Materials Performance

JUN 2016

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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36 JUNE 2016 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 55, NO. 6 COATINGS & LININGS P Aluminum oxide/titanium dioxide (Al 2 O 3 /TiO 2 ) nanostructured ceramic coatings were prepared on AISI H13 (UNS 720813) steel substrates by at- mospheric plasma spraying. The x-ray diffraction pattern shows that α-Al 2 O 3 , γ-Al 2 O 3 , rutile-TiO 2 , AlN, and AlNi 3 phases exist in the coatings. Oxida- tion test results show that the nano- structured coating with Al 2 O 3 -40 wt% TiO 2 provides better oxidation resis- tance than the others. Thermal shock test results indicate that the effect of TiO 2 content on the thermal shock lifetime is signifcant, and the Al 2 O 3 -13 wt% TiO 2 nanostructured coating ex- hibits superior thermal shock resis- tance compared to Al 2 O 3 nanostruc- tured coatings with 3, 20, and 40 wt% TiO 2 at a spraying power of 35 KW. Plasma spraying can make good use of the high temperature and velocity of a plasma jet for successfully depositing pow- ders as coatings with a relatively dense structure and high adhesion. 1-2 This tech- nolog y uses a process in which powder particles are heated to a melted or semi- melted condition and propelled as drop- lets at high velocities so they impact the substrate and then f latten while quickly solidifying. 3 The quality of the coating is related to many parameters, including temperature, velocity, and spraying power of the plasma jet, as well as types of pow- der, size of the powder particles, and their melting behavior. In past decades, nanostructured materi- als have been studied extensively, 4-5 with indications that nanostructure can signifi- cantly increase the performance of ma- t erial s. 6-7 Atmosph eric plasma spraying (APS), one of the most extensively used spraying techniques in industry, can be used to deposit thick ceramic coatings on sub- strate materials. The agglomerating process (i.e., accumulating nanoparticles into mi- cron-sized aggregates) is an essential part of the production of nanostructured coatings by APS. Aluminum oxide (Al 2 O 3 ) (alumina) is commonly used for electrical isolation be- cause of its high dielectric strength and its ability to produce hard, even, and stable coatings at high temperatures. It has been found that the addition of titanium dioxide (TiO 2 ) can improve the fracture toughness of as-sprayed alumina coatings. 8 While the oxidation and thermal shock properties of Al 2 O 3 /TiO 2 nanostructured ce- ramic coatings prepared by plasma spraying have not been studied previously, 9 the me- chanical properties have been investigated. The next generation of advanced engines, with further increases in thrust-to-weight ratios, call for higher gas turbine inlet tem- peratures, which will require the design of new coating structures with better oxidation resistance and thermal shock properties. This realization led to the study of oxidation and thermal shock properties of Al 2 O 3 /TiO 2 nanostructured ceramic coatings. These coatings have outstanding me- chanical properties, such as enhanced abra- Oxidation and Thermal Shock Resistance of As-Sprayed Coatings n. Xiang, Y.Q. guo, C. Wang, J.R. Jin, Y.J. ge, and R.g. Song, Jiangsu Key Laboratory of Materials Surface Science and Technology, Changzhou University, Changzhou, China

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