INVESTIGATION OF THE STRUCTURE AND OXIDATION MECHANISM OF FEALCR/AL2O3 DETONATION SPRAYED COATINGS

Oxidation resistance of detonation sprayed coatings obtained from FeAlCr/Al2O3 powder produced by the method of mechanically assisted self-propagating high-temperature synthesis  (MASHS) using aluminothermic reactions has been investigated. The powder has a sufficiently homogeneous composite structure  consisting of chromium-alloyed ordered B2–FeAl and fine inclusions of α-Cr2O3 and α-Al2O3. Detonation coatings sprayed on  a stainless steel substrate have a typical layered coating structure  without cracks or spalling. The coating thickness is 250–300 μm,  microhardness is 5,9–6,1 GPa. Coatings of a synthesized powder  mainly inherit its structure and phase composition although some  aluminum and chromium oxidation takes place when spraying. The features of cyclic and isothermal oxidation of the obtained  coatings in air within a temperature range of 900–1000 °C have  been studied. The oxidation resistance of synthesized powder detonation coatings after 48 h of oxidation in air at 950 °C is close to that of coatings obtained from FeAl–FexAly powder with an  aluminum content of 45 wt.%. At the same time, the coefficient of  linear  thermal expansion of FeAlCr/Al2O3 coatings is closer to that  of the substrate, and their creep resistance is higher as compared  with the substrate due to the presence of fine inclusions of refractory oxides. α-Cr, Cr2O3 and a lot of fine alumina inclusions present in the synthesized powder and formed when spraying are supposed to  accelerate the protective film formation while suppressing the nucleation and growth of hematite at early oxidation stages at  temperatures up to 950 °C. 

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