Showing papers in "Surface & Coatings Technology in 2016"
TL;DR: A review of particle-containing PEO coatings formed on Mg, Al and Ti alloy substrates can be found in this article, where the main focus is given to the uptake mechanism of particle into PEO layers and the introduced microstructural and functional changes.
Abstract: Plasma electrolytic oxidation (PEO) processing for light metals is known for decades and has been established as a well-known industrial surface treatment offering a reasonable wear and corrosion protection. However, long-term protection is compromised by the intrinsic porosity and limited range of composition in the PEO layer. A novel approach is to introduce particles to the electrolyte, aiming at their in-situ incorporation into PEO coatings during growth. The idea is that with the help of particles the defects can be sealed, and the composition range and the functionalities of produced coatings can be enhanced. So far, multifunctional coatings with anticorrosion, self-lubrication, anti-wear, bioactive and photocatalytic properties were produced with the aid of particle addition. The properties of particle itself, together with electrical and electrolyte parameters during PEO processing determine the way and efficiency of particle uptake and incorporation into the coatings. Normally incorporation of the particles into the coating can range from fully inert to fully reactive. This paper reviews recent progress on particle-containing PEO coatings formed on Mg, Al and Ti alloy substrates. The main focus is given to the uptake mechanism of particle into PEO layers and the introduced microstructural and functional changes.
356 citations
TL;DR: In this article, the effects of incorporation of two different shapes functionalization fullerene C60 (FC60) and functionalization graphene (FG), into the polymer matrix on the tribological and anti-corrosion performances of epoxy coating were investigated.
Abstract: This study investigated the effects of incorporation of two different shapes functionalization fullerene C60 (FC60) and functionalization graphene (FG), into the polymer matrix on the tribological and anti-corrosion performances of epoxy coating. The structural and morphological characterization was examined using Fourier transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, transmission electron microscopy and scanning electron microscopy. It was found that the functional groups had been grafted on the surface of C60 and G. The tribological and anti-corrosion results indicated that composite coatings showed a lower friction coefficient, wear traces area and higher anti-corrosion in comparison with neat epoxy, owing to the balance of reinforcement, lubrication and barrier properties of nanofillers and cracks generated by them, and optimal additive concentration of FC60 and FG both were 0.5 wt.%. Furthermore, this work opens up that FC60/EP coatings exhibited better tribological performance but worse corrosion resistance ability compared with FG/EP coatings due to the different shapes of nanofillers. Different tribological and anti-corrosion mechanisms were analyzed in details.
249 citations
TL;DR: In this paper, different aspects of electrodeposition, microstructure, corrosion, oxidation, wear, and mechanical properties of Ni-W alloys and nano/micro composites are reviewed.
Abstract: Nowadays, application of nanocrystalline nickel-tungsten (Ni-W) alloys is receiving a great interest because they are an efficient replacement for hard chromium coatings owing to their premium hardness, wear, and corrosion properties. Moreover, heat-treated nanocrystalline Ni-W alloys demonstrate proper mechanical properties as well as thermal stability at high temperatures. The current paper reviews different aspects of electrodeposition, microstructure, corrosion, oxidation, wear, and mechanical properties Ni-W alloys and nano/micro composites. Besides, heat treatment effects on properties and thermal stability of these alloys are also reviewed.
178 citations
TL;DR: In this article, the microstructure, mechanical properties, fracture toughness and adhesive strength were investigated via X-ray diffraction (XRD), nanoindentation and micro-scratch tests.
Abstract: CrN, CrTiN, CrAlN and CrTiAlN coatings were deposited on Si (100) wafers, and their microstructure, mechanical properties, fracture toughness and adhesive strength were investigated via X-ray diffraction (XRD), nanoindentation and micro-scratch tests. Besides an F.C.C. crystal structure, TiN0.3 (004) and AlN (222) phases were found in the CrTiN and CrAlN coatings while the crystallinity of the CrTiAlN coating decreased. The hardness of the CrN (14.5 GPa), CrTiN (13.9 GPa) and CrAlN (17.7 GPa) coatings was determined by their grain sizes while the CrTiAlN coating with the most compact morphology exhibited the highest hardness of 22.0 GPa. In addition, CrTiN (KIc = 2.73 MPa· m ), CrAlN (KIc = 2.70 MPa· m ) and CrTiAlN coatings showed a stronger crack resistance than the CrN coating (KIc = 1.06 MPa· m ), especially the CrTiAlN coating without any radial cracks. However, the CrTiAlN coating encountered circumferential cracks and premature delamination (Adhesive energy Gc = 70 J/m2) because of its highest compressive stress (4.64 GPa). Based on the results here, it is concluded that a decent compressive stress of 3.0 GPa is expected to help thin films prevent from radial and circumferential cracks simultaneously.
135 citations
TL;DR: In this paper, the microstructure, phase constituents, bonding strength and in vitro cellular responses of composite coatings were investigated, and it was shown that the addition of graphene oxide has enhanced both the crystallinity of deposited apatite particles and the bonding strength of the as-synthesized composite coating.
Abstract: As novel nanomaterials, graphene and its derivations have been applied into hydroxyapatite as reinforcements for biomedical applications. However, graphene/hydroxyapatite composites serving as implant coating have rarely been studied. In this study, graphene oxide (GO)/hydroxyapatite (HA) composite coatings have been firstly fabricated by electrochemical deposition technique on titanium (Ti) substrate. Then, the microstructure, phase constituents, bonding strength and in vitro cellular responses of composite coatings were researched. Raman spectroscopy and transmission electron microscopy corroborated that graphene oxide was successfully incorporated into the composite coatings. Results revealed that addition of GO have enhanced both the crystallinity of deposited apatite particles and the bonding strength of the as-synthesized composite coatings. Moreover, in vitro cell culture assessment showed better biocompatibility of composite coatings compared with the pure HA coating and pure Ti substrate. These results suggested that GO/HA composite coatings might be a promising candidate in the field of biomaterials, especially for implant coatings.
124 citations
TL;DR: In this paper, a portfolio of characterization techniques for wear-resistant hard coatings is presented, including atom probe tomography, electron backscatter diffraction and synchrotron X-ray nanodiffraction.
Abstract: Due to economical demands to further increase the efficiency of production processes, it is essential to exploit the full potential of wear resistant hard coatings. This is, however, possible only if the coating microstructure and properties are well characterized. Thus, in the present work, recently suggested advanced characterization techniques for coatings are reviewed. The application of atom probe tomography, electron backscatter diffraction and synchrotron X-ray nanodiffraction enables previously unrevealed insights in their chemical composition, microstructure and crystallographic structure. For the determination of mechanical and tribological properties at elevated temperatures, high-temperature nanoindentation and high-temperature ball-on-disk tests in combination with in-situ measurement techniques are discussed. Utilization of micromechanical tests for coatings provides information about their fracture toughness and rupture strength. High-temperature X-ray diffraction and biaxial stress temperature measurements for the determination of the coefficient of thermal expansion are compared. The thermal conductivity as well as the specific heat capacity of coatings can be studied using the 3- ω technique, time domain thermoreflectance and differential scanning calorimetry. The introduced portfolio of characterization techniques enables the determination of a complementary microstructural, mechanical and thermo-physical fingerprint of wear resistant hard coatings, which allows to understand the complex structure–property relations in these materials and subsequently to further improve their performance.
113 citations
TL;DR: In this article, the reactions between molten aluminum magnesium silicates (CMAS) at 1300°C and atmospheric plasma spray (APS) deposited environmental barrier coatings on SiC substrates have been investigated.
Abstract: The reactions between molten calcium aluminum magnesium silicates (CMAS) at 1300 °C and atmospheric plasma spray (APS) deposited environmental barrier coatings on SiC substrates have been investigated. The tri-layer coatings comprised a silicon bond coat protected by a layer of mullite and either Yb 2 SiO 5 (ytterbium monosilicate, YbMS) or Yb 2 Si 2 O 7 (ytterbium disilicate, YbDS) as the topcoat. The APS deposition process resulted in two-phase top coats; the YbMS coating contained Yb 2 O 3 regions in a matrix of Yb 2 SiO 5 while the YbDS coating contained Yb 2 SiO 5 in a matrix of Yb 2 Si 2 O 7 . Exposure of both coatings to a model CMAS resulted in dissolution of the topcoat accompanied by a rapid rise in the concentration of Yb in the melt, and formation of the same Ca 2 Yb 8 (SiO 4 ) 6 O 2 apatite reaction product phase. The thickness of the apatite layer initially varied with (time) 1/4 , but transitioned to approximately parabolic kinetics after 5–10 h of CMAS exposure. The reaction mechanism on the YbMS layer was consistent with recent observations on Y 2 SiO 5 , wherein molten CMAS transport to the undissolved silicate was controlled by diffusion through thin amorphous films at the apatite grain boundaries. The reaction mechanism for the YbDS layer was more complex, and involved preferential reaction with the YbSiO 5 rich regions, resulting in a reaction zone that contained CMAS, the apatite reaction compound and undissolved Yb 2 Si 2 O 7 . The coating composition and microstructure significantly influenced the mechanism and rate at which the YbDS top coat was consumed by the reaction.
103 citations
TL;DR: In this article, the influence of current density, deposition mode and the presence of saccharin as an additive on the microstructure, sulfur content, grain size and microhardness of nanocrystalline Ni coatings was studied.
Abstract: The main purpose of the present work is to study the influence of current density, deposition mode and the presence of saccharin as an additive on the microstructure, sulfur content, grain size and microhardness of nanocrystalline Ni coatings. Towards this purpose, nanocrystalline nickel (Ni) coatings were deposited at various current densities in Watt's bath using direct, pulse and pulse reverse current (PRC) electrodeposition and subsequently characterized for sulfur content, grain size and hardness. It was observed that, the current density has no influence on the grain size/hardness of nanocrystalline Ni coatings in direct and pulsed current electrodeposition mode. However, the grain size increased from ~ 20 to ~ 200 nm with decrease in current density in PRC mode of deposition. In addition a substantial change in microstructure and texture of PRC Ni coatings was also evident. The experimental results have been rationalized based on the adsorption–desorption type of mechanism during electrodeposition.
101 citations
TL;DR: In this paper, a self-lubricating Ni-P-MoS2 composite coating has been successfully deposited on a mild steel substrate by electrodeposition, and the effects of MoS2 on the tribological coatings have been investigated.
Abstract: Tribological coatings with low coefficients of friction are in high demand by various industries since they can improve machine efficiency and have an environmental impact. A self-lubricating Ni-P-MoS2 composite coating has been successfully deposited on a mild steel substrate by electrodeposition. The effects of MoS2 on the tribological coatings have been investigated. Compared to a pure Ni-P coating, the Ni-P-MoS2 composite coating exhibited a dramatic reduction in friction coefficient against a bearing steel ball from 0.45 to 0.05. Examination and analysis of the worn surfaces and wear debris, the composite coating showed minimum wear and oxidation compared to the severe wear and oxidation observed in the pure Ni-P coating. The evolution of MoS2 particles in sliding wear has been elucidated.
94 citations
TL;DR: In this article, a one-step electrospinning technique was used to prepare a protective super-hydrophobic PVDF-ZnO nanocomposite coating for aluminum against corrosion.
Abstract: A one-step electrospinning technique was used to prepare a protective superhydrophobic PVDF–ZnO nanocomposite coating for aluminum against corrosion. The wettability and morphology of the prepared coating surfaces was characterized using water contact angle and contact angle hysteresis measurements, scanning electron microscopy, Fourier transform infrared spectroscopy and atomic force microscopy. In addition, the corrosion resistance for Al with PVDF polymer and the PVDF–ZnO nanocomposite coatings compared to the bare Al was investigated by electrochemical impedance spectroscopy and Tafel polarization techniques. The results showed that, the water contact angle and the contact angle hysteresis of the prepared PVDF–ZnO nanocomposite coating were 155 ± 2 and 4.5 ± 2°, respectively. In addition, compared to the sprayed PVDF–ZnO coating, the concentration of ZnO nanoparticles in the electrospun coating was only one sixth to obtain the same water contact angle, better distribution of ZnO nanoparticles was achieved without using any dispersing agent. The analysis of the corrosion results revealed that, the superhydrophobic PVDF–ZnO coating showed a corrosion protection efficiency for Al that is much higher than that of the PVDF one.
90 citations
TL;DR: In this article, a nanostructured hydroxyapatite (HA) coating was grown on selected Mg alloy (Mg-3Zn) through the electrophoretic deposition (EPD) technique.
Abstract: The present work deals with developing a HA coated Mg alloy material system for application in orthopaedic implants. A nanostructured hydroxyapatite (HA) coating was grown on selected Mg alloy (Mg–3Zn) through the electrophoretic deposition (EPD) technique. The mechanical integrity of the coating is established as a function of surface roughness of the substrate and annealing temperature of the coating. Coating on a substrate with lower roughness shows a uniform layer and very few cracks. The mechanical properties of the surfaces help in optimizing the coating conditions to get a better integrated HA coating on the Mg surface. The HA coating shows an impressive 25 times improvement in corrosion resistance of the Mg alloy surface during in vitro exposure. The coating also helps in better growth of bone cells on the Mg surface. This study establishes the potential of electrophoretic deposition of HA coating on Mg–3Zn alloy in orthopaedic application.
TL;DR: In this article, the residual stress and failure mode of thermal barrier coating (TBC) containing metallic bond coat (BC) and ceramic top coat (TC) with and without thermally grown oxide (TGO) were predicted using a micromechanical-based finite element method (FEM).
Abstract: The residual stress and failure mode of thermal barrier coating (TBC) containing metallic bond coat (BC) and ceramic top coat (TC) with and without thermally grown oxide (TGO) were predicted using a micromechanical-based finite element method (FEM). Actual microstructures of the TBC taken by a scanning electron microscope (SEM) were utilized as the representative volume elements (RVEs) in the computational model. Failure mode of the representative volume was numerically simulated as thermal stress localization during thermal cycle. Computations were done on the representative volume to quantitatively assess the effects of thermal and mechanical properties of the TBC constituents as well as the presence of TGO on the macroscopic mechanical response of the TBC. Comparisons of computed results with experiments verified that, the computational method can successfully predict residual stress and crack initiation mode of the studied thermal barrier coatings. Moreover, based on the computed results, both shear and normal failure mode occur in the thermal barrier coating which is in good agreement with experimental findings.
TL;DR: In this article, the authors provide a comprehensive discussion and highlights the recent progress for the utilization of Polyelectrolyte Multilayers (PEMs) as stimuli-responsive components for fabrication of coatings with smart self-healing functionality.
Abstract: This review provides a comprehensive discussion and highlights the recent progress for the utilization of Polyelectrolyte Multilayers (PEMs) as stimuli-responsive components for fabrication of coatings with smart self-healing functionality. The demand for self-healing coatings is rapidly growing due to their great potential to diminish degradation and reduce the maintenance cost. PEMs, constructed via different layer-by-layer assembly technologies, represent one of the most promising smart materials for fabrication of healable coatings. Based on the nature of the employed components for multilayer fabrication (e.g. polyelectrolytes, nanoparticles, inhibitors), PEMs have the ability to provide unique or multiple-responsive functionality, stimulated by different triggering mechanisms (e.g. pH, temperature, light), for effective and controlled on-demand release of corrosion inhibitor. Different approaches have been adapted for utilizing the responsive-PEMs as key component for developing protective coatings with active feed-back functionality. The first approach is based on the incorporation of inhibitor-loaded nanocontainers coated with PEM shells as the smart self-healing component in the formulated coating matrix (e.g. sol–gel or epoxy based coating). Various nanocontainers coated with PEM shells have been used including hollow PEM capsules, silica nanoparticles, mesoporous silica and titania nanoparticles, halloysite nanotubes and layered-double hydroxides. The second approach is based on the direct deposition of the PEMs/inhibitor complexes onto the metal surface. In the latter case, the self-healing action of PEMs is based on multiple and synergistic mechanisms.
TL;DR: In this article, the effects of laser power, WC particle content and rare earth element (La) on the quality of the Ni/WC composite coatings were investigated, and the influences of WC content on microstructure and hardness were investigated.
Abstract: Ni/WC composite coatings with different weight percentage (0–60%) of WC particle were produced on a stainless steel by diode laser-cladding technology with the aim to improve wear resistance of the stainless steel in the present study. The effects of laser power, WC particle content and rare earth element (La) on the quality of the coatings were investigated. The influences of WC content on microstructure and hardness were investigated. The friction and wear behavior of the laser-clad coatings at room temperature and elevated temperatures of 600 °C and 700 °C were evaluated using a ring-on-block tribometer. Results revealed that the laser-clad composite coatings with WC content ranging from 20 wt.% to 60 wt.% were free of cracks and pores by controlling laser power level and adding 0.4 wt.% La. An increase in WC content increases wear resistance significantly at three test temperatures except for the Ni-20% WC coating. The phase structure of the oxidation films formed during the wear test process played important role on the wear behavior of the laser-clad coatings.
TL;DR: In this article, the effects of the tailored gradient interface on wear performance were discussed, and it revealed that the existence of gradient interface showed a very important role in improving the wear performance of the SLM-processed WC/Inconel 718 composite parts.
Abstract: The WC/Inconel 718 composites were fabricated by selective laser melting (SLM). The laser processing parameters played an important role in determining the microstructure and performance of the WC/Inconel 718 composite parts. With the decrease in the laser scanning speed, the densification rate increased and achieved 97.8% at a scanning speed of 350 mm/s. As an optimal scan speed of 450 mm/s was applied, the WC/Inconel 718 composite part obtained a mean microhardness as high as 393.2 HV 0.1 . At the same time, a regular and orderly gradient interface with a mean thickness of 0.27 μm surrounded by a diffusion layer was obtained. What is more, the chemical composition of the gradient interface and the diffusion layer were X 3 C 17 and XC 4 (X = W, Ni, Cr, Fe), respectively. Meanwhile, the composite acquired a considerably low coefficient of friction (COF) of 0.35 with almost no fluctuation and attendant wear rate of 2.5 × 10 − 4 mm 3 N − 1 m − 1 and the wear mechanism changed continuously from severe abrasive wear to adhesive wear. Subsequently the effects of the tailored gradient interface on wear performance were discussed. It revealed that the existence of gradient interface showed a very important role in improving the wear performance of the SLM-processed WC/Inconel 718 composite parts.
TL;DR: In this paper, a calcium phosphate conversion coating (CPCC) was applied to an AZ60 Mg alloy through an easily controlled phosphating method, and the effects of pH and temperature of the solution on the coating process, microstructure, porosity, and electrochemical and immersion corrosion behaviors of the CPCC were analyzed.
Abstract: In order to control the biodegradation rate and improve the surface biocompatibility of magnesium (Mg) alloys, a calcium phosphate conversion coating (CPCC) was deposited onto an AZ60 Mg alloy through an easily controlled phosphating method. The effects of pH and temperature of the phosphating solution on the coating process, microstructure, porosity, and electrochemical and immersion corrosion behaviors of the CPCC were analyzed. The optimum coating conditions were deduced according to the coating quality, and electrochemical and immersion corrosion performance. The results show that the pH and temperature can significantly affect the coating process, microstructure, and coating porosity percentage, and thus influence the corrosion protection efficiency and the corrosion rate of the CPCC coated Mg alloy.
TL;DR: In this article, a ternary monolithic coating or multiple layers of one or more layers of TiAlN, ZrN, CrN, NbN, TiN, TaN, Si3N4, and/or HfN are presented.
Abstract: Coating used for radioactive fuel or a structural component in radioactive fuel reactors, e.g., nuclear fuel cladding alloys, can include a ternary monolithic coating or multiple layers of one or more layers of TiAlN TiZrN, TiCrN, TiNbN and/or CrN, ZrN, NbN, TiN, TaN, HfN. TiHfN, TaHfN, TaNbN, or mixed combinations and/or CrN, ZrN, NbN, TiN, TaN, Si3N4, and/or HfN. In addition, one or more layers can be comprised of a nitride, oxide, or carbide or mixed combination (i.e., carbonides, oxynitrides, oxycarbides, etc.) from Ti, Al, Zr, Cr, Si, Nb, Hf, or mixed combination (i.e., TiAlC 1-x N x ). The multilayer coating can be doped with a dopant.
TL;DR: In this paper, the authors used a simulation of simulated body fluid (SBF) to evaluate the performance of PEO coatings in terms of friction and wear resistance properties compared to Ti6Al4V alloy.
Abstract: In this study, coatings, consisting of hydroxyapatite and titanium oxide bioceramic phases, were produced on Ti6Al4V alloy by plasma electrolytic oxidation for different times in a solution containing calcium acetate and β-calcium glycerophosphate. The phases of anatase, rutile, TCP (Ca3(PO4)2), perovskite-CaTiO3 and hydroxyapatite (HAp, Ca10(PO4)6(OH)2) were detected in the PEO coatings. The crystallinity of these phases was enhanced with increasing treatment time. The friction and wear resistance properties of the PEO coatings in simulated body fluid (SBF) were substantially improved compared to Ti6Al4V alloy. The corrosion resistance of the PEO samples in SBF was determined by an electrochemical method, and found to be significantly improved compared to Ti6Al4V alloy due to the existence of titanium oxide and the calcium phosphate-based phases. The amount of apatite induced at the PEO surface increased with increasing immersion time in SBF at 36.5 °C. According to the SEM images and FTIR results, after soaking in SBF for 14 days, the amount of secondary apatite formed in the coating electrolytically oxidized for 90 min was maximized due to high surface area and high amount of TiO2 and HAp in the coating structure.
TL;DR: In this article, the shot peening parameters which directly influence the arc height of the Almen strip and its characteristics are optimized within the context of Almen intensity, surface roughness and surface hardness via response surface methodology.
Abstract: In this study, the shot peening parameters which directly influence the arc height of the Almen strip and its characteristics are optimized within the context of Almen intensity, surface roughness and surface hardness via response surface methodology. Determination of the Almen intensity by trial and error method depending on the experience of the technician (measuring the arc height of Almen strips by changing the parameters repeatedly for each shot peening process) makes the optimization approaches valuable. The optimization is considered to perform by selecting surface roughness and surface hardness as the responses in order to classify the shot peening processes by taking into consideration of wide range of plastic deformation level. The effect of input parameters air pressure, shot diameter and peening duration on the Almen intensity, surface roughness and surface hardness is to be determined by using ANOVA regression analysis. Based on the estimated models, optimum peening conditions are introduced via response optimizer. The model adequacy is verified by the confirmation tests.
TL;DR: In this paper, the authors investigated the effect of nanoparticles on current-time responses, surface morphology, thickness, chemical and phase composition of ceramic composite coatings on titanium by micro-arc oxidation (M.A.O.).
Abstract: The aim of this work is to study how nanoparticles incorporate into the prepared ceramic composite coatings on titanium by micro-arc oxidation (M.A.O.) technique in electrolytes containing nanoparticles and modify the surface characteristics. In order to achieve this goal, SiC and SiO 2 nanoparticles (as main and auxiliary particles, respectively) were added to aluminate based electrolytes and M.A.O. process was performed under constant voltage regime using a pulsed power supply. Finally, the effect of addition of nanoparticles on current-time responses, surface morphology, thickness, chemical and phase composition of coatings were investigated. The obtained results showed that addition of nanoparticles (7.5 g/l) to the electrolytes, had no effect on the current-time responses and coating thickness of samples. However it caused a reduction in the size of micro-pores and surface roughness of M.A.O. coatings. It was also concluded that nanoparticles incorporate into the coating with the aid of both electrophoretic force and micro-sparks.
TL;DR: In this article, the corrosion resistant films were fabricated on Mg alloy AZ31 substrates by steam coating method using Al(NO 3 ) 3 ·9H 2 O aqueous solution as a steam source.
Abstract: The corrosion resistant films were fabricated on Mg alloy AZ31 substrates by steam coating method using Al(NO 3 ) 3 ·9H 2 O aqueous solution as a steam source. The treatment temperature was maintained at 433 K, while the treatment time was varied at 3, 5, 7 and 9 h. X-ray diffraction (XRD) analysis demonstrated that the coated films were composed of a mixed structure of Mg(OH) 2 and Mg–Al layered double hydroxide (Mg–Al LDH) phases. As revealed by the scanning electron microscopy (SEM) observation, the surface of coated films had a good uniformity of changing treatment times. The deposition rate increased exponentially with increasing treatment time. Fourier transform infrared (FT-IR) spectra showed that carbonate and nitrate ions were co-existed in the interlayer of Mg–Al LDH. The potentiodynamic polarization curves of the film coated for 7 h exhibited the lowest corrosion current density, which was almost four orders of magnitude lower than that of bare AZ31. The enhanced corrosion resistance was well consistent with the increase of Mg–Al LDH content in the films.
TL;DR: In this article, a superhydrophilic and underwater superoleophobic mesh that can be applied to separate oil/water mixtures is prepared by spraying chitosan-silica nanoparticles-glutaraldehyde composite on the stainless steel mesh.
Abstract: To develop an effective and simple approaches for the cleaning-up of the oily wastewater, a superhydrophilic and underwater superoleophobic mesh that can be applied to separate oil/water mixtures is prepared by spraying chitosan–silica nanoparticles–glutaraldehyde composite on the stainless steel mesh. The mesh can separate a series of different oil/water mixtures with > 99.0% separation efficiency in the harsh environment such as acidic, saline or alkaline conditions, making it promising for practical oil/water separation applications.
TL;DR: In this paper, the authors compared the performance of pack cementation (PC) and chemical vapor deposition (CVD) on carbon/carbon composites and found that the PC-SiC coating transformed from linear to parabolic with dramatically improved oxidation resistance, which might be attributed to the decreased viscosity of SiO 2 -rich glass.
Abstract: SiC coatings were prepared on carbon/carbon composites by pack cementation (PC) and chemical vapor deposition (CVD). The PC coating was composed of hexagonal platelets of α-SiC, while the CVD coating consisted of spherical particles of β-SiC. Their oxidation behaviors were investigated at 1173 K, 1473 K and 1773 K. Compared with the CVD-SiC coating, bubbles appeared in the PC-SiC coating at lower oxidation temperature and the oxide layer was thicker, which might be ascribed to the formation of aluminosilicate glass in the PC-SiC coating. With the increasing temperature, the oxidation behavior of the PC-SiC coating transformed from linear to parabolic with dramatically improved oxidation resistance, which might be attributed to the decreased viscosity of SiO 2 -rich glass and the good healing effect for cracks. The oxidation protective ability of the CVD-SiC coating was worse than that of the PC-SiC coating, because of the higher viscosity of pure SiO 2 glass and the inferior interface adhesion between the coating and the substrate.
TL;DR: In this paper, the authors investigated in situ impedance spectroscopy in order to achieve insights in the coating formation mechanisms and identify suitable means for real-time control of essential coating characteristics and properties.
Abstract: Pulsed bipolar plasma electrolytic oxidation (PEO) processes carried out under potentiostatic control in electrolytes containing calcium acetate and sodium phosphate with Ca:P ratio of 2 were investigated by in situ impedance spectroscopy in order to achieve insights in the coating formation mechanisms and identify suitable means for real-time control of essential coating characteristics and properties. The coating thickness, morphology, chemical and phase compositions have been studied by non-destructive eddy current techniques, scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction analysis. The results demonstrate successful deposition of about 25 μm thick porous surface layers composed of amorphous calcium phosphates along with crystalline hydroxyapatite, tricalcium phosphate perovskite and titania phases. It was established that the growth of the PEO is controlled by anodic process of titanium oxidation, whereas precipitation of calcium phosphate containing compounds occurred via chemical mechanisms. Plasma discharge was responsible for partial crystallisation and decomposition of the deposited compounds. Characteristic responses related to anodic oxidation of Ti and processes associated with plasma discharge were identified in the impedance spectra of the PEO process. Kinetic parameters of charge transfer under conditions of high-voltage electrolysis have been evaluated and discussed.
TL;DR: In this article, the effect of current density on the microstructure and corrosion properties of the PEO coating was investigated, and the results showed that the coating was predominantly amorphous only at 30 mA/cm(2) and with increasing current density, increasing fractions of crystalline phases were formed.
Abstract: Plasma electrolytic oxidation coatings were produced on AM50 Mg alloy in alkaline phosphate based electrolyte with montmorillonite clay additives employing current densities of 30, 60, and 120 mA/cm(2). The effect of current density on the microstructure and corrosion properties of the coating was investigated. The clay additives got melted and reactively incorporated into the coating forming an amorphous phase, at all the current densities. However, the coating was predominantly amorphous only at 30 mA/cm(2) and with increasing current density, increasing fractions of crystalline phases were formed. Higher current densities resulted in increased thickness of the coating, but reduced the compactness of the coatings. Electrochemical impedance spectroscopy tests in 0.5 wt.% (0.08 M) and 3.5 wt.% (0.6 M) NaCl solution revealed that the coatings processed at 30 mA/cm(2) exhibited a relatively better initial corrosion resistance owing to its relatively defect-free barrier layer and compactness of the coating. However, the presence of amorphous phases in significant amounts and lack of MgO in the coating resulted in increased rate of dissolution of the coatings and degradation of corrosion resistance. Coatings produced at higher current densities exhibited initial inferior corrosion resistance due to a more defective barrier layer and increased porosity in pore band and outer porous layer. However, the increased amount of crystalline phases and an increased amount of MgO, which resisted dissolution, counterbalanced the negative effects of defective barrier and increased porosity resulting in a relatively lower rate of the degradation of the corrosion resistance. Thus, the corrosion resistance of all the coatings continuously decreased with time and became similar after prolonged immersion in NaCl solution. Increasing current density, therefore, did not prove to be beneficial for the improvement of the corrosion performance of the PEO coatings. (C) 2016 Elsevier B.V. All rights reserved.
TL;DR: In this article, micro-arc oxidation (MAO) coatings were prepared on AZ31B magnesium alloy using alkaline silicate electrolyte at different current densities (0.026, 0.046 and 0.067 A/cm2).
Abstract: Micro-arc oxidation (MAO) coatings were prepared on AZ31B magnesium alloy using alkaline silicate electrolyte at different current densities (0.026, 0.046 and 0.067 A/cm2). Field Emission Scanning Electron Microscopy (FESEM) analysis of the coating revealed an irregular porous structure with cracked morphology. Compositional analysis carried out for MAO coating showed the presence of almost an equal amount of Mg and O (34 wt.%) apart from other elements such as F, Si and Al. The cross-sectional FESEM images clearly portrayed that the MAO coating was dense along with the presence of very few fine pores. The surface roughness (Ra) of the coatings increased with an increase in the current density. Potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) studies were carried out for both the bare and MAO coated AZ31B Mg alloy in 3.5% NaCl solution. The corrosion potential (Ecorr) and corrosion current density (icorr) values obtained for the bare substrate were − 1.49 V and 46 μA/cm2, respectively. The coating prepared at 0.046 A/cm2 exhibited the lowest icorr value of 7.79 × 10− 10 A/cm2 and highest polarization resistance (41.6 MΩ cm2) attesting to the better corrosion resistance of the coating compared to other samples. EIS results also indicated almost similar corrosion behavior for the MAO coatings. Mott–Schottky analysis showed n-type and p-type semiconductor behavior for the oxide layer present on the bare magnesium alloy and MAO coatings respectively.
TL;DR: In this article, the effect of different ratios of B 4 C and TiB 2 reinforcing particles on the microstructure and wear resistance of surface layers was studied. And the results showed that the incorporation of b 4 C to the surface increased the hardness and wear resilience of composite layers in comparison with FSPed AA6063 alloy.
Abstract: Friction stir processing (FSP) was used to produce mono and hybrid surface composite layers of aluminium matrix containing B 4 C and TiB 2 particles. For this purpose the AA6063 was used as the base material. Different fractions of milled B 4 C and in situ TiB 2 –10 wt.%Al composite powder produced by mechanical alloying were incorporated into the matrix by FSP. The effect of different ratios of TiB 2 and B 4 C reinforcing particles on the microstructure and wear resistance of surface layers was studied. Microstructural evaluation of the samples was conducted by optical microscopy and field emission scanning electron microscopy (FESEM) of the cross-sections of surface composite layers. Microhardness testing was conducted across the cross-sections of FSPed samples to obtain hardness profiles and pin on disk dry sliding wear test was conducted on FSPed samples. The results showed that the incorporation of B 4 C and TiB 2 reinforcing particles to the surface increased the hardness and wear resistance of composite layers in comparison with FSPed AA6063 alloy. Moreover, 100%TiB 2 surface composite layer exhibited the highest hardness and best wear behaviour compared to other fractions.
TL;DR: In this paper, the authors review the rationale behind the application of laser surface modification for achieving cavitation erosion resistant surfaces of fluid handling components, such as ship propellers & rudders, turbine, diesel engine, cylinder liner, pump impeller vanes, control valves, hydraulic turbines, bearings, pipes, ultrasonic cleaners and mechanical heart valves.
Abstract: With the increasing demands of economical, reliable and durable hydraulic and pneumatic systems, it is necessary to minimize the material damage from cavitation erosion (CE) when systems are handling cavitating and corrosive fluids. Cavitation erosion is a nausea for many engineering components, such as ship propellers & rudders, turbine, diesel engine, cylinder liner, pump impeller vanes, control valves, hydraulic turbines, bearings, pipes, ultrasonic cleaners and mechanical heart valves, which are exposed to the high-speed flowing or vibratory fluids. This paper reviews the rationale behind the application of laser surface modification for achieving CE resistant surfaces of fluid handling components. The problem of CE may be tackled by enhancing the surface properties of the base materials (ferrous and non-ferrous alloys) with various laser surface modification techniques including laser transformation hardening (LTH), laser surface melting (LSM), laser surface alloying (LSA), laser cladding (LC), laser dispersion (LD) and laser plasma hybrid spraying (LPHS). The CE performance of a variety of laser-surface modified layers/coatings is discussed in this review. In particular, coatings of hard-facing alloys, shape memory alloys, surface metal or intermetallic matrix composites and cermets on ferrous and non-ferrous alloys are included. The mechanisms of the enhancement in cavitation erosion resistance (Re) are discussed.
TL;DR: In this article, the effect of nano-particle incorporation in an electrolyte bath on the structure, micro-hardness, wear resistance, corrosion performance, and passivation behavior of electro-co-deposited Ni-matrix composite coatings was investigated.
Abstract: The effect of the concentration of Al2O3–SiC nano-particles in an electrolyte bath on the structure, micro-hardness, wear resistance, corrosion performance, and passivation behavior of electro-co-deposited Ni-matrix composite coatings was investigated. Structure and texture studies were done by X-ray diffraction. The Vickers micro-hardness and wear resistance of the produced nano-composite coatings were evaluated and compared with the results of the pure Ni coating. The corrosion and passivation behaviors of the prepared coatings were investigated in an acidic 0.5 M Na2SO4 solution by a potentiostat–galvanostat device. It was found that by the nano-particle incorporation, the crystallographic texture of the Ni-matrix changes and the Ni crystallite size is considerably reduced to the nano-metric range. It was also realized that the micro-hardness, wear resistance, corrosion performance, and passivation behaviors of the coatings are significantly improved by the incorporation of the Al2O3 and SiC nano-particles into the Ni-matrix, provided that the optimum concentration of the nano-particles is utilized in the electrolyte bath.
TL;DR: In this paper, the submicron-sized WC particles were incorporated into high velocity oxy-fuel (HVOF) sprayed WC-Co coatings with the aim of improving properties of the coatings.
Abstract: In this paper, the submicron-sized WC particles (~ 300 nm) with the content of 3 wt.% and 5 wt.% are incorporated into high velocity oxy-fuel (HVOF) sprayed WC-Co coatings with the aim of improving properties of the coatings. XRD analyses suggest a small amount of decarburization of the incorporated WC phase after the composite coating deposition. The SEM microstructure showed even distribution of WC particles at the interfaces of WC-Co splats, indicating significantly enhanced wear resistance of the coatings with the wear rate as much as ~ 10− 7 mm3/N·m. The content of submicron-sized WC particles plays an important role in determining the wear performances of the coatings. The increment of submicron-sized WC particles causes a decrease in wear rate from 6.09 × 10− 7 mm3/N·m to 5.15 × 10− 7 mm3/N·m. Also, the Vickers microhardness of the coatings enhances as the increasing of WC particle ratio (reaches 1365 HV with the content of the WC particles of 5 wt.%). The wear failure analysis gives further insight into the mechanism of the property enhancement. The change of stress state and crack initiation at splats' interfaces act as the predominant mechanism, which is caused by the presence of submicron-sized WC particles at splats' interfaces.