Thermal barrier coatings (TBCs) allow increasing combustion temperatures of gas turbines and diesel engines thus improving the system performance. Residual stresses due to the differences of thermal expansion coefficient between metallic bond coat and ceramic top coat as well as the stresses due to the oxidation of the bond coat and the consequent increase in the thermally grown oxide (TGO) layer lead to ceramic debonding and subsequent failure of the thermal barrier system in service conditions. Extensive research has been carried out to minimize such events by applying multilayered coatings, intermediate diffusion or protective layers and other methods. In this work the TBC systems were obtained by applying distinct bond coats and top coats. The bond coats were applied by High Velocity Oxygen Fuel (HVOF) and the ceramic top coats were applied by Air Plasma Spraying (APS). Residual stresses were measured by the Modified Layer Removal Method (MLRM). Isothermal high temperature oxidation tests were performed and the results were correlated with the post spraying stress state and the coating thermal history. Results show that the residual stresses are mainly influenced by the thermal history regarding the quenching of individual splats and the plastic deformation of ceramic deposits.

The use of HVOF to produce surface coatings is much known. However, the spraying of inner parts or using it to reproduce a mold form is not always easy due to the high bonding strength of HVOF coatings. On the other hand, plasma formed parts are being used in the aerospatial industry for many years partly because the ease of the releasing process. Using the experience and the method developed in the CPT some years ago, some new materials have been sprayed to obtain thick axy-symmetrical self-standing forms. The process involves mechanical removal method and for these reason, the mould can be used several times with minimal maintenance. Amongst the releasing methods, the more simple is mechanical but it could turn out to be complex if the adhesion by impingement takes place too strongly. Hence, the impingement of the material is studied in this work. The materials are mechanical blends of WC-Co with Co-based alloys. However, prior to spraying, the most suitable material is chosen for a concrete purpose. The work includes a study of the spraying parameters in the structure and the properties of the coatings. XRD, SEM-EDS, roughness, microhardness, ASTM G 99-90 and ASTM G 65-91 wear test are performed to characterize the samples.

Over the last years, the grain size reduction to the nanometric scale has experienced an increasing interest because of its enhanced properties. This study is based on WC-Co cermet materials, which have a great application in the wear resistance materials field. In the Thermal Spray Center (CPT) of the University of Barcelona, two coatings using nanostructured and bimodal WC-Co cermet powders have been obtained by means of High Velocity Oxygen-Fuel (HVOF) technique. Both were sprayed under the same spraying parameters. Structural characterization for both feedstock materials and coatings have been performed using XRD, SEM and TEM. The friction wear resistance of the coatings has been studied by Ball-on-Disk test (ASTM G99-90), and the abrasive wear resistance has been quantified by Rubber-Wheel test (ASTM G65-91). Finally, the corrosion resistance has been studied by electrochemical techniques and a salt fog spray test. The nanostructured coating shows more hardness, but the bimodal coating shows better abrasive and friction wear resistance. Both coatings shows good corrosion resistance, better than the conventional coatings of WC-Co. The bimodal powder have the added advantage of being not as expensive as the nanostructured powder, and even providing better properties.

Bulk, welded or laser cladded Stellite based materials are widely used in chemical industry due to their excellent combined properties against corrosion and wear processes and as a superalloy they have a high melting point and are designed to withstand high temperature for long periods of time. Problems related with poor inter-splat bonding arise when this kind of materials are sprayed with HVOF because it is characterized by having relatively low flame temperatures and high particle speed, and so dwell time may not be long enough to melt or soften Stellite particles completely. For these reasons, typical structured composed by a superposition of non-melted particles are obtained when spraying with propylene fuel gas. The aim of this work is to study the effect of using Hydrogen as a fuel gas and also to study the effect of the variation of the propylene flame characteristics. The coatings are characterized by SEM-EDS, XRD, and ASTM G99-90 sliding wear test has been done to compare the coatings. SWLI has been used to measure the volume lost after the wear test. Splat morphology studies have been also done in order to compare the melting behavior of the impinging particles.

Thermal and kinetic history of particles inside the jet plume of atmospheric plasma spray (APS) provide the particles with a certain velocity and temperature prior to the impact onto the substrate. Adjusting these velocity and temperature allows to control final coating's properties. The properties of the obtained coatings mostly depend on particle's conditions prior to the impingement. A set of experiments were done in order to optimize an atmospheric plasma process by means of an online monitoring system. The study is done by changing some spraying parameters that certainly affect the velocity and the temperature of the in-flight particles. Plasma gas flow rates and spraying distance were the parameters changed in this work, whereas all the other spraying conditions were kept constant. On-line monitoring system Spray-Watch (Oseir Ltd.) was used to achieve the parameters optimization by the measurement of velocity, temperature and spatial distribution of the Ni20Cr inflight particles. The study of the coated samples includes microstructure characterization by means of Optical Microscopy (OM), Scanning Electron Microscopy (SEMEDS) and X-ray diffraction to study the effect of the spraying parameters in phase composition. Roughness measurements and mechanical properties are also included.

A number of experiments were carried out to optimize the thermal spraying of stainless steel using online monitoring. The experiments were designed to determine the influence of spraying conditions on in-flight particle behavior and layer properties. By measuring the speed, temperature, and spatial distribution of the particle stream, the monitoring system made it possible to optimize spray parameters and thus produce stainless steel layers with tailor-made properties. Paper includes a German-language abstract.