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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38 JUNE 2016 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 55, NO. 6 COATINGS & LININGS FIGURE 2 Isothermal oxidation curves of nanostructured ceramic coatings (a) AT3, (b) AT13, (c) AT20, and (d) AT40 obtained at different levels of spraying power at an air temperature of 1,323 °K. time. This suggests that the oxidation resis- tance increased with increasing TiO 2 con- tent. For the AT40 coatings, the weight gain was <4.3 g/cm 2 at all levels of spraying power in each oxidizing period. Al 2 O 3 /TiO 2 nanostructured ceramic coatings typically include pores and impurities, and oxygen molecules can more easily permeate into the coatings through these defects. The smaller nanostructured TiO 2 particles can fill the gaps in the coatings and even form a solid solution phase with Al 2 O 3 to increase the density of the coatings. Consequently, the oxidation resistance increases with in- creasing TiO 2 content. Figure 2 also shows that AT3, AT20, and AT40 coatings exhib- ited the most oxidation resistance at spray- ing powers of 25, 35, and 30 KW, respec- tively. The AT13 coating showed a uniform horizontal oxidation resistance at spraying powers of 25 and 30 KW. Thermal Shock Property The thermal shock lifetimes of Al 2 O 3 / TiO 2 nanostructured ceramic coatings at dif ferent le vel s of spraying power are shown in Figure 3. Increasing the spraying power elevated the thermal shock resis- tance of the coatings. When the spraying power increased, the nanoparticles were fully melted, which decreased the number of defects in the coatings. The AT13 coating showed relatively superior thermal shock resistance; and at a spraying power 35 KW, the AT13 coating exhibited the best ther- mal shock lifetime of 35 cycles. Figure 3 shows that the thermal shock resistance of the AT3 coating was inferior compared to those of the AT13, AT20, and AT40 coatings, while the thermal shock re- sistances of the AT13, AT20, and AT40 coat- ings were almost at the same level. This suggests that TiO 2 at 13 wt% offers near- optimum improvem ent of th e th ermal shock resistance, but offers little additional improvement at higher concentrations. Conclusions • T h e A l 2 O 3 / Ti O 2 n a n o s t r u c t u r e d ceramic coatings prepared by APS were mainly composed of α-Al 2 O 3 , γ-Al 2 O 3 , rutile-TiO 2 , AlNi 3 , and AlN; and the γ-Al 2 O 3 content slightly increased with increased spraying power. • The Al 2 O 3 /TiO 2 coatings consisted of a typically lamellar structure with a large quantity of semi-molten nano- par ticles inlaid into th e lam ellar melted structure. • The AT40 coating exhibited the most oxidation resistance compared to the other formulations. The TiO 2 content had a positive effect on improving the oxidation resistance of coatings.

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