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南京航空航天大学硕士学位论文 i 摘摘 要要 -TiAl 基合金密度低,具有高的比强度和比弹性模量,使用温度与高温 Ni基合金相近,但其密度仅为高温 Ni 基合金的一半,因此被认为是新一代高温结构候选材料之一,可广泛应用于汽车或航空发动机的高温部件。然而,-TiAl基合金的耐磨性能和抗高温氧化能力不足严重限制了其应用范围,成为亟待解决的关键问题。 利用表面处理技术在 -TiAl 基合金表面形成改性层是提高其摩擦学性能和抗高温氧化能力的重要手段。但常规的表面处理技术,如离子氮化、物理气相沉积、离子注入等获得的表面改性层,只适用于改善其在常温下中低载荷和中低滑动速度下的摩擦学性能,在高温高载荷、高滑动速度条件下,以上改性层往往由于改性层厚度不够、抗高温氧化能力差、韧性不足或结合强度低等问题而易导致失效。 针对上述问题,本文提出采用双层辉光等离子渗金属技术(DGPSAT),在-TiAl 基合金表面形成渗 Cr 及 Cr-C 共渗的改性层,随后用 OM,EDS,XRD,SEM 分析了改性层的显微组织、化学成分及其相组成,并测试了其表面弹性模量、表面显微硬度、高温(500)和常温摩擦磨损性能以及抗高温(830)氧化能力。 试验结果表明:(1)在一定的试验参数条件下,-TiAl 基合金可获得理想的表面改性层,其成分由表层向基体内部呈梯度分布,改性层与基体为完全冶金扩散层结合,表面弹性模量得到大幅度降低;(2)双层辉光等离子渗 Cr 和Cr-C 复合渗对提高 -TiAl 基合金的耐磨性能和高温抗氧化性能均起到有益作用,尤其是 Cr-C 复合渗,其表面显微硬度大大提高,表现出有益的耐磨性能和抗高温氧化能力。 关键词: -TiAl 基合金,辉光等离子铬碳共渗,耐磨性,高温抗氧化性能 南京航空航天大学硕士学位论文 iiABSTRACT The -TiAl based alloy has specialties of low density, high specific strength and high elastic modulus. Its working temperature is closely up to Ni based alloy, but the density of -TiAl is a half of Ni based alloy. So the -TiAl based alloy is considered to be one of the promising high temperature structural materials, for example the advanced automotive and aerospace engine components. However, the key problems in the practical use of the -TiAl based alloy are its poor wear resistance and high-temperature oxidation resistance. Surface treatment techniques are very effective ways to improve tribological properties -TiAl alloy and high-temperature oxidation resistance. Ion nitriding, physical vapor deposition and ion-implantation techniques etc. can be used under the room temperature, low-medium loading and sliding velocity condition. However,the surface-modification layers are easily destroyed because of their poor load-bearing capacity and bonding strength under the high temperature, high loading and sliding velocity condition. To solve these problems, this paper proposed to form Cr and Cr-C surface-modification layers on -TiA1 alloy by using the double glow plasma surface alloying technique。The microstructure, composition and phase structure of the surface modified layers will be analyzed by means of OM, EDS, XRD and SEM,respectively, and the elastic modulus of the Cr-C alloy layer, the micro-hardness, wear resistance at both high (500) and room temperature and high-temperature (830)oxidation resistance will be tested. The results show that: (1) the better modified layers can be acquired under specifically technological parameters. The composition of the surface modified layer distributed gradually from the surface to substrate of the -TiAl substrate, the modified layer is metallurgically bonded to the -TiAl substrate; (2) The plasma chromising and the duplex treatment of chromising layer and carburization are proved to be beneficial to the wear resistance at both high (500) and room temperature and high-temperature oxidation resistance of the -TiAl based alloy. Especially, the comparison with that of -TiAl based alloy, the combined treatments make the surface micro-hardness of the -TiAl based alloy increasing greatly, and the wear 南京航空航天大学硕士学位论文 iiiresistance and high-temperature oxidation resistance have been enhanced obviously. Keywords: the -TiAl based alloy, glow plasma chromising and carburization, wear resistance, high-temperature oxidation resistance 南京航空航天大学硕士学位论文 iv图表清单 图清单图清单 图 1.1 Ti-Al 合金二元相图. 4 图 1.2 -TiAl 的单胞晶体结构. 4 图 1.3 航空航天发动机用材料的发展趋势 . 5 图 1.4 CF6-80C2 发动机 -TiAl 低压涡轮叶片构成的五级转子(a)及单个叶片(b)26. 6 图 1.5 飞机叶片和压气机盘之间的微动磨损情况28. 7 图 1.6 双层辉光等离子渗金属基本原理示意图 .11 图 2.1 双层辉光等离子渗金属渗具布置示意图 . 15 图 2.2 实用双层辉光等离子渗金属炉 . 16 图 2.3 试验方案思路框图 . 18 图3.1不同温度条件下TiAl十Cr合金层的横截面金相照片(a) 980, (b)1060,(c)1150. 21 图3.2不同时间参数下的TiAl+Cr合金层的横截面金相照片(a)2h, (b)4h, (c)6h. 23 图 3.3 不同气压参数下的 TiAl+Cr 合金层的横截面金相照片 (a) 30Pa,(b) 35Pa,(c)40Pa. 25 图 3.4 不同气压参数下的 TiAl+Cr 合金层的表面显微硬度值. 25 图 3.5 TiAl+Cr 合金层横截面的 SEM 照片. 26 图 3.6 TiAl+Cr 合金层横截面成分分布曲线. 26 图 3.7 TiAl+Cr 合金层的 XRD 图谱 . 27 图 4.1 TiAl
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