Improved oxidation resistance of CoNiCrAlTaHfY/Co coating on C/C composites by vapor phase surface alloying
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FOCUS ISSUE
THE SCIENCE AND TECHNOLOGY OF VAPOR PHASE PROCESSING AND MODIFICATION OF SURFACES
Improved oxidation resistance of CoNiCrAlTaHfY/Co coating on C/C composites by vapor phase surface alloying Qi Guo1, Tianxu Meng2, Wenqiang Ding2, Wen Xi2, Naiming Lin2, Shengwang Yu2, Xiaoping Liu2,a) 1
Research Institute of Surface Engineering, Taiyuan University of Technology, Taiyuan 030024, China; and Taiyuan Heavy Industry Co., Ltd., Smelting & Casting Subco, Taiyuan 030024, China 2 Research Institute of Surface Engineering, Taiyuan University of Technology, Taiyuan 030024, China a) Address all correspondence to this author. e-mail: [email protected] Received: 19 August 2019; accepted: 11 November 2019
A CoNiCrAlTaHfY/Co composite coating was prepared on the etched C/C composites by using duplex vapor phase surface alloying treatments, i.e., Co alloying and Co–Ni–Cr–Al–Ta–Hf–Y alloying. Microstructures and oxidation behavior of the coated C/C composites were analyzed by scanning electron microscopy, energydispersive spectroscopy, and X-ray diffraction. The result showed that the CoNiCrAlTaHfY/Co composite coating, 25 lm in thickness, was compact and composed of CrCoTa, AlCo2Ta, AlxCry, AlxNiy, and Co. The coating adhesion can be enhanced by microwave plasma chemical vapor deposition etching of matrix surface and adding a Co intermediate layer between the CoNiCrAlTaHfY top layer and C/C composites substrate. The honeycomb structure after etching was helpful to alloying element absorb and diffuse into substrate surface, and the composite coating continuation was improved by the Co buffer layer. After exposing in air for 180 min at 1000 °C, the bulk C/C composites volatilized while the loss rate of coated C/C composites was 0.82%, showing an improved oxidation resistance. Mixed oxides mainly containing Al2O3 and Cr2O3 were formed in the composite coating surface and protected the C/C composites from oxidation in air.
Introduction Although C/C composites have been paid more attention in aerospace, brake material of automotive, and medical fields due to their high thermal stability, low density, and coefficient of thermal expansion (CTE) [1, 2, 3, 4], their application still be limited by the poor oxidation resistance above 370 °C [5, 6, 7, 8, 9, 10]. Adding borate or ZrC and SiC in bulk C/C composites could increase the oxidation resistance, but the matrix property was deteriorated [11, 12]. Surface coating is also an effective approach to increase oxidation resistance of C/C compositions. Borate glass coatings had a protective effect below 800 °C since the good fluidity of the coatings caused original holes sealing and crack closing [10, 13, 14, 15]. Good anti-oxidation property of SiC-coated C/C composites related to the decreased CTE between SiC coating and substrate [16, 17, 18]. Coatings of Ir, Hf, Cr, etc., prepared by plasma spraying also showed an improved high-temperature oxidation resistance [19, 20, 21, 22, 23].
ª Materials Research Society 2019
MCrAlY (M 5 Ni, Co, etc.) coatings are often used for t
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