Thermal insulation performance is a measurement of the thermal protection offered by the thermal barrier coatings (TBCs) to the substrate, therefore, it is essentially important to compare different double ceramic layer (DCL) TBCs on the premise of the same thermal resistance. In this study, a series of LZO/YSZ DCL-TBCs, with the equivalent thermal insulation to 500 µm thick YSZ TBCs, were prepared, and their lifetimes were evaluated by thermal gradient cyclic test at the top coat surface temperature of 1300°C. Result show that, the lifetime of DCL-TBCs was more than doubled compared to 500 µm thick YSZ TBCs, when 100µm thick YSZ coating was substituted by LZO coating. In addition, the lifetime of DCL-TBCs decreased with the increase of LZO substitutional ratio. X-ray diffraction analysis revealed that LZO maintains the pyrochlore structure after thermal cyclic test. Microstructure examination demonstrated that, with the increase of LZO substitutional ratio, the delamination position transferred from near top/bond coating interface to near LZO/YSZ interface and finally to the inside of LZO coating. Therefore, this study would shed light to further coating structure optimization towards the next generation advanced DCL-TBCs.

The non-parabolic isothermal oxidation kinetics of low pressure plasma sprayed MCrAlY bond coat was investigated. To qualitatively explain the abnormal growth phenomenon of thermally grown oxides (TGO), the changes that occurred to their microstructure during the oxidation process were studied. Based on these observations, a modified model was developed to understand and quantitatively predict the non-parabolic oxidation and growth kinetics of TGO. This modified model, which fits well with experimental results, provides a novel method to quantitatively predict the long-term growth behaviour of TGO, and thereby benefits the development of long-life and highly reliable thermal barrier coatings.

Thermal cycle lifetime is essentially important to the application of thermal barrier coatings (TBCs) on the premise of the same thermal resistance. In this study, equivalent thermal insulation conception is introduced to the design of dense vertical crack (DVC) structured TBCs and the lamellar structured TBCs, to fairly compare the lifetime of TBCs with different structure. DVC-structured TBCs with the equivalent thermal insulation to lamellar YSZ TBCs were prepared, and their lifetimes were evaluated by thermal gradient cyclic test. Cross-sectional morphology and phase constitution before and after failure were examined by scanning electron microscope and X-ray diffraction, respectively. The failure mode was analysed. This study would shed light to further coating structure optimization.

Inter-lamellae bonding within thermal sprayed coatings is one of the most important factors influencing the properties and performance of coatings. It has been revealed that there exists a critical bonding temperature for a molten ceramic splat to form the bonding to the same splat surface. The erosion behaviors of thermal sprayed coatings are significantly influenced by the interface bonding between lamellae. In this study, the erosion behavior of plasma-sprayed TiO 2 , Al 2 O 3 and YSZ coatings deposited at different deposition temperatures was investigated. The cross section of plasma sprayed coatings was characterized by the scanning electron microscope. It was revealed that the coatings deposited at room temperature exhibit a typical lamellar structure with numerous unbonded interfaces, whereas the coatings prepared at the temperature above the critical bonding temperature present a dense structure with well bonded lamellae. The erosion rate significantly decreases with the improvement of interface bonding. In addition, the erosion mechanisms of the conventional coatings and the lamellae well bonded coatings were further discussed. The unbonded interfaces act as precracks accelerating the erosion of plasma-sprayed coatings. Thus, controlling inter-lamellae bonding based on the critical bonding temperature is conducive to the improvement of erosion resistance of plasma-sprayed ceramic coatings.

In the present study, a novel and practical method, white light interference, was proposed to characterize the lamellar pores covered by thermally sprayed YSZ and LZ splats. In this method, only an ordinary optical microscopy (OM) was employed. Colorful Newton rings and parabolic shapes of the lamellar pores were widely observed by OM. The crack spacing and the shapes of the lamellar pores captured by OM were well consistent with those by scanning electron microscopy (SEM) and focus ion beam (FIB). Besides, mechanical analyses were carried out and the results were well consistent with those by OM. Most importantly, the essential fact that the lamellar pores resulted from transverse cracking/delamination in thermal sprayings was highly elaborated.

Ni20Cr splats were sprayed onto polished substrates at different preheating temperatures in an argon atmosphere by Low Pressure Plasma Spray to reveal the dominating factor on the effective interface bonding formation. The splat morphology, microstructure and splat-substrate interface bonding were characterized by SEM and EBSD. The interface for examination of typical splats was prepared by FIB. Disk splats were obtained on AISI 304 stainless steel substrates preheated to temperatures of 100 °C (cooling from 350 °C), 350 and 550 °C. Moreover, typical distinct two-zone microstructure feature was observed on the splat surface by SEM and EBSD, including central coarse grain and marginal fine grain. When the preheating temperature was higher than 350 °C, effective bonding formed only in the entire central coarse zone, whereas no effective bonding was observed in the fine grain zone. By using glass, copper, nickel and 304 SS as substrates, it was found that increasing thermal conductivity of metallic substrates has little effect on splat diameter and morphology and however decreased the area fraction of central coarse grain zone. It was revealed that the melt/substrate interface temperature plays a crucial role on the interface bonding formation.

This study investigates the correlation between thermal barrier coating (TBC) lifetime and thermally grown oxide (TGO) layer thickness. YSZ TBCs were deposited by atmospheric plasma spraying on Ni-base substrates and subjected to burner cycling tests with a thermal gradient and isothermal furnace testing. Both tests revealed that thermal cycling lifetime decreases with increasing TGO thickness, following a power law function, and for a critical TGO thickness of 5-6 μm, the failure mode changes from cracking within the YSZ layer to interface cracking around the TGO. Although either test can be used to evaluate TBC performance, burner cycling tests are better suited for evaluating ceramic topcoats, while furnace cycling test results integrate the effects of bond coat properties, especially oxidation resistance, as well as ceramic topcoat cracking resistance. The two tests can thus be used together to assess the factors that control TBC failure.

One way to reduce plasma jet velocity and prolong the dwell time of spray particles in the jet is to enlarge the orifice of the torch nozzle. In this study, normal and modified nozzles are used to deposit YSZ particles on ceramic and superalloy substrates by plasma spray-physical vapor deposition (PS-PVD). The modified nozzle is shown to increase the evaporation of YSZ particles and thus the quantity of Zr atoms and Zr 1+ ions in the plasma jet, which allows columnar structured coatings to be realized at higher deposition rates using a conventional 80 kW plasma spray system. The columnar ceramic coatings are also shown to have good conformity on cold-sprayed MCrAlY bond coats with high surface roughness.

In this work, liquid plasma spraying is used to deposit composite coatings for potential use as cathodes in intermediate-temperature solid oxide fuel cells. A suspension containing well-distributed Gd-doped ceria (GDC) nanoparticles in a lanthanum strontium cobalt ferrite precursor solution was used as the feedstock, and GDC concentration was varied to study its effect on phase composition, microstructure, surface morphology, and electrochemical performance. The results are presented and discussed.

This study demonstrates a novel method for improving the corrosion resistance of cold sprayed Al6061 coatings. Large stainless steel particles were added to a commercial Al6061 powder and the mixture was deposited on Mg alloy AZ31B substrates using nitrogen gas at low working pressure and temperature. It is shown that the stainless steel particles had a shot-peening effect, thus increasing the density as well as the corrosion resistance of Al6061 coatings. SEM examination showed that no stainless steel particles were incorporated in the coating.

Interparticle bonding is considered the most important factor in cold sprayed coatings, determining mechanical properties as well as physical and chemical behaviors. In this study, a Cu feedstock with low oxygen content is deposited with relatively high spray pressure and temperature in order to improve interparticle bonding and obtain a coating cohesive strength. Mechanical bonding between deposited particles is deduced from fracture morphology and the deformation behavior of Cu particles is simulated by finite element analysis.

In this study, stainless steel splats were deposited on preheated stainless steel substrates with oxide scales of different thickness in inert low-pressure plasma spay (LPPS) conditions to examine the effect of in-situ oxidation of prior splats on the morphology and bonding of subsequently formed splats. Splat-substrate interface cross-sections were prepared by focus-ion-beam milling. Splat morphology and bonding state with the substrate were characterized by SEM. The results show that with oxide films up to 35 nm thick, disk-type splats are deposited that bond well to the substrate except in the periphery region. As oxide films become thicker (100 nm) and present a surface with micro-scale roughness, splats take on a finger-like shape with poor bonding at the interface.

Transparent hydrophobic materials have broad application prospects in industry and daily life due to its transparent and super-hydrophobic characteristics, while its performance will be significantly influenced by the materials and its surface morphology. Hydrophobicity and transparency are competitive properties from the viewpoint of surface roughness. However, there are still a lot of problems to be solved to satisfy hydrophobicity and transparency simultaneously in the prepared surface. A novel and simple method to fabricate transparent hydrophobic surface is introduced in the present paper. Micron and sub-micron mixed Al 2 O 3 powders were deposited on the glass and plastic substrate by vacuum cold spray. The coatings were modified by 1,1,2,2- Tetrahydroperfluorodecyltrimethoxysilane (FAS) to reduce the surface energy. The surface morphology was characterized by scanning electron microscopy (SEM) and 3D laser microscopy (LSM). The transmittance of the coating was also investigated. The results show that the as-sprayed surfaces exhibit submicron structure. After FAS absorbing treatment, the contact angle of water droplets on the coatings ranged from 108° to 136° depending on the local surface morphology, and the transmittance of Al 2 O 3 coatings are all above 80% in the range of visible light.

A new method to fabricate micro-nano scaled surface with super-hydrophobicity is introduced in the present paper. Micro-nano hierarchical structure coatings based on silica (SiO 2 ) micron particles were successfully deposited on the stainless steel substrates by high-velocity oxygen fuel (HVOF) spraying which were modified by 1,1,2,2- Tetrahydroperfluorodecyltrimethoxysilane (FAS) to reduce surface energy. The influences of the HVOF process parameters on the wettability of the coatings were investigated. The coatings were characterized by scanning electron microscopy (SEM), 3D laser microscopy (LSM), and Fourier transform infrared spectrometer (FTIR). The results show that the as-sprayed surfaces exhibit micro-nano hierarchical structure. The water droplets are strongly adhesive to the as-sprayed surface, while by FAS absorbing treatment, the surfaces exhibit super-hydrophobicity, whose contact angle with water droplets are as high as 150°, and the water droplets tend to roll on the surface with extremely low adhesion with a sliding angle of 3°

In this study, YSZ coatings are deposited by plasma spray-physical vapor deposition using a shroud to limit expansion of the plasma jet and increase its heating ability. Optical emission spectroscopy shows that the shroud significantly increases the evaporation of YSZ particles in the jet, resulting in coatings with a hybrid columnar structure. SEM examination of coating surfaces and cross-sections reveal micro and nanoscale features and, in each case, the mechanisms of formation are discussed.

The aim of this study is to better understand the formation of nonbonded splat-to-splat interfaces in thermally sprayed ceramic coatings. To that end, the surfaces between splats in plasma-sprayed La 0.5 Sr 0.5 CoO 3 (LSCO) coatings were examined and compared to free splat surfaces. The results show that free splat surfaces are relatively smooth, while adjacent surfaces at intersplat interfaces are quite rough. The observation implies that nonbonded splat-to-splat interfaces were never bonded, having fractured due to interface shear stress generated during splat cooling.

In this study, MCrAlY-Al 2 O 3 composite powders were produced by ball milling and deposited by plasma, HVOF, and cold spraying. The results show that Al 2 O 3 fractions can be well controlled using composite powder due to non-preferential impact debonding of the matrix and Al 2 O 3 . The microstructure of spray powders is well retained in HVOF and cold-sprayed coatings due to the unmelted or partially molten condition of the spray particles. In the case of plasma-sprayed coatings, however, most Al 2 O 3 particles segregate at lamellar interfaces, forming a continuous oxide scale on the splat. The cold-spray coatings exhibit the highest hardness due to the work hardening effect of kinetic deposition.

In earlier experiments, plasma-sprayed Al 2 O 3 coatings were deposited on preheated Al 2 O 3 substrates to study the effect of substrate temperature on splat formation and phase transformations. The aim of the present work is to develop a model to better understand the factors that affect phase selection during the solidification of Al 2 O 3 splats. A model based on one-dimensional heat transfer and classic nucleation theory is presented and used to simulate the rapid solidification process and the influence of process parameters on phase selection. The model accounts for under-cooling phenomena, heterogeneous nucleation, and nucleation kinetics. The findings indicate that the relationship between initial substrate temperature and phase selection is primarily based on the catalytic effect of the alumina substrate on the nucleation of Al 2 O 3 phases as a function of contact angle.

In this study, WC-CoWC coatings were produced by HVOF spraying using bimodal-structured WC-Co powder with both micro- and nano-sized WC particles. Due to the melting characteristics of the powder during spraying, the microsized particles are retained in the deposit, but the nanosized particles dissolve into the Co matrix, forming a Co-W-C ternary phase. Compared to coatings sprayed from conventional WC-CoWC powder, the bimodal coatings are more resistant to corrosion and wear and are comparable in microhardness.

Lanthanum-doped strontium titanate (LST) and samarium-doped ceria (SDC) are promising materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). In this study, LST-SDC composite anodes are produced by suspension plasma spraying and the effects of annealing are assessed. XRD results show that the coatings and powders have the same phase structure. The coatings have a fine porous structure which is beneficial for gas permeability and long three-phase boundaries that facilitate anode reactions. A single cell based on the LST-SDC composite anode was found to perform well at 650-800°C. The results show that annealing improves interface bonding between particles in the anode and at the interface between the anode and electrolyte.