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Showing papers in "Surface & Coatings Technology in 2008"


Journal ArticleDOI
TL;DR: An overview of the literature on the treatment of textiles with non-thermal plasmas is given in this article, where a review is given on plasma treatment effects or results rather than on textile applications that benefit from the treatment.
Abstract: This article attempts to give an overview of the literature on the treatment of textiles with non-thermal plasmas. Because of the enormous amount of potential uses of non-thermal plasmas for the modification of textile products, categorizing the applications is difficult, and therefore a review is given on plasma treatment effects or results rather than on the textile applications that benefit from the treatment.

525 citations


Journal ArticleDOI
TL;DR: In this paper, the development and industrialization of superhard and tough nanocomposite coatings is summarized and documented by selected illustrative examples, which can significantly increase the lifetime and cutting speed of machining operations.
Abstract: Recent progress in the development and industrialization of superhard and tough nanocomposite coatings, which consist of hard transition metal nitride nanocrystals “glued together” by about 1 monolayer of silicon nitride, is summarized and documented by selected illustrative examples. It is shown that already the presently available superhard nanocomposites applied on machining, stamping and forming tools significantly increase their lifetime and the cutting speed, and consequently also the overall productivity of the machining operations. Further improvement of the presently available and newly developed nanocomposite coatings will push the machining technology towards new horizons. Besides of the superhard nanocomposites, also medium hard, but very tough thick coatings with low internal stress applied to forming tools increase their lifetime by at least one order of magnitude.

357 citations


Journal ArticleDOI
TL;DR: In this article, the effect of the sized silver (Ag) nanoparticles on the optical property of SPR was studied. And the authors showed that surface plasmon resonance enhanced the absorption by the sample with Ag nanoparticles above that of the sample without nanoparticles.
Abstract: This work studies the effect of the sized silver (Ag) nanoparticles on the optical property of SPR. Nanoparticles were prepared on fluorine-doped-tin-oxide (FTO) coated glass substrates by RF magnetron sputtering with various deposition times and the subsequent rapid thermal annealing (RTA) to control the particle size. To make the Ag films, Ag films of different thicknesses were first deposited on either glass or FTO substrate by a vacuum sputtering technique. Some of the samples founded nanoparticles by rapid thermal annealing. The substrates with and without nanoparticles were then sensitized by immersing them in a 0.2 mM N719 dye solution. Finally, the effect of the absorption coefficient was investigated by adsorbing it on fine silver Ag islands. The surface plasmon resonance enhanced the absorption by the sample with Ag nanoparticles above that of the sample without nanoparticles. In this study, the peak position of the surface plasmon characteristic absorption increased with the grain size of the nanoparticles in a red-shift. The structure and the quantity of Ag particles were very critical to the surface plasmon resonance effect.

244 citations


Journal ArticleDOI
TL;DR: In this article, the authors present a brief overview of stress and preferred orientation in nitride-based thin films, either in the form of single-, multi-layered or nanocomposite coatings.
Abstract: Nitride-based coatings are nowadays widely studied both from fundamental and technological point of views due to their unique physical and mechanical properties. Among the binary nitrides, TiN is the most stable thermodynamically and has been widely used due to the combination of its covalent and metal-like characteristics. Coatings produced by Physical Vapor Deposition (PVD) techniques generally exhibit a crystallographic texture, which in turn may strongly affect their properties, such as hardness, wear resistance, or diffusion barrier properties in microelectronic devices. Therefore great efforts have been made in recent years to understand the underlying mechanisms governing texture development in nitride thin films. In particular, the issue of stress build-up during PVD growth and its possible interplay with film preferred orientation is essential to address. We present a brief overview of stress and preferred orientation in nitride-based thin films, either in the form of single-, multi-layered or nanocomposite coatings. X-ray Diffraction (XRD) was used in the standard θ –2 θ configuration to study the texture development with film thickness, while the sin 2 ψ method combined with linear elasticity theory was employed to determine the complete strain/stress state. XRD measurements were made in the framework of the crystallite group method, which is of prime importance in thin films exhibiting a mixed texture, as it enables to selectively measure the elastic strain in a given subset of grains. For PVD films grown with energetic particles, the appropriate modeling requires the use of a triaxial stress tensor, including a hydrostatic stress component to take into account the local distortions induced by growth-defects. This approach enables us to determine the ‘stress-free and defect-free lattice parameter’, a 0 , solely linked to chemical effect. Illustrations will be given for fiber-textured TiN and ZrN films deposited on Si substrates, epitaxial TiN layers as well as epitaxial TiN sub-layers in TiN/Cu multilayers grown on (001) MgO single crystal substrates. Ternary TiN-based coatings, either in the form of solid solutions or nanocomposites will be also investigated.

240 citations


Journal ArticleDOI
TL;DR: In this paper, the surface of AM50 magnesium alloy using four different electrolytes containing 10.5% each of K 3PO4 and Na3PO4 in combination with either potassium or sodium hydroxides was analyzed using scanning electron microscopy and X-ray diffraction.
Abstract: In this work coatings were developed on the surface of AM50 magnesium alloy using four different electrolytes containing 10 wt.% each of K3PO4 and Na3PO4 in combination with either potassium or sodium hydroxides. Electrolyte conductivity and breakdown voltage were measured in order to correlate the property of the coating to the nature of electrolyte. Further, the coatings were examined using scanning electron microscopy for surface morphology and cross sectional investigation, X-ray diffraction for phase determination, and electrochemical impedance spectroscopy for corrosion resistance evaluation. The effect of employing different ions in the electrolytes results in different surface morphologies, chemical phases and, consequently, the corrosion resistance of the coatings. The EIS results indicate the presence of porous and compact layers in the structure of the PEO coatings, whilst the overall coating resistance mainly results from the compact layer, the role of the porous layer as a barrier against corrosion is negligible. Finally, a correlation between the passive current density of the bare alloy and the corrosion resistance of the PEO coating is proposed.

236 citations


Journal ArticleDOI
TL;DR: In this article, a thermal analysis using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) was performed on standing CrNx and Cr1−−xAlxN films with two different Al atomic percentages with respect to the metal sublattice.
Abstract: Freestanding CrNx and Cr1 − xAlxN films with two different Al atomic percentages with respect to the metal sublattice (x = 0.23 and x = 0.60) were produced by pulsed closed field unbalanced magnetron sputtering (P-CFUBMS). The dynamic oxidation behavior of the films has been characterized by thermal analysis using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The structure of the films at different thermal-annealing temperatures were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) in an effort to understand different phase transitions and oxidation reactions observed on the DSC curves. The peak temperatures of the main exothermic/endothermic oxidation reactions in the DSC signals at different heating rates were applied to the Kissinger model for determination of activation energies. The mechanical properties of the films at different heat-annealing states were measured by nano-indentation. It was found that the CrNx films oxidized in air after 600 °C by the dissociation of fcc (face center cubic)-CrN to h(hexagonal)-Cr2N and nitrogen and, after 900 °C by the dissociation of h-Cr2N to Cr and nitrogen in the film. The addition of Al to CrN film can further improve the oxidation resistance, especially for the high temperature above 800 °C. The oxidation degradation in two Cr-Al-N films started with dissociation of fcc-CrAlN to h-Cr2N and nitrogen in the film. The presence of thermally stable Al–N bonding in the fcc-CrAlN structure can suppress the reduction of nitrogen in the film. A dense (Cr,Al)2O3 layer (either amorphous or crystalline) formed at early oxidation stage (

228 citations


Journal ArticleDOI
TL;DR: In this paper, X-ray diffraction was used to detect the amorphous structure of Titanium dioxide (TiO2) films on stainless steel substrates, and the electrochemical measurements showed that the equilibrium corrosion potential positively shifts from − 0.96 eV for bare stainless steel to − ǫ 0.63eV for TiO2 coated stainless steel.
Abstract: Titanium dioxide (TiO2) films have been deposited onto stainless steel substrates using atomic layer deposition (ALD) technique. Composition analysis shows that the films shield the substrates entirely. The TiO2 films are amorphous in structure as characterized by X-ray diffraction. The electrochemical measurements show that the equilibrium corrosion potential positively shifts from − 0.96 eV for bare stainless steel to − 0.63 eV for TiO2 coated stainless steel, and the corrosion current density decreases from 7.0 × 10− 7 A/cm2 to 6.3 × 10− 8 A/cm2. The corrosion resistance obtained by fitting the impedance spectra also reveals that the TiO2 films provide good protection for stainless steel against corrosion in sodium chloride solution. The above results indicate that TiO2 films deposited by ALD are effective in protecting stainless steel from corrosion.

220 citations


Journal ArticleDOI
TL;DR: A numerical simulation of crack development within APS TBC systems is presented in this article, revealing a small influence influence of both on the stress state in the thermal barrier coating system subjected to temperature loading.
Abstract: A numerical simulation of crack development within APS TBC systems is presented. The TGO thickening and creep deformation of all system constituents is modelled. Two dimensional periodic unit cell is used to examine the effect of interfacial asperity on stress distribution and subsequent delamination of APS TBC. A study of cyclic loading and of creep of the base material on the stress distribution close to the asperity at the TGO/BC interface is made, revealing a small influence influence of both on the stress state in the thermal barrier coating system subjected to temperature loading. Cohesive zone elements at the oxide/ceramic interface model the development of the interfacial micro-crack. The finite element analysis shows that the development of the interfacial crack allows for a micro-crack formation within APS TBC. Subsequent TGO growth results in a tensional zone within the oxide layer. Linking of the micro-cracks at the interface and within TBC through TGO could lead to a coating delamination in the unit cell.

210 citations


Journal ArticleDOI
TL;DR: In this paper, a multiwalled carbon nanotube (CNT) reinforced aluminum nanocomposite coatings were prepared using cold gas kinetic spraying, which resulted in coatings of the order of 500μm in thickness.
Abstract: Multiwalled carbon nanotube (CNT) reinforced aluminum nanocomposite coatings were prepared using cold gas kinetic spraying. Spray drying was used to obtain a good dispersion of the nanotubes in micron-sized gas atomized Al–Si eutectic powders. Spray dried powders containing 5 wt.% CNT were blended with pure aluminum powder to give overall nominal CNT compositions of 0.5 wt.% and 1 wt.% respectively. Cold spraying resulted in coatings of the order of 500 μm in thickness. Fracture surfaces of deposits show that the nanotubes were uniformly distributed in the matrix. Nanotubes were shorter in length as they fractured due to impact and shearing between Al–Si particles and the Al matrix during the deposition process. Nanoindentation shows a distribution in the elastic modulus values from 40–229 GPa which is attributed to microstructural heterogeneity of the coatings that comprise the following: pure Al, Al–Si eutectic, porosity and CNTs.

203 citations


Journal ArticleDOI
W.R. Chen1, Xijia Wu1, Basil R. Marple1, D.R. Nagy, P. C. Patnaik1 
TL;DR: In this paper, the growth of thermally grown oxide (TGO) layers and their influence on crack formation were studied for two thermal barrier coating (TBC) systems with CoNiCrAlY bond coats produced by APS and high-velocity oxy-fuel (HVOF) techniques.
Abstract: The growth of thermally grown oxide (TGO) layers and their influence on crack formation were studied for two thermal barrier coating (TBC) systems with CoNiCrAlY bond coats produced by (i) air plasma spray (APS) and (ii) high-velocity oxy-fuel (HVOF) techniques. All samples received a vacuum heat treatment and were subsequently subjected to thermal cycling in air. The TGOs were predominantly comprised of layered alumina, along with some oxide clusters of chromia, spinel and nickel oxide. However, after extended oxidation, the alumina layer formed in the APS-CoNiCrAlY bond coat transformed to chromia/spinel, while that formed in the HVOF-CoNiCrAlY bond coat remained stable. TGO thickening in the APS-CoNiCrAlY bond coat generally exhibited a three-stage growth behavior, which resembles a high temperature creep curve, whereas growth of the alumina layer in the HVOF-CoNiCrAlY bond coat showed an extended steady-state stage. Crack propagation in these two TBCs was found to be related to the growth and coalescence of oxide-induced cracking, connecting with pre-existing discontinuities in the topcoat. Hence, crack propagation during thermal cycling appeared to be controlled by TGO growth.

202 citations


Journal ArticleDOI
TL;DR: In this article, the influence of low temperature plasma nitriding on the wear and corrosion resistance of AISI 420 martensitic stainless steel was investigated, and the wear resistances of the nitrided samples were determined with a ball-on-disc wear tester.
Abstract: The influence of low temperature plasma nitriding on the wear and corrosion resistance of AISI 420 martensitic stainless steel was investigated. Plasma nitriding experiments were carried out with DC-pulsed plasma in 25% N2 + 75% H2 atmosphere at 350 °C, 450 °C and 550 °C for 15 h. The composition, microstructure and hardness of the nitrided samples were examined. The wear resistances of plasma nitrided samples were determined with a ball-on-disc wear tester. The corrosion behaviors of plasma nitrided AISI420 stainless steel were evaluated using anodic polarization tests and salt fog spray tests in the simulated industrial environment. The results show that plasma nitriding produces a relatively thick nitrided layer consisting of a compound layer and an adjacent nitrogen diffusion layer on the AISI 420 stainless steel surface. Plasma nitriding not only increases the surface hardness but also improves the wear resistance of the martensitic stainless steel. Furthermore, the anti-wear property of the steel nitrided at 350 °C is much more excellent than that at 550 °C. In addition, the corrosion resistance of AISI420 martensitic stainless steel is considerably improved by 350 °C low temperature plasma nitriding. The improved corrosion resistance is considered to be related to the combined effect of the solid solution of Cr and the high chemical stable phases of ɛ-Fe3N and αN formed on the martensitic stainless steel surface during 350 °C low temperature plasma nitriding. However, plasma nitriding carried out at 450 °C or 550 °C reduces the corrosion resistance of samples, because of the formation of CrN and leading to the depletion of Cr in the solid solution phase of the nitrided layer.

Journal ArticleDOI
TL;DR: In this paper, the existence of the bow shock was found to be dependent on the length of the nozzle's supersonic potential core, and the amount of standoff distance between the potential core and the substrate.
Abstract: Cold Spray involves the deposition of metallic powder particles using a supersonic gas jet. When the nozzle standoff distance is small, a bow shock is formed at the impingement zone between the supersonic jet and the substrate. It has long been thought that this bow shock is detrimental to process performance as it can reduce particle impact velocities. By using computational fluid dynamics, Particle Image Velocimetry and Schlieren imaging it was possible to show that the bow shock has a negative influence on deposition efficiency as a result of a reduction in particle velocity. Furthermore, the existence of the bow shock was shown to be dependent on the length of the nozzle's supersonic potential core. Experiments were carried out with aluminium, copper and titanium powders using a custom-made helium nozzle, operating at 2.0 MPa and 20 °C, and a commercial nitrogen nozzle operating at 3.0 MPa and 300 °C. In all cases, it was found that there is a direct relationship between standoff distance and deposition efficiency. At standoff distances less than 60 mm, the bow shock reduced deposition efficiencies by as much as 40%.

Journal ArticleDOI
TL;DR: In this article, detailed damage analysis of a plasma sprayed ZrO 2 /8 ¾wt −% Y 2 O 3 -MCrAlY-CMSX-4 TBC system during isothermal and cyclic oxidation tests with different dwell times at high temperature have been performed.
Abstract: Detailed damage analyses of a plasma sprayed ZrO 2 /8 wt–% Y 2 O 3 –MCrAlY–CMSX-4 TBC system during isothermal and cyclic oxidation tests with different dwell times at high temperature have been performed The resulting failure mode, ie the particular delamination crack path, is strongly dependent on the temperature cycle applied Isothermal exposure promotes crack propagation within the TGO, whereas thermal cycling shifts the crack path towards the TBC Thermal cycling with dwell time at high temperature leads to a mixed delamination crack path (partly within TBC and TGO) The respective correlation between TBC lifetimes and duration of high temperature dwell time per cycle (cycle frequency) is shown and discussed

Journal ArticleDOI
TL;DR: In this article, the authors investigated the effect of the incorporation of solid lubricant into micro-reservoirs produced by Laser Surface Texturing (LST) and its effect on the tribological properties of surfaces under dry friction.
Abstract: Incorporation of solid lubricant into micro-reservoirs produced by Laser Surface Texturing (LST) and its effect on the tribological properties of surfaces under dry friction is studied. The density of the dimple reservoirs and the height of the bulges around them are investigated in terms of the longevity of solid lubricant films burnished on LST steel surfaces. Friction tests were performed using a ball-on-flat device. Optimum density (40–50%) of the dimples is revealed. It is shown that the adhesion of solid lubricant in the space between the dimples is provided by mechanical engagement of particles in the rough surface and by smearing the solid lubricant around the dimples. Best results are obtained with the surfaces that were lapped to half of the height of bulges. Long wear life of burnished film on LST steel surfaces is apparently provided by preservation of thin MoS 2 film around the bulges and by supply of solid lubricant from the dimples to the surface.

Journal ArticleDOI
TL;DR: In this article, two types of HVOF thermal spray coatings (Cr 3 C 2 -NiCr and WC-Ni) obtained with different spray conditions were studied and compared with conventional micro-cracked hard chromium coatings.
Abstract: Cr 3 C 2 –NiCr and WC–Ni coatings are widely used for wear applications at high and room temperature, respectively. Due to the high corrosion resistance of NiCr binder, Cr 3 C 2 –NiCr coatings are also used in corrosive environments. The application of WC–Ni coatings in corrosive media is not recommended due to the poor corrosion resistance of the (pure Ni) metallic matrix. It is well known that the addition of Cr to the metallic binder improves the corrosion properties. Erosion–corrosion performance of thermal spray coatings is widely influenced by ceramic phase composition, the size of ceramic particles and also the composition of the metallic binder. In the present work, two types of HVOF thermal spray coatings (Cr 3 C 2 –NiCr and WC–Ni) obtained with different spray conditions were studied and compared with conventional micro-cracked hard chromium coatings. Both as-sprayed and polished samples were tested under two erosion–corrosion conditions with different erosivity. Tungsten carbide coatings showed better performance under the most erosive condition, while chromium carbide coatings were superior under less erosive conditions. Some of the tungsten carbide coatings and hard chromium showed similar erosion–corrosion behaviour under more and less erosive conditions. The erosion–corrosion and electrochemical results showed that surface polishing improved the erosion–corrosion properties of the thermally sprayed coatings. The corrosion behaviour of the different coatings has been compared using Electrochemical Impedance Spectroscopy (EIS) and polarization curves. Total material loss due to erosion–corrosion was determined by weight loss measurements. An estimation of the corrosion contribution to the total weight loss was also given.

Journal ArticleDOI
TL;DR: In this article, nanosized titanium dioxide (TiO 2 ) powders were used to connect substrate and hydroxyapatite (HA) in order to reduce the HA decomposition due to ion migration from the metal substrate into the HA.
Abstract: Nanosized hydroxyapatite (HA) powders were prepared by a chemical precipitation method and electrophoretically deposited on Ti6Al4V substrates. The powders were calcined before the deposition process in order to obtain crack-free coating surfaces. As an inner layer between Ti6Al4V substrate and HA coating, nanosized titanium dioxide (TiO 2 ) powders were deposited, using different coating voltages, in order to connect substrate and HA tightly. Moreover, this layer is considered to be acting as a diffusion barrier, reducing the HA decomposition due to ion migration from the metal substrate into the HA. After the sintering stage, adhesion strengths of coatings were measured by shear testing, phase changes were studied by X-ray diffraction, and coating morphology was analyzed through scanning electron microscopy observations. Results showed that usage of the TiO 2 inner layer prevented HA decomposition. Furthermore, decreasing the voltage used in TiO 2 deposition resulted in crack-free surfaces and increased adhesion strength of the overall coating.

Journal ArticleDOI
TL;DR: In this paper, the authors used high kinetic energy XPS (HIKE-XPS) on magnetron-sputtered nc-TiC/a-C thin films to show that this feature represents a third chemical environment in the nanocomposites, besides the carbide and the amorphous carbon.
Abstract: X-ray photoelectron spectroscopy (XPS) spectra of sputter-etched nc-TiC/a-C nanocomposite thin films published in literature show an extra feature of unknown origin in the C1s region. This feature is situated between the contributions of carbide and the carbon matrix. We have used high kinetic energy XPS (HIKE-XPS) on magnetron-sputtered nc-TiC/a-C thin films to show that this feature represents a third chemical environment in the nanocomposites, besides the carbide and the amorphous carbon. Our results show that component is present in as-deposited samples, and that the intensity is strongly enhanced by Ar+-ion etching. This third chemical environment may be due to interface or disorder effects. The implications of these observations on the XPS analysis of nanocomposites are discussed in the light of overlap problems for ternary carbon based systems.

Journal ArticleDOI
TL;DR: In this paper, the effect of laser power, traverse speed and wire feed rate on the weight and dimension of the deposited single tracks was investigated and the microstructure and hardness of the single tracks were examined.
Abstract: In this paper the deposition of Ti–6Al–4V wire with High Power Diode Laser was investigated by producing single tracks. The effect of the wire feeding direction and angle was firstly studied. The influence of laser power, traverse speed and wire feed rate on the weight and dimension of the deposited single tracks was then investigated. The microstructure and hardness of the single tracks were examined. Deposition with diode laser and wire was proved to provide a high deposition rate with good quality. Columnar grains were found in the deposits. Wire feeding orientation, laser power, traverse speed and wire feed rate were verified as factors which influenced the quality of the deposit. With similar energy level, different power/traverse speed produced deposits with different hardness value. Hardness values tended to increase from the deposit, via the re-melted zone till to the heat affected zone, and then decrease again when the measurements were taken in the unaffected base material.

Journal ArticleDOI
TL;DR: In this article, the physical and chemical phenomena occurring at flight of injected liquid droplet of solution and suspension are shown and related to the formation of coatings and their microstructure.
Abstract: Technology, microstructure and properties of nanostructured coatings obtained using different feedstock including: (i) powders composed of agglomerated nanocrystals; (ii) solutions; and (iii) suspensions are discussed. The methods of nanostructured coarse powders manufacturing are reviewed together with the problems related to formulation of solutions and suspensions. A particular attention is paid to the key problem at liquid feedstock spraying, namely to their delivery and injection into jets or flames. The physical and chemical phenomena occurring at flight of injected liquid droplet of solution and suspension are shown and related to the formation of coatings and their microstructure. Some microstructural, chemical, mechanical and electrical properties of coatings are collected and related to the operational processing parameters by regression equations derived from the design of spray experiments. Finally, the possible applications of nanostructured coatings are briefly discussed.

Journal ArticleDOI
TL;DR: In this article, the surface morphology and microstructure of the nickel matrix was significantly altered due to the presence of titania nanoparticles, and the Vickers microhardness showed a tendency to increase with the amount of particle incorporation.
Abstract: Nanocomposites containing titania nanoparticles in a nickel matrix have been prepared by means of electrocodeposition from two different types of nickel plating baths, viz. an acidic sulfamate and an alkaline pyrophosphate bath. The surface charge and sedimentation behavior of the titania particles in these electrolytes were characterized by zeta potential and stability measurements. A maximum particle incorporation of 4.3 wt.% titania was found for the alkaline pyrophosphate bath. The structure and mechanical properties of the coatings have been investigated as a function of the particle content. The surface morphology and microstructure of the nickel matrix was significantly altered due to the presence of titania nanoparticles. In the case of both nickel baths, the Vickers microhardness showed a tendency to increase with the amount of particle incorporation. The wear resistance increased with decreasing current density and due to the particle incorporation.

Journal ArticleDOI
TL;DR: In this paper, the influence of the substrate bias and deposition temperature on the coating structure and properties is investigated, and a good correlation between the residual stress and lattice constant under various deposition conditions is found.
Abstract: Nitride films are deposited from a single equiatomic AlCrMoSiTi target by reactive DC magnetron sputtering. The influence of the substrate bias and deposition temperature on the coating structure and properties are investigated. The bias is varied from 0 to − 200 V while maintaining a substrate temperature of 573 K. And the temperature is changed from 300 to 773 K whilst maintaining a substrate bias of − 100 V. From X-ray diffraction analysis, it is found that all the as-deposited coatings are of a single phase with NaCl-type FCC structure. This is attributed to the high mixing entropy of AlN, CrN, MoN, SiN, and TiN, and the limited diffusion kinetics during coating growth. Specific aspects of the coating, namely the grain size, lattice constant and compressive stress, are seen to be influenced more by substrate bias than deposition temperature. In fact, it is possible to classify the deposited films as large grained (~ 15 nm) with a reduced lattice constant (~ 4.15 A) and low compressive residual stresses for lower applied substrate biases, and as small grained (~ 4 nm) with an increased lattice constant (~ 4.25 A) and high compressive residual stresses for applied biases of − 100 V or more. A good correlation between the residual stress and lattice constant under various deposition conditions is found. For the coatings deposited at − 100 V, and at temperatures above 573 K, the hardness could attain to the range of 32 to 35 GPa. Even after annealing in vacuum at 1173 K for 5 h, there is no notable change in the as-deposited phase, grain size or lattice constant of the coatings but an increase in hardness. The thermal stability of microstructure is considered to be a result of the high mixing entropy and sluggish diffusion of these multi-component coatings. For the anneal hardening it is proposed that the overall bonding between target elements and nitrogen is enhanced by thermal energy during annealing.

Journal ArticleDOI
TL;DR: In this paper, the effect of current density on the grain size of electrodeposited nickel coatings was investigated by using X-ray diffraction analysis and modified Williamson-Hall relation.
Abstract: The aim of this work was to investigate the effect of current density on the grain size of electrodeposited nickel coatings. For this purpose, nanocrystalline nickel coatings were deposited from a Watts bath containing 5 g/l sodium saccharin as an additive, by direct current electroplating at different current densities. X-ray diffraction analysis and modified Williamson–Hall relation were used to determine the average grains size of the coatings. The experimental results showed that the coating grains size decreased sharply by increasing the current density from 10 mA/cm 2 to 75 mA/cm 2 . Nanocrystalline nickel coating with average grain size smaller than 30 nm can be achieved at the current densities higher than 50 mA/cm 2 . Furthermore, a general and simple theoretical model based on atomistic theory of electrocrystallization has been made in order to find out the relationship between the grain size and current density. According to this model the variation of log (d) versus log (i) was linear which is in accordance with experimental results for the current densities lower than 75 mA/cm 2 .

Journal ArticleDOI
TL;DR: In this article, the effects of ultrasonic impact peening and laser-shock peening without protective and confining media on microstructure, phase composition, microhardness and residual stresses in near-surface layers of an austenitic stainless steel AISI 321 are studied.
Abstract: The effects of ultrasonic impact peening (UIP) and laser-shock peening (LSP) without protective and confining media on microstructure, phase composition, microhardness and residual stresses in near-surface layers of an austenitic stainless steel AISI 321 are studied. An X-ray diffraction analysis shows both significant lines broadening and formation of strain-induced e- and α-martensite after UIP with additional peaks found near austenite ones in the low-angle part after LSP supposedly due to formation of a dislocation-cell structure in the surface layer. TEM studies demonstrate that a nano-grain structure containing either only austenitic grains with e-martensite (at strains up to 0.42) or both austenite and α-martensite grains (at higher strains) can form in the surface layer after UIP. Highly tangled and dense dislocation arrangements and even cell structures in fully austenitic grains are revealed both at the surface after LSP and in the layer at a depth of 80 μm after UIP. UIP is found to produce a sub-surface layer 10 times thicker and about 1.4 times harder than that formed by LSP. A mechanism of formation of the dislocation-cell structure in such steels (with a low stacking fault energy) is discussed. A nucleation process of α-martensite is discussed with respect to strain, strain rate, local heating and mechanical energy accumulated/applied to the surface layer under conditions of UIP and the LSP and compared to literature data for different loading schemes.

Journal ArticleDOI
TL;DR: In this article, sediment co-deposition (SCD) technique from a Watt's type electrolyte containing nano-Al2O3 particles was used to improve the corrosion and high temperature oxidation resistance of composite coatings.
Abstract: Ni–Al2O3 composite coatings were prepared by using sediment co-deposition (SCD) technique from a Watt's type electrolyte containing nano-Al2O3 particles. The corrosion resistance and high temperature oxidation resistance of resulting composite coatings were investigated. It was found that the incorporation of nano-Al2O3 particles in Ni matrix refined the Ni crystal and changed the preferential orientation of composite coatings. Meanwhile, the corrosion and oxidation resistance were improved after the incorporation of nano-Al2O3 particles into Ni matrix. The nano-Al2O3 content in deposits plays an important role for improving the corrosion and oxidation protection. The corrosion and oxidation resistance of Ni-Al2O3 nano-composite coatings produced via SCD technique are superior to that of CEP technique. Compared to pure Ni and Ni-Al2O3 composite coatings fabricated using CEP technique, the Ni–7.58 wt.% Al2O3 composite coating obtained by SCD technique exhibits better corrosion resistance and enhanced high temperature oxidation resistance. Moreover, the mechanism of corrosion and high temperature oxidation resistance of Ni–Al2O3 nano-composite coatings are discussed.

Journal ArticleDOI
TL;DR: In this paper, a nanocrystalline surface layer was fabricated on a 38CrMoAl steel plate by means of a surface mechanical attrition treatment (SMAT), and the average grain size in the top surface layer (10 pm thick) is about 10 nm, and the grain size stability can be maintained up to 450 degrees C. The results of the investigation showed that this new gas nitriding technique can effectively increase the hardness and wear resistance of the resulting surface layer in comparison with conventional gas n-riding, demonstrating a significant advancement for materials processing.
Abstract: A nanocrystalline surface layer was fabricated on a 38CrMoAl steel plate by means of a surface mechanical attrition treatment (SMAT). The average grain size in the top surface layer (10 pm thick) is about 10 nm, and the grain size stability can be maintained up to 450 degrees C. The effect of the surface nanocrystalline layer on the gas nitriding process at a lower temperature was investigated by using structural analysis and wear property measurements. The surface nanocrystallization evidently enhances nitricling kinetics and promotes the formation of an ultrafine polycrystalline compound layer. The results of the investigation showed that this new gas nitriding technique can effectively increase the hardness and wear resistance of the resulting surface layer in comparison with conventional nitriding, demonstrating a significant advancement for materials processing. (c) 2008 Elsevier B.V. All rights reserved.

Journal ArticleDOI
TL;DR: In this article, the effect of borohydride, thallium acetate, ethylenediamine and sodium hydroxide concentrations, and the coating bath temperature on both the coating rate and boron content of the electroless Ni-B films was investigated systematically.
Abstract: The effect of borohydride, thallium acetate, ethylenediamine and sodium hydroxide concentrations, and the coating bath temperature on both the coating rate and boron content of the electroless Ni–B films was investigated systematically. The Ni–B coating rate increased with the increase in thallium acetate and sodium hydroxide concentrations, but it was not very sensitive to the borohydride concentration. Below 90 g L − 1 ethylenediamine concentration the coating efficiency was significantly low and above this value as the ethylenediamine concentration increased the coating rate decreased slightly. Below 85 °C the coating rate was very low and above this temperature it was insensitive to the bath temperature. The boron content of Ni–B film increased with the increase in the borohydride concentration and the bath temperature, and decreased with the increase in thallium acetate and ethylenediamine concentrations. Up to 50 g L − 1 sodium hydroxide concentration, the boron content of the film increased and above this concentration it was insensitive to the sodium hydroxide concentration. As the boron content of Ni–B film increased, both the corrosion resistance and microhardness of Ni–B film increased. Heat treatment brought significant improvement in the microhardness but the corrosion resistance of Ni–B film was observed to decrease due to the disappearance of the amorphous characteristics of the as-deposited Ni–B film and the formation of the Ni–B compound phases.

Journal ArticleDOI
TL;DR: In this article, an attempt has been made to develop an amorphous coating with Fe 48 Cr 15 Mo 14 Y 2 C 15 B 6 bulk metallic glass on AISI 4140 substrate by laser surface processing.
Abstract: Fe-based bulk metallic glasses exhibit very high hardness, elastic modulus/limit and wear/corrosion resistance. In the present investigation, an attempt has been made to develop an amorphous coating with Fe 48 Cr 15 Mo 14 Y 2 C 15 B 6 bulk metallic glass on AISI 4140 substrate by laser surface processing. Following coating, the microstructure and phase aggregate were analyzed by scanning electron microscope and X-ray diffraction, respectively. Microhardness and wear resistance were assessed using Vickers microhardness tester and ball-on-plate wear testing machine, respectively. The coating thickness varied directly with incident laser power and interaction time. Despite trials with wide range of process parameters, the present experiments were unable to retain complete amorphous surface microstructure after laser surface coating. Numerical prediction of the thermal profile and related parameters suggest that the cooling rate and thermal gradient experienced by the coated zone were fairly high. Yet failure to retain amorphous/glassy microstructure of an otherwise bulk metallic glassy alloy suggests that compositional changes (solute redistribution) within the coated zone and across the coating–substrate interface are responsible for nucleation and growth of crystalline phases from the melt. However, correlation between coating parameters and surface microstructure and properties allowed determination of the optimum conditions that ensured fine grained uniform microstructure with a significant improvement in hardness and wear resistance.

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TL;DR: SPS and SPPS as mentioned in this paper can be classified into two categories: suspension plasma spraying and solution precursor plasma spraying, and they can be divided into two classes: SPS can process a suspension of sub-micrometric-sized or even nano-metric-sized solid particles dispersed in a solvent.
Abstract: The interest to manufacture on large surfaces thick (i.e., 10 to 20 μm, average thickness) finely structured or nano-structured layers is increasingly growing since about 10 years. This explains the interest for suspension plasma spraying (SPS) and solution precursor plasma spraying (SPPS), both allowing manufacturing finely structured layers of thicknesses varying between a few micrometers up to a few hundred of micrometers. SPS aims at processing a suspension of sub-micrometric-sized or even nano-metric-sized solid particles dispersed in a solvent. The liquid solvent permits to inject particles in the thermal flow (i.e., due to their size, a carrier gas cannot play this role). SPTS aims at processing a solution of precursors under the same conditions. Upon evaporation of the liquid, the precursor concentration increases until precipitation, pyrolysis and melting of small droplets. Compared to conventional plasma spraying, SPS and SPPS are by far more complex because fragmentation and vaporization of the liquid control the coating build-up mechanisms. Numerous studies are still necessary to reach a better understanding of involved phenomena and to further develop the technology, among which injection systems, suspension and solution optimizations, spray kinematics, etc. This review presents some recent developments in this field.

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TL;DR: In this paper, the authors present a survey of the design of experiments for thermal spraying and post-spray treatment of polyurethane polysilicon polyurethanylene glycol (PPGP) coatings.
Abstract: The designs of experiments (DOE) methodology useful for thermal spraying and associated processes of post-spray treatment are thoroughlyreviewed. The designs Hadamard (Plackett–Burman), two-level full and fractional factorial and also the response surfaces methodology arebriefly described. The designs enable to obtain a polynomial regression equation which expresses the influence of process parameters on theresponse. The methods of determining of the significant coefficients of the regression equation (factors) are discussed. Examples of the applicationof different designs to determine the response equations with the responses related to microstructure, mechanical, electrical and other propertiesofcoatings deposited using different thermal spray and post-spray processes are presented and discussed.© 2008 Elsevier B.V. All rights reserved. Keywords: Design of experiments; Parameters of thermal spraying processes 1. IntroductionThermal spraying is the family of coating depositionprocesses in which molten, semi-molten or solid particles aredeposited onto a substrate. The microstructure of the coatingsresults from their solidification and sintering [1]. The processesuse hot gas, flame or plasma to accelerate the particles and toheat them up. Obtained coatings have alamellar microstructure,which determines many of coatings properties. Since theoptimization of coatings properties for a given specificationneeds a careful control of the operational spray parameters andthe statistical methods can be useful in preparation of theexperiments. The initial step in the design of experiments is achoice of variables being process parameters. In the simplestcase, the parameters are fixed at low (−1) and high (+1) level.The experimental space is defined inside these parametersvalues. The choice of parameters needs some understanding ofthe processas thereare as many as 50processvariables[2].Thefirst group of variables is related to the feedstock and concerns,supposing powder feedstock, mainly [3]:• size distribution of powder;• powder feed rate;• powdermorphology,suchase.g.shape,internalporosity,etc.Typical variables for atmospheric plasma spraying are asfollows:• composition of working gas, such as e.g. vol.% of hydrogenin argon–hydrogen mixture;• spray distance;• powder feed rate;• electric power input;• carrier gas flow rate.For high velocity oxy-fuel spraying, it is useful to add alsoanother variable which is the ratio of fuel gas to oxygen [4]as well as other parameters for arc spraying, flame sprayingor cold gas spraying. Another problem concerns pre-spray(sand blasting) and post-spray treatment (laser glazing, hotisostatic pressing, infiltration…), which also is frequently

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TL;DR: SiC-reinforced Al-12Si alloy coatings were produced using the Cold Gas Dynamic Spraying process as mentioned in this paper, and the microstructural features of the resulting coatings are examined and the mechanical properties, in particular the adhesion strength and the hardness, of the composite coatings.
Abstract: SiC-reinforced Al–12Si alloy coatings were produced using the Cold Gas Dynamic Spraying process. Blends of several compositional variations of Al–12Si and SiC particles were created and subsequently sprayed. The microstructural features of the resulting coatings are examined and the mechanical properties, in particular the adhesion strength and the hardness, of the composite coatings are reported. The results show that, depending on the initial SiC volume fraction of the blend, between 50% and 33% of the SiC in the feedstock powder was retained in the coatings. The adhesion strength of the coatings to their substrates was found to slightly decrease with increasing SiC content while the inclusion of SiC particles within the Al–12Si matrix improved significantly the hardness of the coating.