Mo 기판위에서 형성된 MoSi_(2)-baso 나노복합코팅층의 저온산화 특성
Low temperature oxidation property of MoSi_(2)-base nanocomposite coatings formed on Mo substrate
합금 저온산화 나노복합코팅층;
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Growth behavior and microstructure of oxide scale formed of MoSi_(2)coating by cyclic oxidation test in air at 500℃ was investigated using field emission-scanning electron microscopy(SEM), cross-sectional transmission electron microscopy(XTEM), glancing angle X-ray diffraction (CRD) and X-ray photolelctron spectroscopy(XPS). MoSi_(2)coating was prepared by chemical vapor deposition (CVD) of Si on a Mo substrate at 1100℃ for 5h using SiCl_(4)-H_(2)precursor gas mixture. After the incubation time of about 454 cycles, the accelerated oxidation behavior was observed in MoSi_(2)coating and the weight gain increase linearly with increasing oxidation cycles. Microstructural analyses revealed that pest oxide scale was formed in three sequential processes. Initilly, nanometer-sized crystalline Mo_(4)O_(11) particles were formed with an amorphous SiO_(2)matrix at MoSi_(2)interface region. Inward diffusing oxygen reacted with Mo_(4)O_(11) to form Mo_(9)O_(26) nano-sized particles. At final stage of oxidation, MoO_(3) was formed from Mo_(9)O_(26) with oxygen and growth of MoO_(3)took place forming massive precipitates with irregular and wavy shapes. The internal stress caused by the growth of massive MoO_(3) precipitates and the volatilization of MoO_(3)was attributed to the formation of many lateral cracks into the matrix leading to pest oxidation of MoSi_(2)coating.