Corrosion Resistance Of Specimens Research Articles

Effect of CeO2 on the microstructure and properties of AlCoCrFeNi2.1 laser cladding coatings

In the process of strengthening the substrate’s surface properties, it is easy to produce cracks or air holes and other defects between the coatings and the substrate, and rare earth elements can improve the microstructure and properties of the metal surface coatings. Using laser cladding(LC) technology, the effect of the addition of rare earth oxides CeO2 on the properties of AlCoCrFeNi2.1 coatings is investigated to find the optimal amount of CeO2 added. AlCoCrFeNi2.1 alloy powder doped with Xwt% (X = 0–3) rare-earth oxide CeO2 was clad on the surface of the H13 steel substrate by laser cladding process using RFL-C3000 laser. The macroscopic morphology, microstructure, hardness, and corrosion resistance of specimens were analyzed and studied by optical microscope (OM), scanning electron microscope (SEM), X-ray diffractometer (XRD), hardness tester, and other equipment. The results show that the addition of the appropriate amount of rare earth oxide CeO2 (3 %) can effectively reduce the cracks, air holes, and inclusions in the composite layer, and promote grain refinement. The addition of 3 wt%CeO2 to AlCoCrFeNi2.1 can improve the microstructure uniformity and surface hardness of the coatings, and significantly improve the wear and corrosion resistance of the composite coatings.

Evaluation of characteristics for microwave-assisted polymer coating of the steel substrate

Abstract Polymeric barrier coatings are one of the most sought-after methods for protecting metallic parts from corrosion and for ensuring a glossy appearance. In this work, pure polyester barrier coating was applied on a steel substrate using a microwave-assisted curing process with an experimental design based on L9 Taguchi orthogonal array. It included three key factors, viz. voltage, powder output from the spray gun and microwave power with three levels of each. The heat required for curing was achieved through electromagnetic-thermal energy conversion with the aid of a graphite susceptor. A multi-physics numerical study was carried out to identify the magnitude of temperature attained at different levels of microwave power and irradiation time. This was used to build the microwave curing set-up. The impact of parametric variation of the microwave-assisted process on the gloss was quantified. In addition, an assessment of dry film thickness, corrosion resistance, and impact strength was performed. Taguchi analysis reveals that out of three factors used, microwave power has the most significant impact on the gloss units. The desired level of impact strength was achieved for all samples, with the exception of the one coated with the factor combination of the least levels. Corrosion resistance for specimens was measured to be 240 h using a standard salt spray test. Specimen prepared with larger power input showed lesser blistering. The results substantiate the feasibility of a microwave-assisted process route for the industrial coating process.

Characterization of the Structure and Wear Resistance of Ni65-Based Coatings via HVOF Flame Spraying and Its Application to Potato Digging Shovels

To improve the tribological properties of a potato digging shovel (PDS), Ni65-based coatings with rare earth oxides additions were fabricated on 65Mn# steel via High-Velocity Oxygen-Fuel (HVOF) flame spraying, the effect of macroscopic surface shape of PDSs on their wear resistance of PDSs was examined, and finally a kind of PDS with a specific macroscopic surface shape and satisfied wear resistance was obtained. The addition of CeO2 and Y2O3 decreased the defects in coatings, refined the microstructure, made hard phases distributed more uniformly and ultimately improved coating properties. According to the XRD analysis results, the Ni65-based coatings were composed of the matrix phase γ-Ni and hard phases formed by Cr, Fe and Ni with B, C and Si. More Cr7C3 phases were detected in coating B than in coating A, but the phases related to Y and Ce were also not detected because of the low content in both EDS and XRD analyses. Heat treatment and HVOF flame sprayed coatings both increased the hardness of specimens, and coating A (621HV1.0) provided a hardness nearly equivalent to that of the heat treatment specimens (617HV1.0), while coating B provided the highest hardness (664HV1.0). For all specimens, laser surface texturing (LST) structures weakened their corrosion resistance. However, the Ni65-based self-fluxing alloy coatings significantly improved the corrosion resistance of specimens, and coating B provided the best corrosion resistance. SEM images show that the main wear mechanism for worn specimens was abrasive wear, and less wear signs were observed on the surface of coating B. Abrasive wear examinations indicate that specimen BJ had the best wear resistance and, compared with specimen W, the mass loss of specimen BJ decreased by 28.56% and 20.83% at relative sliding speeds of 2.35 m/s and 3.02 m/s, respectively. However, considering the negative effect of LST structures on the corrosion resistance of specimens, the processing techniques of specimen A and specimen B are more applicable to PDSs. The macroscopic surface shapes affected the wear resistance of PDSs and ZF had the lowest mass loss but the highest draught force; comparatively, YS had a better balance on the draught force reduction and wear resistance. Finally, YS with coating B, which decreased the mass loss by more than 27.17%, is recommended in this paper. On the whole, the conclusions in this paper provide a reference for the design of potato digging shovels with lower draught force and better tribological properties.

Electrochemical Behavior of Cu-MWCNT Nanocomposites Manufactured by Powder Technology

This paper presents an experimental investigation of the fabrication of Cu–multi-walled carbon nanotube (MWCNT) nanocomposites prepared via the electroless chemical deposition technique followed by the powder metallurgy (PM) method. To enhance the dispersion and wettability of MWCNTs with a Cu matrix, MWCNTs were given an electroless coating of Ag nanoparticles. MWCNTs with 0.4, 0.8, and 1.2 wt.% were first coated with 5 wt.% Ag nanoparticles, then mechanically milled with Cu nanoparticles using a 10:1 ball-to-powder ratio for 60 min at 300 rpm. The mixed samples (35 g) were subjected to a compression pressure of 700 MPa and sintered at 950 °C in a hydrogen-inert gas furnace. Mapping and microstructure analyses were conducted to analyze the constituents’ homogeneity. In addition, the electrochemical properties and corrosion resistance of specimens were investigated. The results revealed that the relative density decreased by raising the MWCNTs’ content. Electrical resistivity increased gradually with the addition of MWCNTs coated by Ag nanoparticles, and the thermal conductivity decreased. It was also revealed that the smallest corrosion rate could be obtained for the sample with 1.2 wt.% MWCNTs, which is the appropriate rate for the electrochemical deposition.

Anisotropic mechanical and corrosion properties of directionally solidified Mg-3Zn-0.2Ca alloy

A Mg-3 wt.%Zn-0.2 wt.%Ca alloy was fabricated by directional solidification, and its mechanical and corrosion properties were investigated from different crystallographic orientations. It was found that the directionally solidified (DSed) Mg-3Zn-0.2Ca alloy had a cellular structure with a preferred<11-20>growth orientation. The {0001} basal planes aligned approximately parallel to the growth direction of DSed alloy. The mechanical properties were measured with compression and nanoindentation tests by loading along with different directions, including the directions parallel (LD) and perpendicular (TD) to the growth direction of the DSed sample. The results indicated that the compression properties, strain hardening rate (θ), hardness (H), and elastic modulus (E) of the DSed Mg-3Zn-0.2Ca alloy were highly anisotropic. The anisotropies of the compression properties, θ, and H are caused by the activation of different deformation mechanisms. The anisotropic E comes from the difference of atomic bonding strengths at different crystallographic planes. The corrosion resistance of DSed Mg-3Zn-0.2Ca alloy exhibited anisotropy as well. The corrosion resistance of the specimen taken along LD is better than that of the specimen taken along TD. Besides, the LD and TD specimens experience much slighter corrosion than the as-cast specimen with randomly crystallographic orientation. The superior corrosion resistance of the LD specimen is beneficial from its surface distributed with more {0001} basal crystallographic planes.

Experimental investigation on ultrasonic surface rolling of Inconel 690TT

ABSTRACT Inconel 690TT has an excellent high-temperature corrosion resistance and has been widely applied in steam generators of pressurized water reactor (PWR) nuclear power plants. In this paper, Inconel 690TT was investigated in the rolling reduction (RR) of the ultrasonic surface rolling process of 0, 0.2, 0.4 and 0.6 mm, respectively. It was found that the specimens with RR of 0 mm were basically equal to the untreated specimens, while the specimens with RR of 0.2 mm were the smoothest and brightest. Some cracks appeared on the surface of specimens with RR of 0.4 and 0.6 mm. Compared with 0 mm, the hardness of specimens with RR of 0.2, 0.4 and 0.6 mm increased by 187.29%, 194.51% and 200.33%, respectively. The wear resistance of specimens with RR of 0.2 mm was improved, while the wear resistance of specimens with RR of 0.4 and 0.6 mm became worse. The corresponding corrosion resistance of specimens with RR of 0.2, 0.4 and 0.6 mm was better than that of 0 mm; meanwhile, the specimen with 0.2 mm RR showed the best influence on improving the surface corrosion performance.

Effect of Plasma-Electrolytic Polishing on the Corrosion Resistance of Structural Steels after Their Anodic Saturation with Nitrogen, Boron, and Carbon

t—The results of plasma-electrolytic polishing of steel specimens after their anodic diffusion saturation with elements, which form interstitial solutions, are considered. The structure and phase composition of the modified layers are studied using the X-ray diffraction analysis and electronic microscopy. The surface roughness and corrosion resistance of specimens in the 3.5% sodium chloride solution are measured. Various morphology of oxide layer is revealed after nitrocarburizing, nitriding, boronizing and borocarburizing of carbon structural steels 20 and 45. The versions of treatment and electrolyte compositions are determined that reduce the surface roughness from 1.00 μm for the control specimen to 0.23 μm after borocarburizing in the solution of boric acid, glycerol and ammonium chloride followed by polishing in the sulfate electrolyte and to 0.40–0.42 μm after nitriding in the ammonia and ammonium chloride solution followed by polishing in the sulfate or chloride electrolyte. It is shown that the corrosion current density of steel 45 can be reduced by almost 4 times after nitriding and polishing in the sulfate or chloride electrolyte.

Assessment of mechanical and corrosion properties of plasma oxidized medical grade NiTi wire

Nitinol is an excellent biomaterial amongst smart materials, which have shape and form memory effects and superelasticity, and is mainly used as orthodontic wire and coronary stent. One of the associated drawbacks, however, is nickel release into bloodstream, which can achieve critical levels. In this work, F2063 Nitinol wire was plasma-oxidized in order to obtain a TiO2 protective layer ranging from 50 to 80 nm, which helps blocking nickel release and enhances corrosion properties, thus avoiding or decreasing foreign body reactions. Two power sources (DC and RF) were evaluated and the resulting surfaces from plasma treated samples were characterized. According to the obtained results, tensile tests showed a slight improvement in superlastic elongation and in vitro corrosion resistance in specimens treated by plasma. The findings also suggest that RF power source is best suited to achieve a desired nano-scale layer in NiTi alloys. In this new light, plasma-assisted treatments can be performed in memory-shape alloys, aiming the obtention of a well adhered, corrosion improving and mechanical properties enhancing coating.

A One-Step Pack Cementation Method for Preparing AlN/Aluminizing Coating with Good Corrosion Resistance

AlN/aluminizing coating with good corrosion resistance on carbon steel was prepared by one-step powder pack method. The phase compositions were analyzed by X-Ray diffraction spectrum (XRD). The cross-sections were investigated by scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS). According the analysis above, the appropriate powder formula and technological parameter were determined: 40 wt.% Al + 50 wt.%Al2O3 + 5 wt.% NH4Cl + 5 wt.%CeO2, heating from 800 °C and maintaining at 900 °C for 6 hours. The corrosion resistance of specimen with AlN/aluminizing coating were measured by electrochemical test. The electrochemical measurement suggested that the corrosion resistance property of carbon steel was remarkably improved by fabricating AlN/aluminizing film. The process of pack cementation method in this fabrication is very simple, low-cost and facile, which opens a promising and effective path for industrial applications for AlN/aluminizing coating on various metallic materials.

Improved corrosion resistance of copper coated by graphene

High quality graphene on a Cu foil was synthesized by atmospheric pressure chemical vapor deposition. The morphology and microstructure of specimens were characterized by optical microscopy, scanning electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy, ultraviolet-visible spectroscopy and X-ray photoelectron spectroscopy. The corrosion resistance of specimens was tested by potentiodynamic polarization and electrochemical impedance spectroscopy. Results show that monolayer and high quality tri-layer graphene are synthesized at 1 000 °C for 5 and 15 min depositions, respectively. The monolayer graphene cannot protect Cu efficiently from oxidation at 300 °C in air and from electrochemical corrosion in a 0.1 mol/L NaCl solution due to its abundant defects and grain boundaries. The tri-layer graphene effectively increases the oxidation resistance and the electrochemical corrosion resistance. The protective performance of tri-layer graphene for a Cu foil is significantly better than that of monolayer graphene.

Effect of Shot Peening on Microstructure and Properties of 34CrMo4 Alloy

Plastic deformation can induce surface modification, such as shot peening (SP) on workpiece surface is the hot issue of recent scientific research. SP is the efficient way to improve mechanical behavior of specimens by inducing sever plastic deformation on their surface. Nevertheless, this surface treatment induced complex microstructural evolutions such as grain refinement, will enhance the corrosion resistance of specimens. In this work, the microstructure and properties of 34CrMo4 alloy of before and after SP for 20 min have been investigated. The evolution of microstructure and properties were analyzed from the surface and cross-section. The microstructure morphology at the different depth was determined by optical microscope. The results show grain size is increasing with the depth, and the microhardness and compressive residual stress decrease gradually. In terms of corrosion resistance, the 50 μm depth specimen has the best property than other depth, which the potential and corrosion current density are-0.484 V and-5.72 Acm-2, respectively. The maximum polarization resistance is 2055 Ωcm2 by capacitive arc radius of electrochemical impedance spectroscopy.

Influence of Dynamic Nonequilibrium Processes on the Mechanical Properties and Corrosion Resistance of Titanium Alloy

We compare the mechanical properties and corrosion resistance of specimens made of sheet two-phase VT22 high-strength titanium alloy in the intact state, after static tension, and after realization of dynamic nonequilibrium processes with subsequent static tension. It is shown that one-time dynamic nonequilibrium processes realized under impact vibration loading significantly increase the initial plastic deformation in this alloy and almost do not affect its corrosion resistance.

The Influence of Processing Parameters on the Surface Integrity of Ni60A Coatings Fabricated by Laser-High Frequency Induction Hybrid Cladding

The surface of much equipment that employed in petrochemical industry is always damaged by corrosion. As a novel technology, laser-high frequency induction hybrid cladding is an effective surface modification technology. Processing parameters, such as laser power, laser scanning speed and induction heating temperature, play an important part in the structural integrity of the coatings. The effects of these processing parameters to cladding integrity were investigated in this paper. Nickel base alloy (Ni60A) claddings were fabricated on the surface of low alloy steel by the way of laser-high frequency induction hybrid cladding and coaxial powder feeding. Macroscopic appearance and porosity of the claddings were systematically investigated by optical microscopy. The corrosion resistance of specimens manufactured by the optimum processing parameters is evaluated in 3.5% NaCl solution by electrochemical test. As the change of processing parameters, the width, height and porosity of laser claddings had an obvious change. Optimum processing parameters was determined because of the overall performance of the claddings. A good metallurgical bonding between Ni60A claddings and substrate was shown by microstructure. The results of the polarization curves turned out that the corrosion resistance of the Ni60A cladding is apparently better than the matrix.

Production and Precipitation Hardening of Beta-Type Ti-35Nb-10Cu Alloy Foam for Implant Applications

In this study, beta-type Ti-35Nb-10Cu alloy foams were produced by powder metallurgy method for dental implant applications. 35% Nb was added to stabilize the beta-Ti phase with low Young’s modulus. Cu addition enhanced sinterability and gave precipitation hardening capacity to the alloy. Sintered specimens were precipitation hardened in order to enhance the mechanical properties. Electrochemical corrosion behavior of the specimens was examined by electrochemical impedance spectroscopy in artificial saliva. Electrochemical impedance spectroscopy results indicated that the oxide film on the surface of foam is a bi-layer structure consisting of outer porous layer and inner barrier layer. Impedance values of barrier layer were higher than porous layer. Corrosion resistance of specimens decreased at high fluoride concentrations and at low pH of artificial saliva. Corrosion resistance of alloys was slightly decreased with aging. Mechanical properties, microstructure, and surface roughness of the specimens were also examined.

Preparation and corrosion resistance of rare earth–silane composite conversion coatings on magnesium–lithium alloy surface

The poor corrosion resistance of magnesium–lithium alloy surface works against its application in aerospace, automobile, electronics, etc. In this research, some kinds of non-toxic and non-polluting rare earth and silane (RE–Si) composite conversion coatings were built up on Mg–Li alloy surface, and formation process of coatings was investigated. The parameters for coating preparation were determined, including immersion time and temperature, pH value of conversion solution and curing time. The optimized technological parameters for preparation of RE–Si composite coating were finally confirmed. The influence of doping nanoparticles on RE–Si composite coating was also discussed, and the microstructure of coatings shows that the addition of nanoparticles can effectively improve the compactness and uniformity of composite coating. The corrosion resistance of specimens with RE–Si composite conversion coating is improved to a great extent compared with those of substrate or specimens with single rare earth (RE) conversion coating or with silane coating. The result also indicates that corrosion resistance of RE–Si composite coating doping with nanoparticles is further improved. Composition of the composite coatings was analyzed, and the effect of RE elements and silane on coating formation process was investigated. Corrosion resistance mechanism of composite coatings on Mg–Li alloy surface was discussed.

A Study of Corrosive Behavior of Al6061 Plasma Sprayed with Titania and Inconel 718

Al6061 has immense use in manufacture of several internal combustion engine parts as well. However the internal parts of an IC engine manufactured using Al6061 are susceptible to corrosion. Water may condense on the cylinder walls or move across the piston rings owing to blow-by and thus be admitted into the crankcase. This usually occurs in cold environment or short duration drive since pertaining to these conditions the engine may still be not hot enough to get rid of this water by evaporation. Upon amalgamation of this condensed water with the sulphur present in considerable quantities especially in low-grade fuels, sulphuric acid is formed thereby leading to a localized corrosion enhancing corrosive environment. In this work, TiO2 and Inconel 718 are plasma sprayed on Al6061 specimen and their ability to protect against corrosion is studied and observed that the corrosion resistance of specimen coated with TiO2 has improved by a considerable margin.

Effect of Passivation Treatments on the Corrosion Resistance of PIM 316L Stainless Steel in a PEM Fuel Cell Simulated Environment

In this work, the corrosion resistance of passivated PIM 316L stainless steel specimens was evaluated in 1M H2SO4 + 2 ppm HF solution at room temperature during 28 days of immersion. Passivation was carried out in HNO3and H2SO4solutions. The electrochemical behavior of the passivated specimens was assessed through electrochemical impedance spectroscopy and anodic polarization curves. Scanning electron microscopy (SEM) was employed to observe the surface of the specimens before and after the passivation treatments. The results pointed to a strong influence of the passivation conditions on the corrosion resistance of the specimens.

Corrosion Behavior of Anodic Films Formed on Aluminium 7A04 Alloy in Boric/Sulphuric Mixed Acid and in Chromic Acid

The corrosion behavior of the anodic oxide film on aluminium 7A04 alloy is investigated in current paper, where the different anodic oxide films are prepared. Morphology observation on different anodic films is carried out by using laser confocal microscopy (LCM) and copper sulfate test. Meanwhile, the electrochemical properties are evaluated through using electrochemical impedance spectroscopy (EIS). The LCM observation shows that the anodic oxide film formed in boric/sulphuric mixed acid is uniform with porous appearance, while the anodic oxide film formed in chromic aid is nonporous one but defective. The copper sulfate test results show that the corrosion regions almost developed from micropores in strong corrosive media. The evaluation of EIS in NaCl solution demonstrates that the corrosion resistance of specimen with anodic oxide film is much better than that without film. Furthermore, the corrosion resistance of anodic film formed in boric/sulphuric mixed acid is better than that formed in chromic acid.

The wear and corrosion resistance of shot peened–nitrided 316L austenitic stainless steel

316L austenitic stainless steel was gas nitrided at 570 °C with pre-shot peening. Shot peening and nitriding are surface treatments that enhance the mechanical properties of surface layers by inducing compressive residual stresses and formation of hard phases, respectively. The structural phases, micro-hardness, wear behavior and corrosion resistance of specimens were investigated by X-ray diffraction, Vickers micro-hardness, wear testing, scanning electron microscopy and cyclic polarization tests. The effects of shot peening on the nitride layer formation and corrosion resistance of specimens were studied. The results showed that shot peening enhanced the nitride layer formation. The shot peened–nitrided specimens had higher wear resistance and hardness than other specimens. On the other hand, although nitriding deteriorated the corrosion resistance of the specimens, cyclic polarization tests showed that shot peening before the nitriding treatment could alleviate this adverse effect.

Improvement of MIC Behavior of Low Alloy Steel with Zn-Rich Epoxy Coating

The microbiological influenced corrosion (MIC) behavior of the low alloy steel with or without Zn-rich epoxy coating in the sterilized medium and sulfate-reducing bacteria (SRB) solution was investigated with electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM) and X-rays diffraction (XRD). Results show that the bacteria in the marine environment affect the corrosion behavior of the ship plate steel and the corrosion resistance of specimen coated with Zn-rich epoxy was improved greatly. The coating protected the test steel effectively in the microbial environment with the cathodic protection in the earlier period and physical barrier protection in the later period.