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Hydroxyapatite (HAp) was deposited by plasma spraying technique with TiSiN adhesive interlayer on the medical-grade 316 LVM stainless steel. The surface topographies of HAp and HAp/TiSiN were evaluated using X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The important mechanical properties of the films such as hardness ($H$) and elastic modulus ($E$) were determined by the nanoindentation test. Lastly, the adhesion and anti-scratch behaviors of the films were evaluated by Rockwell-C indentation and nanoscratch test, respectively. The elemental analysis showed the values of Ca/P (at.%/at.%) ratio to be 1.80 and 1.59 in HAp and HAp/TiSiN coatings, respectively. The mechanical properties of HAp film with TiSiN interlayer were greatly improved from 1.23$\pm$0.26GPa to 10.6$\pm$1.12GPa for hardness and from 18$\pm$3GPa and 29.8$\pm$ 5GPa for elastic modulus, respectively. The results of the Rockwell-C indentation test showed a significant reduction in HAp coating delamination with TiSiN interlayer which can be categorized with HF2 or HF3 Daimler–Benz quality ranking. What is more, the nanoscratch profile of HAp coating showed wider scratch with evidence of deformation at the edges which got significantly reduced with the TiSiN interlayer. The results are suggestive of improved mechanical properties, viz. hardness and elastic modulus, and improved adhesion strength of HAp coating with TiSiN interlayer.

The effect of spraying power and immersion time on the microstructure and electrochemical corrosion behavior of plasma-sprayed Ni-5wt.%Al alloy coatings were studied. The spraying powers have a great influence on the electrochemical corrosion behavior of the coatings by affecting their surface roughness and porosity. The self-corrosion current density of the coatings was much lower when the surface roughness and porosity of the coatings were both lower. In addition, with the increase of immersion time, the self-corrosion current density of the coatings was decreased first, then increased, and finally decreased, which may be related to the formation and disappearance of Al₂O₃ in the coatings.

As the most favorable technology, plasma spray has been used to produce the hydroxyapatite (HA) coatings with the desired phase, high crystallinity, adequate porosity, and good biocompatibility. The characteristics of the HA coating are affected by many variables of the fabricating process, such as the starting particle size, spraying distance, gas flow rate, and electric arc power, etc. This paper reviews the effect of the plasma spraying parameters on the morphology and microstructure of the HA coating, and introduces several typical HA coatings fabricated with different plasma spraying parameters.

Ni-Al nanoparticles coating (NAN) was manufactured via atmospheric plasma spraying (APS) and thermal treated under hydrogen atmosphere at 1300${}^{\circ }$C (TNAN) remained 1 h, and NiAl microparticles coating (NAM) was manufactured as a reference. Nanoscale particles were observed in NAN by TEM, and these nanoscale particles disappeared in TNAN. Many pores and cracks were observed in NAM. Few pores and cracks were observed in NAN, and no pores and cracks were found in TNAN with SEM. A scanning electrochemical microscopy (SECM) testing in 3.5% (wt.) NaCl solution for 3 h revealed that NAM underwent several pitting corrosion, NAN pitting corrosion was relatively minor, and TNAN had no pitting corrosion.

Surface micro/nanotopography of orthopedic implants plays a significant role in determining their biological performance. In this study, plasma jet was for the first time utilized to modulate the micro/nanostructure of the plasma-sprayed 50% Nb₂O₅-TiO₂ coating on the biomedical Ti alloy based on its high temperature and super-high cooling rate characteristics. Results show that the plasma jet can modulate the shape, dimension and distribution of the surface grains in a process-parameter-dependent manner, thus being able to tailor the micro/nanotopography of the surface coating. In vitro cell culture experiments proved that the plasma jet-induced topographical changes have great effects on the osteogenic activity of the MC3T3-E1 cells cultured on the coating surface.

Various typical engineering components fail from surface under aggressive conditions like oxidation and hot corrosion. This paper is focused on the responsible failure mechanism of oxidation and hot corrosion. The surface properties like corrosion resistance can be enhanced by introducing a layer of Ni-based materials by using thermal coating techniques. The coatings developed by using processes like high velocity oxy-fuel, plasma spray and cold spray exhibits some surface defects like porosity, surface roughness and un-melted particles. Such defects can be further minimized by using optimization of process parameters and various heat treatment processes. The current study is restricted to the analysis of Ni-based coatings developed using high velocity oxy-fuel, plasma spray and cold spray process. In this paper, the optimization of various process parameters along with heat treatments has been discussed in regard to the tailoring of microstructure and the mechanical properties of the developed coatings.

Conventional and nanostructured zirconia coatings were deposited on In-738 Ni super alloy by atmospheric plasma spray technique. The hot corrosion resistance of the coatings was measured at 1050°C using an atmospheric electrical furnace and a fused mixture of vanadium pent oxide and sodium sulfate respectively. According to the experimental results nanostructured coatings showed a better hot corrosion resistance than conventional ones. The improved hot corrosion resistance could be explained by the change of structure to a dense and more packed structure in the nanocoating. The evaluation of mechanical properties by nano indentation method showed the hardness (H) and elastic modulus (E) of the YSZ coating increased substantially after hot corrosion.

An intermediate temperature solid oxide fuel cell (ITSOFC) based on 8YSZ electrolyte, La_0.6Sr_0.4CoO_3-δ (LSCo) cathode, and Ni-8YSZ anode were fabricated by atmospheric plasma spraying (APS) technique. The cell components i.e. anode, electrolyte and cathode were consecutively deposited onto a porous Ni-plate substrate. The results showed that the spray parameters played an important role in controlling microstructure and performance of the cell component coating. The spray parameters were investigated by an orthogonal experiment in order to prepare a thin gas-tight 8YSZ electrolyte layer. By proper selection of the spray parameters the sprayed NiO+8YSZ layer after reducing with hydrogen showed a good electrocatalytic activity for H₂ oxidation. With the similar treatment, the deposited LSCo cathode showed a good cathode performance and chemical compatibility with 8YSZ electrolyte. Output power density of the APS fabricated cell achieved 410 mW/cm² at 850□ and 260 mW/cm² at 800□. The main factors affecting the cell performance were discussed. Electrochemical characterization indicated that IR drop of 8YSZ electrolyte, cathodic polarization, and the contact resistance at LSCo/8YSZ interface were the main factors restricting the cell performance.

Mechanical evaluations of plasma sprayed HA coatings have assumed vast importance in the orthopaedic applications where the demands of operational stresses of the coatings are stringently required. The determination of the mechanical properties such as Knoop hardness, elastic modulus, fracture toughness and bond strength are therefore essential and necessary for the assessment of the service behaviour and performance of the bioceramic coatings. The inherent properties of the coatings have been investigated and were found to have direct and impacting relationship with the feedstock characteristics, processing conditions as well as microstructural deformities. The presence of inter- and intralamellar thermal microcracks, voids and porosities with limited true contact between lamellae were found to degrade the mechanical characteristics of the coatings.

This paper aims to provide an insight to the mechanical properties of the HA coatings by plasma spray process, and the effect of microstructural defects on the resultant mechanical and structural integrity of the coatings. The elastic response behaviour and fracture toughness of both the as-sprayed and heat-treated HA coatings using Knoop and Vickers indentations at different loadings have been investigated. Results have shown that the mechanical properties (hardness, modulus, fracture toughness and bond strength) of the coatings have improved significantly despite increasing crack density after heat treatment. These properties were also found to deteriorate with increasing spray distance and particle size.

Plasma spraying of hydroxyapatite coatings onto titanium alloy implants is a standard procedure that is widely used in medical technology. However, the adhesive strength to substrate of such coatings is generally insufficient. Adhesion of these coatings to the substrate is considered being dominated by mechanical attachment to rough surface rather than by chemical bonding between the substrate and coating. This paper presents investigations into influencing factors of the sand-blasting process on the surface roughness of substrate. The most important factors were found to be sand size, followed by air pressure, sand type, and blasting time. The surface texture parameters and surface profiles were measured using a Talysurf 120L machine interfaced with a PC and equipped with the surface texture analysis software. The relationship between surface roughness and adhesion of the HA coating was investigated. Residual stress in plasma-sprayed coatings has been an inherent problem caused by the large difference in the coefficient of thermal expansion (CTE) between the coating and substrate materials coupled with the high cooling rate. The cooling rate may be decreased by the substrate roughness. The performance of the coating was highly related to the residual stress. An X-ray diffraction (XRD) technique was applied to measure the residual stresses in HA coatings, which had been plasma-sprayed on substrates with different surface roughness. It is shown that substrate surface roughness has effect on not only mechanical attachment of the coating but also the residual stress in the coating.

Bioactive glasses promise several advantages in orthopaedic applications, in particular as coating material of metallic substrates. The bioactivity of the glasses is linked to their capability of producing an intense effect on bone tissue through the formation of a surface reaction layer. In this work the AP40 bioactive glass-ceramic was deposited by plasma spray on sand-blasted Ti-6A1-4V substrates. In order to investigate the bone-bonding mechanism of this glassy material, a study of the surface structural changes of the deposited layer after exposure to simulated body fluid (SBF) is reported.

A series of instrumental investigations were carried out on the powders of the biological glass, on the deposited layers and on the coatings after 5, 20, 25 and 30 days of immersion in SBF. X-ray diffraction (XRD) both in thin film (GID) and in Bragg-Brentano (θ-2θ) configuration, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were utilised mainly to verify the crystallographic and compositional transformations with time. θ-2θ XRD spectra show that the glassy layer contains a crystalline phase of hydroxylapatite, which increases after the immersion in the physiological media. At the same time the GID analyses showed a reduction of the thickness of the coating.