This study investigates the effect of nozzle material on cold sprayed aluminum coatings produced using a downstream lateral injection system. It is shown through experimentation that nozzle material has a significant impact on deposition efficiency and particle velocity. It is proposed that the effects are related to complex interactions between particles and internal nozzle walls. The results obtained lead to the conclusion that nozzles with higher thermal diffusivity transfer more heat to particles when they make contact with internal surfaces, which increases deposition efficiency even though particle velocities are reduced.

The corrosion resistance of thermal barrier coatings against CMAS deposit at high temperature is significantly affected by the microstructure of the coatings. Enhancing the bonding ratio between splats can reduce the inter-connected pores and then obstructs the penetration of the molten CMAS into the coatings. In this study, atmospheric plasma sprayed ZrO 2 contains 8 wt. % Y 2 O 3 (8YSZ) coating with improved lamellar bonding ratios was deposited with full-molten droplets at an enhanced deposition temperature. The microstructure of the dense 8YSZ coating and conventional 8YSZ coating before and after thermal exposure with CMAS were characterized. It was clearly revealed that by adjusting the microstructure and designing a ceramic layer with high bonding ratio, the corrosion resistance of the thermal barrier coating could be enhanced. Moreover, by designing double-ceramic-layer (DCL) TBCs composed of a porous ceramic layer and well-bonded ceramic layer, the TBCs with high CMAS corrosion resistance and low thermal conductivity can be achieved.

The evaporation of both CeO 2 and La 2 O 3 in high temperature plasma arc leads to deviation of plasma sprayed La 2 Ce 2 O 7 coating composition from the starting powder particle. Such change results in significantly inhomogeneity of compositions within a coating which influences the performance of calcium-magnesium-alumina-silicate (CMAS) corrosion. In this study, the pellets with different Ce / La ratio were interacted with molten CMAS glass. The penetration of molten CMAS on different pellets was characterized by scanning electron microscopy and energy dispersive spectrum (EDS) and the phase of different powder mixtures treated at 1250 °C was characterized by X-ray diffraction ( XRD ). The effects of pellets with different Ce / La ratio on the CMAS corrosion after thermal exposure at 1250 °C for 50 h were investigated. The result demonstrated that pellets with ratio of Ce / La greater than or equal to 1.0 were completely dissolved into the molten CMAS, at the same time the others were also damaged, forming diffusion layer and reacted layer, respectively. The difference of the ratio of Ce / La indeed affected their performance against CMAS attack.

A new challenge in the field of Solid Oxide Fuel Cells (SOFCs) concerns the reduction of their operating temperature down to 700°C. Apatite ceramics are interesting alternatives for SOFC electrolytes due to their high ionic conductivity at this temperature. The present work reports on the manufacturing and characterization of La 9 SrSi 6 O 26.5 coatings obtained by atmospheric plasma spraying at two different plasma spray powders. The microstructure and the composition of the as-sprayed and heat-treated coatings were investigated by several techniques including X-Ray Diffraction, Inductively Coupled Plasma - Atomic Emission Spectroscopy as well as Scanning and Transmission Electron Microscopy. The porosity level of the coatings was evaluated by the Archimedean method and image analysis. The studies revealed that the as-sprayed apatite coatings were composed of an amorphous phase, a crystalline apatite phase and chemical heterogeneities due to Si volatilization in the high-temperature plasma. Furthermore, a heat treatment made it possible to obtain denser, fully crystallized apatite coatings and also improved their ionic conductivity.

Magnesium doped lanthanum silicate with apatite-type structure was prepared by solid state sintering, as a solid electrolyte for intermediate-temperature solid oxide fuel cells. The electrolyte layers were fabricated by APS, followed by post heat treatments, and their structures and phase were characterized by SEM and XRD. It is showed that an amount of amorphous oxides exist in as-sprayed electrolyte layer, and then disappear after a post heat treatment in air furnace at temperature up to 1000°C. The gas permeation of electrolyte layers was measured by a specific instrument with pure H 2 and O 2 at room temperature. The conductivity of plasma sprayed electrolytes was studied by impendence spectroscopy in the range of 500-900°C in air.

This work investigates the effect of calcium-magnesium aluminosilicate (CMAS) deposits on thermal barrier coatings. CMAS infiltration was achieved by means of a cement tape containing synthetic glass powder. The tape was placed on coating surfaces and melted in a tube furnace or with a flame burner. The resulting coating failures were investigated by examining thermomechanical and thermochemical interactions between the coatings and aluminosilicate deposits. It was found that the porous nature of thermal spray TBCs makes them vulnerable to CMAS attack even before discernible chemical reactions start. Possible mitigation approaches are proposed for improving coating life under such conditions.

Coating operations over glass ceramic substrates represent a new field for thermal spray applications. Due to the unique thermal and mechanical properties of glass ceramics, especially the low or even negative CTE, coating processes must be adapted to reduce the distribution of thermal stresses in the system and to not damage the substrate. This study investigates the deposition of a complex-shaped ceramic-metallic multilayer coating system that could potentially serve as a heating element in a glass ceramic cooking plate. To ensure coating adhesion, the substrates are preheated and their surfaces are grit blasted. In order to minimize stresses associated with the deposition of metal, the movement of the spraying mechanism was automated with robot control and new masking concepts were developed to ensure the accuracy of the shape and placement of the coating. The influence of spraying parameters on coating properties and residual stress distribution is analyzed as well.

This paper presents and assesses a thermal spraying process for applying electrically insulating layers on glass ceramic substrates. It reviews the crystal structure of glass and glass ceramic and explains how it influences splat morphology, phase transformation, and the properties of plasma-sprayed materials. It is observed that substrate preheating is necessary with glass ceramics as is substrate cooling; the former to promote adhesion, the latter to control residual stress. Spray parameters such as plasma power and powder feed rate also have an effect on residual stress and must be controlled as well. Paper includes a German-language abstract.

In this paper, a quantitative model of the viscous behavior of two-phase particles hitting a substrate is used to optimize a plasma spraying process for silicon-nitride composite layers. The model is derived from the observed behavior of Si 3 N 4 -YAS (Y 2 O 3 -Al 2 O 3 -SiO 2 ) layers and provides a basis for further study of ceramic-matrix composite layers. Paper includes a German-language abstract.

This paper examines the dielectric properties of silicate coatings including mullite (3Al 2 O 3 -2SiO 2 ), steatite (MgSiO3), spodumene (Li 2 O-Al 2 O 3 -4SiO 2 ), and olivine with near-forsterite (Mg 2 SiO 4 ) composition. The materials were sprayed using a water-stabilized plasma gun and the deposits were removed from the substrate, polished, and sputtered with aluminum on both sides. Electrical tests consisting of voltage, resistance, and capacitance measurements showed that the relative conductivity of plasma-sprayed silicates is stable between 200 Hz and 1 MHz, which is suitable for many insulation applications. Paper includes a German-language abstract.

Stoichiometric cordierite (2MgO-2Al2O3-5SiO2) with additions of titania have been investigated for use as coatings on low thermal expansion refractory concretes. These concretes have coefficients of thermal expansion on the order of 2 ppm/°C. Titania additions of up to 8 mole percent were investigated and the effect of titania in the crystallization of cordierite was examined. Cordierite coatings were air plasma sprayed and both glass and crystalline coatings were produced. The crystalline structure of the coating was found to be dependent upon the preheat temperature of the substrate. Preheats greater than 700 °C produced a mixture of a quartz solid solution and indialite whereas glass coatings were produced at preheats less than 700 °C. Coefficients of thermal expansion for the cordierite materials were dependent upon titania addition and generally increased with addition of titania. In the glass state, the thermal expansion was modestly increased (4.6 to 4.9 ppm/°C) with titania additions, but the quartz and indialite forms of the cordierite increased from 1.2 to 4.7 ppm/°C as the titania addition increased from 0 to 8 mole percent.

The plasma-spray process is specified by the associated processing parameters, where these influence the properties of the resultant deposits. This article describes the preparation and processing of composite powders for use in thermal spraying by mixing high purity zircon and alumina powders. The spheroidized powder were obtained by high energy ball milling and rapid solidification from the molten state during plasma spraying. The article discusses the processes involved in spray drying and plasma spheroidization, describing thermal analysis and mullitization kinetics in the spheroidized alumina/zircon mixtures.

This paper compares the wear properties of HVOF-sprayed WC/12Co hardcoatings produced from different powder feedstock materials, including conventional, nanophase, and mixed powders. The mixed or multimodal feed powder is designed to minimize the amount of material that goes through a high temperature cycle during spraying, thus potentially limiting the extent of decarburization in the resulting coating. As will be shown, decarburization is indeed minimal in a multimodal coating, which translates into exceptional resistance to abrasive and sliding wear. Another favorable factor is the ability to increase the volume fraction of hard WC phase in such a coating, thereby further enhancing its wear resistance.