Functional composite electrochemical coating Ni-Co-Al2O3 -an alternative to chromium plating

The physico-mechanical properties of composite electrochemical coatings (CEC) nickel-cobalt-aluminum oxide were investigated depending on the electrolyte parameters and electrolysis conditions. The previously developed low-concentration chloride electrolyte for nickel plating was used as an electrolyte to replace environmentally hazardous chromium plating electrolytes containing hexavalent chromium, which is prohibited by the laws of many countries. The wear resistance of the obtained CEC was determined on a three-ball friction machine. This made it possible to establish that the wear resistance of the CEC exceeds the wear of chrome coatings in dry friction mode by 2-2,5 times and is comparable to chromium in the friction mode with lubrication. In the dry friction mode, the higher wear resistance of the nickel-cobalt-alumina coating is explained only by the higher hardness of the latter. Probably, upon destruction of the coating, the particles of the alloying addition act as a solid lubricant, which causes an increase in the resistance of the CEC during wear. The microhardness of the CEC was determined using a PMT-3 microhardness tester and amounted to 6-25 GPa. The microhardness value was influenced by the concentration and properties of the dispersed phase, as well as the electrolysis conditions - the temperature and pH of the electrolyte, and the cathode current density. “Corrodcote” test was used in the study of corrosion. According to its data, the corrosion resistance of CEC is 2-3 times higher than the corrosion resistance of chromium deposits. The results obtained make it possible to recommend the developed functional CEC of nickel-cobalt-alumina instead of chromium coatings as corrosion- and wear-resistant.

The Development of Fine Surface Roughness of FeCrAl Substrate by Gamma Alumina Coating Material Through Nickel Oxide Catalyst

The most commonly used method for protecting atmospherically exposed steel against corrosion, is the application of protective organic coating systems. It is widely recognized that the stability of the coating-substrate interface is related to the interfacial adhesion forces and electrochemical properties of this region. This study aim to develop fine surface roughness by ultrasonic and electroplating coating methods that applied for FeCrAl catalytic converter. This method consists of thwo methods which are ultrasonic bath that carried out by frequency of 35 kHz and various ultrasonic times of 1, 1.5, 2, 2.5 and 3 hours is imposed and the electroplating was conducted for several variation times of 15, 30, 45, 60 and 75 minutes, current density of 8 A/dm2. The result shows that the surface roughness of UB samples in between 0.11 to 0.21 µm, UBdEL samples of 0.81 to 2.17 µm, UB+EL samples of 0.64 to 1.63 µm and EL samples of 0.69 to 1.11 µm. The finest surface of each techniques are located at UB 1.5 h, UBdEL 45 minutes, UB 1.5 h+EL 30 minutes and UB 30 minutes. That data is supported by coating thickness of coated FeCrAl substrate where UB samples in between 2 -2.8 µm, UBdEL samples of 4.1 to 5 µm, UB+EL samples of 9.1 to 12 µm and EL samples of 6.2 to 11.3 µm.

Evaluation of hybrid sol-gel alumina coating for electrical resistance applications

In an electric motor, bearing plays a vital role in the performance and reliability which fails frequently due to electrical pitting. To avoid this issue, the bearing can be coated with insulation material. In this present investigation, hybrid sol-gel coating was carried out on bearing steel by dip-coating method. The hybrid sol-gel was prepared using aluminium isopropoxide and calcined alumina powder. The ratio of Sol-Gel to calcined alumina and thickness of the coating was optimized to attain a crack-free surface coating. The crack behaviour was studied. The characterization of Hybrid Sol-Gel was carried out using Fourier-transform infrared spectroscopy and the surface morphology was observed using an optical microscope. The electrical resistance of the coating was measured using an insulation resistance tester. The crack-free surface coating of 40 microns was achieved at a low sol-gel to calcined alumina ratio. The electrical resistance of the coating is found suitable for bearing application. The thermodynamically stable hybrid sol-gel i.e., α alumina -ϒ alumina coating surface is proposed for electrical insulation coating.

Correlation between pre- and post-treatments of additively manufactured 316L parts and the resulting low cycle fatigue behavior

Purpose The currently existing restrictions regarding the deployment of additively manufactured components because of poor surface roughness, porosity and residual stresses as well as their influence on the low-cycle fatigue (LCF) strength are addressed in this paper. Design/methodology/approach This study aims to evaluating the effect of different pre- and post-treatments on the LCF strength of additively manufactured 316L parts. Therefore, 316L specimens manufactured by laser powder bed fusion were examined in their as-built state as well as after grinding, or coating with regard to the surface roughness, residual stresses and LCF strength. To differentiate between topographical effects and residual stress-related phenomena, stress-relieved 316L specimens served as a reference throughout the investigations. To enable an alumina coating of the 316L components, atmospheric plasma spraying was used, and the near-surface residual stresses and the surface roughness are measured and investigated. Findings The results have shown that the applied pre- and post-treatments such as stress-relief heat treatment, grinding and alumina coating have each led to an increase in LCF strength of the 316L specimens. In contrast, the non-heat-treated specimens predominantly exhibited coating delamination. Originality/value To the best of the authors’ knowledge, this is the first study of the correlation between the LCF behavior of additively manufactured uncoated 316L specimens in comparison with additively manufactured 316L specimens with an alumina coating.

The Influence of Nanostructured Alumina Coating on Bonding and Optical Properties of Translucent Zirconia Ceramics: In Vitro Evaluation

Thin, non-retentive, monolithic restorations fabricated from novel translucent zirconia ceramics are widely used in contemporary dentistry. Because of the chemical inertness of zirconia, debonding of such restorations remains the main clinical complication. Limited evidence on the bonding performance of novel translucent zirconia exists; therefore, the present study aimed to evaluate, in vitro, the shear-bond strength (SBS) of translucent zirconia modified with a nanostructured alumina coating (NAC). The SBS of resin cement to translucent zirconia, materials containing 3, 4 or 5 mol.% of yttria modified with NAC, was measured and related to airborne-particle abraded (APA) zirconia surfaces. Half of each of the specimen groups (n = 20) were subjected to 37,500 thermocycles in water. In addition, to evaluate the effect of NAC on thin translucent zirconia discs (n = 10), the translucency parameter (TP) was measured and compared with APA. The results were statistically analyzed using a t-test and one-way ANOVA. NAC provided higher resin-zirconia SBS compared to APA, not affecting the zirconia optical properties. APA, on the other hand, lowered TP for all types of zirconia. NAC did not impair the mechanical or optical properties of translucent zirconia materials and should be regarded as a zirconia pretreatment alternative to APA.

Surface Analysis, Mechanical and Corrosion Behavior of Welded Steel in 1M HCl Corrosive Media with Epoxy/Alumina Coating

Asparagus roots were dried in four selected driers vacuum, fluidized bed, tray, and solar dryer at temperatures starting from 40 to 70 °C. The drying kinetics of asparagus roots was studied with the analysis of the influence of all stated drying conditions on the drying rate, dehydration ratio, rehydration characteristic, color characteristics, and energy consumption. With an increase in the temperature required for drying asparagus, there is an increasing trend of dehydration ratio (DR) and decreasing trend of drying time. The rehydration characteristics are found to be increases with a decrease in drying temperature from 70-60 °C but decrease with a further decrease in drying temperature from 60-40 °C. The energy consumption based on the drying conditions showed great thermal sensitivity and was found higher for low-temperature drying. The results of color characteristics (Chroma, hue angle, and ΔE) showed that the cream color of roots was relatively unaffected by drying. However, the brightness of roots was observed to be increased. Eleven thin-layered drying mathematical models were applied to experimental data of different drying conditions, and the model best describing its behavior was selected based on the coefficient of determination (R2), sum square error (SSE), and root mean square error (RMSE). All selected models give good fitting results (R2 > 0.96) and found the cubic model as the most suitable model for all treatments (R2 > 0.99).

Decomposition of Hydroxylammonium Nitrate Solution Over Nanoporous CuO Supported on Honeycomb

We investigated the influence of a copper loading strategy over a honeycomb structure on the catalytic performance during the decomposition of a hydroxylammonium nitrate (HAN) aqueous solution. Copper was supported on the honeycomb surface by means of a metal coating method (MC), i.e., a method of directly coating a metal, and a metal alumina coating method (MAC), i.e., a method of coating a mixture of metal and alumina. The properties of the catalysts were analyzed by N2 adsorption, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The Cu(16.8)/honeycomb-MC catalyst showed a lower decomposition onset temperature during the decomposition of the HAN aqueous solution compared to that over the Cu(7.0)/honeycomb- MAC catalyst, an outcome ascribed to the higher copper loading and the higher dispersion of copper in the Cu(16.8)/honeycomb-MC catalyst compared to that in the other catalyst. The Cu(16.8)/honeycomb-MC catalyst was confirmed to have both excellent activity and heat resistance during the decomposition of a HAN aqueous solution.