Research on the Role of Surface Treatment of the Metal Surface on the Strength of the Metal-Ceramic Bond.

AIM: The aim of the present study is to investigate the metal-ceramic bond strength as a result of three different surface treatment methods: (1) oxidation, (2) oxidation and sandblasting, and (3) double oxidation on the metal substrate. MATERIALS AND METHODS: A total of 72 metal substrates were made from two different types of metal-ceramic alloys (n = 36): group I, Ni-Cr and group II, Co-Cr alloys. Each group was further divided and subjected to three different surface treatments (n = 12): (1) oxidation in accordance with the manufacturer's instructions; (2) oxidation according to the manufacturer's instructions and then sandblasting with Al2O3, with a grain size of 110 µm, a pressure of 75 psi for 10 sec with a distance of 5 cm and steam cleaning; and (3) double oxidation. The bond strength of the specimens was evaluated with the three-point bending process. The data were recorded, tabulated, and statistically analyzed. RESULTS: For group I, the materials with oxidation based on the specifications, show mean value of 64.02 Nt. The oxidation and sandblasting materials have mean 55.92 Nt. The double oxidation materials have mean 55.47. For group II, the materials with oxidation based on the specifications, show mean value of 58.46 Nt. The oxidation and sandblasting materials have a mean value of 42.56 Nt. The double oxidation materials have mean 42.96 Nt. CONCLUSION: The best method of treatment of the metal substrate is specification oxidation, in terms of the strength of the metal-ceramic bond. Further treatment of the metal substrate reduces the strength of the metal-ceramic bond. CLINICAL SIGNIFICANCE: A prerequisite for clinical success of metal-ceramic prosthetic restorations is the increased strength of the bond between ceramic material and metal substrate. With that in mind, the present research gives important insight into best practices for prosthetic restorations.

Defects engineering on CrOOH by Ni doping for boosting electrochemical oxygen evolution reaction.

The design and construction of active centres are key to exploring advanced electrocatalysts for oxygen evolution reaction (OER). In this work, we demonstrate thein situconstruction of point defects on CrOOH by Ni doping (Ni-CrOOH/NF). Compared with pure CrOOH/NF, Ni-CrOOH/NF showed enhanced OER activity. The effect of the amount of Ni introduced on the OER performance was investigated. Ni0.2-CrOOH/NF, the best introduction of Ni, uses a low overpotential of 253 mV to achieve a current density of 10 mA cm-2with a high turnover frequency of 0.27 s-1in 1.0 M NaOH. In addition, the electrocatalytic performance of Ni0.2-CrOOH/NF showed little deterioration after 1000-cycle cyclic voltammetry scanning. In the potentiostatic test, activity was stable for at least 20 h.

Comparison of Marginal Fit of Metal Copings in Two Different States with and without Using Ring Liners: An In Vitro Study.

AIM AND OBJECTIVE: To compare the marginal fit of Ni-Cr copings made by casting in two different states (dry and wet) with either cellulose ring liners or no ring liners. MATERIALS AND METHODS: An in vitro study was conducted on 40 patterns which were invested, and a burnout casting procedure was used, using a Ni-Cr alloy to obtain the cast copings. The cast copings were divested, cleaned, and run through a finishing procedure. The copings were seated on the stainless steel die and microscopically evaluated for marginal discrepancies at two predetermined reference points using an optical microscope (Rieichert, Austria). Statistical analysis was done using Pearson's correlation coefficient and Chi-square test, keeping 95% confidence intervals and having a p value of less than 0.05 statistically significant. RESULTS: Our results identified marginal discrepancies in all the Ni-Cr cast copings, which significantly differed from each other. The copings obtained from casting with a cellulose ring liner in a wet state showed a significantly higher value followed by casting using a cellulose ring liner in a dry state. The mean marginal discrepancy values were within the clinically acceptable range for all the Ni-Cr cast copings included in two groups. CONCLUSION: Our study concludes that the copings cast with a cellulose ring liner in dry states had the least amount of vertical marginal discrepancies as compared to those that were cast with a ring liner in two different forms or those cast without a ring liner, suggesting that the use of cellulose ring liner in a dry state is favorable for all casting procedures. CLINICAL SIGNIFICANCE: Measuring gaps or discrepancies at margins is the commonly used method to determine the fit of Ni-Cr copings. In order to minimize marginal inaccuracies, various authors have suggested different methods to improve the marginal adaptation of cast restorations. There are compensation methods like setting expansion, hygroscopic expansion, and thermal expansion of the investment, which are used to assess metal shrinkage during cooling.

Microcomputed tomography a noninvasive method to evaluate the fit of a restoration as compared to conventional replica technique.

AIM: The aim of the study was to compare the assessment methods used to evaluate the fit of Ni-Cr metal copings. SETTINGS AND DESIGN: Comparative- Invitro study design. MATERIALS AND METHODS: A stainless steel die simulating a prepared first maxillary premolar was used as a master die. Wax pattern copings were fabricated by the conventional dipping wax technique (n = 20) on the master die and were cast in Ni-Cr alloy. The finished copings were fitted on the master die and scanned by the micro-computed tomography (CT) scanner. Multiple projections of the sample were reconstructed to evaluate the marginal and internal fit at 5 predetermined locations. The same copings were used for the replica technique and were evaluated under a stereomicroscope in the same locations. STATISTICAL ANALYSIS USED: Shapiro-Wilk's test and Unpaired t-test. RESULTS: The marginal fit values observed were 127.71 and 95.06 µm, chamfer area fit values were 151.97 and 132.7 µm, axial area fit values were 62.36 and 46.14 µm, axio-occlusal area fit values were 139.52 and 123.6 µm, occlusal area fit values were slightly higher with 217.91 and 193.1 µm, respectively, in replica and micro-CT technique. There was no statistically significant difference observed in the fit between the two assessment methods (α > 0.05). CONCLUSIONS: There was no difference observed in the marginal and internal fit of Ni-Cr metal copings with the two methods of assessment. However, the micro-CT technique proved to be simpler, noninvasive, and time-saving assessment method.

The Effect of Porcelain Firing on Electrochemical Behavior of a Dental Alloy in Hydrogen Peroxide.

PURPOSE: The aim of this study was to evaluate changes in electrochemical corrosion properties of porcelain firing simulated nickel-chromium dental casting alloy exposed to a 10% hydrogen peroxide bleaching agent. MATERIALS AND METHODS: The electrochemical corrosion behavior of a Ni-Cr alloy was evaluated by cyclic polarization test in the aerated electrolyte (pH = 6.5). Test groups were produced in as-cast (group 1, control group) and simulated porcelain firing (group 2: heat-treated/mean value; group 3: heat-treated/cycle) conditions. Scanning electron microscopy (SEM) was also used to examine the alloy surfaces before and after the corrosion test. RESULTS: The ranking of the groups with respect to Ecorr and Icorr was as follows: 1, 2, 3 and 3, 1, 2, respectively. Group 3 exhibited the greatest and group 2 displayed the least corrosion tendencies. An increase in corrosion rates was observed after heat treatment/cycle state. Post-corrosion SEM photographs were also consistent with the test results. CONCLUSION: Within the parameters of this study, a single heat treatment is insufficient to cause upheaval in corrosion behavior of a Ni-Cr alloy subjected to 10% hydrogen peroxide.

Corrosive and cytotoxic properties of compact specimens and microparticles of Ni-Cr dental alloy.

PURPOSE: Nickel-chromium (Ni-Cr) dental alloys have been widely used in prosthodontic practice, but there is a permanent concern about their biocompatibility due to the release of metal ions. This is especially important when Ni-Cr metal microparticles are incorporated into gingival tissue during prosthodontic procedures. Therefore, the aim of this study was to examine and compare the corrosion and cytotoxic properties of compact specimens and microparticles of Ni-Cr dental alloy. MATERIALS AND METHODS: Ni-Cr alloy, Remanium CSe bars (4 mm diameter), were made by the standard casting method and then cut into 0.5-mm-thick disks. Metal particles were obtained by scraping the bars using a diamond instrument for crown preparation. The microstructure was observed by an optical microscope. Quantitative determination and morphological and dimensional characterization of metal particles were carried out by a scanning electron microscope and Leica Application Suite software for image analysis. Corrosion was studied by conditioning the alloy specimens in the RPMI 1640 medium, containing 10% fetal calf serum in an incubator with 5% CO2 for 72 hours at 37°C. Inductively coupled plasma-optical emission spectrometry was used to assess metal ion release. The cytotoxity of conditioning medium (CM) was investigated on L929 cells using an MTT test. One-way ANOVA was used for statistical analysis. RESULTS: After casting, the microstructure of the Remanium CSe compact specimen composed of Ni, Cr, Mo, Si, Fe, Al, and Co had a typical dendritic structure. Alloy microparticles had an irregular shape with a wide size range: from less than 1 µm to more than 100 µm. The release of metal ions, especially Ni and Mo from microparticles, was significantly higher, compared to the compact alloy specimen. The CM prepared from compact alloy was not cytotoxic at any tested dilutions, whereas CM from alloy microparticles showed dose-dependent cytotoxicity (90% CM and 45% CM versus control; p < 0.005). CONCLUSION: Ni-Cr microparticles showed less corrosion resistance and lower biocompatibility than compact alloy. This could affect health on long-term exposure, especially in sensitized individuals.

Electrochemical corrosion and surface analyses of a ni-cr alloy in bleaching agents.

PURPOSE: The aim of this study was to evaluate the corrosion behavior of a Ni-Cr dental casting alloy subjected to 10% hydrogen peroxide (HP) and 10% carbamide peroxide (CP) bleaching solutions and to determine the composition of the surface oxide layer formed on the alloy specimens. MATERIALS AND METHODS: Ten cylindrical specimens (4 mm in diameter × 25 mm in height) were cast from a Ni-Cr alloy (Wiron 99) and divided into two groups (n = 5). A potentiodynamic polarization test was used to compare the corrosion rates of specimens in HP and CP (pH = 6.5). Before cyclic polarization tests, all alloy specimens were allowed to reach a steady open circuit potential (Ecorr ) for a period of 1 hour. Then tests were initiated at 100 mV versus standard calomel electrode (SCE) below Ecorr and scanned at a rate of 1 mV/s in the anodic direction until reaching 1000 mV over the Ecorr value. The scan then was reversed back to the Ecorr of the specimens. The open circuit potentials (Ecorr ) and the current densities (Icorr ) were determined using the anodic Tafel regions extrapolating from the curves. Differences in Ecorr and Icorr were determined using one-way ANOVA (α = 0.05). In addition, corrosion rates were calculated from these curves. Before and after polarization tests, a scanning electron microscope (SEM) examination accompanied by energy dispersive X-ray spectroscopy (EDS) was used to analyze the surface morphology. The surface characterization of the passive film formed on alloy specimens was also performed by using X-ray photoelectron spectroscopy (XPS). RESULTS: In this study, bleaching agents had an effect on the anodic process for two groups. Although no statistical difference was identified between the groups for both corrosion parameters, results indicated that the effect of CP on the corrosion behavior was less than that of HP. These results agreed with the SEM observations. XPS data showed that oxide layers formed on all groups contained mainly Cr2 O3 , NiO, and MoO3 , and the amounts of oxides formed on CP-treated specimens were higher than HP treated ones. Also, molybdenum rates were increased with CP application compared to HP. CONCLUSIONS: The comparison of the effects of the two bleaching agents at 10% showed that the alloy suffered less corrosion with CP than HP. This result was also confirmed by the SEM and XPS data. The presence of Mo on the oxide layer affected the oxide layer, leading to lower corrosion rates.

Pulsed electroplating of ZrO2-reinforced Ni-Cr alloy coatings from the duplex complexing agents-containing bath for engineering applications: Importance of operating conditions.

The progress in tribocorrosion performance of the engineering parts is in dire need of improving their surface properties. In the present contribution, Ni-Cr-ZrO2 layers were electrodeposited on St37 steel. The stress was put on optimizing the process factors, including the parameters involved in pulsed current electrodeposition and level of the ZrO2 reinforcing nanoparticles (0-20 g/L) in the bath. The surface characteristics of the electrodeposits were evaluated using FESEM, EDS, AFM, and XRD. The tribomechanical characteristics of the films were determined using a Vickers microhardness tester and pin-on-disk apparatus. The electrochemical behavior of the samples was studied using OCP, EIS, PDP, and immersion techniques. The results demonstrated that the included ZrO2 nanoparticles led to more homogenous, rougher, and defect-free surfaces, while they did not change the phase composition of the alloy electrodeposits. The polarization resistance of the Ni-Cr alloy coating increases by 6.7 times when 10 g/L of the reinforcing nanoparticles is added to the electrolyte. A decrease of ≈42 % in the mean COF value was obtained by the incorporation of 10 g/L ZrO2 nanoparticles into the plating bath. The coating system developed holds the promise to address both technical requirements and health concerns.

Corrosion Behavior of Ni-Cr Alloys with Different Cr Contents in NaCl-KCl-MgCl2.

This study investigates the corrosion behavior of Ni-Cr binary alloys, including Ni-10Cr, Ni-15Cr, Ni-20Cr, Ni-25Cr, and Ni-30Cr, in a NaCl-KCl-MgCl2 molten salt mixture through gravimetric analysis. Corrosion tests were conducted at 700 °C, with the maximum immersion time reaching up to 100 h. The corrosion rate was determined by measuring the mass loss of the specimens at various time intervals. Verifying corrosion rates by combining mass loss results with the determination of element dissolution in molten salts using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). Detailed examinations of the corrosion products and morphology were conducted using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Micro-area elemental analysis on the corroded surfaces was performed using an energy dispersive spectrometer (EDS), and the elemental distribution across the corrosion cross-sections was mapped. The results indicate that alloys with lower Cr content exhibit superior corrosion resistance in the NaCl-KCl-MgCl2 molten salt under an argon atmosphere compared to those with higher Cr content; no corrosion products were retained on the surfaces of the lower Cr alloys (Ni-10Cr, Ni-15Cr). For the higher Cr alloys (Ni-20Cr, Ni-25Cr, Ni-30Cr), after 20 h of corrosion, a protective layer was observed in certain areas. The formation of a stable Cr2O3 layer in the initial stages of corrosion for high-Cr content alloys, which reacts with MgO in the molten salt to form a stable MgCr2O4 spinel structure, provides additional protection for the alloys. However, over time, even under argon protection, the MgCr2O4 protective layer gradually degrades due to chloride ion infiltration and chemical reactions at high temperatures. Further analysis revealed that chloride ions play a pivotal role in the corrosion process, not only facilitating the destruction of the Cr2O3 layer on the alloy surfaces but also possibly accelerating the corrosion of the metallic matrix through electrochemical reactions. In conclusion, the corrosion behavior of Ni-Cr alloys in the NaCl-KCl-MgCl2 molten salt environment is influenced by a combination of factors, including Cr content, chloride ion activity, and the formation and degradation of protective layers. This study not only provides new insights into the corrosion resistance of Ni-Cr alloys in high-temperature molten salt environments but also offers significant theoretical support for the design and optimization of corrosion-resistant alloy materials.

The Influence of Al and Nb on the Low Oxygen Pressure Pre-Oxidation Behavior of Fe-35Ni-20Cr-xAl-yNb Alloys at 1000 °C.

To investigate the impact of Al and Nb elements on the formation of a protective oxide layer on the surface of Fe-35Ni-20Cr-xAl-yNb (x = 0, 2, 4, 6 wt.%; y = 0, 1, 2 wt.%) alloys, their oxidation behavior was examined at 1000 °C, 10-17 atm. and 10-25 atm. oxygen pressure, and the oxidation mechanism was analyzed by Factsage and Pandat calculations. Enhancing the Al content at 10-17 atm. inhibited the generation of FeCr2O4 on the alloy surface and increased the Al content in the M2O3 layer. When the Al content exceeded 6 wt.%, the oxide film partially peeled off. It was found that the addition of Nb increased the activity of Cr and Al and decreased the activity of Ni and Fe and promoted the formation of Al2O3, and the appearance of Nb2O5 in the subsurface layer increased the density of the oxide film. In addition, under an oxygen pressure of 10-25 atm., the only protective layer on the surface of the alloy comprised of Al2O3. The experimental results demonstrated that the Fe-35Ni-20Cr-4Al-2Nb alloy generated a continuous and dense Al2O3 protective film, and the reduction in oxygen pressure and the addition of Nb elements were favorable for selective external oxidation of Al2O3.

Fabrication of Co-Based Cladding Layer by Microbeam Plasma and Its Corrosion Mechanism to Molten Salt.

Corrosion of the molten salts Na2SO4 and NaCl has become one of the major factors in the failure of steel components in boilers and engines. In this study, CoNiCrAlY cobalt-based cladding layers with different NiCr-Cr3C2 ratios were prepared by microbeam plasma cladding technology. The influence of the NiCr-Cr3C2 content on the microstructure, mechanical properties, and molten salt corrosion resistance of CoNiCrAlY was investigated. The CoNiCrAlY with a 25 wt.% NiCr-Cr3C2 (NC25) cladding layer possessed the highest microhardness (348.2 HV0.3) and the smallest coefficient of friction (0.4751), exhibiting great overall mechanical properties. The generation of protective oxides Cr2O3, Al2O3, and spinel phase (Ni,Co)Cr2O4 is promoted by the addition of 25 wt.% NiCr-Cr3C2, which significantly reduces the corrosion of the cladding layer, and this effect is much more obvious at 950 °C than that at 750 °C. Furthermore, its corrosion mechanism was clarified. From the findings emerge a viable solution for the design and development of new high-temperature corrosion-resistant coatings.

Effect of pores on microscopic wear properties and deformation behavior of Ni-Cr alloy coating.

CONTEXT: Molecular dynamics (MD) was carried out to simulate the friction behavior of Ni-Cr alloy coating containing pores. The mechanical properties, displacement, abrasion depth, and defect change patterns of the coating under nano-friction were studied. It was found that the stacking fault would extend to the pores, and both tangential and normal forces decreased when the grinding ball was above the pores. Meanwhile, the pores changed the extension direction of shear strain inside the coating, and stress concentrations were generated at the pores. In addition, the deformation behavior inside the coating was influenced by the processing depth, the smaller the relative height of the grinding ball and the pore, the greater the atomic deformation around the pore. The pores changed the path of atomic movement, resulting in less deformation of the coating below the pores. The presence of pores promoted the generation of surface steps and increased the amount of wear on the coating. It was also found that pores facilitated energy release and provided space for dislocation extension, and the large accumulation of dislocations led to frictional strengthening near the pores, which enhanced the properties of the material below the pores. It was found that the increase of the pore size caused the normal force decrease and the wear performance of the coating decrease, but the thermal insulation performance would be improved. METHODS: In this paper, nanoscale modeling was performed in the large-scale atomic/molecular parallel simulator (LAMMPS) simulation environment. The model was visualized and analyzed in three dimensions by Open Visualization Tool (OVITO), the common neighbor analysis (CNA) method was used to obtain the atomic structure information, and the dislocation analysis (DXA) method was applied to obtain the dislocations.

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.

Research on Energetic Micro-Self-Destruction Devices with Fast Responses.

Information self-destruction devices represent the last protective net available to realize information security. The self-destruction device proposed here can generate GPa-level detonation waves through the explosion of energetic materials and these waves can cause irreversible damage to information storage chips. A self-destruction model consisting of three types of nichrome (Ni-Cr) bridge initiators with copper azide explosive elements was first established. The output energy of the self-destruction device and the electrical explosion delay time were obtained using an electrical explosion test system. The relationships between the different copper azide dosages and the assembly gap between the explosive and the target chip with the detonation wave pressure were obtained using LS-DYNA software. The detonation wave pressure can reach 3.4 GPa when the dosage is 0.4 mg and the assembly gap is 0.1 mm, and this pressure can cause damage to the target chip. The response time of the energetic micro self-destruction device was subsequently measured to be 23.65 µs using an optical probe. In summary, the micro-self-destruction device proposed in this paper offers advantages that include low structural size, fast self-destruction response times, and high energy-conversion ability, and it has strong application prospects in the information security protection field.

Effect of Sandblasting Parameters and the Type and Hardness of the Material on the Number of Embedded Al2O3 Grains.

BACKGROUND: Is abrasive blasting accompanied by the phenomenon of driving abrasive particles into the conditioned material? METHODS: Three hundred and fifteen cylindrical disks of three types of metal alloy (chromium/cobalt, chromium/nickel, titanium, and sintered zirconium dioxide) were divided into four groups (n = 35) and sandblasted at pressures of 0.2, 0.4, or 0.6 MPa with aluminum oxide (Al2O3), grain size 50, 110, or 250 µm. Then, the surface topography was examined using a scanning microscope, and the amount of embedded grain was measured using quantitative metallography. For each group, five samples were randomly selected and subjected to Vickers hardness testing. In the statistical analyses, a three-factor analysis of variance was carried out, considering the type of material, the size of gradation of the abrasive, and the amount of pressure. RESULTS: The smallest amounts of embedded abrasive (2.62) were observed in the ZrO2 treatment, and the largest (38.19) occurred in the treatment of the Ti alloy. An increase in the gradation and the pressure were a systematic increase in the amount of embedded grain. CONCLUSIONS: After abrasive blasting, abrasive particles were found on the surface of the materials. The amount of driven abrasive depends on the hardness of the processed material.

Effects of Cold Rolling Reduction Rate on the Microstructure and Properties of Cu-1.16Ni-0.36Cr Alloy after Thermo-Mechanical Treatment.

In this paper, a Cu-Ni-Cr alloy was prepared by adding a Ni-Cr intermediate alloy to copper. The effects of the cold rolling reduction rate on the microstructure and properties of the Cu-1.16Ni-0.36Cr alloy after thermo-mechanical treatment were studied. The results show that the tensile strength of the alloy increased while the electrical conductivity slightly decreased with an increase of the cold rolling reduction rate. At a rolling strain of 3.2, the tensile strength was 512.0 MPa and the conductivity was 45.5% IACS. At a rolling strain of 4.3, the strength further increased to 536.1 MPa and the conductivity decreased to 41.9% IACS. The grain size and dislocation density decreased with an increase of the reduction rate in the thermo-mechanical treatment. However, when the rolling strain reached 4.3, the recrystallization degree of the alloy increased due to an accumulation of the dislocation density and deformation energy, resulting in a slight increase in the grain size and a decrease in the dislocation density. The texture strength of the brass increased due to the induced shear band, with an increase of the cold rolling reduction rate. The reduction rate promoted a uniform distribution of nano-scale Cr precipitates and further enhanced the strength via precipitation strengthening.

Facile Synthesis of Mesoporous Nanohybrid Two-Dimensional Layered Ni-Cr-S and Reduced Graphene Oxide for High-Performance Hybrid Supercapacitors.

This study describes the single-step synthesis of a mesoporous layered nickel-chromium-sulfide (NCS) and its hybridization with single-layered graphene oxide (GO) using a facile, inexpensive chemical method. The conductive GO plays a critical role in improving the physicochemical and electrochemical properties of hybridized NCS/reduced GO (NCSG) materials. The optimized mesoporous nanohybrid NCSG is obtained when hybridized with 20% GO, and this material exhibits a very high specific surface area of 685.84 m2/g compared to 149.37 m2/g for bare NCS, and the pore diameters are 15.81 and 13.85 nm, respectively. The three-fold superior specific capacity of this optimal NCSG (1932 C/g) is demonstrated over NCS (676 C/g) at a current density of 2 A/g. A fabricated hybrid supercapacitor (HSC) reveals a maximum specific capacity of 224 C/g at a 5 A/g current density. The HSC reached an outstanding energy density of 105 Wh/kg with a maximum power density of 11,250 W/kg. A 4% decrement was observed during the cyclic stability study of the HSC over 5000 successive charge-discharge cycles at a 10 A/g current density. These results suggest that the prepared nanohybrid NCSG is an excellent cathode material for gaining a high energy density in an HSC.

The Oxygen Evolution Reaction Drives Passivity Breakdown for Ni-Cr-Mo Alloys.

Corrosion is the main factor limiting the lifetime of metallic materials, and a fundamental understanding of the governing mechanism and surface processes is difficult to achieve since the thin oxide films at the metal-liquid interface governing passivity are notoriously challenging to study. In this work, a combination of synchrotron-based techniques and electrochemical methods is used to investigate the passive film breakdown of a Ni-Cr-Mo alloy, which is used in many industrial applications. This alloy is found to be active toward oxygen evolution reaction (OER), and the OER onset coincides with the loss of passivity and severe metal dissolution. The OER mechanism involves the oxidation of Mo4+ sites in the oxide film to Mo6+ that can be dissolved, which results in passivity breakdown. This is fundamentally different from typical transpassive breakdown of Cr-containing alloys where Cr6+ is postulated to be dissolved at high anodic potentials, which is not observed here. At high current densities, OER also leads to acidification of the solution near the surface, further triggering metal dissolution. The OER plays an important role in the mechanism of passivity breakdown of Ni-Cr-Mo alloys due to their catalytic activity, and this effect needs to be considered when studying the corrosion of catalytically active alloys.

Prediction of In-Flight Particle Properties and Mechanical Performances of HVOF-Sprayed NiCr-Cr3C2 Coatings Based on a Hierarchical Neural Network.

High-velocity oxygen fuel (HVOF) spraying is a promising technique for depositing protective coatings. The performances of HVOF-sprayed coatings are affected by in-flight particle properties, such as temperature and velocity, that are controlled by the spraying parameters. However, obtaining the desired coatings through experimental methods alone is challenging, owing to the complex physical and chemical processes involved in the HVOF approach. Compared with traditional experimental methods, a novel method for optimizing and predicting coating performance is presented herein; this method involves combining machine learning techniques with thermal spray technology. Herein, we firstly introduce physics-informed neural networks (PINNs) and convolutional neural networks (CNNs) to address the overfitting problem in small-sample algorithms and then apply the algorithms to HVOF processes and HVOF-sprayed coatings. We proposed the PINN and CNN hierarchical neural network to establish prediction models for the in-flight particle properties and performances of NiCr-Cr3C2 coatings (e.g., porosity, microhardness, and wear rate). Additionally, a random forest model is used to evaluate the relative importance of the effect of the spraying parameters on the properties of in-flight particles and coating performance. We find that the particle temperature and velocity as well as the coating performances (porosity, wear resistance, and microhardness) can be predicted with up to 99% accuracy and that the spraying distance and velocity of in-flight particles exert the most substantial effects on the in-flight particle properties and coating performance, respectively. This study can serve as a theoretical reference for the development of intelligent HVOF systems in the future.

Multiresponse Optimization of Selective Laser Melting Parameters for the Ni-Cr-Al-Ti-Based Superalloy Using Gray Relational Analysis.

The selective laser melting technology is of great interest in the aerospace industry since it allows the implementation of more complex part geometries compared to the traditional technologies. This paper presents the results of studies to determine the optimal technological parameters for scanning a Ni-Cr-Al-Ti-based superalloy. However, due to a large number of factors affecting the quality of the parts obtained by selective laser melting technology, the optimization of the technological parameters of the scanning is a difficult task. In this work, the authors made an attempt to optimize the technological scanning parameters which will simultaneously correspond to the maximum values of the mechanical properties ("More is better") and the minimum values of the dimensions of the microstructure defect ("Less is better"). Gray relational analysis was used to find the optimal technological parameters for scanning. Then, the resulting solutions were compared. As a result of the optimization of the technological parameters of the scanning by the gray relational analysis method, it was found that the maximum values of the mechanical properties were achieved simultaneously with the minimum values of the dimensions of a microstructure defect, at a laser power of 250 W and a scanning speed of 1200 mm/s. The authors present the results of the short-term mechanical tests for the uniaxial tension of the cylindrical samples at room temperature.