 6 × 10−4 min−1 and 4 × 10−3 min−1, respectively. 2,2′,5-Trichlorobphennyl, 2,2′,5,5′-Tetrachlorobiphenyl, 2,3′,4,4′,5-Pentachlorobiphenyl, and 2,2′,3,4,4,5,5′-Heptachlorobiphenyl were detected in raw sludge and after the photocatalytic oxidation through Cr3+ and Ni2+ co-doped TiO2 TF reactor, their total concentration was reduced from 4.36 mg kg−1 to 9.76 × 10−3 mg kg−1.

Electrodeposition of Graphene Oxide Modified Composite Coatings Based on Nickel-Chromium Alloy

Composite electrochemical coatings (CECs) based on nickel-chromium alloy and modified with multilayer graphene oxide (GO) were obtained. The electrodeposition process of these coatings was studied in the potentiodynamic mode. The structure and the composition of nickel–chromium–GO CECs were studied by scanning electron microscopy and laser microspectral analysis. Nickel–chromium–GO CECs are dense and uniform. The carbon content in them increases when moving from the substrate to the surface. It was established that the addition of GO particles into the composition of electrolytic coatings with a nickel-chromium alloy results in the increase in their microhardness from 4423–5480 MPa to 6120–7320 MPa depending on the cathodic current density.

Corrosion of construction materials of separator in molten carbonates of alkali metals

The mitigation of steels and alloys corrosion is one of the great challenges for application of high-temperature devices in contact with molten salts. The current research estimates corrosion resistance of the following construction materials: Crofer APU 22, austenitic steel 12Cr18Ni10Ti and two types of austenitic nickel-chromium alloy: CrNi78Ti, CrNi78Ti + 5% wt. W. The measurements are performed by exposition of samples within 24 h in the molten mixture of carbonates of lithium and potassium at 650 °C. The rates and mechanism of materials corrosion under these conditions are determined. The process occurring on the surface while contact of the materials and steels with carbonate melt are investigated.Accurate quantitative data on materials interaction with alkali carbonate melt have been obtained by gravimetrical and physico-chemical methods. The high-temperature corrosion of Fe and Ni austenitic materials has turned dramatically different from both their low-temperature corrosion and each other. There are mixed passivating oxide films on the surface of the only iron-based materials.In addition, the resulting layers of corrosion products are well bonded to the substrate and have protective properties and can be used as protective coatings in molten salts of other compositions, including alkali metal fluorides.

Study of the texture and residual stresses in multilayer Nb/Mo coatings obtained by inverted magnetrons

This work is devoted to the study of the formation of the structure, crystallographic texture and residual stresses in multilayer Nb/Mo coatings deposited by inverted magnetrons on a tubular substrate made of a chromium-nickel alloy. Microprobe analysis of the obtained samples did not show the presence of Nb–Mo solid solutions resulting from mutual diffusion, which is most likely caused by low heating of the coating material during deposition. The results of the studies show that in the outer layers of the multilayer coating, residual stresses are characterized by relatively low values. It is likely that the alternation of layers of refractory metals that differ in thermal linear expansion coefficient values leads to mutual compensation of thermal stresses. Thus, the value of the residual stresses of a multilayer coating of any thickness is comparable to a two-layer coating. The texture effect in a multilayer coating is insignificant compared to the effect of solid solution formation, so high-temperature annealing will help to equalize the elastic characteristics and, accordingly, the stress state in the coating.

Wear-Resistant TiCN-Based Ceramic Materials for High-Load Friction Units

The tribological properties of matrix and skeletal titanium carbonitride composites were studied in dry friction conditions in air. Experiments on wetting of the TiCN–Cr3C2 composite by nickel–chromium alloys and copper using the sessile drop method were performed to choose matrix composition and ascertain whether the samples could be produced by impregnation of the porous skeleton. The sessile drop experiments showed that nickel and its alloys formed a low contact angle on the TiCN–Cr3C2 composite (θ ≈ 8°). In particular, Ni3Al intermetallic had θ < 5°, allowing it to be used as a metal matrix. The same situation was observed for copper. A technique was developed for producing TiN–Cr3C2 composites by impregnation of the porous skeleton with Ni3Al and copper melts, and the tribological behavior of the cermets was tested in dry friction conditions. When the starting composite was impregnated with Ni3Al intermetallic, the friction coefficient decreased (μ = = 0.25). Structural studies were conducted with a MIM-10 metallographic microscope and X-ray diffraction with a DRON-2 diffractometer. The hardness and contact area thickness were measured employing a Falcon 9 hardness tester (manufactured in the Netherlands). Thin cross sections were made to examine the structure and phase composition of the contact area. The structure was analyzed using X-ray diffraction and scanning electron microscopy. The effect exerted by hardness of the counterface (steel 45, 40Kh, ShKh15) on the tribological properties of the TiCN–Cr3C2 composite was established. When steel hardness was 60 HRC, the friction coefficient increased with friction distance. These results were, however, obtained at low speeds and loads. Friction losses decreased with loading increasing from 2 to 6 MPa at 12 m/sec: friction coefficient reduced to 0.23. The TiCN–20% Cr3C2 cermets impregnated with Ni3Al may be recommended as antifriction materials for use in high-speed and high-load friction units.

CHARACTERISTICS OF METAL ALLOYS PROPERTIES FOR DENTAL CASTING AFTER THEIR REPEATED REMELTING

The aim: To study clinical and experimental substantiation of the possibility of using cobalt-chromium and nickel-chromium alloys after repeated remelting for non-removable one-piece prosthetics. Materials and methods: Experimental studies of Remanium GM 700 and Remanium CSe dental alloys have been carried out. To study the physical and mechanical properties of alloys, samples were obtained by sequential six-fold remelting in a Tiegelschleuder TS casting dental unit manufactured by Degussa. All samples were subjected to chemical analysis and metallographic studies by methods generally known in metallurgy, which included studies of microhardness, elasticity, tensile deformation, bending deformation and alloy structure after repeated remelting. Results: Thus, the obtained results of the chemical, physicomechanical and structural properties of the remelts indicate that the Remanium GM 700 and Remanium СSe alloys can be reused many times for the manufacture of one-piece orthopedic structures in that they are identical with certified alloys. Conclusions: In terms of structure, qualitative and quantitative composition of elements, physical and technological properties, the Remanium GM 700 and Remanium CSe alloys have been repeatedly remelted meet the requirements of materials used in biologically active environments of the patient’s body. High-quality and cost-effective remelted multiple times Remanium GM 700 and Remanium CSe alloys can be recommended for use in practical prosthetic dentistry six times.

Optimization of machining parameters in wire cut electrical discharge machining Inconel 600 using untreated brass wire

Abstract WEDM is one of the precise and modern machining path leading in obtaining the efficient manufacturing techniques. In view of machining nickel–chromium alloy, one of the hard-to-cut materials, present paper deals with electro-machining of Inconel 600 using un-treated brass wire. Experiment has been conducted with varying in current, pulse on and pulse off time at constant voltage and di-electric fluid flushing rate. To minimize the experiments and material, a design of experiments was employed based on the L9 orthogonal array was selected. In WEDM pulse rating plays a critical role on surface roughness and material removal rate. Therefore the investigation was carried out to correlate best optimum conditions favouring for lower surface finish and higher material removal rate. Mathematical regression is carried out at alpha of 0.5. Anova analysis was carries out and found that for surface roughness and material removal rate current is most contributing parameter. A mathematical models has been generated in co-relation with input parameters and found that for surface roughness Rsq is 93.32 and for material removal rate Rsq is 92.37.

Depth Profiles of Residual Stresses in Inconel 718Machined with Uncoated and Coated Tools

Inconel 718 is one of the super-alloy materials, belonging to nickel-chromium alloy family, which has major applications in aerospace sector such as engine parts and turbine components. Durability of these components during engineering performance is affected by residual stresses induced in them in the course of their manufacturing processes. The concept of the present paper is to provide an insight view of induced residual stresses in Inconel 718 work piece, when machined with coated (TiN) and uncoated tools at optimum conditions. For this purpose, turning experiments have been conducted on IN718 material through statistical approach using L9 orthogonal array. Taguchi optimization method is exercised with the emphasis on minimizing the cutting forces resulted during machining. The residual stresses generated in the work piece at the optimum conditions employed for both the tools have been evaluated using XRD method. Conditions such as cutting speed of 60 m/min, feed at 0.068 mm/rev and depth-of-cut of 0.10 mm have been optimized for achieving minimum cutting forces during machining of IN 718 using both coated and uncoated tools. However, tensile stresses on the initial surface layer and compressive stresses in the sub-surface layers are found higher in the work piece material machined with uncoated tool. Surface roughness and temperature developed on the surface of the machined bar are higher in case of uncoated tool than those with coated tool.

Effect of Sprue Design in Nickel-Chromium Cast Crown Margin

Objective: To determine the effect of sprue design on the marginal accuracy of the casting. Material and Methods: It was an experimental in-vitro study. There are forty-four crowns of single sprue group with a forty-four double sprue group that was compared in 6 different locations of the margin. The sections were inspected under a microscope at 50X magnification and took a micrograph. The radius from an actual casting edge to a possibly excellent margin was then documented as marginal discrepancy (d), in µm. The marginal discrepancy was documented for each of the six sections per casting. Thus 264 sections were measured for each group. Data were analysed using (ANOVA) for analysis of variance. For bivariate analyses, Chi-square and Student t test were used. The significance level was set at < 0.05. Results: The marginal discrepancy was greater in the single sprue group of cast crown (43.1 ± 4.74 µm) and in double sprue group of cast crown was less (25.7 ± 4.25 µm). This difference is statistically significant (p<0.05). The correlation between single sprue group of casting with a double sprue group of casting by student’s t-test where determination height was 95%. Conclusion: Double sprue design produces a higher accurate margin than single sprue design in the nickel-chromium alloy cast crown.

Surfactant effect of impurity sulphur in ductility dip cracking of a high-chromium nickel model alloy

The sensitivity to ductility dip cracking was measured in two model high chromium nickel alloys, with the same composition, apart from different sulphur contents. The newly developed Refusion Cracking Test was used, that consists in repetitive refusion lines conducted at the specimen surface. Grain boundary cracks develop in the heat affected zone near the refusion line. Cracking is much more pronounced in the sulphur-enriched alloy, which demonstrates a strong deleterious effect of sulphur. However post-mortem analyses using WDS and STEM-EDS revealed no segregation of sulphur at grain boundaries. In contrast, grain boundary fracture surfaces are covered with sulphur. This suggests a dynamic type of grain boundary embrittlement where sulphur acts as a surfactant, facilitating crack opening. Sulphur is efficiently provided to the crack tip as it propagates, due to accelerated diffusion by plastic deformation. This allows crack growth rates higher than 10 µm/s.

Atomic Scale Mechanisms of Multimode Oxide Growth on Nickel-Chromium Alloy: Direct In Situ Observation of the Initial Oxide Nucleation and Growth.

The initial growth mode of oxide on alloy plays a decisive role in the development of protective oxide scales on metals and alloys, which is critical for their functionality for high temperature applications. However, the atomistic mechanisms dictating that the oxide growth remain elusive due to the lack of direct in situ observation of the initial oxide nucleation and growth at atomic-scale. Herein, we employed environmental transmission electron microscopy and the first-principles calculations to elucidate the initial atomic process of nickel-chromium (Ni-Cr) alloy oxidation. We directly revealed three different oxide growth modes of initial NiO islands on Ni-Cr alloy upon oxidation by O2, which result in distinct crystallography and morphology. The multimode oxide growth leads to irregular-shaped oxides, which is shown to be sensitive to the local mass transport. This localization of oxide growth mode is also demonstrated by the identified vigorous competence in oxide growth and thus shown to be kinetically controlled. The concept exemplified here provides insights into the oxide formation and has significant implications in other material and chemical processes involving oxygen gas, such as corrosion, heterogeneous catalysis, and ionic conduction.