Showing papers in "Surface & Coatings Technology in 2011"
TL;DR: In this article, a brief review of HIPIMS operation is given in a tutorial manner, illustrated by some original data related to the self-sputtering of niobium in argon and krypton.
Abstract: High power impulse magnetron sputtering (HIPIMS) is pulsed sputtering where the peak power exceeds the time-averaged power by typically two orders of magnitude. The peak power density, averaged over the target area, can reach or exceed 10 7 W/m 2 , leading to plasma conditions that make ionization of the sputtered atoms very likely. A brief review of HIPIMS operation is given in a tutorial manner, illustrated by some original data related to the self-sputtering of niobium in argon and krypton. Emphasis is put on the current–voltage–time relationships near the threshold of self-sputtering runaway. The great variety of current pulse shapes delivers clues on the very strong gas rarefaction, self-sputtering runaway conditions, and the stopping of runaway due to the evolution of atom ionization and ion return probabilities as the gas plasma is replaced by metal plasma. The discussions are completed by considering instabilities and the special case of “gasless” self-sputtering.
TL;DR: In this paper, the performance of three titanium nitride coatings: TiN, TiON, and TiAlN for biomedical applications were assessed in terms of their surface properties electrochemical corrosion in simulated body fluid and cytotoxicity.
Abstract: In the present study, the performance of three titanium nitride coatings: TiN, TiON, and TiAlN for biomedical applications were assessed in terms of their surface properties electrochemical corrosion in simulated body fluid and cytotoxicity. Layers of TiN, TiON and TiAlN were deposited onto CP–Ti substrates by DC reactive magnetron sputtering method using a combination of a Ti, Ti–Al targets and an Ar–N 2 mixture discharge gas. The presence of different phases was identified by XRD analysis. The morphology was determined through atomic force microscopy (AFM) imaging. The XPS survey spectra on the etched surfaces of TiN film exhibited the characteristic Ti2p, N1s, O1s peaks at the corresponding binding energies 454.5, 397.0, and 530.6 eV respectively. The characteristic Raman peaks were observed from the Laser Raman spectrometer. Platelet adhesion experiments were done to examine the interaction between blood and the materials in vitro. On Control samples (CP Ti), platelets were seen as aggregates, whereas on coated samples, platelets were seen as singles, without any significant spreading. Cytocompatibility studies of coated samples were carried out with bare titanium (CP Ti — ASTM B 348) as controls. L-929 mouse fibroblast cells were used for samples. All materials showed good cytocompatbility with cell lines used.
TL;DR: Preparation of a highly crystalline nano hydroxyapatite (HA) coating on commercially pure titanium (Cp-Ti) using inductively coupled radio frequency (RF) plasma spray and their in vitro and in vivo biological response are reported.
Abstract: This paper reports preparation of a highly crystalline nano hydroxyapatite (HA) coating on commercially pure titanium (Cp-Ti) using inductively coupled radio frequency (RF) plasma spray and their in vitro and in vivo biological response. HA coatings were prepared on Ti using normal and supersonic plasma nozzles at different plate powers and working distances. X-ray diffraction (XRD) and Fourier transformed infrared spectroscopic (FTIR) analysis show that the normal plasma nozzle lead to increased phase decomposition, high amorphous calcium phosphate (ACP) phase formation, and severe dehydroxylation of HA. In contrast, coatings prepared using supersonic nozzle retained the crystallinity and phase purity of HA due to relatively short exposure time of HA particles in the plasma. In addition, these coatings exhibited a microstructure that varied from porous and glassy structure at the coating-substrate interface to dense HA at the top surface. The microstructural analysis showed that the coating was made of multigrain HA particles of ~200 nm in size, which consisted of recrystallized HA grains in the size range of 15- 20 nm. Apart from the type of nozzle, working distance was also found to have a strong influence on the HA phase decomposition, while plate power had little influence. Depending on the plasma processing conditions, a coating thickness between 300 and 400 μm was achieved where the adhesive bond strengths were found to be between 4.8 MPa to 24 MPa. The cytotoxicity of HA coatings was examined by culturing human fetal osteoblast cells (hFOB) on coated surfaces. In vivo studies, using the cortical defect model in rat femur, evaluated the histological response of the HA coatings prepared with supersonic nozzle. After 2 weeks of implantation, osteoid formation was evident on the HA coated implant surface, which could indicate early implant- tissue integration in vivo.
TL;DR: In this paper, the authors used optical emission spectroscopy (OES) in the visible and near ultraviolet (NUV) band (285 nm-800 nm) to characterize the PEO plasma and found that the plasma discharge behavior significantly influenced the microstructure and morphology of the oxide coatings and hence the corrosion resistance.
Abstract: Magnesium alloys are increasingly being used as lightweight materials in the automotive, defense, electronics, biomaterial and aerospace industries. However, their inherently poor corrosion and wear resistance have, so far, limited their application. Plasma electrolytic oxidation (PEO) in an environmentally friendly aluminates electrolyte has been used to produce oxide coatings with thicknesses of similar to 80 mu m on an AJ62 magnesium alloy. Optical emission spectroscopy (OES) in the visible and near ultraviolet (NUV) band (285 nm-800 nm) was employed to characterize the PEO plasma. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the coated materials, and potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in a 3.5% NaCl solution were used to determine the corrosion behavior. It was found that the plasma discharge behavior significantly influenced the microstructure and the morphology of the oxide coatings and, hence the corrosion resistance. The corrosion resistance of the coated alloy was increased by changing the current mode from unipolar to bipolar, where the strong plasma discharges had been reduced or eliminated. (C) 2011 Elsevier B.V. All rights reserved.
TL;DR: In this paper, a laser-clad high entropy alloy coating was applied on Ti-6Al-4V alloy by laser cladding and the phase equilibrium of the coating material was calculated using the CALPHAD method.
Abstract: TiVCrAlSi high entropy alloy coatings were deposited on Ti–6Al–4V alloy by laser cladding. SEM, XRD and EDS analyses show that, the as-clad coating is composed of (Ti,V) 5 Si 3 and a BCC solid solution. After annealing at 800 °C for 24 h under vacuum, the coating is composed of (Ti,V) 5 Si 3 , Al 8 (V,Cr) 5 , and a BCC solid solution. The temperature-dependent phase equilibrium for the coating material calculated by using the CALPHAD method, indicates that above 880 °C the stable phases existing in the coating material are a BCC solid-solution and (Ti,V) 5 Si 3 . When the temperature is below 880 °C, the stable phases are (Ti,V) 5 Si 3 , Al 8 (V,Cr) 5 , and a BCC solid solution. In order to validate the calculation results, they were compared with TiVCrAlSi alloy samples prepared by arc melting, encapsulated in quartz tubes under vacuum, annealed at 400–1100 °C for 3 days and water-quenched. XRD analysis shows that the experimental phase composition agrees with the thermodynamic calculations. After vacuum annealing, there is a small increase of hardness for the laser clad TiVCrAlSi coating, which is due to the formation of Al 8 (V,Cr) 5 . The oxidation tests show that the TiVCrAlSi coating effectively improves the oxidation resistance of Ti–6Al–4V at 800 °C in air. The formation of a dense and adherent scale consisting of SiO 2 , Cr 2 O 3 , TiO 2 , Al 2 O 3 and a small amount of V 2 O 5 is supposed to be responsible for the observed improvement of the oxidation resistance.
TL;DR: In this paper, the authors used fused and crushed yttria stabilized zirconia (YSZ) to improve the strain tolerance of atmospheric plasma sprayed (APS) TBCs.
Abstract: Thermal barrier coatings (TBCs) with high strain tolerance are favorable for application in hot gas sections of aircraft turbines. To improve the strain tolerance of atmospheric plasma sprayed (APS) TBCs, 400 μm–500 μm thick coatings with very high segmentation crack densities produced with fused and crushed yttria stabilized zirconia (YSZ) were developed. Using a Triplex II plasma gun and an optimized spraying process, coatings with segmentation crack densities up to 8.9 cracks mm − 1 , and porosity values lower than 6% were obtained. The density of branching cracks was quite low which is inevitable for a good inter-lamellar bonding. Thermal cycling tests yielded promising strain tolerance behavior for the manufactured coatings. Samples with high segmentation crack densities revealed promising lifetime in burner rig tests at rather high surface (1350 °C) and bondcoat temperatures (up to 1085 °C), while coatings with lower crack densities had a reduced performance. Microstructural investigations on cross-sections and fracture surfaces showed that the segmentation crack network was stable during thermal shock testing for different crack densities. The main failure mechanism was delamination and horizontal cracking within the TBC near the thermal grown oxide layer (TGOs) and the TBC.
TL;DR: In this paper, the authors review the results on the tribological behavior of nanocomposite coatings composed of nanoplatelets of transition metal dichalcogenides (TMD) immersed in a C-rich amorphous matrix.
Abstract: In this paper, we review the results on the tribological behavior of nanocomposite coatings composed of nanoplatelets of transition metal dichalcogenides (TMD) immersed in a C-rich amorphous matrix. It is shown that such a microstructure produces low friction coefficients under different operating conditions such as air humidity, contact pressure or temperature. Special attention is paid to the analysis of the worn surfaces after the tests by Raman spectroscopy, Auger electron spectroscopy and transmission electron microscopy. Nanoscale analysis of the wear track has revealed the formation of a thin tribolayer exclusively consisting of TMD platelets oriented to exhibit the lowest friction. In some cases, the depth reorientation of the originally randomly oriented TMD platelets as a reaction to the sliding process has been observed. This self-adaptation explains the low friction coefficient together with a high load-bearing capacity and a limited sensitivity to air humidity. Finally, future perspectives for self-lubricant nanocomposite coatings based on the TMD-C concept are presented.
TL;DR: In this paper, the number of layers of a few layers of carbon basal plane was determined by atomic force microscopy and Raman spectroscopy, and the wear characteristics were also assessed using the AFM.
Abstract: Friction and wear characteristics of multi-layer graphene films deposited on a Si substrate by mechanical exfoliation were investigated by atomic force microscopy (AFM). The graphene films consisted of a few layers of carbon basal plane. The number of graphene layers was determined by AFM and Raman spectroscopy. For the AFM friction measurement, loads in the range of − 5 to 30 nN were applied on the Si tip that slid against the graphene specimen. It was found that graphene films exhibited much lower friction (from 0.36 to 0.62 nN) than bare Si surface (from 1.1 to 4.3 nN) when the applied loads ranged from 3 to 30 nN. The wear characteristics were also assessed using the AFM. Detectable wear of graphene was generated when sliding was performed for 100 cycles under 5 μN applied load. The wear mechanism of graphene was proposed to be due to breakage of in-plane bonds between carbon atoms and shearing at the interface of graphene layers.
TL;DR: In this article, the effect of deposition conditions on the evolution of surface microstructure, crystallographic microtexture, microhardness, and sliding wear behavior of pure nickel and nickel composite coatings are presented.
Abstract: In this work, pure nickel and nickel composite coatings (Ni–Al 2 O 3 , Ni–SiC, and Ni–ZrO 2 ) were deposited from Watts bath using direct current (DC), pulsed current (PC), and pulsed reverse current (PRC) electrodeposition conditions. Detailed investigations on the effect of deposition conditions on the evolution of surface microstructure, crystallographic micro-texture, microhardness, and sliding wear behavior of pure nickel and nickel composite coatings are presented. For all the coatings, the PC and PRC deposition conditions resulted in more random/weak crystallographic texture compared to DC deposition. The composite coatings deposited using PC and PRC deposition also exhibited significant improvement in microhardness and wear resistance due to enhanced reinforcement of nanoparticles in the coatings. Also, the effect of nanoparticle content of the electrolyte bath on the surface microstructure, tribological properties, and level of reinforcement in the Ni–Al 2 O 3 composite coating is investigated. The reinforcement of nanoparticles in the Ni–Al 2 O 3 composite coatings increased linearly with the amount of nanoparticle loading in the electrolyte bath. The microhardness and wear resistance of the Ni–Al 2 O 3 composite coatings also improved with increasing Al 2 O 3 content in the coatings.
TL;DR: In this paper, ZrO 2 nanoparticles well dispersed in an electrolyte were effectively incorporated in an oxidized surface passivation layer on AZ91 Mg alloy by a plasma electrolytic oxidation (PEO) process.
Abstract: ZrO 2 nanoparticles well dispersed in an electrolyte were effectively incorporated in an oxidized surface passivation layer on AZ91 Mg alloy by a plasma electrolytic oxidation (PEO) process. The electrophoretic reaction and mechanical mixing in molten magnesium oxide were the main factors leading to incorporation of ZrO 2 nanoparticles in the magnesium oxide layer. Incorporated ZrO 2 nanoparticles were mainly located in pores that were generated during the PEO process. The results of a potentiostatic polarization analysis and a salt spray test clearly indicated that the corrosion resistance of the PEO treated layer was significantly improved by the incorporation of ZrO 2 nanoparticles.
TL;DR: In this article, the influence of electrophoretic deposition parameters including Bioglass® concentration, electric voltage and deposition time on deposition yield was studied by an orthogonal Taguchi array of L18 type.
Abstract: This article presents experimental results on the electrophoretic deposition (EPD) of bioresorbable chitosan/45S5 Bioglass® composite coatings for orthopaedic implants based on the Taguchi design of experiments (DOE) approach. The influence of EPD parameters including Bioglass® concentration, electric voltage and deposition time on deposition yield was studied by an orthogonal Taguchi array of L18 type. Multivariate analysis of variance (MANOVA) and regression analysis based on the partial least-square method were used to identify the significant factors affecting the deposition yield and its stability during constant-voltage EPD. The coatings were characterised by high resolution scanning electron microscope (SEM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). It is shown that the co-deposition of polymer/Bioglass® system is very sensitive to the concentration of Bioglass® particles. The addition of Bioglass® to the chitosan suspension alters the deposition rate due to variation of pH, suspension conductivity, and zeta potential. For low Bioglass® concentrations, co-deposition of the chitosan and the bioactive glass particles occurs while at the higher concentrations massive deposition of the bioactive glass particles controls the deposition yield. The optimum condition for a high deposition rate with low standard deviation and homogeneous microstructure is achieved when an almost equal concentrations of chitosan and Bioglass® is utilized. The validity of the approach is shown by confirmation experiments at the predicted optimal condition, and the mechanism of electrophoretic co-deposition of the polymer/glass system is discussed.
TL;DR: In this paper, the microstructural characteristics of Ti-6Al-4V single beads and their dependence on process parameters are addressed, and experiments reveal fundamental micro-structural and process characteristics which are helpful for the repeatable and predictable manufacturing and understanding of multi-layered components.
Abstract: In this paper, the microstructural characteristics of Ti–6Al–4V single beads and their dependence on process parameters are addressed. Single beads represent the smallest – and therefore fundamental – unit of additive manufactured components. Bead-on-plates and single beads are produced using a 3.5 kW Nd:YAG laser and Ti–6Al–4V wire. Within 71 sets of process parameters laser beam power, welding speed, and wire-feed speed are varied. The microstructures are investigated by light and scanning electron microscopy, and are divided into several zones according to the thermal history underwent. Microstructural differences of the beads are correlated to the process parameters and discussed. The experiments reveal fundamental microstructural and process characteristics which are helpful for the repeatable and predictable manufacturing and understanding of multi-layered components.
TL;DR: In this paper, the effects of shot peening process parameters on the treated material were investigated by using a three dimensional numerical model, comprising the target plate and a number of shot impacts; their number is defined as the minimum required for a realistic simulation and minimum computational cost.
Abstract: An investigation of the effects of controlled shot peening (CSP) process parameters on the treated material is presented. For this purpose, a three dimensional numerical model is developed, comprising the target plate and a number of shot impacts; their number is defined as the minimum required for a realistic simulation and minimum computational cost. The numerical model is verified by comparing the predicted residual stress (RS) fields to experimental. A parametric study of the shot velocity and impinging angle on the CSP products is performed for 4 shot types, i.e. S110, S230, S330 and S550. The main advantages of the present numerical model are: a) the relatively high number of shots introduced in the simulation compared to other publications that use only one shot, b) the number of shots dependency on the desired coverage, c) the thorough selection of numerical parameters, d) the high-strain rate material behaviour used for the target plate, e) the capability to calculate CSP effects on the target plate as function of coverage, f) the computed data which include RS field, surface roughness, cold work and geometrical stress concentration factor (Kt) and finally g) the computed results which are validated by experimental measurements.
TL;DR: In this article, it is argued that it is only the strain energy within the TGO produced during cooling that contributes significantly to this damage development and not that within the top coat.
Abstract: The spallation of thermal barrier coatings can be life-limiting but its prediction has proven to be a difficult problem. The final spallation event can often occur by buckling and is driven by the release of strain energy within the ceramic top coat and within the underlying thermally-grown oxide (TGO) layer if the delamination interface is at the TGO/bond-coat interface. Prior to this event, substantial sub-critical damage must develop at one or both of the TGO interfaces. It is argued in this paper that it is only the strain energy within the TGO produced during cooling that contributes significantly to this damage development and not that within the top coat. A critical strain energy within the TGO layer is suggested as a possible pragmatic method of predicting spallation. A critical assessment of proposed mechanisms which implicate bond coat oxidation in the failure process is also undertaken in the paper. Attention is given to: the role of phase changes in the bond coat; the influence of the mechanical constraint imposed by the top coat on the mechanical stability of the bond coat interface; the effect of the growth of the TGO on a non-planar interface on stress development; the importance of localised Al depletion in nucleating a fast-growing non-protective TGO.
TL;DR: In this article, an Al metallic coating and an Al/Cu bimetallic coating were prepared on the surface of a carbon fiber-reinforced polymer matrix composite (PMC) using a cold spray system with nitrogen as process and powder carrier gas.
Abstract: In the present work, an Al metallic coating and an Al/Cu bimetallic coating were prepared on the surface of a carbon fiber-reinforced polymer matrix composite (PMC) using a cold spray system with nitrogen as process and powder carrier gas. The microstructure, microhardness, and bond strength of the resultant coatings are analyzed. The bonding mechanism of the coatings, especially the deposition behavior of the Al particles on the PMC surface is discussed. Results had shown that cold spraying enables the deposition of the metallic and bimetallic coatings directly onto the PMC surface with precise process control and reasonable bonding of feedstock and substrate material. The surface metallization of PMC via cold spraying process presents promising application prospects.
TL;DR: In this article, the effect of atmospheric pressure plasma treatment on carbon fiber tensile strength and interfacial bonding strength to polyimide, polyacrylonitrile (PAN) based carbon fibers are treated with atmospheric pressure oxygen/helium plasmas for different durations.
Abstract: Plasma treatment is frequently used to modify carbon fiber surfaces to improve adhesion of the fiber to matrices although it may also influence carbon fiber tensile strength. In order to determine the effect of atmospheric pressure plasma treatment on carbon fiber tensile strength and interfacial bonding strength to polyimide, polyacrylonitrile (PAN) based carbon fibers are treated with atmospheric pressure oxygen/helium plasmas for different durations. Tensile strength change of the fiber is studied at different gage lengths before and after the plasma treatment. Interfacial bonding between the carbon fiber and a thermoplastic polyimide matrix is evaluated using a single fiber composite test system. Weibull analysis of the single fiber tensile test data shows no obvious changes in the tensile strength at short gage lengths after plasma treatment while the fiber strength tends to decrease at larger gage lengths. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) show that the plasma treatments roughen the fiber surfaces. X-ray photoelectron spectroscopy (XPS) analysis of fiber surface shows a significant increase of oxygen concentration after plasma treatment and the oxygen containing functional groups reach their maximum levels after 32 s treatment time and further increasing treatment time does not achieve a higher level of oxidation. Plasma treatments decrease dynamic water contact angles and increase the surface energy of the carbon fibers as measured by the modified Wilhelmy method. The interfacial shear strength is improved 21% after the atmospheric pressure plasma treatment for 32 s. It is concluded that the increase of oxygen containing functional groups and changing of the surface topology may contribute collectively to the improvement of fiber/resin interfacial adhesion.
TL;DR: In this article, two kinds of phosphate conversion coatings, including zinc phosphate coating and zinc-calcium phosphate coating, were prepared on the surface of AZ31 alloy in phosphate baths.
Abstract: Two kinds of phosphate conversion coatings, including zinc phosphate coating and zinc–calcium phosphate coating, were prepared on the surface of AZ31 alloy in phosphate baths. The morphologies of these coatings were observed using scanning electron microscopy. Their chemical compositions and structures were characterized using energy-dispersive X-ray spectrum, X-ray photoelectron spectroscopy and X-ray diffraction. The corrosion resistance of the coatings was evaluated by potentiodynamic polarization technique. The results show that the flowerlike Zn–Ca phosphate conversion coatings are mainly composed of hopeite (Zn 3 (PO 4 ) 2 ·4H 2 O). They have a quite different morphology from the dry-riverbed-like Zn phosphate coatings that consist of MgO, MgF 2 , Zn or ZnO and hopeite. Both of the zinc and zinc–calcium phosphate coatings can remarkably reduce the corrosion current density of the substrates. The Zn–Ca coating exhibits better corrosion resistance than the Zn coating. Introduction of calcium into the phosphate baths leads to the full crystallinity of the Zn–Ca coating.
TL;DR: In this article, the MPP technique has been utilized to reactively deposit thick Cr 2 N and CrN coatings (up to 55μm) on AISI 440C steel and cemented carbide substrates in a closed field unbalanced magnetron sputtering system.
Abstract: As a variation of high power pulsed magnetron sputtering technique, modulated pulse power (MPP) magnetron sputtering can achieve a high deposition rate while at the same time achieving a high degree of ionization of the sputtered material with low ion energies. These advantages of the MPP technique can be utilized to obtain dense coatings with a small incorporation of the residual stress and defect density for the thick coating growth. In this study, the MPP technique has been utilized to reactively deposit thick Cr 2 N and CrN coatings (up to 55 μm) on AISI 440C steel and cemented carbide substrates in a closed field unbalanced magnetron sputtering system. High deposition rates of 15 and 10 μm per hour have been measured for the Cr 2 N and CrN coating depositions, respectively, using a 3 kW average target power (16.7 W/cm 2 average target power density), a 50 mm substrate to target distance and an Ar/N 2 gas flow ratio of 3:1 and 1:1. The CrN coatings showed a denser microstructure than the Cr 2 N coatings, whereas the Cr 2 N coatings exhibited a smaller grain size and surface roughness than those of the CrN coatings for the same coating thickness. The compressive residual stresses in the CrN and Cr 2 N coatings increased as the coating thickness increased to 30 μm and 20 μm, respectively, but for thicker coatings, the stress gradually decreased as the coating thickness increased. The CrN coatings exhibited an increase in the scratch test critical load as the thickness was increased. Both CrN and Cr 2 N coatings showed a decrease in the hardness and an increase in the sliding coefficient of friction as the coating thickness increased from 2.5 to 55 μm. However, the wear rate of the CrN coatings decreased significantly as the coating thickness was increased to 10 μm or higher. The 10–55 μm CrN coating exhibited low wear rates in the range of 3.5–5 × 10 −7 mm 3 N −1 m −1 . To the contrary, the Cr 2 N coating exhibited relatively low wear resistance in that high wear rates in the range of 3.5 to 7.5 × 10 −6 mm 3 N −1 m −1 were observed for different thicknesses.
TL;DR: In this article, a systematic analysis of the anodization condition influence on the nanoporous alumina structural features was done and the results showed that the pore diameter increases with potential, temperature and time of anodisation, while the interpore distance is influenced solely by the potential.
Abstract: Anodic aluminum oxide (AAO) is a well known template for nanofabrication. Structural features of AAO like pore diameter, interpore distance, porosity, pore density can be fully controlled by operating conditions of anodization. Typically, self-organized two-step anodization is carried out at low temperature (below room temperature) and is a time consuming process. There are individual experiments describing anodization at temperatures close to room temperature. In our study, furthermore, a systematic analysis of the anodization condition influence on the nanoporous alumina structural features was done. The anodization temperature was ranging from 35 to 50 °C increasing significantly current density of the processes, which has increased oxide film growth rate. The anodizing potential ranged from 20 to 60 V and time of the anodization steps was 30, 60 or 120 min. The data obtained has shown that the pore diameter increases with potential, temperature and time of anodization, while the interpore distance is influenced solely by the potential. Temperature and time changes do not affect the interpore distance. Porosity is also influenced by potential, temperature and duration of anodization. Pore density is influenced only by the potential. The synthesis of AAO reported here gives possibilities to obtain the AAO templates in a faster and cheaper way, essential for researchers applying anodic alumina as a template.
TL;DR: In this paper, microwave cladding was explored as a new processing method for enhancement of surface properties of austenitic stainless steel (SS-316) using microwave radiation as the heating source.
Abstract: In the present work microwave cladding was explored as a new processing method for enhancement of surface properties of austenitic stainless steel (SS-316). Cladding of nickel based powder (EWAC) was developed using microwave radiation as the heating source. This paper explains the possible mechanism of clad formation using microwave hybrid heating with the help of a schematic model. The developed clads were characterized using field emission scanning electron microscope (FE-SEM), energy dispersive X-ray spectroscope (EDS), X-ray diffraction (XRD) and measurement of Vicker's microhardness. Typical X-ray diffraction (XRD) pattern of the clad showed the presence of chromium carbide, nickel silicide and nickel iron phases that eventually contribute to enhancement in microhardness of the clads. Clads of approximately 1 mm thickness were developed without any visible interfacial cracking and had significantly less porosity (1.09%). Microstructure of clad transverse section revealed good metallurgical bond with SS-316 substrate by partial mutual diffusion of constituent elements. The microstructure of the clad was found dominantly cellular in nature. Chromium was observed segregated around the cell boundaries while iron and nickel were identified inside the cells. Chromium carbides (Cr 23 C 6 , Cr 3 C 2 ) were formed during the processing and appeared at the cell boundaries. Vicker's microhardness study revealed that the hardness profile varies within the clad zone and the average microhardness of the developed clad was observed to be 304 ± 48 H v .
TL;DR: In this article, a new quantum electronic activation model for the diamond and diamond-like atomic rearrangement of carbon atoms appears to be confirmed by various elder and more recently published experimental results.
Abstract: Considering that diamond can grow without combination of pressure and heat, other effects in addition to ion impact thermal spikes effects must exist, which are ruling the growth of diamond and ta-C films (tetrahedral amorphous carbon). A newly proposed quantum electronic activation model for the diamond and diamond-like atomic rearrangement of carbon atoms appears to be confirmed by various elder and more recently published experimental results. It is based on various types of effects producing activation energy, before producing heat. Thus, it is possible to excite electron–hole pairs, which during their diffusion produce some transversal transient polarization, which under specific conditions can result in a new metastable atomic structure. This article focuses on published work on atomic rearrangements, which have been observed during annealing of diamond and some kinds of DLC (diamond-like carbon) coatings, such as a-C:H and a-CNx coatings. These atomic rearrangements were explained by using essentially Raman spectroscopy results, which are reviewed in this article, before being discussed with additional new proposed aspects on fundamentals to consider and which have been up dated in their interpretation. The considered atomic rearrangement model appears then also to be in agreement with some formerly discussed catalytic effects, which under specific conditions, favorize the growth of diamond and more diamond-like carbon films. It is expected that this new quantum electronic atomic rearrangement model will not be limited only to diamond, ta-C and DLC materials.
TL;DR: In this paper, the HA-chitosan composite powders were prepared by a simple dry-powder mixing process and then used for coating by AD and the results revealed that the coating layers had similar compositions to the corresponding powders and exhibited fairly dense microstructures and, hence, AD was found to be a very effective method for the fabrication of dense ceramic polymer composite coatings with a well-controlled composition.
Abstract: Magnesium (Mg) and its alloys are potential biometallic materials for their good biocompatibility and excellent biological performances. However, Mg alloys corrode too quickly in chloride containing solutions, including the human body fluid and blood plasma, which may result in the abrupt failure of implants made of Mg alloys. Dense and well-adherent HA–chitosan composite coatings were deposited on AZ31 Mg alloy substrate using aerosol deposition (AD) in order to improve both the corrosion resistance and biocompatibility of AZ31 Mg alloy. The HA–chitosan composite powders having chitosan contents of up to 20 wt.% were prepared by a simple dry-powder mixing process and then used for coating by AD. The coatings obtained from the corresponding powders were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and electrochemical measurement. The results revealed that the coating layers had similar compositions to the corresponding powders and exhibited fairly dense microstructures and, hence, AD was found to be a very effective method for the fabrication of dense ceramic–polymer composite coatings with a well-controlled composition. All of the coatings exhibited high adhesion strengths ranging from 24.6 to 27.7 MPa and showed higher corrosion resistances than the bare AZ31 Mg substrate, implying that the corrosion resistance of AZ31 Mg alloy is enhanced by the HA–chitosan composite coating deposited using AD. In addition, the biocompatibility of the alloy was remarkably improved by the HA coating and the incorporation of chitosan into the coating.
TL;DR: The phase transition from cubic to wurtzite with increasing Al content in the alloys is correlated with changes of electronic structure and bonding in the systems and the predicted phase stability regions and the broad dual-phase transition regions are validated by experiments.
Abstract: Transition metal aluminium nitride (TM–Al–N) thin films are valued for their excellent mechanical (e.g. hardness) as well as protective (e.g. oxidation resistance) properties. This paper addresses the structure and phase stability of group IVB TM–Al–N systems Ti1−xAlxN, Zr1−xAlxN, and Hf1−xAlxN. The predicted stability regions of the rock salt cubic structures are x ≤ 0.7, x ≤ 0.45, and x ≤ 0.45, respectively, while the wurtzite-type single phase field is obtained for x ≥ 0.7, x ≥ 0.68, and x ≥ 0.62 respectively. The predicted phase stability regions and the broad dual-phase transition regions in the case of Zr1−xAlxN and Hf1−xAlxN are validated by experiments. Furthermore, the phase transition from cubic to wurtzite with increasing Al content in the alloys is correlated with changes of electronic structure and bonding in the systems.
TL;DR: In this article, a novel Selective Laser Melting (SLM) process was applied to prepare bulk-form TiC/Ti 5 Si 3 in-situ composites starting from Ti/SiC powder system.
Abstract: A novel Selective Laser Melting (SLM) process was applied to prepare bulk-form TiC/Ti 5 Si 3 in-situ composites starting from Ti/SiC powder system. The influence of the applied laser energy density on densification, microstructure, and mechanical performance of SLM-processed composite parts was studied. It showed that the uniformly dispersed TiC reinforcing phase having a unique network distribution and a submicron-scale dendritic morphology was formed as a laser energy density of 0.4 kJ/m was properly settled. The 96.9% dense SLM-processed TiC/Ti 5 Si 3 composites had a high microhardness of 980.3HV 0.2 , showing more than a 3-fold increase upon that of the unreinforced Ti part. The dry sliding wear tests revealed that the TiC/Ti 5 Si 3 composites possessed a considerably low friction coefficient of 0.2 and a reduced wear rate of 1.42 × 10 − 4 mm 3 /Nm. The scanning electron microscope (SEM) characterization of the worn surface morphology indicated that the high wear resistance was due to the formation of adherent and strain-hardened tribolayer. The densification rate, microhardness, and wear performance generally decreased at a higher laser energy density of 0.8 kJ/m, due to the formation of thermal cracks and the significant coarsening of TiC dendritic reinforcing phase.
TL;DR: In this article, thin (25 nm) and highly uniform Al2O3 coatings have been deposited at relatively low temperature of 80 and 100 °C onto various bio-based polymeric materials employing the ALD technique.
Abstract: Thin (25 nm) and highly uniform Al2O3 coatings have been deposited at relatively low temperature of 80 and 100 °C onto various bio-based polymeric materials employing the atomic layer deposition (ALD) technique. The work demonstrates that the ALD-grown Al2O3 coating significantly enhances the oxygen and water vapor barrier performance of these materials. Promising barrier properties were revealed for polylactide-coated board, hemicellulose-coated board as well as various biopolymer (polylactide, pectin and nano-fibrillated cellulose) films.
TL;DR: In this article, the electroless Ni-P/Cu-Ni multilayers are electroless deposited onto polyester fabric as a function of the deposition time of Ni−P and compared with Ni·P and Cu−Ni deposits.
Abstract: Nickel–phosphorus/copper–nickel (Ni–P/Cu–Ni) multilayers are electroless deposited onto polyester fabric as a function of the deposition time of Ni–P and compared with Ni–P and Cu–Ni deposits. Their surface morphology, microstructure and composition are analyzed by using scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive X-ray (EDX). Their electromagnetic interference (EMI) shielding effectiveness (SE) is evaluated and corrosion resistance is characterized by electrochemical polarization measurements. The results show that with the same weight of the deposits, the EMI SE of the Ni–P/Cu–Ni plated fabric is higher than that of the Ni–P plated fabric, while the corrosion resistance of the Ni–P/Cu–Ni plated fabrics is better than the Cu–Ni plated fabrics. Ni–P improves corrosion resistance and greatly enhances the electromagnetic shielding property of Ni–P/Cu–Ni deposits. Furthermore, the EMI SE and corrosion resistance of the Ni–P/Cu–Ni deposits increase with the rise of deposition time of Ni–P. Therefore, electroless Ni–P/Cu–Ni plated fabric is the most appropriate material that will meet the requirements of both corrosion resistance and EMI SE in most textile applications.
TL;DR: In this paper, an attempt has been made to deposit HA and HA reinforced with 10 ¾wt.% (80Al 2 O 3 −20TiO 2 ) by plasma spray process on Ti6Al4V substrate.
Abstract: Hydroxyapatite coatings suffer from poor mechanical properties like fretting fatigue, toughness and abrasive wear resistance. These properties can be enhanced by incorporation of secondary ceramic and metallic reinforcements in HA. An attempt has been made to deposit HA and HA reinforced with 10 wt.% (80Al 2 O 3 –20TiO 2 ) by plasma spray process on Ti6Al4V substrate. These coatings have been characterized using SEM/EDAX, XRD and FTIR spectroscopy. Corrosion studies have been done in SBF solution. Bio compatibility study is not included in this work. Reinforcement has enhanced the tensile strength. There is marginal improvement in microhardness and surface roughness with reinforcement. Both pure and reinforced coatings show superior resistance against corrosion in simulated body fluid.
TL;DR: In this article, the authors report the recent developments in optical applications of polymer-based nanocomposites, with a special focus on energy-related issues, and discuss potential industrial applications of such materials, together with their drawbacks and advantages, in relation to their optical properties.
Abstract: This review reports the recent developments in optical applications of polymer-based nanocomposites, with a special focus on energy-related issues. Hybrid organic–inorganic materials exhibit remarkable optical properties, which are of interest for applications in diverse fields. Inorganic nanoparticles with unique properties can be added to a conjugated polymer matrix in order to design both composites or thin films that are used as an active layer of electronic devices in modern display technology (organic light emitting diodes) and energy conversion (organic photovoltaic cells). Potential industrial applications of such materials are discussed, together with their drawbacks and advantages, in relation to their optical properties.
TL;DR: In this paper, the tribological properties were evaluated by a ball-on-disk tribometer in the temperature range 25-600°C with the presence of alumina and 440C steel.
Abstract: Cr–Al–Si–N coatings with high and low Cr/Al ratios (CrAlSiN and AlCrSiN, respectively) were deposited on WC substrates by cathodic arc and compared with a reference Cr–Al–N coating. The silicon content was close to 3 at.%. X-ray diffraction analysis showed that CrAlN and CrAlSiN coatings exhibited the cubic Cr(Al)N structure, whereas in AlCrSiN a mixture of cubic Cr(Al)N and wurtzite-type AlN was identified. All three coatings showed excellent thermal stability and oxidation resistance up to 800 °C. The tribological properties were evaluated by ball-on-disk tribometer in the temperature range 25–600 °C. Two materials were used as counterparts: alumina and 440C steel. Sliding against 440C steel balls led to the extensive wear of the balls and transfer of the ball material to the surface of the coatings. The coatings were not damaged. When sliding against alumina balls, the coating wear was low up to testing temperature 300 °C. At 400 °C, CrAlSiN coating was partially worn through. CrAlN and AlCrSiN coatings were almost immediately worn out at 600 °C. The analysis of the wear debris identified high-temperature adhesive failure of the coatings.
TL;DR: In this paper, the inner layer on AZ31 was composed of dome-shape precipitates densely packed and rod-like crystals growing from each dome in the radial direction, while the outer layer consisted of an inner dense layer and an outer coarse layer in the similar manner for pure Mg.
Abstract: Hydroxyapatite (HAp) coatings were formed directly on AZ31 magnesium alloy and pure Mg in a 250 mmol/L C 10 H 12 N 2 O 8 Na 2 Ca aqueous solution of pH 8.9. Treatment time was varied from 2 h to 6 h. Crystal phase, morphology and composition of the coatings were investigated. Immersion and polarization tests in a 3.5 wt.% NaCl solution were performed to examine the corrosion behavior of the HAp-coated specimens. The HAp coating of AZ31 with short treatment time had defects which decreased with an increase in treatment time. The HAp coatings of AZ31 consisted of an inner dense layer and an outer coarse layer in the similar manner for pure Mg. The inner layer on AZ31 was composed of dome-shape precipitates densely packed. The outer layer was composed of rod-like crystals growing from each dome in the radial direction. The (002) plane of HAp of inner layer and rod-like crystals roughly oriented to the substrate. Magnesium ion-release and corrosion current density were remarkably reduced with HAp coatings. Each of these values was on the same order of magnitude between HAp-coated AZ31 and pure Mg. The ion release from AZ31 slightly decreased with an increase in treatment time. The original inner dense layer of AZ31 remained after the immersion. It is suggested that the protectiveness of HAp coating relays on the inner layer and does not significantly depend on the kind of Mg substrate.