Showing papers in "Surface & Coatings Technology in 2021"
TL;DR: In this article, the Ni45 powders were deposited on steel substrate by traditional low speed laser cladding and high-speed laser claddings, respectively, and the cladding efficiency, surface forming, cross-sectional microstructure, microhardness, wear and corrosion resistance properties of the traditional and high speed laser-cladded Ni45 alloy coatings were compared.
Abstract: High-speed laser cladding technology can significantly improve the efficiency of coating preparation and effectively widen the application range of laser cladding. In this study, the Ni45 powders were deposited on steel substrate by traditional low speed laser cladding and high-speed laser cladding process, respectively. The cladding efficiency, surface forming, cross-sectional microstructure, microhardness, wear and corrosion resistance properties of the traditional and high-speed laser cladded Ni45 alloy coatings were compared. It can be seen that the thickness of the high-speed laser cladding coating was much thinner than that of the traditional laser cladding coating. Compared with traditional laser cladding, high-speed laser cladding could achieve a cladding speed of 76.86 m/min and a cladding efficiency of 156.79 cm2/min. The microstructure of the two kinds of coatings shows the same growth law, but the microstructure in high-speed laser cladding was smaller and denser, and the columnar crystal interval was narrower, only about 6 μm. It is found that the cooling rate of the traditional laser cladding coating was smaller than that of the high-speed laser cladding, and as the cladding speed increased, the cooling rate became higher and higher. The cross-section microhardness of the traditional laser cladding coating was relatively uniform of 337 HV0.2, while the microhardness of high-speed laser cladding surface increased to about 543 HV0.2. In addition, the wear and corrosion resistance of high-speed laser cladded coatings were better than that of traditional laser cladded coatings. As the cladding speed increased, the wear and corrosion resistance of the cladded coatings became better.
121 citations
TL;DR: In this article, the influence of the vibration parameter on the degree of undercooling and nucleation rate of the molten metals was investigated, and the experimental results showed that the grain size obtained under the application of ultrasonic vibration was finer than that obtained under condition of conventional laser cladding.
Abstract: Laser cladding has shown advantages in metal component forming. However, the accompanying issues, such as inner microstructural defects and poor mechanical properties, require further investigation. In this study, laser cladding technology was combined with ultrasound to improve the performance of the formed parts. Based on the cooperative effect of acoustic streaming and acoustic cavitation during the metal solidification process, the influence of the vibration parameter on the degree of undercooling and nucleation rate of the molten metals was investigated. The experimental results show that the grain size obtained under the application of ultrasonic vibration was finer than that obtained under condition of conventional laser cladding. When the amplitude was 25 μm, the average grain size was 0.522 times of that of non-vibration. The phase structure of the precipitates and the chemical composition changed markedly. In addition, the effects of high-frequency vibration on the mechanical properties of the cladding layer were also analysed through contrast experiments. The results indicate that applying high-frequency vibration can effectively reduce porosity, while improving the microhardness and wear resistance. Quantitatively, the friction coefficient was 0.628 times that without ultrasound and 0.709 times that of conventional processing when the amplitude was 25 μm.
64 citations
TL;DR: With WC as the reinforcing phase particles, the Fe-WC composite coatings with mass fractions 0-60% of WC were fabricated on a 15CrNiMo cone bit steel by laser cladding as mentioned in this paper.
Abstract: With WC as the reinforcing phase particles, the Fe-WC composite coatings with mass fractions 0–60 wt% of WC were fabricated on a 15CrNiMo cone bit steel by laser cladding The phase composition, microstructure, microhardness, friction and wear properties of the composite coatings were studied Moreover, special attention was paid to investigate the thermal damage forms of WC particles and its influence mechanism on the structure evolution and wear properties The research results reveal that most of the WC particles maintain their complete morphology, but some WC particles are melted due to the thermal damage type of dissolution-collapse-precipitation The degree of burning loss rate is related to the quantity distribution and average particle size of WC in local area Main surrounding structures of WC are composed of equiaxed and cellular crystals, and few short columnar crystals The microhardness of the WC-Fe composite coating increases with increasing WC particles content Compared with the microhardness (6217HV02) of the Fe-based coating, the microhardness of the WC-Fe composite coating gradually increased from 7299HV02 to 10292HV02, and its average relative wear resistance is 13 times that of the coating without WC particles Moreover, combined with existing WC and W2C, as well as the presence of precipitated M23C6, M7C3 and η phases, which significantly improve the wear resistance of WC-Fe composite coatings In summary, the main wear mechanisms of Fe-based coatings reinforced by WC particles are abrasive wear accompanied by varying degrees of adhesive wear and three-body abrasive wear
63 citations
TL;DR: In this article, the evolution in microstructure, microhardness, and wear behavior of high-entropy alloy (HEA) coatings was investigated comprehensively to explore the effect of Si element.
Abstract: AlCoCrFeNiSix (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) high-entropy alloy (HEA) coatings were deposited on the surface of AISI 304 stainless steel via laser cladding technology with different content of Si element. The evolution in microstructure, microhardness, and wear behavior of the coatings was investigated comprehensively to explore the effect of Si element. The results showed that the HEA coatings consisted of disordered Fe-Cr and ordered Al-Ni solid solution phases with a body-centered cubic (BCC) structure. Si element dissolved into the solid solutions, leading to lattice distortion. As Si content increased, the microstructure was refined, and a small quantity of Cr23C6 phase was precipitated along the grain boundaries. The microhardness of the coatings was linearly proportionate to Si content. The quantitative analysis revealed that the improvement of microhardness was dominated by the effect of dislocation strengthening, rather than solution strengthening and fine-grain strengthening. With the increase in Si content, the average friction coefficient and wear rate of the HEA coatings were all reduced remarkably, and the main wear mechanism evolved from adhesive wear, abrasive wear and delamination wear to oxidation wear. These phenomena were believed to be associated with the formation of the oxide film on the worn surface, which was identified as Fe2O3, Fe3O4, Cr2O3, SiO2, and SiO.
60 citations
TL;DR: In this article, a micro-arc oxidation (MAO) coating was prepared on the AZ31 magnesium alloy in advance, and on the basis of the MAO coating, the graphene oxide (GO)/MgAl-layered double hydroxide composite was prepared by hydrothermal chemical transformation in pure GO solution.
Abstract: The preparation of excellent anti-corrosion coatings is necessary for practical large-scale applications. In this study, a micro-arc oxidation (MAO) coating was prepared on the AZ31 magnesium alloy in advance. Then, on the basis of the MAO coating, the graphene oxide (GO)/MgAl-layered double hydroxide (MgAl-LDH) composite was prepared by hydrothermal chemical transformation in pure GO solution with the mixed oxide of aluminum and magnesium in the MAO coating as the endogenous cation, without introducing any kind of salts. The chemical states, structural composition and morphology of the GO/LDH-MAO coating were confirmed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The potentiodynamic polarization revealed that 0.1 GO/LDH-MAO coating (3.89 × 10−9 A/cm2) is more resistant to corrosion than MAO coating (9.89 × 10−6 A/cm2) in 3.5 wt% NaCl solution. The organic combination of Mg Al LDH and GO can obviously enhance the corrosion protection ability of the coating. This research explored in detail the possible corrosion protection mechanisms regarding GO/LDH-MAO coatings, which supplied the feasibility for enhancing the anti-corrosion performance of MAO coating.
57 citations
TL;DR: In this article, the authors reviewed recent promising approaches towards improved biostability of Mg alloys during in vitro contact with simulated body fluid (SBF) as well as in vivo exposure to ECF.
Abstract: Several magnesium alloys are increasingly used for a variety of biomedical applications, owing to their favorable mechanical and biomedical properties. However, in vivo corrosion in aqueous environment including Cl ion-rich extracellular fluid (ECF) requires the application of protective coatings as well as the development of advanced alloy formulations with increased corrosion resistance and uniform, non-localized dissolution modes. This contribution reviews recent promising approaches towards improved biostability of Mg alloys during in vitro contact with simulated body fluid (SBF) as well as in vivo exposure to ECF. Emphasis is being put on surface coatings for corrosion protection as well as on functional osseoconductive coatings that stimulate tissue ingrowth.
51 citations
TL;DR: In this paper, three coatings (pure Co, Co-Ti3SiC2, and Co-Cu/Ti3 SiC2) were fabricated on the Ti6Al4V by laser cladding to improve the wear-resistant properties.
Abstract: The poor tribological property of Ti6Al4V strictly limits its application as high-speed moving parts, so three coatings (pure Co, Co-Ti3SiC2, and Co-Cu/Ti3SiC2) were fabricated on the Ti6Al4V by laser cladding to improve the wear-resistant properties. The phase, microstructure, microhardness, and wear morphology of the coatings were characterized to investigate their performance. At room temperature, due to the good synergistic effect between Cu and Ti3SiC2, Co-Cu/Ti3SiC2 coating had good tribological performance that the friction coefficient and wear rate was 0.146 and 1.76 × 10−7 mm3/N·m, respectively. This paper deeply explores the effects of Ti3SiC2 and Cu in the coatings which will provide theoretical basis for enriching the laser cladding material system, and also provides a technical reference for the commercial application of Ti6Al4V.
45 citations
TL;DR: In this article, a review of the experimental techniques used for residual stress measurements; such as X-ray diffraction, neutron diffraction and material removal, curvature measurement and deformation techniques, are concisely reviewed from the context of being applied to cold spray deposits.
Abstract: Cold spray technology provides protective coatings, additive manufacturing and repair to a wide array of industrial sectors. Alternative tags for cold spray include, kinetic metallisation, kinetic fusion, hypersonic spray, gas dynamic cold spray, cold spray printing, and cold spray additive manufacturing. These processes employ the same physics principles of accelerating micrometre-sized particles to supersonic velocities that impact and adhere onto a suitably prepared substrate. Numerical modelling has been used extensively to study particle impact modelling. The prediction of critical velocity, deformation mechanism and, more recently, residual stresses have been areas of interest that have been evaluated by numerical methods such as Lagrangian, Eulerian, Smoothed Particle Hydrodynamics, Coupled Eulerian-Lagrangian, and Molecular Dynamics. The crucial findings of these models are summarised, and their comparative outcomes assessed with a critical analysis of their merits and weaknesses. The process parameters applied in the simulations such as particle diameter, impact velocity, pre-heat temperature and material chemistry is compiled. The experimental techniques used for residual stress measurements; such as X-ray diffraction, neutron diffraction, material removal, curvature measurement and deformation techniques, are concisely reviewed from the context of being applied to cold spray deposits.
45 citations
TL;DR: In this paper, an in-situ NbC reinforced Fe-based coating was fabricated on the middle carbon steel surface by laser cladding with the mixture of niobium and boron carbide powder.
Abstract: In-situ NbC reinforced Fe-based coating was fabricated on the middle carbon steel surface by laser cladding with the mixture of niobium and boron carbide powder, aiming at revealing the mechanism of in-situ synthesis and improving the hardness and wear performance. The possibility and mechanism of in-situ synthesis were explored for the first time by combining simulation with experiment. The phase composition, microstructure characteristics and evolution mechanisms of the coatings were investigated by X-ray diffraction and scanning electron microscopy. The strengthening mechanism of hard phases on hardness and wear performance of coating were analyzed in detail. The results show that Marangoni convection promoted the melting of particles and improved the uniformity of solute atoms. The composite coating is mainly comprised of reinforced phases (NbC, Fe2B, B4C) and the matrix ([Fe Cr] solid solution). The dispersive NbC particles (average diameter ~ 1.03 μm) in-situ formed at the grain boundary achieved the dispersion and fine-grained strengthening effect. The hardness of the composite coating is 866.36 HV0.5, which is 3.95 times and 4.16 times that of the substrate and Fe-based coatings. The volume loss of composite coating reduced more than five times as compared to the substrate and Fe-based coating, and the wear mechanism changed from abrasive wear to adhesive wear due to the addition of Nb and B4C powders.
43 citations
TL;DR: In this article, a novel Ni1.68 eutectic HEA coating with nano-lamellar microstructure was successfully designed by binary eUTectic compositions strategy, thermodynamic calculation and simple experimental approach.
Abstract: In this work, a novel Ni1.5CrCoFe0.5Mo0.1Nb0.68 eutectic HEA coating with nano-lamellar microstructure was successfully designed by binary eutectic compositions strategy, thermodynamic calculation and simple experimental approach. Compared with the predicted eutectic compositions, the actual eutectic composition had a higher Nb content due to the increased solid solubility of Nb in the FCC phase. The Ni1.5CrCoFe0.5Mo0.1Nbx (x = 0.55 hypoeutectic, 0.68 eutectic, 0.8 hypereutectic) HEA coatings were prepared by laser cladding, which were composed of FCC phase with lattice parameter of a = ~3.59 A and Laves phase with lattice parameter of a = b = ~4.82 A and c = ~7.80 A. The FCC phase was enriched in Ni, Cr, Co and Fe elements, while the Laves phase was enriched in Nb and Mo elements. Typical eutectic lamellar and hypoeutectic/hypereutectic microstructures were obtained at the central regions, while the columnar crystals formed at the interfacial regions. The average micro-hardness of Nb0.55, Nb0.68 and Nb0.8 coatings were calculated as ~573.5 HV, ~665.8 HV and ~715.6 HV respectively. From x = 0.55 to x = 0.8, the wear resistance of Ni1.5CrCoFe0.5Mo0.1Nbx HEA coatings are increased, and the dominant wear mechanism of the HEA coatings transforms from adhesive wear to abrasive wear.
42 citations
TL;DR: In this article, the plastic deformation behavior of Ti6Al4V titanium alloy subjected to 300°C-warm laser shock peening (WLSP) was inferred from its microstructure evolution and mechanical properties.
Abstract: The plastic deformation behavior of Ti6Al4V titanium alloy subjected to 300 °C-warm laser shock peening (WLSP) was inferred from its microstructure evolution and mechanical properties. Through dynamic strain aging (DSA), WLSP achieved higher dense dislocations than room temperature laser shock peening (LSP). In addition, significant 10 1 — 2 deformation twinning activity was observed after WLSP. Twinning activity at such an ultrahigh strain rate and high temperature is a first-time observation in titanium alloy, and was attributed to an enhanced dislocation dissociation mechanism during WLSP. Moreover, an amorphization layer was generated on the top surface of the WLSP-processed sample, but not on the LSP-processed sample. This amorphization was effected by the increased free energy provided by the multiplying dislocations and deformation twins, combined with the reduced energy barrier of the crystal-to-amorphous transformation at high temperature. Relative to LSP, WLSP increased the width and depth of the compressive residual stress in the titanium alloy by 36.2% and 21.8% respectively, and improved the surface microhardness by 5%. The latter enhancement was conferred by the increased density of dislocations and deformation twins. Overall, WLSP improved the mechanical properties of the titanium alloy.
TL;DR: A hemostatic material able to quickly stop wound bleeding by successively constructing carboxymethyl chitosan, gelatin, and alginate onto a cotton gauze surface through a simple layer-by-layer process is developed and demonstrated great potential in medical applications.
Abstract: We developed a hemostatic material able to quickly stop wound bleeding by successively constructing carboxymethyl chitosan (CMC), gelatin, and alginate onto a cotton gauze surface through a simple layer-by-layer (LbL) process. Briefly, we grafted CMC onto the cotton fibers through an esterification reaction with the hydroxyl groups of the cellulose chains, and then built a gelatin layer on the CMC layer by the ionic reactions with CMC. Finally, we integrated alginate by the lamellar structure through the cross-linking reactions caused by the Ca2+ ions permeated from the gelatin layer. Characterization analyses demonstrated that the resulting composite dressing possessed high fluid absorption, excellent biocompatibility, and hemocompatibility. A better hemostatic performance was also revealed in animal tests compared with cotton gauze, and it showed a short hemostasis time and a small amount of blood loss in the mouse liver injury model and mouse-tail amputation model. Moreover, the composite dressing also exhibited a significant promotion effect of wound healing in a mouse defect wound model. This new composite dressing, which was prepared by natural raw materials, is a promising candidate for wound dressing and demonstrated great potential in medical applications.
TL;DR: In this article, laser cladding and laser remelting methods were adopted to prepare Fe-based amorphous coating on H13 steel surface and the organization and properties after laser claddings and laser re-elting were compared.
Abstract: Laser cladding and laser remelting methods were adopted to prepare Fe-based amorphous coating on H13 steel surface. And the organization and properties after laser cladding and laser remelting were compared. The results show that, the amorphous content of the coating decreased after laser remelting, and arc crystalline band was formed in the coating, at the same time, after laser remelting, the elements were in ladder-shaped distribution in the amorphous region and crystalline region. After laser remelting, defects on the coating like cracks or pores decreased obviously, but there was a transcrystalline crack extending to the matrix through the crystalline region in the remelting laser beam. The hardness of the crystalline region after remelting increased by about 200 HV compared with that in the amorphous region, and the overall corrosion resistance of the remelting layer was higher than the cladding layer.
TL;DR: In this paper, a superhydrophobic MgAl-layered double hydroxide with F− intercalation (LDH-F) was fabricated by a facile method and further modification by stearate (St) anions.
Abstract: In this work, a superhydrophobic MgAl-layered double hydroxide with F− intercalation (LDH-F) was fabricated by a facile method and further modification by stearate (St) anions. Then, the composite was dispersed in the epoxy resin to prepare anti-corrosion coatings, which was applied for corrosion protection of Mg alloy. This kind of coatings protects Mg alloy from some aspects. Firstly, the superhydrophobic film impedes the water molecules penetrating into Mg substrate. Secondly, the superior anions exchange ability of LDH can be used to stockpile chloride ions and the release of fluorine ions can react with magnesium ions to form a magnesium fluoride (MgF2) protective film at the corrosion area of the Mg alloy. Lastly, the LDH itself layered structure is a physical barrier. The fabricated composites were comprehensively characterized with Fourier Transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), water contact angle (CA) and scanning electron microscopy (SEM). Electrochemical Impedance Spectroscopy (EIS) was conducted to investigate the corrosion behavior of various composite coatings and the results demonstrated that the impedance modulus of the superhydrophobic layered double hydroxide epoxy (LDH-F-St-EP) coating reached 1.2 × 109 Ω cm2, showing excellent anti-corrosion performances.
TL;DR: In this article, the photocatalytic performance of SiO2-TiO2@PDMS and the wettability of the coated surface were tested and characterized, and the effect of microstructure and composition of the as-prepared coating on its properties was studied.
Abstract: In this paper, SiO2-TiO2 composite particles were prepared by loading nano-TiO2 onto the surfaces of amorphous SiO2 microspheres, which were then modified with PDMS to obtain a SiO2-TiO2@PDMS ternary compound. The photocatalytic performance of SiO2-TiO2@PDMS and the wettability of the coated surface were tested and characterized. Moreover, the effect of microstructure and composition of SiO2-TiO2@PDMS on its properties was studied. The results showed that SiO2-TiO2@PDMS possessed a certain degree of photocatalytic activity and the coating was almost superhydrophobic. Furthermore, the wettability and adhesion to water droplets of the SiO2-TiO2@PDMS coating were affected by the heat-treatment temperature; the mechanism of the above phenomena was also analysed. Moreover, the as-prepared coating exhibited excellent repellent effects towards acid (pH = 2), alkaline (pH = 11), and organic dye droplets. A mechanically damaged coating maintained its liquid repellence, indicating that the good mechanical stability of the coating. The superhydrophobicity of the as-prepared coating did not decrease after UV irradiation for 8 h, illustrating that the as-prepared coating had a great UV irradiation resistance. In addition, the as-prepared coating was environmentally friendly and free of fluorides and is therefore suitable for practical applications.
TL;DR: A sealing process for micro-arc oxidation (MAO) coatings on AZ31 Mg alloy was successfully realized by a secure, environmentally, and chemical-free steam treatment.
Abstract: A sealing process for Micro-arc oxidation (MAO) coatings on AZ31 Mg alloy was successfully realized by a secure, environmentally, and chemical-free steam treatment. The surface and cross-sectional morphologies, chemical composition and chemical bonding states of the sealed MAO coatings were characterized by using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR) measurements. The corrosion resistance of sealed MAO coatings in 3.5 wt% NaCl solution was evaluated by electrochemical measurements. The results showed that steam sealing treatment could influence the surface morphology and chemical composition. The sample treated at 453 K for 2 h had the best corrosion resistance. The sealing mechanism was also discussed.
TL;DR: SFAgSTN shows excellent antibacterial, osteogenic differentiation, and new bone formation activity, and can be used as a highly potential anti-infective bone repair implant.
Abstract: Surface modification of surgical grade titanium implants to promote bone cell integration and prevent infection is an urgent problem in orthopedic surgery. The synergistic effect of silk fibroin (SF) and strontium (Sr) has the dual functions of promoting bone formation and inhibiting osteoclasts, and silver (Ag) has excellent antibacterial activity. Therefore, this research uses technologies such as anodizing, hydrothermal synthesis, and layered self-assembly to load SF-Ag into Sr-loaded titanium dioxide nanotubes (SFAgSTN), which makes the titanium surface produce “antibacterial-bone formation” effect. The results of water contact angle and protein adsorption show that SFAgSTN has proper hydrophilicity and protein adsorption capacity, which indicates its excellent biocompatibility. The antibacterial test shows that the functional coating has excellent antibacterial activity because it can inhibit the proliferation of E. coli and S. aureus at the same time. The cross-linking effect of silk fibroin can slow down the release rate of Ag+, avoid the sudden release of ions, extend its antibacterial cycle and reduce the cytotoxicity of Ag+. In vitro, the SFAgSTN coating can promote the adhesion, proliferation and differentiation of MC3T3-E1 osteoblasts, showing good cell compatibility. In vivo, SFAgSTN promotes early osseointegration between Ti substrate and bone tissue. SFAgSTN shows excellent antibacterial, osteogenic differentiation, and new bone formation activity, and can be used as a highly potential anti-infective bone repair implant.
TL;DR: In this article, the effects of the boriding treatments on mechanical properties (hardness, modulus of elasticity, fracture toughness) and high temperature oxidation resistance were investigated using optical and scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffractometry.
Abstract: Nickel-based superalloy Nimonic 80A was pack-borided in a solid medium at temperatures of 850 °C and 950 °C for 2 h and 4 h using silicon-free boriding powders. To investigate the effects of the boriding treatments on mechanical properties (hardness, modulus of elasticity, fracture toughness) and high temperature oxidation resistance, the layers grown on the surfaces were characterized using optical and scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffractometry, and evaluated using microhardness, nanoindentation, wear and oxidation tests. Wear tests were performed on untreated and borided Nimonic 80A alloys using a ball-on-disc tribometer at room temperature and at 500 °C under dry sliding conditions. Oxidation tests were carried out in air at 1000 °C for 5 h, 25 h and 75 h. Characterization studies revealed a smooth, 22 to 86 μm thick crack-free boride layer consisting mainly of Ni2B and minor quantities of CrB, Cr2B and Cr5B3 in the borided samples. The hardness and elastic modulus of the boride layer was measured as 15.57–18.95 GPa and 142–217 GPa, respectively. Increasing the boriding temperature and time increased the concentrations of chromium in the boride layer. The hardness and elastic modulus of the boride layer increased with chromium content while its fracture toughness decreased. The boriding treatments improved the dry sliding wear resistance. Increasing boriding time and temperature generally led to a higher wear resistance values. However, the treatments had no significant effect on oxidation resistance. The results of this study show that boriding can significantly improve the wear resistance of Nimonic 80A without compromising its oxidation resistance.
TL;DR: In this article, a comparative study of the high-temperature abrasive wear of H13 steel surfaces modified by laser melting and cladding with Stellite 6 and 30% WC was performed.
Abstract: The study is aimed to analyse the comparative behaviour of the high-temperature abrasive wear of H13 steel surfaces modified by laser melting and cladding with Stellite 6 and Stellite 6 + 30 wt% WC. 3-body abrasive tests were conducted at room temperature, 450 °C, 550 °C, and 650 °C. The microstructural evolution, microhardness, wear surface morphology and mechanisms, and various phases formed during laser surface modifications were also studied. The laser remelting of H13 steel surface increased its room temperature microhardness to 750 ± 35 HV0.01, whereas laser cladding of Stellite 6 powder yielded hardness of around 600 ± 20 HV0.01 in the clad layer; and Stellite 6/WC composite clad layer had marginally higher hardness than the Stellite 6 clad layer in the matrix and much higher hardness of ~3000 HV0.01 at the sporadically distributed WC particle sites. Though the room temperature microhardness of laser remelted H13 surface is the highest, the volumetric wear loss in it was comparable to that of the Stellite 6 cladding. However, Stellite 6/WC composite layer recorded a relatively less volumetric loss as WC particles resisted the abrasive wear. With increasing temperature, the wear loss in laser remelt surfaces increased at a fast rate, while that in Stellite 6 and composite clad layers varied marginally with no definite trend. Overall, Stellite 6/WC composite cladding performed better than others in the current temperature range.
TL;DR: In this paper, a CoCrFeNiSi high entropy alloy (HEA) coating without pores or slag defects was prepared on 304 stainless steel surface by laser cladding.
Abstract: In this study, CoCrFeNiSi high entropy alloy (HEA) coating without pores or slag defects was prepared on 304 stainless steel surface by laser cladding. Thermodynamic parameters of CoCrFeNiSi HEA were calculated. Microstructure and phase composition were analyzed by means of scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Comparative studies on hardness, high temperature erosion and oxidation performances were conducted between the CoCrFeNiSi HEA and Stellite-6 Co-based alloy coatings. The results show that laser cladding CoCrFeNiSi HEA coating was composed of single FCC structure. Typical metallurgical bonding between cladding coating and the substrate was formed. Microhardness of CoCrFeNiSi HEA coating reached to approximately 580HV0.2, which was higher than that of Co-based alloy coating (485HV0.2). There was little surface hardness reduction at 500, 600 and 700 °C for CoCrFeNiSi and Co-based alloy coatings. Erosion tests were conducted using quartz sand particles at 20, 500, 600 and 700 °C with an impact angle of 30, 60 and 90°, respectively. The HEA coating showed comparatively lower erosion rates than Co-based alloy coating under all test conditions. The erosion morphologies of both coatings showed that ploughing and micro-cutting were the two primary erosion mechanisms at oblique impact angles, while the erosion mechanism was replaced by the formation of craters and platelets at normal impact angles. A dense and continuous oxidation film could form on HEA coating at 700 °C which may protect the coating from erosion at high temperature to some extent.
TL;DR: In this paper, a novel approach was introduced to fabricate hybrid polymer nanocomposite coating containing epoxy/polyurethane blend, multi-walled carbon nanotubes (MWCNTs) and SiO2 nanoparticles.
Abstract: The present paper aims to introduce a novel approach to fabricate hybrid polymer nanocomposite coating containing epoxy/polyurethane blend, multi-walled carbon nanotubes (MWCNTs) and SiO2 nanoparticles. For this purpose, MWCNTs and SiO2 nanoparticles were first functionalized with silane and silyl compounds, respectively, and then mixed with epoxy resin and polyurethane prepolymer along with dimethylthiotoluenediamine (DMTDA) as hardener. Eventually, the nanocomposite coatings containing 0–0.75 wt% of MWCNTs and 0–2.5 wt% of SiO2 nanoparticles was sprayed on carbon steel plates, poured on appropriate dies and analyzed using Fourier Transform Infrared Spectroscopy (FTIR), pull off, hardness, tensile, impact and wear tests. Moreover, surface roughness and wear mechanisms were tested using Scanning Tunneling Microscopy (STM) and Scanning Electron Microscopy (SEM), respectively. It has been shown that reinforcing of the matrix with inappropriate amount of nanoparticles (NPs) will negatively effect on the samples' pull off strength, hardness, and modulus of elasticity. However, in case of using the hybrid of 0.75 wt% MWCNTs and 0.75 wt% SiO2 NPs, the modification will be ended in the least impact strength and surface roughness along with about 600% of increase in the elastic modulus. Furthermore, sample with 0.75 wt% MWCNTs and 2.5 wt% SiO2 nanoparticles exhibited the highest hardness/elastic modulus ratio (59.23) and approximately 600% increase in wear resistance. Finally, voids elongation and joining were identified as the main wear mechanisms for the toughened samples.
TL;DR: In this paper, the effects of Ag doping on the microstructure, chemical bonding, mechanical properties, and adhesion stability of diamond-like carbon (DLC) films were systematically investigated.
Abstract: Silver (Ag)-doped diamond-like carbon (Ag-DLC) films were deposited on Si wafer and Co-Cr-Mo alloy substrates using a hybrid deposition technique that combined high-power pulsed magnetron sputtering (HPPMS) and high-power pulsed plasma-enhanced chemical vapor deposition (HPP-PECVD). The Ag concentration (0.0–10.0 at.%) in Ag-DLC films was controlled by adjusting the number of Ag rods in the mosaic silver-graphite target. The effects of Ag doping on the microstructure, chemical bonding, mechanical properties, and adhesion stability of DLC films were systematically investigated. The results demonstrated that Ag doping could refine the columnar structure in DLC films and change the shape and size of DLC surface hillocks. The residual stress in the DLC films decreased as the Ag concentration increased, which effectively improved the adhesion between the films and substrates. The fraction of sp3 bonds in the carbon structure decreased with increasing Ag concentration, which resulted in a reduction in the film hardness when the Ag concentration was higher than 3.2 at.%. Ag doping could improve the wear performance of DLC films, and the Ag-DLC film with 3.2 at.% Ag had excellent wear resistance. Compared with pure DLC films, the Ag-DLC films had better adhesion stability in physiological solutions, which is beneficial for the long-term service of DLC films in vivo applications.
TL;DR: In this article, boride layers were grown on the surface of a Co1.04 high-entropy alloy (HEA) by boronizing at temperatures of 900, 950 and 1000°C for 4h using nanosized boroniizing powders.
Abstract: Boride layers were grown on the surface of a Co1.19Cr1.86Fe1.30Mn1.39Ni1.05Al0.17B0.04 high-entropy alloy (HEA) by boronizing at temperatures of 900, 950 and 1000 °C for 4 h using nanosized boronizing powders. Characterizations were carried out by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), microhardness measurements, nanoindentation tests, surface profilometry and ball-on-disc type wear tests. The tribocorrosion behavior of the boronized HEAs and the untreated alloy were investigated in air and in 5% HCl. Microstructural examinations revealed complex metal boride layers on the surfaces of the boronized HEAs, consisting mainly of Cr2Ni3B6, Fe0.4Mn0.6B, Cr0.4Mn0.6B and CrFeB2 phases. The boride layers were silicide-free, with thickness and hardness values of 31.95–64.36 μm and 23.49–28.09 GPa, respectively. The boronized HEAs exhibited reduced friction coefficients and low wear losses in both ambient air and 5% HCl compared to the untreated HEA. Due in part to the lubricating and cooling effect of the solution, the untreated HEA and the boronized HEAs showed reduced wear losses in 5% HCl compared to air. In air, the wear mechanism of the boronized HEAs was abrasive wear combined with polishing, while in the as-cast HEA the wear mechanism was abrasive wear accompanied by plastic deformation. In 5% HCl, the wear mechanism of the boronized HEAs was abrasive wear accompanied by oxidation and pitting, while in the as-cast HEA the wear mechanism was abrasive wear combined with pitting.
TL;DR: In this article, the authors used cyclic nanoindentation to characterize the tribologically induced surface fatigue behavior of single-layer tungsten-doped (a-C:H:W) and multilayer silicon oxide containing (aC: H:Si:O/a-c:H)25 amorphous carbon coatings under cyclic loading.
Abstract: Diamond-like carbon (DLC) coatings, frequently used to reduce wear and friction in machine components as well as on forming tools, are often subjected to cyclic loading. Doping of DLC coatings with metals or metal carbides as well as the usage of multilayer architectures represent promising approaches to enhance toughness, which is beneficial for the coatings' behavior under cyclic loading. In this study, we utilized cyclic nanoindentation to characterize the tribologically induced surface fatigue behavior of single-layer tungsten-doped (a-C:H:W) and multilayer silicon oxide containing (a-C:H:Si:O/a-C:H)25 amorphous carbon coatings under cyclic loading. Columnar growth was observed for both coatings by focused ion beam microscopy and scanning electron microscopy, while the multilayer architecture of the (a-C:H:Si:O/a-C:H)25 coating was verified by the silicon content using glow-discharge optical emission spectroscopy. In cyclic nanoindentation of the (a-C:H:Si:O/a-C:H)25 multilayer coating, stepwise small changes in indentation depth were observed over several indentation cycles. The surface fatigue process of the single-layer a-C:H:W covered a smaller number of indentation cycles and was characterized by an early steep increase of the static displacement signal. Microscopical analyses hint at grain deformation, sliding at columnar boundaries, and grain detachment as underlying fatigue mechanisms of the a-C:H:W coating, while the (a-C:H:Si:O/a-C:H)25 multilayer coating showed transgranular crack propagation and gradual fracturing. In case of the (a-C:H:Si:O/a-C:H)25 multilayer coating, superior indentation hardness (HIT) and indentation modulus (EIT) as well as a higher HIT3/EIT2 ratio suggest a higher resistance to plastic deformation. A high HIT3/EIT2 ratio, being an indicator for hindered crack initiation, combined with the capability of stress relaxation in soft layers contributed to the favorable surface fatigue behavior of the (a-C:H:Si:O/a-C:H)25 multilayer coating observed in this cyclic nanoindentation studies.
TL;DR: In this article, the optimal condition for obtaining composite coating is investigated via studying the effects of different content B4C on the performance of Ni-B/B4C coatings, including the surface morphology, microstructure, hardness and electrochemical properties.
Abstract: Ni-B/B4C composite coatings on N80 steel were achieved by pulsed electrodeposition (PED). The optimal condition for obtaining composite coating is investigated via studying the effects of different content B4C on the performance of Ni-B/B4C coatings, including the surface morphology, microstructure, hardness and electrochemical properties. Scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive spectrometer (EDS) were used to analyze the surface morphology, crystal morphology and element type and content of the composite coatings. The hardness of coatings was investigated by micro-hardness test. The electrochemical properties of coatings were demonstrated by electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscope (SECM). Results show that the grain was uniformly deposited on the surface of N80 steel, and no pinholes and microcracks were captured. Besides, the average Vickers hardness of the Ni-B/B4C was the highest (1030.61 HV), and the average coefficient of friction (COF) is 0.22 (the average COF of Ni-B is 0.49). In 3.5 w% NaCl solution, Ni-B/B4C (2 g L−1) exhibits good corrosion resistance, with a corrosion voltage of − 0.30 − 0.010 + 0.010 V, and a corrosion current of − 1.15 − 0.220 + 0.219 μA.
TL;DR: In this article, the structure of paper is transferred to a target material to form a mechanical protection layer for nanomaterials that were deposited from solution-phase, i.e., spray-coating.
Abstract: Solution-phase deposition of nanomaterials represents a highly promising technology with strong industrial application potential for the fabrication of superhydrophobic surfaces. An important barrier towards the adaptation of such materials and processes in a broad range of applications is the limited mechanical durability of the nanostructures. Herein, we present a universal solution to this challenge by benefiting from the unique micro-structure of paper. Our approach is based on transferring the structure of paper into a target material, to form a mechanical protection layer for nanomaterials that were deposited from solution-phase, i.e. spray-coating. We demonstrate this concept through the transfer of the structure of paper to a free-standing PDMS film using a simple molding process. Spraying a dispersion of alkyl-silane functionalized silica nanoparticles on the structured free-standing film results in a hierarchically structured superhydrophobic surface with a water contact angle of 175° ± 2° and a sliding angle
TL;DR: In this article, the secondary solid-state friction stir processing of the as-cast Mg-10%B4C composite with a flowenhancing double-pin tool was carried out and the ensuing result was compared with that of a single pin tool.
Abstract: Large and irregular particle sizes of B4C in the Mg matrix are performance-impeding challenges of the as-cast Mg-B4C composites. In an attempt to overcome this, the secondary solid-state friction stir processing of the as-cast Mg-10%B4C composite with a flow-enhancing double-pin tool was carried out and the ensuing result was compared with that of a single-pin tool. The microstructure, hardness, tensile strength, wear, and the fractured surface of the processed composites were investigated and compared. The extra pin-shearing effect and the complex pin-induced interactive material flow of the double-pin tool induce better refinement of the B4C particles in the Mg-10%B4C composite. The use of a double-pin tool increases the stirred and recrystallized vortex/swirl width, kernel average misorientation (KAM) fraction, dislocation density, hardness value at the stirred center (117 HV), and tensile strength (194 MPa) of the Mg-10%B4C composite as compared to the single-pin tool. The double-pin tool changes the fracture path of the composite away from the stirred center owing to the improved material flow and properties of the stirred center. The tribological properties (weight loss, wear rate, and coefficient of friction) of the processed composites are equally improved by the double-pin tool. A double-pin tool is thus recommended for the improvement of material flow, particle-disintegration, mechanical and tribological properties of Mg-based metal matrix composite.
TL;DR: In this paper, anodic electrochemical exfoliation of graphite into graphene sheets (GS) in aqueous media was demonstrated by applying a constant potential of +10 V between two identical graphite sheets in 0.1 M ammonium sulfate.
Abstract: In this work, we have demonstrated a prompt anodic electrochemical exfoliation of graphite into graphene sheets (GS) in aqueous media. For the synthesis of GS, a constant potential of +10 V has been applied between two identical graphite sheets in 0.1 M aqueous ammonium sulfate. The exfoliated GS were characterized via standard analytical tools such as Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy with energy dispersive spectrum (FE-SEM with EDS). Further, the electrochemical performance of GS coated Ni foam (GS/Ni foam) was assessed by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) techniques in 2 M KOH. The quasi-rectangular shaped voltammograms and triangular shaped GCD curves in a three-electrode system was evidenced the double-layer capacitance of GS/Ni foam, which exhibited maximum specific capacitance of 84.82 and 40. 83 F/g at 2 mV/s, and 0.1 A/g of current density, respectively. Moreover, the symmetric two-electrode performance of GS/Ni foam was also examined, which showed good energy density (3.03 Wh/kg) and power density (562.5 W/kg). This study proves that the anodically exfoliated GS can act as a good symmetric supercapacitor in KOH.
TL;DR: In this article, the surface morphology, microstructure, microhardness and residual stress of LAM-fabricated CrMnFeCoNi high-entropy alloy (HEA) were characterized before and after laser shock peening.
Abstract: The present work aims to fabricate CrMnFeCoNi high-entropy alloy (HEA) possessing outstanding wear and corrosion properties via laser additive manufacturing (LAM) and subsequent laser shock peening (LSP). The surface morphology, microstructure, microhardness and residual stress of LAM-fabricated specimen were characterized before and after LSP. Additionally, sliding wear and electrochemical corrosion experiments were conducted to evaluate the suitability of LSP for improving wear and corrosion resistance. Results indicated that friction coefficients and wear rates of LAM-fabricated specimens obviously decreased after LSP. Both untreated and LSP-treated specimens displayed uniform wear mechanisms, including abrasive and adhesive wear, while the wear damage level of the high-energy LSP-treated specimen was the mildest. Moreover, LSP-treated specimens exhibited lower corrosion current density and higher corrosion potential as compared with the untreated specimen, suggesting an enhancement in corrosion resistance. The hardened surface layer had positive effects on inhibiting furrow and spalling to resist material removal, and the compressive residual stress enhanced the adhesion of tribo-layers on the worn surface to protect the underlying layer from further damage. The grain refinement and compressive residual stress synergistically contributed to form compact passive films, thereby restraining the aggression of corrosive ions to enhance the corrosion resistance.
TL;DR: In this paper, layered TiO2 ceramic layers were produced on the Ti6Al4V/316L structures by an anodic oxidation method at different coating times (15, 30, and 60 min).
Abstract: In this study, layered Ti6Al4V/316L substrates were formed by Laser Powder Bed Fusion. TiO2 ceramic layers were produced on the Ti6Al4V/316L structures by an anodic oxidation method at different coating times (15, 30, and 60 min) to advance the wear features of layered Ti6Al4V/316L structure. The surface characterizations, wear and electrochemical behaviors of all specimens were examined via scanning electron microscopy, X-ray diffraction, a microhardness device, a reciprocating tribo-tester, and electrochemical corrosion experiments. According to the outcomes, the wear and corrosion resistance of the anodic oxidized specimens were higher compared to untreated 316L and layered Ti6Al4V/316L substrates, and the best results were obtained from the anodized specimen treated for 60 min.