The galvanic codeposition of ceramic particles for the production of metal matrix composite coatings is a research domain of wide interest as these deposits could be used for a large field of applications, especially in cases where high wear and corrosion resistance are required. Geothermal wellhead valves could be a possible application. These valves are subjected to corrosion and wear at high pressures and temperatures in sour gas environment. The aim of this work is the production and characterization of nickel matrix micro- and nano-composite deposits. Three types of deposits have been produced: pure Ni deposits, Ni containing SiC micro-particles and Ni containing SiC nano-particles. A Ni sulphammate electroplating bath containing the particles in suspension has been used and the deposition was carried out using both direct and pulse current at different frequencies. ASTM 387 gr.22 steel plates were used as substrate. The microstructure of the obtained deposits has been observed by Scanning Electron Microscope at both top surface and cross section after metallographic etching. The SiC content along the whole thickness of the deposits has been evaluated by Glow Discharge Optical Emission Spectroscopy and Vickers microhardness measurements have been performed in cross section. Wear test at both room temperature and at 300°C have been performed on pure and composite nickel deposits using a ball on disc configuration. The wear tracks have been analysed using a profilometer and SEM to determine the wear coefficient and mechanism of each type of coating. The corrosion resistance of the coatings has been evaluated by potentiodynamic polarization curves in a solution containing S~(2-), SO_4~(2-), CI~- ions to simulate the condensation on the valve walls. The codeposition of SiC particles leads to a significant increase of both microhardness and wear resistance. Moreover, the codeposition of SiC nano-particles causes a grain refinement of the nickel matrix thus leading to an increase of the corrosion resistance.
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