The sliding wear behavior of thermally sprayed aluminum oxide is fairly well studied, but little is known about its fretting behavior under cyclic tribological loads. This study investigates the fretting behavior of plasma sprayed alumina and the related influence of TiO 2 additions. Three Al 2 O 3 -TiO 2 composites are sprayed on steel substrates using commercial powders and the resulting layers are characterized based on hardness, porosity, surface morphology, phase composition, and fretting behavior. The results of the study show that TiO 2 additions reduce microhardness and increase coating toughness. The effect of TiO 2 on fretting behavior and surface wear is assessed after 10, 50, 100, 250, and 500 load cycles based on SEM imaging, friction measurements, and debris formation. Observations and test results are presented and discussed. Paper includes a German-language abstract.

The effects of the plasma spray process parameters on the microstructure and properties of coatings have been recognized for a long time. It is now clearly proved that the quality and the properties of the deposits are strongly dependent on the in-flight particle characteristics as well as on the splat morphology. The aim of this study was to examine in detail: firstly the interaction between an Al 2 O 3 /13%TiO 2 powder and the spraying process, secondly the splat formation in order to understand the morphology of the deposits. A good way to reach a better understanding of the particle/ plasma interaction is to determine the particle parameters at impact. The particles parameters: velocity, temperature and diameter, prior to their impact on the substrate were measured by the DPV-2000 diagnostic system. The effect of particle velocity, temperature and size on the splat morphology and deposits properties for different plasma conditions were examined. The splat morphology was characterized using the Sommerfeld dimensionless number, K; the value of which is directly related to the impact mode. These analyses were correlated to microhardness, roughness and to the tribological properties of the coatings.

Plasma sprayed thermal barriers are used as insulating materials in the hot sections of gas turbines to decrease the metal temperatures during service and men allow a higher combustion temperature for better engine efficiency. They usually contain a bond coating to protect the substrate from high temperature oxidation and a top coat with a low thermal conductivity. This study evaluate and identify the mechanisms of degradation of a vacuum plasma sprayed NiCoCrAlYTa bond coat subjected to thermal cycling at high temperature. The microstructure and micro-composition of the coating layer were analyzed by scanning electron microscopy and energy dispersive X-ray analysis to elucidate the improvement and degradation mechanisms of the material. The thermal cycling provokes some morphological and chemical modifications changes within this material. These modifications provoke a perturbation of the heat transfer within the material.

Inconel thermal spray coatings are potential candidates for wide industrial applications. However, the coating structure resulting from thermal spray processes characterized by unmelted particles, oxides and porosity can severely hinder their corrosion resistance in aggressive media. The aim of the present work was to optimize elaboration parameters in order to enhance their chemical stability. Electrochemical criteria were used to identify the ability of those coatings to form a passive film in a sulfuric acid solution and also to determine their local corrosion resistance in a chloride solution. Results show that the passivity state is strongly conditioned by the coating microstructure. Coatings free of unmelted particles exhibit a notably reduced passive current density while the localized corrosion resistance seems conditionned by the amount of interlamellar oxide.

The tribological behavior of Mo/NiCrBSi coatings obtained by atmospheric plasma spray was studied under dry conditions using an Amsler machine. Discussion is made on the effects of the plasma gas mixture and of the preheating of the substrate. The wear process of Mo/NiCrBSi in situation of dry rolling-sliding contact versus cast iron was observed using a profilometer, an optical microscope, and a scanning electron microscope. It was found that the wear mechanism could be divided into two steps : the first one corresponds to an abrasive wear; it results from the difference in hardness between the counter-specimen and the Mo/NiCrBSi coating. The second one corresponds to an adhesive wear resulting from the transfer of cast iron from the counter-specimen to the coating.

One cause of aseptic loosening of total hip replacement (THR) results from the hard polymetylmethacrylate (PMMA) bone cement debris embedded within some of acetabular cups [1]. To prevent this failure, PMMA can be replaced by a titanium coating with a specific roughness to promote the bone bonding. In this work, inert and atmospheric plasma spraying was used to coat Ti.6A1.4V implants with titanium.] In order to evaluate the effect of the deposition process on the coating corrosion resistance, different electrochemical techniques were implemented in physiological (i. e., Ringer) and in acidic solutions. Results show that the spraying parameters and the coating morphology affect the corrosion behaviour. Thus, if the reactivity is not affected by the pH evolution, the pitting sensitivity depends on the process. It was found that coatings deposited under inert gas are free of oxides and dense, even when the atmosphere contains some hydrogen. In that case a significant improvement of the intrinsic localized corrosion resistance is observed versus deposits obtained using atmospheric plasma spraying.