1,720,994 research outputs found
Silicon carbide based thermal spray powder, method of preparation and use
No full textA silicon carbide-based thermal spray powder contains at least one boride chosen from zirconium boride, titanium boride and hafnium boride. The powder is prepared by mixing and aggregation of powders containing the compounds in question. Said thermal spray powder is used to deposit, via the plasma spraying technique, a silicon carbide-based coating on a metallic or non-metallic substrate. The figure shows the X-ray crystallogram obtained, for a silicon carbide-based powder, according to the invention, after thermal spraying. The substantial identity of this crystallogram with the one obtained prior to thermal spraying demonstrates that the silicon carbide has been deposited on the substrate without decomposing
Process for the realisation of ceramic matrix composite layers and related composite material
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Mechanical properties of ceramic matrix composite for high temperature applications obtained by plasma spraying
No full textNose and wing leading edges for future generations space vehicles will withstand very high temperature in an oxidizing environment. UHTC (Ultra High Temperature Ceramics) materials are very promising candidate materials for such applications. An innovative, proprietary methodology was developed to produce, by plasma spraying deposition, a ceramic composite containing SiC particles (25 wt%) dispersed in a ZrB2 matrix. With such a technique both coatings and self standing parts were fabricated. In the present paper, the results of mechanical characterisations, carried out on self standing samples, are presented. Tensile and bending properties were determined by mechanical tests on as sprayed samples and on samples exposed at high temperature (2173 K) in oxidising conditions. Experimental results clearly evidenced the possibility to use the plasma spraying technology and suggest that the so fabricated ZrB2-SiC material is suitable to be adopted as protective coating
Effects of pressure deposition on plasma jet and coatings microstructure
No full textPressure inside the spray chamber plays a key role during coatings manufacturing by thermal spraying and coating properties can be strongly affected by the selected pressure value. Spraying at low pressure results in a longer plasma jet length, higher particle velocity, lower coating porosity and higher purity and phase stability. For what concerns plasma-particle interactions, a reduction of pressure value drastically decreases heat transfer towards particles, therefore high power plasma equipment must be used to achieve a suitable melting degree of sprayed po cyders. Effects of low pressure values are well known, but few investigation have been carried out on effects of pressure for values higher than 1,000 mbar. In this paper a preliminary evaluation of pressure effects on plasma jet modifications, particle velocity and coatings microstructure is presented. By using the very innovative CAPS (Controlled Atmosphere Plasma Spraying) system, Ni-20%Al powders were sprayed at different pressure values, up to 3,600 mbar. The length and width of the visible part of the plasma jet was measured and controlled. Average particle velocity was also evaluated as a function of pressure. Coatings, manufactured on stainless steel substrates, were characterized by means of scanning electron microscopy and energy dispersive spectroscopy, x-ray diffraction and Vickers microhardness measurements. Results indicate that the higher the spraying pressure the lower the plasma jet length and particle velocity, but also a lower selective evaporation of aluminum and higher microhardness values were observed
High temperature characterization of an UHTC candidate materials for RLV's
No full textNose and wing leading edges of the future generations re-entry vehicles will withstand very high temperature in an oxidizing environment. UHTC (Ultra High Temperature Ceramics) materials are very promising candidate materials for such applications. An innovative, proprietary methodology was developed to produce, by plasma spraying deposition, a ceramic composite containing SiC particles (25 wt %) dispersed in a ZrB2 matrix. With such a technique both coatings and self standing parts were fabricated. In spite of the well known difficulty to obtain plasma sprayed coatings containing SiC, characterization results evidenced that the used process did not affect the phase composition. The high temperature behaviour of such a composite was characterised and the formation of a passivation layer, composed by mixed oxides of Si and Zr, was assessed, thus confirming that the developed material can withstand high temperatures in oxidizing atmosphere, as requested by the envisaged application
High temperature behaviour of plasma sprayed ZrB2-SiC composite coatings
No full textZrB2-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 2000degreesC. 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 ZrB2. 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 1800degreesC) confirmed the outstanding behaviour of this materials obtained by plasma spraying. This paper is focussed on preliminary studies of oxidation behaviour for plasma sprayed ZrB2-SiC Composites suitable for thermal protection shields
Plasma Sprayed Ultra High Temperature Ceramics for Thermal Protection Systems
No full textThe use of plasma sprayed ultra high temperature ceramics for thermal protection systems (TPS) was discussed. TPS must be able to withstand thermal and aeroconvective environments and mechanical stresses associated with launch vibrations. Optimization of plasma spraying parameters which are based on a DOE approach were also studied. It was found that high temperature testing can give thermal stability and thermal shock resistance to fabricated samples
Analytical characterization of various titanium nitride based coatings obtained by reactive plasma spraying
No full textPerspectives for Tribological Applications of Titanium Coatings Containing TIxNy Phases Deposited by Reactive Plasma Spraying
No full textAustrian Tribology Society publ
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