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Plasma-sprayed YSZ coatings have been widely employed as thermal insulation coatings in gas turbine for its low thermal conductivity. Thermal conductivity of ceramic coatings is closely related to coating microstructure. In the present study, YSZ coating was deposited on a stainless steel by atmospheric plasma spraying using a fuse-crushed 8wt.%Y₂O₃-stablized ZrO₂ powder at different spray distances from 70 mm and 100 mm. The microstructure of YSZ coatings was quantitatively characterized through visualization of lamellar structure assisted by electroplating Ni and subsequent EDX line analysis. The thermal conductivity of YSZ coatings with different microstructures was tested by a laser flash technique. Results showed that the mean lamellar bonding ratio was 32% and almost kept unchanged for the coatings deposited at 70 mm and 85 mm and it was reduced by 25% when distance was increased to 100 mm. The thermal conductivity of the coatings largely depended on the mean bonding ratio between lamellae and increased with the bonding ratio.

The durability and reliability of thermal barrier coatings(TBCs) have become a major concern of hot-section components due to lack of a reliable life prediction model. In this paper, it is found that the failure location of TBCs is at the TBC/TGO interface by a sequence of crack propagation and coalescence process. The critical crack length of failure samples is 8.8mm. The crack propagation rate is 3-10µm/cycle at the beginning and increases largely to 40µm/cycle near coating failure. A life prediction model based a simple fracture mechanics approach is proposed.

A Mo(Si,Al)₂ coating is developed to protect Nb_ss/Nb₅Si₃ in situ composite by plasma spraying. The binary layers of this coating consist of an inner interdiffusion layer surrounded by Mo(Si,Al)₂ layer with C40 crystal structure. After oxidation at 1250°C for 100h, Mo(Si,Al)₂ coating exhibited an excellent protection against oxidation and good adherence to substrate. The oxidation curve followed parabolic law and even after oxidation at high temperature for 100h, the weight gain per unit area of Mo(Si,Al)₂ coating is 8.24mg/cm². No evident spalling of coating to substrate was observed but a continuous and compact layer of Al₂O₃ was formed on coating surface to prevent oxidation below coating and substrate.

The starting nano-TiO₂ feedstock was agglomerated by spray-drying process. Nano-TiO₂ coatings on transparent glasses were prepared by atmospheric plasma spraying (APS). The variation of the anatase content, porosity and grain size with the arc current is investigated extensively. Result shows that the nano-TiO₂ phase is composed of anatase and rutile phase. The content of anatase in the sprayed coatings decreased and the grain size increased with the arc current increasing, and the porosity first increased and then decreased. As-sprayed nano-TiO₂ coatings obtained at the spraying current of 400 A have the best photocatalytic property due to the synergistic effect of the fractions of anatase phase and the rate of porosity.

The life time and quality of thermal spray coatings are strongly influenced by the technological parameters of the coating process and characteristics of the coated surface. In this paper, 16Mn steel substrates of different surface roughness are coated by Cr₃C₂-NiCr using a plasma spray technique. The adhesion of the coating to the substrate has been studied in relation to the roughness of the substrate and the plasma current of the spraying process. The results showed that the adhesion of the Cr₃C₂-NiCr coating to 16Mn steel substrate is strongly influenced by the roughness and the current intensity. The range of substrate surface roughness and current intensity at which the Cr₃C₂-NiCr exhibited high adhesion to the steel substrate are discussed in this paper.

Thermal barrier coatings of Al₂O₃–ZrO₂ were prepared by air plasma spraying on the surface of 20G steel. Phase constitution, microstructures and elemental distributions of the coatings were studied by X-ray diffraction, scanning electron microscope and electron probe X-ray microanalysis. The results show that the plasma spray coating mainly consists of α-Al₂O₃, c-ZrO₂, and t-ZrO₂. The bond state of the interface between the top layer and bond layer is fine, and the bond layer has a good combination with the substrate. ZrO₂ and Al₂O₃ structures can closely integrate together and form compact top layer system.

The low bonding strength between plasma sprayed hydroxyapatite (HA) coatings and substrates is one of the problems, which should be solved. In this paper, the as-sprayed HA coatings were retreated by laser remelting. The microstructure and element analysis in coatings were studied by electron probe microanalyzer (EPMA) and the accessory of energy spectrum analyzer. The results show that the bonding state can be improved greatly after laser remelting and it is a metallurgical combination between transition layers and substrates. Generally, with the increase of laser power and the decrease of scanning speed, the bonding state between the surface and transition layer will be improved much more, but the value of Ca/P ratio will deviate much more from 1.67. In this experiment, the optimum technological parameter is that the laser power is 600 W and the scanning speed is 11.2 mm/s.

Two types of hydroxyapatite (HA) coatings onto carbon/carbon composite (C/C composites) substrates, deposited by plasma spraying technique, were immersed in a simulated body fluid (SBF) in order to determine their behavior in conditions similar to the human blood plasma. Calcium ion concentration, pH value, microstructure, and phase compositions were analyzed. Results demonstrated that both the crystal Ca–P phases or the amorphous HA do dissolve slightly, and the dissolution of CaO phases in SBF was evident after 1 day of soaking. The calcium-ion concentration was decreased and the pH value of SBF was increased with the increasing of the immersing time. The precipitation was mainly composed of HA, which was verified by X-ray diffraction (XRD) and electron-probe microanalyzer.

Thermal barrier coatings (TBCs) is one of the main key technology for the high-pressure turbine blades which are the main components of the high-performance aerospace engines. It offers protection for underline metallic components from corrosion, oxidation and localized melting by insulating the metal from hot gases in the engine core. The properties and lifetime of TBCs are greatly influenced by the preparation technology, which includes plasma spraying (PS), physical vapor deposition (PVD) and laser re-melting (LM). In this paper, three technologies used to prepare the TBCs are reviewed. Resulting features of coating fabricated by each technology are also discussed such as: the porosity, the thermally grown oxide (TGO), the erosion resistance, the thermal shock and so on. Especially, it is pointed out that the performances of gradient coating and nano-coating are better than the traditional coatings. In addition, it is widely accepted that laser can be applied to re-melt the PS coating and even directly clad the gradient coating. In the future, the traditional preparation technology should be improved continually in order to enhance the coating lifetime, enhance the properties of coating and lower the cost of process. Moreover, the researches on gradient-nano-structured coatings preparation are absent and should be done with emphasis since the nano-structure and gradient structure can both benefit the lifetime and properties of coatings.

In this study, the tribological properties of Cr₂O₃–40% TiO₂ coating for brake disc materials were investigated in braking performances. Plasma spraying technique was used in order to deposit coating materials onto cast iron disc with ventilation channels substrate. The braking performances of discs were tested according to SAE J2430 test standard. Microstructures of discs were characterized by means of light microscope (LM), scanning electron microscope (SEM) and energy-dispersive spectrometry (EDS). The surface hardness and roughness were measured with testers. In general, it is noted from the LM and SEM images that there was an infinite gradation between coating layer, binding material and the lamellar graphite cast iron and that bonding resistance was excellent. The coated disc exhibited less wear, approximately the same coefficient of friction and longer life than the uncoated disc. As a result, the coated disc could be a much better alternative for new-generation brake discs in the motor vehicles than the uncoated disc.

To improve hydroxapatite (HA) coatings on the titanium substrate, HA/Ti composite was formed on substrates using Radio-frequency (RF) plasma spraying process, as this composite layer may reduce the residual stress due to the large difference in the liner thermal expansion coefficient between the substrate and HA. HA/Ti composite was prepared by controlled feeding of HA and Ti powder, as the composition of coatings becomes HA-rich toward the outmost. Coating layer was evaluated by SEM-EDX, XRD and tensile testing. Orientation in c-axis direction of prepared coatings was observed from X-ray diffraction patterns. HA/Ti composite coating gave a higher adhesive (tensile) strength over 10 MPa than direct HA coatings on substrate.