Plasma-sprayed ceramic coatings are deposited such that flattened splats together with some nonmelted particles are present in the coatings. In this study, the nonmelted particles in plasma-sprayed alumina coatings were examined by scanning electron microscopy, confocal Raman analysis, and X-ray diffraction analysis with the aim of quantitative evaluation of the coating microstructure. Results showed that the nonmelted particles can be clearly identified from the cross-sectional microstructure due to the morphology that results from the high hardness of the nonmelted particles. The obvious gap at the interface between nonmelted particles and the surrounding splats suggests weak interface bonding. Raman analysis revealed that there was little α-Al 2 O 3 phase in the flattened splats region, which confirms that this phase in the coating appears only from nonmelted particles. Attention should be paid to the weak bonding of the nonmelted particles relative to the flattened splats during the preparation of samples for quantitative characterization of coating microstructure.

Ceramic coatings are applied in mechanical components subject to high temperature conditions, normally are deposited by plasma thermal spraying process. In this work, the porosity of YSZ ceramic coatings, deposited with different parameters conditions were analyzed by optical microscopy, scanning electron microscopy using back-scatter electron (SEM-BSE) detector and ultrasonic technique. It was verified that porosity measurement by optical and scanning electron microscopy is very sensitive with respect to metallographic preparation, mainly cutting process, and gray level adjustment. SEM-BSE technique showed less scatter results with easier porosity visualization, compared with optical microscopy. The porosity of the coatings was also measured by ultrasonic technique. It was observed that the ultrasonic velocity increase with porosity reduction. Ultrasound technique showed a good correlation with OM and SEM porosity measurement.

Nanostructured and conventional Alumina–13wt.% Titania powders were thermally sprayed using air plasma spray(APS) process. Scanning electron microscopy (SEM) was used to examine the morphology of the agglomerated powders and the cross section of the alumina-titania coatings. The microstructure and phase composition of the coatings were characterized by X-ray diffraction (XRD), and scanning electron microscopy (SEM).The fatigue and mechanical properties of the coatings were investigated. SEM analyses were also carried out on the fracture surfaces of fatigue-tested samples to assess the mechanisms of deformations. The experimental data indicated that the nanostructured coated samples exhibited higher stiffness, hardness, and fatigue strength compared to the conventional coated samples.

Porous materials possess many unique properties. Many processes have been employed to fabricate porous materials. Recently, it was found that a porous deposit can be created through controlling the deposition of semi-molten spray powder particles. In this study, porous 316L stainless steel deposits were prepared by flame spraying under different spray conditions to aim at controlling deposit porosity. During deposition the temperature of the substrate and/or deposit surface was kept at 600°C to ensure bonding formation between the spray particle and underlying particle. To understand the deposition process mechanism, the velocity of spray particles was quantitatively measured and the morphology of deposited isolated particles was characterized by scanning electron microscopy to estimate the melting degree of spray particles before impact. The microstructure of porous 316L stainless steel deposits was characterized by scanning electron microscopy and deposit porosity was estimated from its cross section by image analysis. It was found that pores were uniformly distributed in the deposit. The results showed that porosity of the 316L deposits changed from 20% to 50% with the change of spray particle melting degrees, resulting from the change of spray parameters. The examination showed that 3D through-deposit pore-net structure was created by viscoplastic flowing of the molten fraction of semi-molten particles which forms the bonding between necks of particles. The present results clearly demonstrated that a porous ferrous alloy based material can be formed by spray deposition through controlling the melting degree of spray particles.

In this study, Fe-based amorphous/nanocrystalline coatings with a composition of Fe 53 Cr 19 Zr 7 Mo 2 C 18 Si have been fabricated by high velocity oxygen fuel (HVOF) spray. Postspray annealing treatment at 750°C was employed to enhance the amorphicity of the as-sprayed coatings. The microstructure, corrosion resistance and algal adhesion behaviors of the as-sprayed and annealed coatings were characterized by scanning electron microscopy, transmission electron microscopy, laser confocal scanning microscopy, X-ray diffraction and electrochemical methods. Results show that the as-sprayed coatings exhibited excellent corrosion resistance and decreased algal adhesion, while the annealed coatings exhibited compromised anticorrosion performance but significantly reduced adhesion of algae.

In order to clarify the bonding mechanism and to control the quality of cold-sprayed coatings, it is necessary to accurately measure the in-flight velocity and impact velocity of a projectile. In this study, the in-flight velocity of an aluminum alloy (A2017) 1 mm sphere shot from a small two-stage light gas gun was measured as being 1 km/s using a laser-cut velocity measurement technique. So as to estimate the impact velocity of the projectile, the projectile was caused to impact targets made of aluminum (A1050), copper (C1012), mild steel (SPCC), and stainless steel (SUS304). After the impact tests, the impact crater shapes of the targets was measured using scanning electron microscopy(SEM), energy dispersive X-ray spectroscopy (EDS), and laser microscopy. The impact velocity of a projectile was estimated from obtained crater depth of the targets. In addition, microstructures of the interface between projectile and target were analyzed by EDS, electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM).

In the present study, the zinc powder (-48 µm) was used to deposit coating by cold spraying using nitrogen as driving gas at different operating temperatures. The microstructure of the deposited coating was characterized by optical microscopy, scanning electron microscopy and transmission electron microscopy (TEM) to reveal the occurrence of fusion during the impacting of spray particles. The selected area electron diffraction analysis was used to examine the microstructural feature at the near interface areas between the deposited particles in zinc coating. Numerical simulation was carried out to estimate the particle temperature increment during the impacting process. The simulation result suggests a possibility of the melting of zinc particles at the localized contact region on impact. The examination of the coating surface provided the evidence for the occurrence of the melting of spray particles on impact. The experimental results showed that the cold-sprayed zinc coating presented a dense microstructure. The nano-structural phase was formed at the near interface areas between deposited particles in zinc coating, while the grains in the size of micrometers similar to that in the powder were retained in the inside of the particles in the coating. Moreover, the TEM observation evidently showed that the amorphous phase was formed at the interface areas between the particles. It can be considered that the amorphous phase in the coating was formed through subsequent rapid solidification of the melted material on impact. This fact provided further evidence to the occurrence of localized melting during impacting of spray particles.

The present paper describes the synthesis of nanocrystalline 316-stainless steel coatings by high velocity oxy-fuel (HVOF) thermal spraying. The feedstock powders were synthesized by mechanical milling to produce flake-shaped agglomerates with an average grain size of less than 100 nm. The powders were introduced into the HVOF spray to successfully produce nanocrystalline coatings. X-ray diffraction analysis and transmission electron microscopy were used to determine the average grain size of the milled powders. Scanning electron microscopy and transmission electron microscopy were used to study the morphology of the nanometric particles and the microstructure of the as-sprayed coatings. The properties of various coating materials were characterized by microhardness measurements performed on the polished surface of the cross section.

The corrosion characteristics of two bespoke Ni-Cr-Mo-B alloy powders sprayed by the high velocity oxy-fuel (HVOF) process have been studied using potentiodynamic and potentiostatic corrosion analysis in 0.5M H2SO4. The deposits have also been microstructurally characterised using X-ray diffraction (XRD), scanning electron microscopy (utilising both secondary electron (SE) and backscattered electron (BE) modes), and transmission electron microscopy (TEM). Results from the microstructural examination of the two alloys have revealed a predominantly amorphous/nanocrystalline (fcc) matrix containing submicron boride precipitates as well as regions of martensitically transformed laths. Apparent recrystallisation of the amorphous matrix has also been observed in the form of cellular crystals with an fcc structure. The oxide stringers observed at splat boundaries were found to be columnar grained α-Cr 2 O 3 , though regions of the spinel oxide NiCr 2 O 4 with a globular morphology were also observed. The coatings of the two alloys exhibited comparable resistance to corrosion in 0.5M H 2 SO 4 , as revealed by potentiodynamic tests. They both had rest potentials approximately equal to -300mV(SCE) and passive region current densities of around 1mAcm-2. Microstructural examination of samples tested potentiostatically revealed the prevalence of degradation at splat boundaries, especially those where significant oxidation of the deposit had occurred.

The low temperature characteristic of cold spraying makes it possible to deposit the coating of temperature sensitive materials, such as nanostructured material, without any significant change in the microstructure of feedstock. In the present study, the Fe and Si powders of particle size less than 75 µm were mixed at a composition of 10wt%Si and ball-milled to produce the nanostructured feedstock. Cold spraying process was used to deposit coating with nitrogen as a driving gas at different temperatures. The microstructure of the as-sprayed nanostructured Fe-Si coating was characterized using optical microscopy, scanning electron microscopy and transmission electron microscopy (TEM). The grain sizes of the feedstock and as-sprayed coating were estimated based on X-ray diffraction analysis. The results showed that the nanostructured Fe-Si coating can be deposited by cold spraying using the ball-milled powders as feedstock. The as-sprayed coating presented a dense microstructure. The average grain size of the as-sprayed coating was comparable to that of the corresponding milled feedstock. No significant effect of the temperature of driving gas on the microstructure of cold-sprayed nanostructured Fe-Si coating was recognized. Moreover, TEM analysis showed that the amorphous phase was present in the as-milled powders and the as-sprayed coating along with the nanocrystalline.

The technology and thermal shock properties and thermal conductivity of plasma sprayed nanostructured yttria-stabilized zirconia thermal barrier coatings (TBCs) are studied in this paper. The TBCs on the substrate of Ni 3 Al based alloy IC-10 were fabricated by using the nanostructured yttria-stabilized zirconia powder under certain plasma spraying conditions. By manipulating the plasma spray process, nanostructured TBCs were obtained. The specimens were thermally shocked from 1000°C, 1100 °C and 1200°C into 20°C water and the morphology and microstructure of the TBCs were evaluated by light microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The thermal diffusivity was tested by a laser pulse method. The results showed that the nanostructured TBCs had more than 30% reduction in thermal conductivity and the thermal shock lifetimes were much longer than that of the conventional TBCs.

In this study, a ZrO 2 – 7 % Y 2 O 3 (YSZ) powder (-90 +16 µm) was nanostructured by high energy ball milling and sprayed using a modern three-cathode plasma generator TriplexPro- 210 as well as a conventional plasma generator F4MB-XL. The parameters were varied in order to investigate their influence on build-up, microstructure and properties of the thermal barrier coatings (TBC). Powders and coatings were characterized in terms of their morphology, microstructure and phase composition by means of light microscopy (LM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray analysis (XRD). Thermo-shock behavior of TBC was evaluated using thermal cyclic tests at 1300 °C and 1150 °C. The results show that the milled powder contained nano-sized particles. TBC from the nanostructured powder by TriplexPro-210 had high porosities and numerous fine pores, leading to lower microhardness and higher thermos-shock resistance than the reference TBC.

The adhesion mechanisms involved in the cold spray coatings are not still well elucidated. The quality of the deposit does depend mainly on particles and dynamic characteristics (which result from nozzle type, nozzle-substrate distance, etc.). The present work is based on the study of particle-substrate and particle-particle interfaces in the tantalum-copper coating-substrate system. The content focuses on the influence of the oxygen content in the starting powder on interface features, consequently on coating properties. Tantalum powders with different oxygen levels were studied using SEM (Scanning Electron Microscopy) and EPMA (Electron Probe Microanalysis). Laser shock spallation of cold-sprayed Ta coatings was developed as a reliable and flexible process to achieve Ta spalls to be deposited at a high-velocity onto Cu targets. The velocity due to the laser shock could be controlled to be similar to that of particles in conventional cold spray. This results in Ta-Cu interfaces, the study of which was carried out to go into interface phenomena involved in cold spray, using TEM (Transmission Electron Microscopy) in particular. Results were compared to those obtained from laser shock spallation of Ta bulk specimens (i.e. made of a conventional Ta sheet). The role of powder oxidation on interface soundness was exhibited. Adhesion was shown to be all the lower as powder oxygen content was higher, using LASAT (“ Laser Shock Adhesion Test”) in addition to direct observation of interfaces. Results were exploited to discuss properties of the corresponding Ta coatings onto Cu, i.e. which were cold sprayed using powders with different oxygen contents.

This paper deals with a comprehensive evaluation of the laser glazing or re-melting route as a possible means of specifically enhancing the performance of thermal sprayed WC-Co coatings. In the present study, a high-power continuous-wave 9kW CO 2 laser was utilized for laser treatment of plasma sprayed as well as detonation sprayed WC-Co coatings. The influence of the two most important laser-related variables, namely laser power and scan speed, on the properties of the laser-treated layers was investigated. Both mere surface densification by melting a thin top layer of the coating as well as melting of the entire portion of the coated layer were targeted during laser treatment. In each case, the laser treated coatings were fully characterized by optical microscopy, scanning electron microscopy, and microhardness measurements. In addition, the influence of laser processing on the elemental distribution, phase constitution and extent of defects in the treated layers was investigated. The tribological performance of the laser-glazed coatings was also evaluated and compared against the performance of their as-sprayed counterparts. The study has revealed significant differences between the response of plasma and detonation sprayed WC-Co layers when subjected to laser treatment. The potential of plasma-sprayed coatings to match the performance of the inherently superior detonation sprayed coatings by adopting laser glazing as a post-processing step has also been assessed.

Aerosol deposition (AD) is a novel method for producing dense nanocrystalline ceramic films at room temperature. Previous studies primarily used flat substrates with varying hardness and roughness. However, the development of micro-device applications is increasing the demand for deposition on structured/patterned surfaces. To investigate the impact of substrate patterns on coating microstructure and growth mechanisms in AD, alumina coatings were deposited on patterned Si substrates. Si wafers with patterns of micropillars were employed. The coatings were characterized using laser scanning microscopy, scanning electron microscopy, and x-ray diffraction. The microstructure and density of coatings in the valleys were influenced by the size of and the spacing between the patterns. The results revealed that coatings initially formed in the valleys before covering the entire pattern. Fragments of the initial powder particles became trapped between the patterns, adhering to the groove bottoms and pillar sides. Subsequent particle impacts and densification processes transformed these fragments, ultimately filling the gaps between the walls. With further deposition, a uniform coating surface was achieved.

The performance and applicability of thermal barrier coatings (TBCs) depend strongly on the top coat and bond coat interface integrity. The interlayer in TBC systems is often processed prior to top coat spraying to tailor its material properties or surface topography. Both, the bond coat spraying process and the further post-processing may significantly influence the thermally grown oxide (TGO) build-up which is crucial in terms of enhancing the TBC lifetime. In this work, NiCrAlY bond coats were sprayed by means of atmospheric plasma spraying. The as-sprayed bond coats were subjected to laser microtexturing which resulted in different bond coat topographies. Then, the samples were exposed to isothermal oxidation conditions under various oxidation dwell times to see the TGO evolution. The preliminary assessment of the oxidation mechanisms and oxide distribution was done by confocal laser scanning microscopy (CLSM). Scanning electron microscopy with energy dispersive X-Ray spectrometry (SEM/EDS) was used in order to analyze the evolution of bond coat structure and chemical composition during the high temperature oxidation.

A new approach is explored to achieve the aluminum alloy powder layer from nanoparticle contained metallic powder mixture feedstock by Low Pressure Gas Dynamic Spray (LPGDS) or Cold Spray (LPCS). In this approach, mixtures of micron-sized aluminum powder (average size of 10 µm) and alloying nano-powder of Cu, Si and TiC (200-500 nm), at appropriate proportions to compositions of Al-5wt%Cu, Al-5wt%Cu-0.75wt%Si and Al- 5wt%Cu-5wt%TiC with polymer binder were prepared by stirring. Then, the powder mixture was compacted into pellets, dryed, and further milled to obtain the particle agglomerates (average size of 50 µm) . The powder feedstock were sprayed by LPCS. In this paper, we investigate the spraying behavior Al-based nanoparticle contained powder mixtures the microstructural development and mechanical properties of deposited layers using a microindentation, scanning probe microscopy, scanning electron microscopy and energy dispersive X-ray analysis.

Monocrystalline lithium fluoride (LiF) windows are used in mineral physics research. Optical Pyrometric Measurements (OPM) during shock tests are done through LiF windows on which a few mm thick plates of tested materials are fixed. Current OPM requires the plates to be glued on the LiF windows. However, this glue is an undetermined source of error for OPM. This study deals with plasma spraying to deposit a tin coating directly on to the polished LiF windows as a substitute to the plate/glue/LiF system. Although seldom used for low melting point materials, plasma spraying was shown to be the appropriate technique for this original material couple and application especially for its flexibility. The study confirmed the feasibility of plasma spraying of tin on polished surfaces of LiF windows. Scanning electron microscopy (SEM), electron probe micro-analysis (EPMA), hydrostatic weigh measurements (HWM), optical and confocal microscopy were used to characterize the coating and substrate.

This paper describes the manufacture of a new ceramic coating system based on Al 2 O 3 /SiC nanocomposite powder prepared by sol-gel processing followed by low pressure plasma spraying (LPPS) onto stainless steel substrates. In order to produce nanocomposite coatings of good adhesion and low porosity, the substrates were water-cooled to minimise thermal stresses associated with coefficient of thermal expansion mismatch and a CoNiCrAlY bond coat was used. The sol-gel powder feedstock and the as-sprayed coatings have been characterised by a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), and Nuclear Magnetic Resonance (NMR). The coating characteristics were compared with a reference Al 2 O 3 coating prepared from commercial feedstock powder. The thermal exposure of the sol-gel powder during spraying caused phase-changes and phase-decomposition. Examination of the sprayed coatings showed that it was possible to maintain the 20-200 nm SiC particles in the final Al 2 O 3 /SiC nanocomposite coating. The coatings also contained both stable α-Al 2 O 3 and metastable γ-Al 2 O 3 . Some minority phases such as silica and aluminosilicate formed in the sol-gel feedstock powder were fully decomposed during LPPS. This preliminary study indicates that sol-gel and LPPS processing is a potential route for the manufacture of nanocomposite coatings, which may offer significant improvements in some aspects of coating properties.

Ni powders prepared by mechanical milling under liquid nitrogen for 15 hr were sprayed using two stoichiometric ratios of the oxygen-fuel mixture in an effort to promote the formation of fine oxide phases. The oxide phases were introduced in an effort to improve mechanical properties and thermal stability of the coatings, via chemical reaction between oxygen and milled powders during flight and after impingement. The microstructure and properties of the milled powders and as-sprayed coatings were characterized by scanning electron microscopy, transmission electron microscopy and nanoindentation. The average grain size of the milled powders was 15.7 ± 5.1 run and ultrafine NiO and Ni 3 N particles with a size less than 5 run were distributed in the milled powders. These fine oxide and particles distributed in the powders were formed as a result of interaction between Ni, N from the milling slurry, and O from the surrounding environment under the energetic milling conditions. The coating microstructure was composed of nanocrystalline grains with an average grain size of 92.5 + 41.6 nm and extremely fine NiO particles of ~5 nm distributed homogeneously inside the grains. Ni 3 N phase was not found in the coating as it appears to have decomposed during HVOF thermal spraying. The coating sprayed with higher oxygen fraction in a hydrogen-oxygen mixture showed no significant increase in hardness and elastic modulus when compared to those of the coating sprayed with lower oxygen fraction in hydrogen-oxygen mixture. This was attributed to the small difference in the volume fraction of NiO particles between the coatings. These results indicate that new techniques of ultrafine dispersoid introduction in nanocrystalline coatings are potentially attractive as a means to improve the mechanical properties of the coating through reactive HVOF spraying.