【作者】 李文川；

【导师】 凌国平；

【作者基本信息】 浙江大学 ， 材料科学与工程， 2011， 硕士

【摘要】 铝化物涂层由于其氧化物致密,具有优良的抗氧化、抗硫化性能,因此被广泛用于燃气涡轮机及火箭发动机、核反应堆、火力发电厂、石油化工设备等领域。A1-Cr合金涂层是铝化物涂层的一种,它除了具备常见铝化物涂层的抗氧化性能外,还具有抗热冲蚀性能和阻氚性能。但A1-Cr合金涂层的制备都在900℃以上高温进行,这将降低基体的力学性能。本文通过在水溶液电镀Cr,之后在摩尔比为2：1的AlCl3-EMIC(氯化1-甲基3-乙基咪唑)离子液体中在Cr镀层表面镀Al,再通过低温热处理,制备Al-Cr合金涂层。用光学显微镜、二次电子及背散射电子、特征X射线能谱及X射线衍射,研究了热处理对A1-Cr涂层组成与结构的影响。用努氏硬度测定仪对合金层的力学性能进行检测。同时对不同A1-Cr合金相的涂层进行了氧化行为的研究。对高Cr含量的6.5μm Cr/15μm Al复合镀层热处理研究表明：500-740℃、5min热处理时,Cr/Al复合镀层在540℃时A1、Cr界面可以形成A1-Cr合金层。在640℃和740℃,5 min～16h时间内,其最外层合金层的相依次为Al4Cr、Al11Cr4、Al9Cr4和Al8Cr5; 740℃、1h可获得Al9Cr4为主相的合金涂层；640℃、16h和740℃、16h获得以A18Cr5为主相的合金涂层；Al8Cr5涂层与基体之间不发生明显的互扩散；短时间或氮气保护热处理可以避免Al-Cr合金涂层外表层空洞形成；在740℃热处理时,5 min-20 min内,反应掉的Cr层及Al9Cr4合金层的厚度与时间的平方跟成线性关系；Al8Cr5、Al9Cr4、Al11Cr4和Al4Cr合金层的硬度和韧性依次减小。对低Cr含量的1.6μm Cr/15μmAl复合镀层热处理的研究表明：低温热处理时,最初高Cr和低Cr含量镀层的反应规律一致,但当Cr层消耗完之后,所形成的Al-Cr合金涂层会与基体发生扩散形成Al-Cr-Fe合金层；1.6μm Cr/15μmAl的复合镀层经600℃、30min热处理,可得到以Al4Cr为主的Al-Cr涂层；Cr、Al镀层在低温扩散反应过程中,最初形成相为Al7Cr相。Al7Cr, Al4Cr和Al8Cr5的Al-Cr合金涂层经690℃、100h氧化,XRD、XPS检测结果表明：A1-Cr合金试样经喷砂后氧化表面粗糙、经抛光后氧化表面平整致密,同时喷砂试样形成的氧化物比抛光试样形成的氧化膜厚；外表面为Al4Cr和Al7Cr的高Cr涂层试样在氧化过程中,涂层会继续反应最终形成Al8Cr5相；XPS检测结果表明,Al-Cr合金相氧化后最外表层为Al2O3;同时Al8Cr5、Al4Cr和Al11Cr2相氧化后表面Al2O3的含量依次增高。更多还原

【Abstract】 Aluminide coating for elevated temperature applications rely on the formation of a continuous, and compact Oxide scales for protection in oxidizing and sulfide environment. Aluminide coating were used widely in gas turbine, rocket engine, nuclear reactor, thermal power plant, petrochemical equipment.Al-Cr alloy coating is one of Aluminide coating, which have good oxidation and sulfuration resistant also have excellent thermal erosion and Tritium permeation resistant. The common formation of Al-Cr alloy coating is above 900℃, which can case degradation in mechanical properties of substrate alloys.In this paper, the Cr/Al composite coatings were obtained on 1Cr17 stainless steel by electrodepositing Cr from aqueous solution followed by electrodepositing Al from AICl3-EMIC (molar ratio 2:1) ionic liquid. The Al-Cr alloy coating can produced by heat treatment to the Cr/Al composite coating. Effects of heat treatment on composition and phase structure of Al-Cr alloy layers were studied by using optical microscope (OM), scanning electron microscope (SEM), backscattered electron (BSE), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The mechanical properties of alloy layer were test by Koop hardness equipment.The oxidation behaviors of different Al-Cr alloy coating were studied.Effects of heat treatment on structure transformation to the 6.5μm Cr/15μm Al composite coating were studied. The result show that an Al-Cr alloy layer at the Cr/Al interface was formed at heat treatment at 540℃in 5min. In time of 5 min～16h at 640℃and 740℃, the outer layer is Al4Cr, Al11Cr4, Al9Cr4and Al8Cr5 in turn. The main phase of alloy layer is Al9Cr4, Al8Cr5 and Al8Cr5 was obtained by the heat treatment of 740℃、1h,690℃、16h and 740℃、16h, respectively. The Al8Cr5 layer formed with single phase does not obviously interdiffuse with the substrate. The voids formed in coating surface within heat treatment under nitrogen and short time are less than that formed under air atmosphere and long time. The thickness of Al9Cr4 and reacted Cr coating is linear relationship with the square root of heat treatment time from 5 min to 20 min at 740℃. The Koop hardness tests show that the AlgCrs, Al9Cr4, Al11Cr4 and Al4Cr layer in turn reduce the hardness and toughness.Study on the lower Cr-containing of 1.5μm Cr/15μm Al composite coating to the form Al-Cr alloy layer by heat treatment at the temperature below Al melting. The result show that the law of the reaction of Cr/Al composition coating between the higher and the lower Cr-containing were the same at the beginning. When the Cr layer in the lower Cr-containing of Cr/Al composition coating is react off, the Al-Cr alloy can reacted with the substrate. For 1.6μmCr,15μm Al composite coatings, the main phase of alloy layer is Al4Cr was obtained by 30min heat treatment at 600℃. The first phase formation in the Cr/Al composition coating by heat treatment is the Al7Cr.The oxidation behavior of the outer layer of Al7Cr, Al4Cr and Al8Cr5 phase were studied in the temperature at 690℃in 100 h. The surface morphology of the sandblasting sample is rough, and of the polishing sample is smooth and dense. The oxidation film of sandblasting sample is thicker than the polishing sample. The Al8Cr5 were formed by oxidation to the outer layer of Al7Cr and Al4Cr phase sample at last. The xps test result show that the surface of oxide of Al-Cr alloy is Al2O3. The containing of the Al2O3 by the oxidation of Al8Cr5, Al4Cr and Al11Cr2 is increased in turn.更多还原