Showing papers in "Surface & Coatings Technology in 2007"
TL;DR: The Electrolytic Plasma Technology (EPT) is an effective surface engineering tool that combines cleaning and coating of metals as mentioned in this paper, which produces plasma at the surface of the work piece.
Abstract: This paper overviews our present understanding of the fundamentals behind Electrolytic Plasma Technology (EPT) in view of the experimental results and theoretical predictions. EPT is an effective surface engineering tool that combines cleaning and coating of metals. During EPT processing, DC voltage is applied to the electrodes in the aqueous electrolyte, which produces plasma at the surface of the work piece. Thermal, chemical, electrical and mechanical effects imparted by EPT to the work piece create unique surface characteristics. The mechanism and metallurgical aspects of the effects are discussed in detail. EPT is under development for industrial applications in specific processes and is being explored for other potential commercial applications. Both of the aspects are presented. The experimental and industrial tests to date demonstrate that EPT is an emerging surface engineering technique with economical commercial applications in the field of surface engineering.
352 citations
TL;DR: An intumescent flame-retardant coating was prepared by unsaturated polyester resin and epoxy resin as two-component matrix resins, ammonium polyphosphate (APP) as acid source, melamine (Mel) as the blowing agent and pentaerythritol (PER) as carbon agent, expandable graphite as synergistic agent, adding titanium dioxide (TiO2), solvent and other assistants as mentioned in this paper.
Abstract: An intumescent flame-retardant coating was prepared by unsaturated polyester resin and epoxy resin as two-component matrix resins, ammonium polyphosphate (APP) as acid source, melamine (Mel) as the blowing agent and pentaerythritol (PER) as carbon agent, expandable graphite as synergistic agent, adding titanium dioxide (TiO2), solvent and other assistants. Results showed that such a coating had excellent physical–chemical properties. When the thickness of the coating on the wood matrix reached 2.0 mm, the limit of fire-endurance could get to 210 min. And the various component thermal characteristics, decompose processes and interactions of the flame-retardant coating system were investigated by DSC and TGA. The contribution of phosphorus to the formation of the final charring layer and their morphological structures was studied by SEM, XRD and FTIR. On the basis, the flame-retardant mechanism of the intumescent flame-retardant coating was systematically investigated.
329 citations
TL;DR: Fluoride conversion coating was synthesized on magnesium (Mg) by immersion treatment in hydrofluoric acid (HF) at room temperature, with the aim of improving the corrosion resistance of Mg in applications as degradable implant material as discussed by the authors.
Abstract: Fluoride conversion coating was synthesized on magnesium (Mg) by immersion treatment in hydrofluoric acid (HF) at room temperature, with the aim of improving the corrosion resistance of Mg in applications as degradable implant material. After an immersion period of 24 h in 48% HF, the samples carried a bronze color, and the conversion coating was dense and free of cracks. Field-emission scanning-electron microscopy (FE-SEM) of the cross-section revealed a coating thickness of about 1.5 μm. Atomic-force microscopy (AFM) recorded an average surface roughness of ∼ 21 nm for the coated sample, similar to that of the untreated one (∼ 17 nm). The coating was mainly composed of magnesium fluoride (MgF 2 ) as identified by thin-film X-ray diffractometry (TF-XRD), consistent with compositional analysis using X-ray photoelectron spectroscopy (XPS). The MgF 2 was in the form of crystallites of a few nm. A small amount of oxygen was present inside the coating, suggesting that some F − ions are replaced by hydroxyl (OH − ) ions in the MgF 2 structure, or that a small amount of Mg(OH) 2 was present. The corrosion resistance of untreated and conversion coated Mg in Hanks' solution was studied using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization tests, and immersion tests. EIS results showed a polarization resistance of 0.18 kΩ cm 2 for the untreated Mg and 5.2 kΩ cm 2 for the coated sample, giving an improvement of about 30 times. Polarization tests also recorded a reduction in corrosion current density from 400 μA/cm 2 to 10 μA/cm 2 , showing an improvement of about 40 times. The galvanic effect between untreated and fluoride-coated Mg samples was small. Immersion tests in Hanks' solution also resulted in a much milder and more uniform corrosion damage on the fluoride-coated samples. The results of the present study showed that fluoride coating by conversion treatment is a simple and promising way of enhancing the corrosion resistance of Mg in Hanks' solution, or that it may be employed as a pretreatment step for subsequent coating.
323 citations
TL;DR: In this paper, the authors investigated the relationship between the cracking of hard, 3-5-μm-thick Zr-Cu-O, Zr−Cu-C, Ti-Cu−C and Si-Me-N using microindentation measurements and found that the resistance of the film to cracking increases with increasing ratio Hf3/Efµ2.
Abstract: This article reports on the investigation of cracking of hard, 3–5 μm thick Zr–Cu–O, Zr–Cu–C, Ti–Cu–C and Si–Me–N (Me = Ta, Zr, Mo, W) magnetron sputtered nanostructured films using microindentation measurements. Main aim of this investigation is to determine the interrelationships between the cracking of film, its structure and mechanical properties and to assess the toughness of thin film. Correlations between the formation of cracks, the mechanical properties of film and substrate, structure of film and macrostress σ generated in the film during its growth were investigated in detail. It was found that the resistance of the film to cracking increases with increasing ratio Hf3/Ef⁎2. It was found that (1) the correct assessment of toughness of the thin film requires to investigate the system thin film/substrate as one unit because mechanical properties of the substrate play a decisive role in the formation of cracks, (2) the strongest parameter influencing the formation of cracks is the film structure and its macrostress σ and (3) nanostructured films with X-ray amorphous structure and small compressive macrostress (σ ≈ − 0.1 GPa) are very stable against the cracking even at high values of the film hardness Hf exceeding 20 GPa.
301 citations
TL;DR: In this article, polyester (PET) and polypropylene (PP) films are modified by a dielectric barrier discharge in air, helium and argon at medium pressure (5.0 Ã 0 Ã kPa), and the plasma-modified surfaces are characterized by contact angle measurements and X-ray photoelectron spectroscopy (XPS) as a function of energy density.
Abstract: In this paper, polyester (PET) and polypropylene (PP) films are modified by a dielectric barrier discharge in air, helium and argon at medium pressure (5.0 kPa). The plasma-modified surfaces are characterized by contact angle measurements and X-ray photoelectron spectroscopy (XPS) as a function of energy density. The polymer films, modified in air, helium and argon, show a remarkable increase in hydrophilicity due to the implantation of oxygen-containing groups, such as C–O, O–C O and C O. Atomic oxygen, OH radicals, UV photons and ions, present in the discharge, create radicals at the polymer surfaces, which are able to react with oxygen species, resulting in the formation of oxygen-containing functionalities on the polymer surfaces. It is shown that an air plasma is more efficient in implanting oxygen functionalities than an argon plasma, which is more efficient than a helium plasma. In an air plasma, most of the created radicals at the polymer surface will quickly react with an oxygen particle, resulting in an efficient implantation of oxygen functionalities. However, in an argon and helium plasma, the created radicals can react with an oxygen particle, but can also recombine with each other resulting in the formation of an oxidized cross-linked structure. This cross-linking process will inhibit the implantation of oxygen, resulting in a lower efficiency. In argon plasma, more ions are present to create radicals, therefore, more radicals are able to react with oxygen species. This can explain the higher efficiency of an argon plasma compared to a helium plasma.
248 citations
TL;DR: In this article, it is argued that delaminations, when observed within the oxide layer, can only be explained by the presence of a significant stress gradient in the coating, governed by these thermal circumstances.
Abstract: Oxide coatings used for various components in the hot section of aero-turbine engines experience temperature gradients at various stages during their flight cycle. One gradient exists during steady-state, due to the combination of the combustion environment next to the free surface and internal cooling of the underlying superalloy substrate. Other gradients develop during cooling of the surface when engine power is reduced. It will be argued that delaminations, when observed within the oxide layer, can only be explained by the presence of a significant stress gradient in the coating, governed by these thermal circumstances. Two extreme cool-down scenarios are envisaged. In one, the surface is cooled suddenly to a lower temperature, followed by slow uniform cooling. In the other, the entire system reduces its temperature uniformly before the temperature gradient in the TBC is eliminated. Criteria for guarding against delaminations within the oxide layer and along the interface with the substrate are provided and the outcome visualized in the form of delamination maps. A comparison with engine experience provides a preliminary assessment of the relevant thermal scenarios, as well as pathways for continuing research.
236 citations
TL;DR: In this article, 12 commercially available WC-Co powders with different average WC grain sizes (0.2, 2, and 6-μm) and cobalt contents (8, 12, 17 and 25-wt%) were sprayed on carbon steel substrates using High Velocity Oxy-Fuel (HVOF) spraying process.
Abstract: Twelve commercially available WC–Co powders with different average WC grain sizes (0.2, 2, and 6 μm) and cobalt contents (8, 12, 17 and 25 wt.%) were sprayed on carbon steel substrates using High Velocity Oxy-Fuel (HVOF) spraying process. Hardness, Young's modulus, and fracture toughness of the coatings were measured. While the hardness and Young's modulus decreased with increasing cobalt content from 1600 to 1100 Hv and from 400 to 300 GPa respectively, the fracture toughness remained in the range from 4 to 6 MPam 1/2 . The coatings with 2 μm carbide showed lower hardness than those deposited from 0.2 and 6 μm carbide. These measured mechanical properties were discussed with the help of microstructures of the coatings investigated by scanning electron microscopy, X-ray diffraction and chemical analysis. Finally, the hardness of the binder phase in these coatings was estimated to range from 1000 to 1300 Hv by applying the mixture rule for composites to the experimental data, demonstrating that such hardening of the binder phase is a key factor affecting the mechanical properties of the coatings.
203 citations
TL;DR: In this article, the microhardness and fretting wear resistance of anodic oxide layers, produced on commercially pure aluminium by potentiostatic anodizing in sulphuric acid under conditions of controlled convection and heat transfer in a reactor with a wall-jet configuration, were evaluated as a function of the electrolyte temperatures in a wide range from 5°C up to 55°C.
Abstract: The microhardness and fretting wear resistance of anodic oxide layers, produced on commercially pure aluminium by potentiostatic anodizing in sulphuric acid under conditions of controlled convection and heat transfer in a reactor with a wall-jet configuration, were evaluated as a function of the electrolyte temperatures in a wide range from 5 °C up to 55 °C. Additionally, information on the microstructure of the anodic films was acquired by FE-SEM analyses whereas image analysis of high-resolution surface images yielded quantitative information on the evolution of the surface porosity as a function of the electrolyte temperature. Hence measured mechanical properties were directly related to the corresponding microstructure. The microhardness of the anodic films progressively decreased with increasing electrolyte temperatures whereas the wear resistance remained constant for the lower considered temperatures from 5 °C to 25 °C, followed by a decreasing wear resistance with increasing electrolyte temperature from 25 °C onwards. Both mechanical properties displayed an important decrease when the electrolyte temperature was raised from 45 °C to 55 °C. FE-SEM analyses indicated the formation of porous oxides with initially equal pore diameters at the metal-oxide interface, though pore widening due to chemical dissolution of the oxide by the electrolyte led to films with cone-shaped pores. This phenomenon became more pronounced with increasing electrolyte temperature and towards the surface of the anodic layer. The deterioration of the microhardness with increasing electrolyte temperatures could mainly be attributed to the increase of the porosity in the outer region of the oxides since the rate of microhardness reduction is almost synchronous with the rate of porosity increase. In contrast, the variation of the wear resistance with increasing anodizing temperature indicates that the degradation of the wear resistance does not only depend on the oxide porosity and is also affected by other characteristics of the oxide.
202 citations
TL;DR: A fluidized bed reactor (FBR) was designed and constructed for the delivery of reactive gases to particle surfaces to functionalize particles at large scale using atomic layer deposition (ALD).
Abstract: A fluidized bed reactor (FBR) was designed and constructed for the delivery of reactive gases to particle surfaces to functionalize particles at large scale using atomic layer deposition (ALD). Nano- and micron-sized particles were effectively fluidized using an inert carrier gas assisted by mechanical agitation of the powder bed. The gas-solid contacting properties of fluidized bed reactors are beneficial for ALD surface reactions, while the frequent solid-solid collisions do not disrupt the self-limiting behavior of ALD reactant gases. Films can be deposited with monolayer control on individual particles of various substrate types, including metals, ceramics and polymers. In situ mass spectrometry was used for real-time monitoring of gaseous product(s) and reactants throughout the ALD reaction. Alumina (Al 2 O 3 ) ALD on particles demonstrates the process control capabilities of this unique, scalable configuration. The applications of Al 2 O 3 ALD films on particles are widely varying but typically involve core substrate surface passivation, which includes thermal oxidation resistance, photocatalytic activity mitigation and the fabrication of electrically insulative metal particles. Particle functionalization is achievable to nanoscale precision on a wide range of substrate types and sizes with minimal waste of costly ALD precursors and process time.
182 citations
TL;DR: In this paper, the authors discussed the tribological mechanisms, scale effects and surface parameters influencing the friction and wear of diamond and DLC-coated surfaces and showed how surface 3D FEM modelling generates stress and strain values at the nano level, within bond layers at coating/substrate interfaces and around cracks and forms the basis for better understanding the origin of wear.
Abstract: Coating a surface with a thin layer changes the surface material properties and is an important tool for controlling friction and wear. The tribological mechanisms, scale effects and parameters influencing the friction and wear of coated surfaces are discussed. The basic friction and wear mechanisms can be reduced to: friction by adhesion, ploughing and hysteresis and wear by adhesion, abrasion and fatigue combined with material fracture. The tribochemical and surface physical effects and surface fatigue taking place before material fracture are treated here as pure surface material modification mechanisms. Scale effects in a tribological contact are illustrated by explaining typical surface roughness related tribological mechanisms for diamond and DLC coated surfaces. For diamond coatings asperity interlocking effects are important for rough surfaces, graphitisation is a dominating mechanism for smooth engineering surfaces and hydrogenising of dangling bonds may be crucial for physically smooth surfaces. For DLC coated surfaces, surface graphitisation is important with rougher surfaces; building up transfer layers and graphitisation is crucial for smooth engineering surfaces and hydrogenising of dangling bonds can explain superlubricity for physically smooth surfaces. An analysis of dominating surface parameters such as elastic, plastic and fracture behaviour of the top surface, the coating, the coating/substrate interface and the substrate in addition to the coating thickness forms the basis for surface modelling. A stress intensity factor analysis of crack growth shows the importance of considering both modes I, II and III loading, crack spacing and location of crack, while crack orientation, location in crack field as well as load biaxiality have minor influences. It is shown how surface 3D FEM modelling generates stress and strain values at the nano level, within bond layers at coating/substrate interfaces and around cracks and forms the basis for better understanding the origin of wear.
181 citations
TL;DR: In this article, the plasma electrolytic oxidation process of aluminium alloys is investigated for two different current waveforms and it is shown that particular conditions may be established which strongly reduce the arcing that usually causes detrimental defects in the oxide layer for treatment time greater than typically 40-50min.
Abstract: The plasma electrolytic oxidation process of aluminium alloys is investigated for two different current waveforms. It is shown that particular conditions may be established which strongly reduce the arcing that usually cause detrimental defects in the oxide layer for treatment time greater than typically 40–50 min. This results in a “softer” process. As a consequence thick homogenous layers may be grown with no large discharge channels. Through the presented results, the importance of the negative charge density relative to the positive one is evidenced thus pointing out the need of using a pulse bipolar current supply.
TL;DR: In this paper, micro-and nano-sized SiC particles were codeposited with nickel by electrolytic plating from a nickel sulfamate bath and the effects of plating parameters such as pH of the plating bath, SiC content in the plated bath, and stirring speed on the deposition behaviors of Ni-SiC composite coating layers were studied.
Abstract: Micro- and nano-sized SiC particles were codeposited with nickel by electrolytic plating from a nickel sulfamate bath and the effects of plating parameters such as pH of the plating bath, SiC content in the plating bath, and stirring speed on the deposition behaviors of Ni–SiC composite coating layers were studied. The result revealed that the micro-sized SiC particles are more negative than the nano-sized SiC particles in the Zeta potential. The codeposition of SiC can be increased by increasing the SiC content in the plating bath and the pH of the plating bath within the present experimental range. In case of micro-sized SiC particles, increasing stirring speed always lowered the codeposition of SiC. In case of nano-sized SiC particles, the codeposition of SiC showed a maximum at the stirring speed of 100 rpm. The nano-sized SiC particles are more difficult to codeposit than the micro-sized SiC particles and showed rougher plated surface compared with the micro-sized SiC particles, which may be attributable to the agglomeration of nano-sized SiC particles in the plating bath.
TL;DR: In this paper, a combination of flame-assisted CVD (FACVD) and thermal APCVD was used to deposit thin films of titania on stainless steel to prevent the photoactivity of iron and chromium from the substrate.
Abstract: This paper describes an innovative method to achieve highly photoactive and antibacterial titania thin films on stainless steel by a novel combination of flame-assisted CVD (FACVD) – to deposit silica, and thermal APCVD – to deposit titania. We compare the chemical and structural characteristics, and photocatalytic activities of thin films of titania deposited onto stainless steel using APCVD from two different precursors. We show that the silica layer acts as a barrier to prevent the deleterious effect on photoactivity of iron and chromium from the substrate, and in particular, we show that the interaction of the precursor chemistry with the steel surface influences the structure of the films. The films were analysed using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and secondary neutral mass spectrometry (SNMS). Photocatalytic activity of the coatings was determined by the destruction of stearic acid layers, monitored using FT-IR spectroscopy. Studies show selected films to be effective as antibacterial coatings against Escherichia coli , with antibacterial performance comparable to reported values of TiO 2 on other substrates. The shape-forming capabilities and mechanical robustness of steel make it an ideal substrate for the exploration of new applications of photocatalysis. Applications of this technology include water purification, air cleaning, self-sterilizing and self-cleaning surfaces such as those used in hospitals or food preparation.
TL;DR: In this paper, the ageing of polypropylene (PP) and polyethylene terephthalate (PET) films, treated with a dielectric barrier discharge operating at medium pressure (5.0 kPa) in air, helium and argon, is studied.
Abstract: Plasma treatment of polymers is gaining more and more popularity as a surface modification technique, since it offers numerous advantages over the conventional chemical processes. Plasma surface treatment is an environmentally benign, fast and versatile technology. However, it has one major disadvantage: the induced modification of the surface is not permanent, since the surface tends to recover to the untreated state. This ageing effect is due to the reorientation of induced polar chemical groups into the bulk of the material. In this paper, the ageing of polypropylene (PP) and polyethylene terephthalate (PET) films, treated with a dielectric barrier discharge operating at medium pressure (5.0 kPa) in air, helium and argon, is studied. This study is performed using contact angle measurements and X-ray photoelectron spectroscopy (XPS). Results show that the working gas used during plasma treatment has a significant influence on the ageing behaviour of both PP and PET films. The air-, helium- and argon-plasma treated PP films have a loss in treatment efficiency of 47%, 35% and 25% respectively, while the air-, helium- and argon-plasma treated PET films have a loss in treatment efficiency of 39%, 34% and 29% respectively. These results can be explained by the different cross-linking degrees of the polymer films after plasma treatment. Increasing the cross-linking degree will hinder the movement of the polymer chains and reduce the ageing effect.
TL;DR: In this article, the general characteristics and adhesion properties of thermal barrier coatings (TBCs) having bond coats applied using High Velocity Oxygen Fuel (HVOF) thermal spraying and plasma sprayed ceramic top coats are studied.
Abstract: Thermal barrier coatings (TBC) are an effective engineering solution for the improvement of in service performance of gas turbines and diesel engine components. The quality and further performance of TBC, likewise all thermally sprayed coatings or any other kind of coating, is strongly dependent on the adhesion between the coating and the substrate as well as the adhesion (or cohesion) between the metallic bond coat and the ceramic top coat layer. The debonding of the ceramic layer or of the bond coat layer will lead to the collapse of the overall thermal barrier system. Though several possible problems can occur in coating application as residual stresses, local or net defects (like pores and cracks), one could say that a satisfactory adhesion is the first and intrinsic need for a good coating. The coating adhesion is also dependent on the pair substrate-coating materials, substrate cleaning and blasting, coating application process, coating application parameters and environmental conditions. In this work, the general characteristics and adhesion properties of thermal barrier coatings (TBCs) having bond coats applied using High Velocity Oxygen Fuel (HVOF) thermal spraying and plasma sprayed ceramic top coats are studied. By using HVOF technique to apply the bond coats, high adherence and high corrosion resistance are expected. Furthermore, due to the characteristics of the spraying process, compressive stresses should be induced to the substrate. The compressive stresses are opposed to the tensile stresses that are typical of coatings applied by plasma spraying and eventually cause delamination of the coating in operational conditions. The evaluation of properties includes the studies of morphology, microstructure, microhardness and adhesive/cohesive resistance. From the obtained results it can be said that the main failure location is in the bond coat/ceramic interface corresponding to the lowest adhesion values.
TL;DR: In this article, conductive copper manganite and cobalt manganites spinel coatings with nominal composition MnCo 2 O 4 and Cu 1.4 Mn 1.6 O 4 were applied on the surface of UNS 430 stainless steel by electroplating and subsequent air annealing.
Abstract: At the usual temperature of solid oxide fuel cell (SOFC) operation, ferritic stainless steels form electrically insulating or poorly conducting oxide scales, which can cause high internal resistance losses and chromium poisoning. In an effort to avoid this problem, we applied conductive copper manganite and cobalt manganite spinel coatings, with nominal composition MnCo 2 O 4 and Cu 1.4 Mn 1.6 O 4 , which were deposited on the surface of UNS 430 stainless steel by electroplating and subsequent air annealing. Microstructural evaluation indicated that the spinel layers inhibited outward diffusion of chromium. Moreover, excellent structural and thermal stability were observed after several thermal cycles at 750 °C and for up to 28 days, and the coating layers showed good adhesion to the substrate.
TL;DR: In this paper, a zinc-carbon nanotubes composite coatings were obtained from a sulphate bath containing dispersed carbon nanotube (CNTs) and electrochemical and weight loss measurements were made to find the corrosion behavior of composite coating.
Abstract: Zn–carbon nanotubes composite coatings were obtained from a sulphate bath containing dispersed carbon nanotubes (CNTs). The electrochemical and weight loss measurements were made to find the corrosion behavior of composite coating. The presence of carbon nanotubes shifts the potential of zinc deposit to more positive values. The composite coatings were porous free and the service life of coating was examined by salt spray test. The electrochemical studies revealed higher resistance of composite coatings to corrosion. The surface morphology was investigated by recording the SEM images of coating before and after corrosion. The mechanism of action against corrosion was established.
TL;DR: In this article, the relationship between the relevant laser cladding parameters (i.e., laser beam scanning speed, laser power and powder feeding rate) and the main geometrical characteristics of a single laser track (height, width, dilution, etc.) were examined.
Abstract: The objective of this work was to create Co-based coatings (compositionally close to Stellite 6) on compacted graphite and gray cast iron substrates with a high power laser (2 kW continuous Nd:YAG) cladding process. The relationships between the relevant laser cladding parameters (i.e. laser beam scanning speed, laser power and powder feeding rate) and the main geometrical characteristics of a single laser track (height, width, dilution, etc.) were examined. A gradual variation of a single processing parameter was used for an appropriate experimental analysis and statistical correlations study between main processing parameters and geometrical characteristics of an individual laser track. These relations lead to the design of a laser cladding processing map that can be used as a guideline for the selection and further tuning of proper processing parameters for laser cladding of extensive layer. The coatings with thickness from 1.0 to 3.3 mm were created on flat substrates without cracks and other major defects. The microstructural features of these coatings were studied using optical microscopy, scanning electron microscopy (Philips XL30 FEG), EDS (EDAX) and XRD. Mechanical properties were determined using microhardness measurement, scratch test (CSM Revetest) analysis at room temperature and using the tribotesting (CSM HT Tribometer) at room and elevated (up to 525 °C) temperatures.
TL;DR: In this paper, a preliminary study of the biocompatibility of plasma sprayed strontium-containing hydroxyapatite (Sr-HA) coatings on a metallic substrate was conducted.
Abstract: The use of strontium-containing hydroxyapatite (Sr-HA) as a biomaterial has been reported recently. In vitro and in vivo studies have shown that Sr-HA promotes osteoblast response and stimulates new bone formation. In order to extend its usage to major load-bearing applications, such as artificial hip replacement, it has been proposed that the material could be used in the form of a coating on implant surfaces. This paper reports a preliminary study of biocompatibility of plasma sprayed Sr-HA coatings on a metallic substrate. Coatings of Sr-HA containing 10 mol% Sr2+ was produced on titanium alloy substrates. The coating exhibited good bonding with the substrate. The bioactivity of Sr-HA coating was evaluated in vitro by immersion in simulated body fluid (SBF). After immersion in SBF, Sr-HA coating exhibited great ability to induce apatite precipitation on its surface. The possible effects of cell–materials interactions of Sr-HA coating were examined by culturing osteoprecursor cells (OPC1) on coating surfaces. The effect of Sr-HA was also compared to a hydroxyapatite (HA) coating, which is widely used in orthopedics and dentistry. The results indicated that Sr-HA coating had good biocompatibility with human osteoblasts. OPC1 cells survived and proliferated well on the surface of coating. Sr-HA coating promoted OPC1 cells attachment, and more local contacts were produced on the surface. The presence of Sr stimulated OPC1 cell differentiation and ALP expression. No deleterious effect on ECM formation and mineralization was found with Sr-HA coating. The results indicated that Sr-HA coating had good mechanical properties and bioactivity in vitro.
TL;DR: In this article, an examination of the ZrO 2 -YO 1.5 -TaO 2.5 system reveals several promising attributes for use in thermal barrier coating applications.
Abstract: An examination of the ZrO 2 –YO 1.5 –TaO 2.5 system reveals several promising attributes for use in thermal barrier coating applications. The rather unique presence of a stable, non-transformable tetragonal region in this ternary oxide system allows for phase stability to high temperatures (1500 °C). Selected compositions with high levels of yttria and tantala have also shown superior resistance to vanadate corrosion than the commercially utilized 7YSZ. In addition, Y + Ta stabilized zirconia compositions within the non-transformable tetragonal phase field exhibit toughness values comparable or somewhat higher than those of 7YSZ, which bodes well for their durability as TBCs. These promising attributes are discussed in this paper in the context of recent experimental work.
TL;DR: In this article, the use of montmorillonite clay (MMT) treated with an organic compound (aminotrimethylphosphonic acid (ATMP)) and dispersed in an epoxy resin to improve corrosion protection of carbon steel was investigated.
Abstract: This study focusses on the use of montmorillonite clay (MMT) treated with an organic compound (aminotrimethylphosphonic acid (ATMP)) and dispersed in an epoxy resin to improve corrosion protection of carbon steel. X-ray diffraction was performed to verify that the individual silicate layers were separated and dispersed in the epoxy resin. Corrosion resistance of the coated steel was evaluated by electrochemical impedance spectroscopy (EIS) and local electrochemical impedance spectroscopy (LEIS). Three systems were tested: the epoxy clear-coat, the epoxy resin containing 2 wt.% clay and the epoxy resin containing 2 wt.% clay modified byATMP (ATMP-modified clay). From conventional EIS, it was shown that the incorporation of clay or ATMP-modified clay in the epoxy matrix significantly improved the barrier properties of the coating. The corrosion resistance of the carbon steel coated by the epoxy resin containing ATMP-modified clay was higher than that obtained for the system containing non-treated clay. Local electrochemical measurements performed on scratched samples revealed the inhibitive role of ATMP at the carbon steel/coating interface.
TL;DR: In this article, the thermal conductivity of mullite-rich plasma electrolytic oxide (PEO) coatings on aluminium alloys has been investigated using a steady-state method.
Abstract: A study has been undertaken of the characteristics exhibited by mullite-rich plasma electrolytic oxide coatings grown on aluminium alloys by using silicate-rich electrolytes. It is found that they can be grown at a higher rate, and to a greater thickness, than alumina PEO coatings on aluminium. The thermal conductivity of these coatings has been measured using a steady-state method. It is shown to be of the order of 0.5 W m− 1 K− 1, which may be compared with ∼ 1.5 W m− 1 K− 1 for pure alumina PEO coatings and ∼ 10–15 W m− 1 K− 1 for dense polycrystalline mullite. Coupled with excellent substrate adhesion and good mechanical properties, this relatively low conductivity makes these coatings attractive for thermal barrier applications. Furthermore, they are shown to exhibit a relatively low global stiffness (∼ 40 GPa), which will reduce the magnitude of thermally-induced stresses and improve the resistance to spallation during temperature changes.
TL;DR: In this article, double glow plasma surface alloying (DG technique) was used to achieve high speed steel and wear resistant alloys on the surfaces of carbon steels, titanium alloys, intermetallic compounds and copper.
Abstract: Based on plasma nitriding technique, Double Glow Plasma Surface Alloying Technology (DG Technique) was developed in 1980 This technique breaks the restriction of traditional plasma nitriding and successfully applies solid alloying elements, such as Ni, Cr, W, Mo, Ti, Al, Nb et al, to realize plasma surface alloying Numerous experiment results concerning the DG technique have demonstrated that various alloys and alloy steels, such as high speed steel, nickel base alloy and wear resistant alloys et al, have been produced upon the surfaces of carbon steels, titanium alloys, Ti–Al intermetallic compounds and copper This paper is written in hope that the differences between plasma nitriding and DG technique will become more apparent Some new development and experiment results of the double glow plasma surface alloying are also shown in this paper For example, Ti–Al–Nb–C alloy has been produced on the surface of TiAl and Ti–Cu and Ti–Cr burn-resistant alloys have been formed on the surfaces of titanium and Ti6Al4V alloy by using this process; When solid graphite is used as carbon supplier, hydrogen-free carburizing has been carried out in order to avoid hydrogen embrittlement of titanium materials; Co–W–Mo–Fe age hardened high speed steel has been produced on the surfaces of carbon steels
TL;DR: In this paper, a dimensionless solidification parameter, which takes into account factors such as the particle diameter and velocity, substrate temperature, splat and substrate thermophysical properties, and thermal contact resistance between the two, has been defined.
Abstract: Splats formed during a thermal spray process may be either highly fragmented or intact and disk-like. To predict this change in splat morphology, a dimensionless solidification parameter ( Θ ), which takes into account factors such as the particle diameter and velocity, substrate temperature, splat and substrate thermophysical properties, and thermal contact resistance between the two, has been defined. Θ is the ratio of the thickness of the solid layer formed in the splat while it is spreading, to the splat thickness. The value of Θ can be calculated from simple analytical models of splat solidification and spreading. If solid layer growth is very slow ( Θ ≪ 1), the splat spreads out to a large extent. Once it reaches maximum spread, it becomes so thin that it ruptures, producing fragmented splats. If, however, the solid layer thickness is significant ( Θ ∼ 0.1–0.3), the splat is restricted from spreading too far and does not become thin enough to rupture, resulting in disk splats. When solid layer growth is rapid ( Θ > 0.3), it obstructs liquid from flowing outward during droplet impact, producing splats with fingers around their periphery. Predictions from the model are compared with experimental data and found to agree well.
TL;DR: In this paper, a comparative study on microstructural characteristics among Cr−Al−N, Cr−Si−N and Cr-Al−Si-N coatings is reported.
Abstract: Cr–Al–N, Cr–Si–N, Cr–Al–Si–N coatings were successfully deposited on WC–Co substrates by a hybrid coating system combining an arc ion plating technique using Cr target, and a magnetron sputtering method using Al and Si targets under N 2 /Ar atmosphere. XRD, HRTEM, and XPS analyses revealed that the synthesized Cr–Al–N coatings consisted of solid-solution (Cr,Al)N crystallites, and the Cr–Si–N and Cr–Al–Si–N coatings with Si content of ∼ 9 at.% were fine composites consisting of (Cr,Si)N and (Cr,Al,Si)N crystallites, respectively, embedded in an amorphous Si 3 N 4 /SiO 2 matrix. The hardness values of the Cr–Si–N (∼ 35 GPa) and the Cr–Al–Si–N (∼ 55 GPa) coatings were significantly increased compared with those of CrN (∼ 23 GPa) and Cr–Al–N (∼ 25 GPa) coatings. Besides, the average friction coefficients of the Cr–Si–N (∼ 0.30) and the Cr–Al–Si–N (∼ 0.57) coatings with Si content of about 9 at.% were largely decreased compared with those of CrN (∼ 0.50) and Cr–Al–N (∼ 0.84) coatings. A comparative study on microstructural characteristics among Cr–Al–N, Cr–Si–N, and Cr–Al–Si–N coatings is reported in this paper.
TL;DR: In this paper, a 10-100 nanometer-thick surface film was developed on pure Mg on exposure to an ionic liquid (IL) based on the bis(trifluoromethanesulfonyl)amide (TFSA) anion.
Abstract: We present the development of a 10–100 nanometer thick surface film upon pure Mg on exposure to an ionic liquid (IL) based on the bis(trifluoromethanesulfonyl)amide (TFSA) anion. This film formation is the result of the oxidative reactivity of the metal in the IL, with the subsequent effect of ultimately protecting the underlying metal from corrosion in aqueous chloride containing solution. Film formation was studied in the IL using an electrochemical droplet cell. It was seen that this film is adherent and subsequently facilitates appreciable protection against corrosion as judged by subsequent electrochemical testing in the form of potentiodynamic polarization and impedance spectroscopy, along with direct observation. The physical film morphology was studied by electron microscopy and focused ion beam.
TL;DR: In this paper, thermal analyses on a conventional (uncoated) diesel piston, made of aluminum silicon alloy and steel, were performed by means of using a commercial code, namely ANSYS.
Abstract: In this study, firstly, thermal analyses are investigated on a conventional (uncoated) diesel piston, made of aluminum silicon alloy and steel. Secondly, thermal analyses are performed on pistons, coated with MgO–ZrO2 material by means of using a commercial code, namely ANSYS. Finally, the results of four different pistons are compared with each other. The effects of coatings on the thermal behaviors of the pistons are investigated. It has been shown that the maximum surface temperature of the coated piston with material which has low thermal conductivity is improved approximately 48% for the AlSi alloy and 35% for the steel.
TL;DR: In this article, a modified Celsian phase incorporating Ca-magnesium alumino-silicate (CMAS) melts produced when siliceous debris is ingested with the intake air and deposits on component surfaces.
Abstract: Environmental barrier coatings (EBCs) based on Ba1 − xSrxAl2Si2O8 (BSAS) have demonstrated potential for the protection of Si-based ceramic matrix composites (CMCs) against moisture-induced degradation in gas turbines. However, EBCs are susceptible to attack by calcium–magnesium alumino-silicate (CMAS) melts produced when siliceous debris is ingested with the intake air and deposits on component surfaces. The mechanism involves the dissolution of BSAS into CMAS and re-precipitation as a modified Celsian phase incorporating Ca, as well as secondary crystalline silicates that may degrade the durability and efficiency of the EBC. The process is aggravated by grain boundary penetration of CMAS into the polycrystalline BSAS. The mechanisms and their potential implications for durability are discussed.
TL;DR: In this article, the surface characteristics of oxide films on commercially pure titanium metals (CP-Ti; Grade 2 and Grade 3) and titanium alloy (Ti6Al4V and Ti6Al7Nb) samples formed by anodic oxidation treatment, and investigated the effects of anodization on the corrosion characteristics.
Abstract: This study evaluated the surface characteristics of oxide films on commercially pure titanium metals (CP-Ti; Grade 2 and Grade 3) and titanium alloy (Ti6Al4V and Ti6Al7Nb) samples formed by an anodic oxidation treatment, and investigated the effects of anodization on the corrosion characteristics. FE-SEM, XRD, and Raman spectroscopy were used to evaluate the micromorphology and crystalline structure of the oxide films. The corrosion resistance of the sample groups was evaluated using open-circuit potential and cyclic polarization tests. After anodic oxidation up to dielectric breakdown with the same electric current, 150–200 nm-sized pores were distributed homogeneously on pure titanium metal samples, partially occluded pores were observed on the Ti6Al4V alloy, and there was an inhomogeneous size and distribution of pores on the Ti6Al7Nb alloy. The titanium dioxide films formed through anodic oxidation contained a phase mixture of anatase and rutile. The cyclic polarization tests showed that all the tested sample groups were not susceptible to localized corrosion. The as-received and anodically oxidized CP-Ti grade 3 groups showed a higher corrosion resistance than the other groups. The mean Ecorr values of the anodically oxidized sample groups, except for the anodized Ti6Al7Nb alloy, showed higher values than those of the respective as-received sample groups. In particular, the Ti6AL7Nb alloy showed a statistically higher Ecorr value in the anodized group than in the as-received group (p
TL;DR: In this paper, epoxy coatings were modified by adding 5 wt., 10 wt.% or 20 wt% of nano-sized titanium powder respectively, and the corrosion performance of the modified coatings was studied by electrochemical impedance spectroscopy (EIS) in 3.5% NaCl aqueous solution.
Abstract: In this paper, epoxy coatings were modified by adding 5 wt.%, 10 wt.% or 20 wt.% of nano-sized titanium powder respectively. Correspondingly corrosion performance of the modified coatings was studied by electrochemical impedance spectroscopy (EIS) in 3.5% NaCl aqueous solution. The results showed that with high ionic resistance through the coating and low breakpoint frequency, the coating with 10 wt.% nano-sized titanium powder possessed the best corrosion resistance among the coatings tested, which might have resulted from the lowest diffusion coefficient for the inward migration of aggressive media through the coating in the given system. (C) 2007 Elsevier B.V. All rights reserved.