Showing papers in "Surface & Coatings Technology in 2013"
TL;DR: A review of surface modification of Mg-based biomaterials with emphasis on surface coatings and ion implantation can be found in this article, where the biodegradability behavior and related mechanism in the physiological environment after surface modification are also described.
Abstract: Biodegradability is a big advantage of magnesium-based materials in biomedical applications such as bone fixation, cardiovascular stents, and even stomach trauma repair. Different from other metals such as stainless steels and Ti alloys, the interface between the Mg-based implants and biological environment is dynamic. In order to improve the surface properties to allow better and more expeditious adaptation to the physiological surroundings, it is imperative to design and construct a surface to satisfy multiple clinical requirements such as mechanical strength, biocompatibility, and degradation rate. This paper reviews recent work pertaining to surface modification of Mg-based biomaterials with emphasis on surface coatings and ion implantation. The biodegradation behavior and related mechanism in the physiological environment after surface modification are also described. Surface modification is a promising means to elevate the performance of Mg-based biomaterials and expected to be extensively applied to surface design of biomaterials.
301 citations
TL;DR: In this article, an oxide and corrosion resistant hydrophobic graphene oxide-polymer composite (GOPC) coating was fabricated on the copper by electrophoretic deposition (EPD), and the GOPC coatings were characterized by scanning, and transmission electron microscope (SEM, TEM), thermogravimetric (TGA and electrochemical impedance spectroscopy (EIS).
Abstract: Oxidation and corrosion resistant hydrophobic graphene oxide-polymer composite (GOPC) coating was fabricated on the copper by electrophoretic deposition (EPD). The GOPC coatings were characterized by scanning, and transmission electron microscope (SEM, TEM), thermogravimetric (TGA) and electrochemical impedance spectroscopy (EIS). At optimal EPD conditions of operating voltage 10 V and deposition time 30s, uniform crack free deposit with thickness 45 nm was achieved. Potentiodynamic polarization and EIS investigation demonstrated the efficacy of GOPC coating in shielding copper from corrosion under stringent environment condition. The electrochemical degradation of GOPC coating is more than three orders of magnitude lower than the bare copper substrate. This was due to the impermeability of GOPC coatings to ion diffusion of oxidizing gas and corrosive liquid solution. The procedure employed is fairly facile, inexpensive and less time consuming.
225 citations
TL;DR: In this paper, the effect of electrical parameters including frequency and duty cycle on the microdischarge behavior and coating growth was investigated at constant current, and a new conceptual model was proposed to explain the concentration distribution of Si on the surface of coatings prepared at different duty cycles.
Abstract: Ceramic coatings were created on the surface of 6061 aluminum alloy using a plasma electrolytic oxidation (PEO) process employing a pulsed direct current (DC) power mode in an alkaline electrolyte. The effect of electrical parameters including frequency and duty cycle on the microdischarge behavior and coating growth was investigated at constant current. Surface features of coatings were studied using scanning electron microscopy. Energy dispersive spectroscopy was employed to investigate elemental distribution on the coating surfaces and cross-sections. Applying lower duty cycles was found to result in increased breakdown voltages and microdischarges with higher spatial density and lower intensity. Further, applying a lower duty cycle was also found to promote the uniformity of silicon distribution in the coating. Based on these new findings, a new conceptual model is proposed to explain the concentration distribution of Si on the surface of coatings prepared at different duty cycles.
203 citations
TL;DR: The fabrication and the characterization of polymers by several types of plasma treatments are reviewed, followed by the introduction of their applications to the materials in drug delivery systems and tissue engineering.
Abstract: Polymers have been widely used for biomedical purposes such as medical devices, tissue engineering scaffolds, and drug carriers for drug delivery system (DDS). Using polymers for such medical devices should be entirely sensible, as polymers are generally very soft, highly cost-effective, and relatively biocompatible. In order to encourage further development in the biocompatibility of the polymers for the enhanced use of the materials, the functionalization of the polymer surfaces has been deliberately introduced. Plasma modification is one of the most efficient ways for the surface treatment of polymers, since plasma treatment could selectively modify the chemical and the physical properties of the surface of the polymers by not affecting the original bulk characteristics of the polymers. Also, plasma surface modification offers shorter treatment time as compared with other surface modification methods. When plasma was applied to the polymer surface, functional groups, graft polymerization, coatings, and molecular crosslinking formation would be introduced with or without the change in the surface roughness of the polymer. The highly functionalized polymers by the plasma modifications would be effectively used for the materials in tissue engineering or drug delivery systems. In this paper, the fabrication and the characterization of polymers by several types of plasma treatments are reviewed, followed by the introduction of their applications to the materials in drug delivery systems and tissue engineering.
189 citations
TL;DR: In this article, the diamond-like carbon (DLC) is used to prevent thrombus formation in vascular applications and the problems of transferring these results to in vivo applications are described.
Abstract: This overview article on diamond-like carbon (DLC) coatings in medical applications covers the interaction of cells and tissue with DLC and alloyed DLC to generate desired cell reactions as well as the release of toxic elements. The promising in vitro results of DLC to prevent thrombus formation in vascular applications are summarized and the problems of transferring these results to in vivo applications are described. Since DLC shows extremely low wear in technical applications, a desired implementation is also to build wear particle free, articulating joint replacements by coating the bearing surfaces. Several in vivo studies using DLC coatings on articulating joints resulted in a failure due to partial coating delamination some years after implantation. It will be shown that this delayed delamination was caused by crevice corrosion (CC) of the adhesion-promoting interlayer and the reason why different corrosion processes may prevent an easy transfer of a successful technical application of DLC onto an implant will be discussed. The main issue for successful, long-term, in vivo applications of DLC coatings on implants is to predict the in vivo survival time and especially the long-term adhesion stability of the coating. The formation at the interface of a few atomic layers of reaction products, usually a metal-carbide, will be addressed. Furthermore, any contamination from residual gas or any cross contamination will result in a different reactively formed interface material with different properties. Delamination can then occur by a slowly advancing crack in this thin carbidic layer governed by the laws of stress corrosion cracking (SCC). It will be shown that if a stable coating adhesion is obtained, DLC coated articulating implants show basically no wear of the coating up to 101 million articulations on a simulator corresponding to about 101 years of in vivo articulation.
189 citations
TL;DR: In this article, the authors provide an overview on the research performed with vanadium containing nitride hard coatings, focusing on aspects regarding the synthesis, structure and properties of these coatings and also includes a discussion on possible future developments and further improvements of the coating design.
Abstract: The current review aims to provide an overview on the research performed with vanadium containing nitride hard coatings. Such coatings were synthesised with the objective of reducing the friction at high temperature via self-adaptation of the coating while still providing a high level of wear resistance. The lubricating effect is based on the formation of vanadium oxides with weakly bonded lattice planes and low melting temperature. The review focuses on aspects regarding the synthesis, structure and properties of these coatings and also includes a discussion on possible future developments and further improvements of the coating design.
173 citations
TL;DR: By means of surface mechanical attrition treatment (SMAT), a nanocrystalline surface layer was formed on a Ti-6Al-4V alloy by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) measurements as discussed by the authors.
Abstract: By means of surface mechanical attrition treatment (SMAT), a nanocrystalline surface layer was formed on a Ti–6Al–4V alloy The corrosion behavior of Ti–6Al–4V in a Ringer's solution was investigated by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) measurements Overall results of all studies identified beneficial impacts of SMAT on corrosion behavior of Ti–6Al–4V alloy The surface oxide film formed on Ti–6Al–4V and its stability in biological environments play a decisive role for the biocompatibility of implants In this study, passive oxide films formed on Ti–6Al–4V surfaces and their natural growth in a Ringer's solution have been investigated by microhardness and X-ray photoelectron spectroscopy (XPS)
164 citations
TL;DR: In this article, the friction and wear properties of the TiN and TiCN coatings were investigated by ball-on-disk tribometer in air, distilled water and artificial seawater.
Abstract: To improve the tribological performance of sea frictional components, TiN and TiCN coatings, were used for surface protection of the components. The coatings were deposited on stainless steel and WC cemented carbides by arc ion plating. The coating topography was observed using scanning electron microscopy (SEM), and the composition and structure were analyzed by energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Hardness and adhesion force were tested by nanoindentation and scratch tester, respectively. The friction and wear properties of the TiN and TiCN coatings were investigated by ball-on-disk tribometer in air, distilled water and artificial seawater. The results showed that both the TiCN and TiN coatings had a strong (111) preferred orientation. The friction coefficients of the coatings in distilled water and artificial seawater were lower than those in air. This indicates the influence of aqueous solutions on the friction coefficient due to the lubricative film formed on the coatings. However, the wear loss of the coatings in artificial seawater was larger than those in air and distilled water, this demonstrates a positive synergism between corrosion and wear in artificial seawater. The TiCN coating shows the best wear resistance in the artificial seawater.
150 citations
TL;DR: In this paper, different examples are presented in order to support the importance of the protein-surface interaction as a first indicator of biocompatibility and biofunctionality, as well as the existing correlation between protein adsorption and the physicochemical surface properties of metal oxide films.
Abstract: Surface modification of biomaterials can improve the performance and lifetime of current metallic implantable devices. Metal oxide coatings represent a potential surface modification to enhance the biocompatibility and other biological-related properties, such as the biocorrosion resistance of the metallic implants. In order to design biocompatible metal oxide coatings with tailored properties, it is necessary to get a deeper understanding of the foreign surface–biological interactions, such as the protein–surface interaction, which is the initial process occurring at the implant-biological ambiance contact. By understanding such interaction and the influence of the physicochemical properties of the oxide films on it; then, it might be possible to properly design oxide coatings for a large variety of implant devices from blood to bone contacting implants. Along the paper, different examples are presented in order to support the importance of the protein–surface interaction as a first indicator of biocompatibility and biofunctionality, as well as the existing correlation between protein adsorption and the physicochemical surface properties of metal oxide films.
144 citations
TL;DR: In this paper, PEO coatings were produced on three different Mg-alloys (AJ62, AM60B and AZ91D) using different processing parameters.
Abstract: Magnesium alloys are considered one of the more promising materials for future use in many engineering applications. However, due to their high chemical and electrochemical reactivity, magnesium alloys have poor corrosion resistance in aqueous environments. Improving their corrosion resistance by coating can greatly extend their application. One promising coating method is plasma electrolytic oxidation (PEO). The nature of the coating formed, and the ultimate corrosion performance depends on the both the processing parameters (electrolyte, current density, current mode, processing time) and specific Mg-alloy substrate. In the present study, PEO coatings were produced on three different Mg-alloys (AJ62, AM60B and AZ91D) using different processing parameters. Scanning electron microscopy was used to characterize the coatings. The corrosion resistance was evaluated using electrochemical impedance spectroscopy (EIS) in an aqueous 3.5% NaCl solution. Relationships are drawn between PEO processing parameters, substrate composition and corrosion performance. Electrochemical impedance spectroscopy data indicate that the bipolar PEO coated AZ91D Mg alloy demonstrates a higher corrosion resistance when compared to coated AM60B, AJ62 and pure Mg.
142 citations
TL;DR: In this article, the effect of the anodic current density and current pulse frequency on the resulting oxide layer was investigated for different electrical working conditions using a pulsed bipolar current supply, and the results showed that the surface roughness may be largely affected by the presence of long-lived and large micro-discharges which developed over the processed surface.
Abstract: The plasma electrolytic oxidation (PEO) of aluminium alloys is investigated for different electrical working conditions using a pulsed bipolar current supply. A particular attention is paid to the effect of the anodic current density (from 10 to 90 A dm − 2 ) and current pulse frequency (from 100 to 900 Hz) on the resulting oxide layer. Micro-discharges are characterized during the process by means of fast video imaging with a time and a space resolution of 8 μs and 0.017 mm 2 , respectively. Correlations are established between the micro-discharge characteristics (surface density, lifetime and size) and the elaborated oxide layers (morphology, growth rate and surface roughness). The highest coating growth rate measured (2.1 μm min − 1 ) is achieved with the combination of the highest current density (75.7 A dm − 2 ) and the highest current pulse frequency (900 Hz). Within these specific current conditions it is concluded that the detrimental effects of numerous micro-discharges are minimized. The results also show that the surface roughness may be largely affected by the presence of long-lived and large micro-discharges which develop over the processed surface. The strongest micro-discharges (live duration up to 0.3 ms and cross-sectional area up to 1 mm 2 ) are mainly observed with the combination of the highest current density (75.7 A dm − 2 ) and the lowest current pulse frequency (100 Hz).
TL;DR: In this paper, a series of EB-PVD thermal barrier coatings including 14YSZ, HfSZ, 29DySZ and CeSZ were evaluated with a 2-hour anneal at 1260°C in air.
Abstract: Corrosive attack of CMAS deposits is studied for a series of advanced EB-PVD thermal barrier coatings including 14YSZ, HfSZ, 29DySZ, CeSZ, La 2 Zr 2 O 7 , and Gd 2 Zr 2 O 7 upon a 2 hour anneal at 1260 °C in air. Furthermore, the effects of volcanic ash deposits on La 2 Zr 2 O 7 , and Gd 2 Zr 2 O 7 are studied. A 7YSZ standard coating is employed for benchmarking the resulting microstructures and the coating performances in terms of infiltration depth and chemical reactivity. While all investigated zirconia-based coatings become fully infiltrated by the deposits, the zirconates form crystalline reaction products that prevent complete infiltration. The La 2 Zr 2 O 7 system is treated as a case study with detailed insight on the newly formed phases via analytical TEM.
TL;DR: In this article, the authors compared three types of WC-10Co4Cr coatings deposited with high-velocity oxygen fuel (HVOF) and highvelocity air fuel spraying processes.
Abstract: This study compares three types of WC-10Co4Cr coatings deposited with high-velocity oxygen fuel (HVOF) and high-velocity air fuel (HVAF) spraying processes. The experimental results indicated that the decarburisation of the WC in the WC-10Co4Cr coating was dramatically influenced by the spraying equipment, and the non-WC phase content in the as-sprayed coatings greatly influenced their performances. The HVAF-sprayed WC-10Co-4Cr coating revealed the lowest degree of decarburisation, achieving the best properties in terms of hardness, fracture toughness, abrasive and sliding wear as well as electrochemical corrosion resistance when compared to the two HVOF-sprayed WC-10Co-4Cr coatings.
TL;DR: In this paper, the influence of substrate bias on chemical composition, microstructure, and mechanical properties of high-entropy alloy nitride films was investigated and the results showed that the films have a face-centered cubic NaCl-type structure.
Abstract: Two high-entropy alloy nitride films, (Al 23.1 Cr 30.8 Nb 7.7 Si 7.7 Ti 30.7 )N 50 and (Al 29.1 Cr 30.8 Nb 11.2 Si 7.7 Ti 21.2 )N 50 , were designed and prepared by reactive magnetron sputtering. The influences of substrate bias (from − 50 V to − 150 V) on chemical composition, microstructure, and mechanical properties of the deposited films were investigated. All the films have face-centered cubic NaCl-type structure. The (Al 23.1 Cr 30.8 Nb 7.7 Si 7.7 Ti 30.7 )N x films deposited at − 100 V exhibit the highest hardness of 36.1 GPa, and the (Al 29.1 Cr 30.8 Nb 11.2 Si 7.7 Ti 21.2 )N x films have its maximum hardness of 36.7 GPa at a substrate bias of − 150 V. Both (Al 23.1 Cr 30.8 Nb 7.7 Si 7.7 Ti 30.7 )N x and (Al 29.1 Cr 30.8 Nb 11.2 Si 7.7 Ti 21.2 )N x films have outstanding oxidation resistance at 900 °C.
TL;DR: In this article, the properties of CrN, AlCrN and AlTiN coatings were evaluated by cyclic impact wear and micro-scale abrasion testing, and it was shown that the CrN coating suffered much more severe impact deformation as compared to the two ternary coatings, and exhibited a non-linear increase of the maximum wear depth with increasing number of impact cycles.
Abstract: The properties of CrN, AlCrN and AlTiN coatings deposited on cemented carbide substrates by a multiple-arc Physical Vapour Deposition (PVD) technique were evaluated by cyclic impact wear and micro-scale abrasion testing. In the impact wear test, a 6 mm diameter tungsten carbide ball was used as the impacting body and the impact frequency (f) was set at 10 Hz. In the micro-scale abrasion test, a micro-blasted 25 mm diameter hardened steel ball was used as the counterface and a suspension of SiC particles (mean size of 4–5 μm) in distilled water as the abrasive slurry. After these wear tests, the wear craters were studied by stylus profilometry, SEM and EDX, to investigate wear behaviour. It is shown that the CrN coating suffered much more severe impact deformation as compared to the two ternary coatings, and exhibited a non-linear increase of the maximum wear depth with increasing number of impact cycles. The impact wear mechanisms of the CrN coating were mainly plastic deformation and micro-delamination. The AlTiN coating exhibited the worst impact wear resistance among the three coatings, mainly due to adhesive wear; in contrast, the AlCrN coating exhibited a lower tendency for the coating to pick-up the ball counterface material, and accordingly demonstrated good impact wear resistance. The AlCrN coating exhibited both the best impact wear performance and the best abrasion resistance amongst the three coatings. The CrN coating exhibited the worst abrasive wear resistance due to its comparatively low hardness. The abrasive wear mechanisms of the CrN coating were a combination of plastic deformation, fine micro-cracking and micro-spallation. The AlTiN coating suffered more severe abrasive wear compared to the AlCrN coating, although both coatings had similar hardnesses.
TL;DR: In this paper, a review of the thermal history of thermally sprayed calcium phosphate coatings as well as their in vitro behavior in contact with simulated body fluid is presented. But since the high temperature process of plasma spraying leads to incongruent melting and thus thermal decomposition of the hydroxyapatite, knowledge of the complex transformation sequence is essential to design coatings with optimum stability and hence biological performance.
Abstract: The development of bioceramic materials is at the forefront of health-related issues in many countries. Arguably, research into ceramic biomaterials has reached a level of involvement and sophistication comparable only to electronic ceramics. Despite the fact that calcium phosphate-based coatings on hip, knee and dental implants have a long history of clinical success the quest of improving the longevity of implants and to impart them with better physiological properties is high up on the agenda of numerous research groups around the world. Coating the stem of modern cementless endoprostheses with a layer of plasma-sprayed hydroxyapatite improves the ingrowth of bone cells and thus assists in anchoring the implant to the cortical bone matter. However, since the high temperature process of plasma spraying leads to incongruent melting and thus thermal decomposition of the hydroxyapatite, knowledge of the complex transformation sequence is essential to design coatings with optimum stability and hence biological performance. This contribution reviews recent research into the thermal history of thermally sprayed calcium phosphate coatings as well as their in vitro behavior in contact with simulated body fluid.
TL;DR: In this article, the thermochemical reactions between calcium-magnesium-aluminosilicate-based road sand and several advanced turbine engine environmental barrier coating (EBC) materials were studied.
Abstract: The thermochemical reactions between calcium-magnesium-aluminosilicate- (CMAS-) based road sand and several advanced turbine engine environmental barrier coating (EBC) materials were studied. The phase stability, reaction kinetics and degradation mechanisms of rare earth (RE)-silicates Yb2SiO5, Y2Si2O7, and RE-oxide doped HfO2 and ZrO2 under the CMAS infiltration condition at 1500 C were investigated, and the microstructure and phase characteristics of CMAS-EBC specimens were examined using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). Experimental results showed that the CMAS dissolved RE-silicates to form crystalline, highly non-stoichiometric apatite phases, and in particular attacking the silicate grain boundaries. Cross-section images show that the CMAS reacted with specimens and deeply penetrated into the EBC grain boundaries and formed extensive low-melting eutectic phases, causing grain boundary recession with increasing testing time in the silicate materials. The preliminary results also showed that CMAS reactions also formed low melting grain boundary phases in the higher concentration RE-oxide doped HfO2 systems. The effect of the test temperature on CMAS reactions of the EBC materials will also be discussed. The faster diffusion exhibited by apatite and RE-doped oxide phases and the formation of extensive grain boundary low-melting phases may limit the CMAS resistance of some of the environmental barrier coatings at high temperatures.
TL;DR: In this paper, a MoS 2 -containing oxide coating on Ti6Al4V alloy was prepared by one-step plasma electrolytic oxidation (PEO) process in a MOS 2-dispersed phosphate electrolyte.
Abstract: A MoS 2 -containing oxide coating on Ti6Al4V alloywas prepared by one-step plasma electrolytic oxidation (PEO) process in a MoS 2 -dispersed phosphate electrolyte. The composition and microstructure of the oxide coatings produced in the electrolytes with and without the addition of MoS 2 were analyzed by X-ray diffractometer (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). Results showed that the MoS 2 particles can be successfully incorporated into the oxide coating during the PEO process and were preferentially located in the micropores. The ball-on-disk sliding tests indicated that MoS 2 -containing oxide coating registered much lower friction coefficient and wear rate than the oxide coating without MoS 2 under dry sliding condition. The improved tribological property of the MoS 2 -containing oxide coating was also discussed.
TL;DR: In this paper, Al-base coating (AlSi10Fe3) was applied to a steel substrate (22MnB5) by hot dipping, and phase formation at the steel/coating interface was investigated by means of ex-situ phase analysis with synchrotron radiation and EBSD.
Abstract: Al-base coating (AlSi10Fe3) was applied to a steel substrate (22MnB5) by hot dipping. The coated steel substrates were austenitized at 920 °C for several dwells, and phase formation at the steel/coating interface was investigated by means of ex-situ phase analysis with synchrotron radiation and EBSD. Phase identification by EBSD and XRD confirmed the formation of Al-rich intermetallics during austenitization. Increasing the dwell time led to Fe diffusion into the Al-base coating as well as Al diffusion into the substrate. As a result of the diffusion processes, Al-rich intermetallics in the coating transformed to more Fe-rich intermetallics. Simultaneously, Al diffusion into the substrate changed the microstructure of the steel substrate near the coating interface. Formation of FeAl intermetallics and thus the mechanical properties of the AlSi10Fe3 coating can be influenced by heat treatment. Higher austenitization temperatures and longer dwell times support the formation of more ductile FeAl intermetallics but also lead to grain growth; thus having a negative effect on the mechanical properties of the steel.
TL;DR: In this paper, the absolute value of coating porosity depends on particle size distribution and could be varied from 3% (fine powders) to 8% (coarse powders).
Abstract: Cold spray deposition of 1–3 mm thick 316L coatings on aluminium substrate using nitrogen as a carrier gas is considered. Dependence of coating properties on particle size distribution and spraying strategy is studied. It was obtained that the absolute value of coating porosity depends on particle size distribution and could be varied from 3% (fine powders) to 8% (coarse powders). The pores are mostly concentrated along the boundaries between deposited layers and the shape of the boundaries is strongly influenced by spraying strategy. It was found that coating deposited using coarse powder has higher microhardness than the one deposited using fine powder, whereas adhesion does not depend on powder granulometry. Eventual decrease of coating porosity is analyzed. In particular, it is shown that laser post re-melting of the deposited coatings can decrease the porosity in the near-surface layers down to
TL;DR: In this article, NiCo-SiC composite coatings were prepared by pulse current (PC) electrodeposition on carbon steel and the effects of the electrodepositing parameters such as duty cycle and pulse frequency on properties and performance of the fabricated coating were investigated.
Abstract: In this work, Ni–Co–SiC composite coatings were prepared by pulse current (PC) electrodeposition on carbon steel. Effects of the electrodepositing parameters such as duty cycle and pulse frequency on properties and performance of the fabricated coating were investigated. The results show that, with the decreasing duty cycle and increasing pulse frequency, the coating morphology changes from a nodular to an acicular structure, with finer grains. Moreover, the amount of SiC particles deposited in the coating is increased. The micro-hardness and corrosion resistance of the coating was enhanced at a low duty cycle and a high frequency (10 Hz in this work), which is related to the increasing amount of SiC particles deposited in the coating.
TL;DR: In this article, a Co-based alloy/TiC/CaF 2 self-lubricating composite coatings were successfully prepared on a Cr-Zr-Cu alloy for continuous casting mold by Nd:YAG laser cladding.
Abstract: In this study, Co-based alloy/TiC/CaF 2 self-lubricating composite coatings were successfully prepared on a Cr-Zr-Cu alloy for continuous casting mold by Nd:YAG laser cladding. The microstructure, phase structure and wear properties were investigated by means of scanning electron microscopy (SEM) incorporating energy dispersive X-ray (EDX) and X-ray diffraction (XRD), as well as dry sliding wear test against GCr15 steel at a temperature of 400 °C. The results showed that the Co-based alloy/TiC/CaF 2 self-lubricating composite coatings had a unique microstructure consisting of well-developed small fine spherical TiC and CaF 2 particles uniformly dispersed in the γ-Co matrix. Average hardness of the Co-based alloy/20% TiC/10% CaF 2 (vol.) self-lubricating composite coating was about twice times that of the pure Co-based alloy coating. It was found that the laser cladding Co-based alloy/TiC/CaF 2 coatings on copper had good friction-reducing and antiwear abilities at temperature up to 400 °C. The composite coating obviously decreased friction coefficient and wear rate as the volume fraction of CaF 2 increased and TiC decreased. The laser cladding Co-based alloy/20% TiC/10% CaF 2 (vol.) composite coating was characterized by mild adhesion wear and plastic deformation and relatively smooth wear surface could be observed.
TL;DR: The blood–biomaterial interfacial events and the evolution of the surface modification strategies are discussed, together with the recent developments on the surface modifications of cardiovascular materials like biomimetic extracellular matrix and accelerated endothelialization, which open a new chapter on designing ideal blood-friendly implantable materials.
Abstract: Cardiovascular implants find wide clinical applications, making a great contribution to the treatment of cardiovascular diseases. Such devices, endovascular stents, artificial vascular grafts, prosthetic heart valves to name a few typical examples, have been the mainstay of cardiovascular surgery. However, failure cases of the implants still exist, which urge us to understand what has happened at the blood-contacting interface and how the tissues have responded during the post-implantation period. Aiming to eliminate these pathological events, various approaches of surface modification of the cardiovascular devices have been used in order to improve hemocompatibility and cytocompatibility. In this review, the blood–biomaterial interfacial events and the evolution of the surface modification strategies are discussed, together with the recent developments on the surface modification of cardiovascular materials like biomimetic extracellular matrix and accelerated endothelialization. These novel surface modification strategies open a new chapter on designing ideal blood-friendly implantable materials.
TL;DR: In this article, a double-layered conversion coating system consisting of magnesium hydroxide and manganese phosphate was applied to magnesium alloy AZ91D using an acidic manganous nitrate and ammonium dihydrogen phosphate solution.
Abstract: A double-layered conversion coating system, consisting of magnesium hydroxide–magnesium/manganese phosphate, was applied to magnesium alloy AZ91D using an acidic manganese nitrate and ammonium dihydrogen phosphate solution. The coating structure, composition and morphology were characterised by SEM, EDX, XRD and XPS. A coating formation mechanism is proposed, and the effect of operating parameters, i.e. pH and temperature, on coating formation was systematically investigated, with optimised conditions able to produce coatings of high corrosion resistance. Corrosion resistance of the coating was evaluated by electrochemical and salt spray testing. The double-layered coating system develops in three stages: initial substrate dissolution, formation of a dense magnesium hydroxide layer, and then co-deposition of magnesium and manganese phosphate film.
TL;DR: In this article, nano-scale surface texturing was made on the rake face close to the main cutting edge of the WC/TiC/Co carbide tools with femtosecond laser, these textured tools were then deposited with WS2 solid lubricant coatings.
Abstract: Nano-scale surface texturing was made on the rake face close to the main cutting edge of the WC/TiC/Co carbide tools with femtosecond laser, these textured tools were then deposited with WS2 solid lubricant coatings. Microstructural and fundamental properties of the textured tools deposited with and without WS2 coatings were examined. Dry cutting tests were carried out with the rake face textured tools (TT), the rake face textured tools deposited with WS2 coatings (TT-WS2), and the conventional carbide tools (CT). Results show that the cutting forces, the cutting temperature, and the friction coefficient at the tool-chip interface of the TT and TT-WS2 tools were significantly reduced compared with that of the conventional carbide tool (CT). The rake face textured tool deposited with WS2 coatings had the most improved cutting performance. The reduced contact length at the tool-chip interface was found to be the main reason for the decrease of friction of the TT rake face textured tool. The thin lubricating film of WS2 solid lubricant on the textured rake face of the TT-WS2 tool contributed to the decrease friction and adhesion between chip–tool interface. It is suggested that deposition of lubricating film on the textured rake face is an effective way to improve the cutting performance of conventional carbide tools in dry cutting.
TL;DR: In this paper, the growth modes and growth modes of different gas mixtures are investigated, and measurements and calculations are provided to explain the resulting microstructures and coating chemistries.
Abstract: Plasma spray physical vapor deposition (PS-PVD) was developed with the aim of depositing uniform and relatively thin coatings with large area coverage. At high power input (~ 150 kW) and very low pressure (~ 100 Pa) the plasma jet properties change considerably compared to conventional plasma spraying and it is even possible to evaporate the powder feedstock material enabling advanced microstructures of the deposits. This relatively new technique bridges the gap between conventional plasma spraying and physical vapor deposition (PVD). Moreover, the resulting microstructures are unique and can hardly be obtained by other processes. In this paper, plasma characteristics of different gas mixtures are investigated. The measurements and calculations provide indications of the growth modes and help to explain the resulting microstructures and coating chemistries. Coatings sprayed from different ceramic powders are discussed.
TL;DR: In this article, Li[Li0.2Mn0.54Ni0.13Co 0.13]O2 with spherical morphology is prepared via co-precipitation method followed by high-temperature treatment and surface coated with a uniform nano-layer of ZrO2 by controlled-hydrolysis of Zirconium(IV) Propoxide.
Abstract: Lithium-rich layered cathode material Li[Li0.2Mn0.54Ni0.13Co0.13]O2 with spherical morphology is prepared via co-precipitation method followed by high-temperature treatment and surface coated with a uniform nano-layer of ZrO2 by controlled-hydrolysis of Zirconium(IV) Propoxide. The results show that Li[Li0.2Mn0.54Ni0.13Co0.13]O2 with a well-ordered layered structure consists of small and homogenous primary particles ranging from 100 nm to 200 nm.The ZrO2 layer with nano-sized particles is coated uniformly on the matrix particle surface. A notable improvement of the cathode coated by ZrO2 is obtained in cycle performance from charge–discharge cycling tests in the range of 2.0–4.8 V, and the optimum amount of ZrO2 coating which maximizes the capacity retention is 1 wt.%. A high initial discharge capacity of 253.1 mAh/g at 0.1C is obtained for the 1 wt.% ZrO2-coated sample, and it maintains a capacity of 207.3 mAh/g after 50 cycles at 0.5C and a capacity of 235.3 mAh/g after 50 cycles at 0.2C. The improved cycling performance of ZrO2-coated Li[Li0.2Mn0.54Ni0.13Co0.13]O2 is attributed to the decrease of electrolyte decomposition reactions and the alleviation of the impedance due to the existence of ZrO2 coating layer.
TL;DR: In this article, microstructural evolutions, mechanical properties and corrosion performance of coatings made of 7075 Al matrix with B4C or SiC reinforcement deposited on T6 6061 Al alloy using the cold gas dynamic spraying process were investigated.
Abstract: In this study, microstructural evolutions, mechanical properties and corrosion performance of coatings made of 7075 Al matrix with B4C or SiC reinforcement deposited on T6 6061 Al alloy using the cold gas dynamic spraying process were investigated. Microstructural surveys have shown that coatings with no discontinuity at the interface as well as with fine grains were obtained and the addition of ceramic particles enhanced the coating density for a prescribed set of spray parameters and nozzle configuration. The presence of ceramic particles in the 7075 Al matrix improved the coatings hardness and wear resistance when compared to unreinforced 7075 Al coatings. Although coatings hardness increased with increasing ceramic particle content, the effect on the coatings wear performance is not that significant. B4C reinforced composite coatings exhibited slightly better wear performance compared to SiC reinforced composite coatings. The cold sprayed coatings showed more noble corrosion potentials but higher corrosion current densities than those of the T6 6061 Al substrate. The addition of ceramic particles into 7075 Al matrix led to increased corrosion current densities when compared to that of unreinforced 7075 Al coating.
TL;DR: In this article, the authors analyzed the fracture toughness of magnetron sputtered titanium nitride (TiN) thin films with a thickness in the 0.3-to 2-μm range.
Abstract: Morphology, structure, residual stress, hardness, and fracture toughness of magnetron sputtered titanium nitride (TiN) thin films, deposited at 300 °C with a thickness in the 0.3- to 2-μm range, were characterized. Film microstructure, the origin of residual stress, and its effect on the fracture toughness and hardness were analyzed. The grain size increased with the film thickness, with 1- to 2-μm-thick films having high pore density. For the 2-μm film, subgrains appeared at grain boundaries. X-ray diffraction showed (200) to (111) preferred orientation transition. The stress in the TiN films changed from highly compressive (− 1.1 GPa) to tensile with the film thickness, reaching 0.68 GPa. Larger grain size, initial porosity, and subgrain generation are reasons for significant changes in the residual stress. Average hardness measured by nanoindentation is 23.2 ± 0.6 GPa. The hardness of the films in compression is higher than in tension. Hardness variation with the film thickness is mainly due to the grain size and microstructure effects. The fracture toughness decreases with the film thickness, depending on the stress state and value. Compressive stress can significantly improve TiN film fracture toughness, while tensile stress seriously degrades it.
TL;DR: In this article, the performance of Ag-DLC coatings with Ag contents ranging from 1.3 at.% to 13.1 at% were characterized by means of XRD and Raman spectroscopy, mechanical and tribological properties.
Abstract: article i nfo Ag-DLC coatings with Ag contents ranging from 1.3 at.% to 13.1 at.% were deposited by DC magnetron sputtering. The coatings were characterized with respect to their structure (by means of XRD and Raman spectroscopy), mechanical and tribological properties (by scratch test, nanoindentation, residual stress mea- surements and pin-on-disk test). The incorporation of 13.1 at.% Ag resulted in the formation of Ag grains of 2-3 nm which promoted the increase of graphite like bonds organized in rings. Regarding the mechanical properties, no variations were found for films with Ag contents lower than 13 at.%; a reduction of both hard- ness and compressive residual stress was then observed for higher values. Pin-on-disk tests were performed at two different contact pressures (690 MPa and 1180 MPa) in dry sliding conditions against a zirconia coun- terpart. For the lower contact pressure the variations in the wear rate are well correlated with the coating structure and mechanical properties, while for the higher contact pressure the presence of Ag is relevant and Ag-DLC coatings are showing higher wear rate than DLC one. SEM analysis revealed the formation of Ag aggregates on the wear track and adhesion of silver to the counterpart.