CHARACTERISATION AND TRIBOLOGICAL BEHAVIOUR OF ALUMINA-TITANIA COATINGS
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Joined: Sep 2010
18-10-2010, 12:03 PM
Alumina-Titania coatings are excellent candidates for providing protection against abrasive wear and resistant to high temperature erosion. Such coatings are desirable in electrical insulation and anti-wear applications; viz. as protective coatings for sleeve shafts, thermo-couples jackets, pump shafts e.t.c.
Plasma spraying is gaining acceptance as a development of quality coatings of various materials on a wide range of substrates. Coatings made with plasma route exhibit excellent wear, corossion resistance and high thermal shock resistance etc. Alumina pre-mixed with Titania powder (Al2O3-13%TiO2) is deposited on mild steel and copper substrates by atmospheric plasma spraying at various operating power level ranging from 11 to 21kW.
The properties of the coatings depend on the materials used, operating condition and the process parameters. The plasma spraying process is controlled by the parameter interdependencies, co-relations and individual effect on coating characteristics. The particle sizes of the raw materials used for coating are characterized using Laser particle size analyzer of Malvern Instruments make. To characterize the coating, Coating interface bond strength is measured using coating pull out method with Instron 1195 confirming to ASTM C-633 standard. Micro-hardness measurement is done on the polished cross section of the samples on the optically distinguishable phases Using Leitz Micro-Hardness Tester.
To ascertain the phases present and phase changes / transformation taking place during plasma spraying, X-ray diffractograms is taken on the raw material and on coatings. The coating quality and behaviour depends on coating morphology and inter-particle bonding of the sprayed powders. The surface and interface morphology of the coatings is observed by Scanning Electron Microscope. Measurement of porosity is made using the image analysis technique. To ensure the coatability of alumina- titania on different substrates, coating thickness is measured on the polished cross-sections of the samples, using an optical microscope. Coating deposition efficiency is also calculated.
To study the suitability of the coatings for wear resistance application, wear properties of these coatings are studied. The erosion wear behaviour of these coatings is evaluated with solid particle erosion tests under various operating conditions. In order to control the wear
loss in such a process, one of the challenges is to recognize parameter interdependencies; correlations and their individual effects on wear so that the coating can be useful for tribolgical application.
Statistical analysis of the experimental results using Taguchi experimental design is presented. Spraying parameters such as impact angle, impact velocity, stand off distance, size of the erodent are identified as the significant factors affecting the coating erosion wear. A prediction model using artificial neural networks is also employed to simulate property-parameter correlations and a fairly good agreement in the experimental and predicted values is obtained. This analysis makes it clear that by appropriate choice of processing conditions, a sound and adherent ceramic coating is achievable with alumina and titania.
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