Wear-resistant cobalt–based alloy (Stellite 12) coatings deposited by plasma transferred arc (PTA), commonly used to protect critical mechanical components in harsh environments, were modified by addition of hard ceramic particles (TiC) and solid lubricant compounds (MoS 2 and CaF 2 ) to improve the overall tribological performance. In this preliminary study, microstructural, microhardness and tribological analyses were carried out to assess: a) the feasibility of PTA deposition of thermally sensitive phases characterised by very low density; b) the effect of the addition of a mixture of soft and hard phases on the coating hardness; c) the effect of the modified composition in terms of wear resistance; d) the effect of the addition in terms of lubrication (friction coefficient and produced heat). Results showed that: a) an appropriate pre-consolidation of feedstock materials can be effective in preserving the heat-sensitive phases within the microstructure of PTA deposits; b) the addition of a total amount of 5% wt. of solid lubricants and reinforcing carbides produced a limited decrease in the coating hardness (about 13%) and an evident improvement in terms of friction coefficient but, on the other hand, a remarkable reduction (about 30%) in wear resistance. Further investigation will be addressed to optimize the composition of modified feedstock to counteract the softening effect of lubricant phases without depressing the self-lubrication behaviour.

The physico-chemical and thermo-mechanical properties of aluminosilicate ceramics (high melting point, low thermal expansion coefficient, excellent thermal shock resistance, low density and good corrosion resistance) make this class of materials a good option for high temperature structural applications. Al 2 O 3 -SiO 2 compounds show an excellent refractory behaviour allowing a wide use as wear resistant thermal barrier coatings, in metallurgical and glass plants and in high temperature heat exchangers. Moreover the low values of thermal expansion coefficient and of complex permittivity allow to extend the use of this ceramic for microelectronic devices, radome for antennas and electromagnetic windows for microwaves and infrared. The present paper presents the results of an extensive experimental activity carried out to produce thick aluminosilicate coatings by plasma spray technique. APS deposition parameters were optimized on the basis of a surface response approach, as specified by design of experiments (DoE) methodologies. Samples were tested for phase composition, total porosity, microstructure, microhardness, deposition efficiency, fracture toughness and modulus of rupture. Finally, coatings were characterized for their particularly interesting electromagnetic properties: complex permittivity was measured at microwave frequency using a network analyzer with wave guide.

Nanocrystalline WC-Co coatings were deposited by high velocity oxy-fuel from commercial nanostructured composite powders. Processing parameters were optimized for maximal retention of the nanocrystalline size and for minimal decarburation of the ceramic reinforcement. Thermo-chemical and gas-dynamical properties of gas and particles flows within the combustion flame were identified in various operating conditions by CFD simulation. Significant improvements of coatings mechanical properties were evidenced: a decrease of the friction coefficient was measured for the nanostructured coatings, together with an increase of microhardness and fracture toughness.

Thermal sprayed ceramic coatings play an important role in those industrial applications where exceptional erosion and wear resistance are required. In particular, nickel-chromium based coatings containing chromium carbide particles dispersion are widely used when environment temperature rises up to 800°C. Thick Cr 3 C 2 -NiCr coatings were produced with two thermal spray processes: Air Plasma Spray (APS) and High Velocity Oxy-Fuel (HVOF). Two different powders have been selected as starting materials. Their dimensional and morphological properties were assessed to verify their sprayability, both in terms of flowability and deposition efficiency. For both APS and HVOF processes, most deposition parameters were selected, after preliminary spraying tests, on the basis of statistical analysis of results, in terms of coating density, hardness and substrate-coating interface quality. The tribological properties of the coatings were evaluated in order to investigate the influence of the deposition process on the behavior of coatings under wear conditions

ZrB 2 -SiC composites are considered a class of promising materials for aerospace applications such as nose and leading edges of re-entry vehicles. Results on such materials obtained by hot isostatic pressing have confirmed their high resistance to the oxidation at temperature up to 2000°C. Ongoing work has shown that such materials can be obtained in the form of coatings by means of Plasma Spraying techniques. On this regard, the most critical aspect was correlated to the decomposition of the SiC phase at a temperature quite lower than the melting point of ZrB 2 . Experimental evidence indicated that such decomposition can be avoided when a proper methodology of preparation of the starting powders is adopted, and if suitable thermal spraying parameters are selected. In any case, high temperature oxidation testing (up to 1800°C) confirmed the outstanding behaviour of this materials obtained by plasma spraying. This paper is focussed on preliminary studies of oxidation behaviour for plasma sprayed ZrB 2 -SiC composites suitable for thermal protection shields.

Reusable space vehicles, which must withstand re-entry into the Earth's atmosphere, require external protection systems (TPS) which are usually in the forms of rigid surface in areas of high or moderate working temperature. High heat fluxes and temperatures related to high performance hypervelocity flights also require the use of TPS materials having good oxidation and thermal shock resistance, dimensional stability, and ablation resistance. Components by these materials are usually fabricated, starting from either billets or plate stocks, by uniaxial hot pressing, and complex parts, such as low radius edges, are then obtained by electrical discharge machining technique. This article investigates an alternative fabrication technology, based on plasma spraying, to produce near net shape components. Results of experimental activities, such as optimization of plasma spraying parameters based on a DOE approach, are reported and discussed.