冷喷涂制备TiAl3型高温防护涂层的研究

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	冷喷涂制备TiAl3型高温防护涂层的研究
	杨婧
学位类型	硕士
导师	熊天英 ; 金花子
	2011
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料加工工程
关键词	冷喷涂 Tial基合金 Tial3涂层高温防护 Cold Spray Tial Alloy Tial3 Type Coating High Temperature Protection
摘要	"TiAl基金属间化合物合金因具有密度低和力学性能优异等特性，成为极具希望的新型高温结构材料，在汽车及航空航天工业具有广泛的应用前景。但是室温韧性不足以及在超过800℃时抗氧化性能较差限制了其进一步应用。在TiAl基合金表面施加抗氧化涂层是提高其抗氧化性能的有效手段。本文采用冷喷涂及后续热扩散处理的方法在TiAl基合金上制备了几种TiAl3型涂层，研究了涂层的组织结构、硬度及高温氧化性能，并分析了涂层的热扩散形成及氧化退化机制。主要研究结果如下：在γ-TiAl基合金上冷喷涂纯Al后经630℃，5h扩散，形成内部为DO22型TiAl3、外部为纯Al的复合涂层。在950℃氧化后，TiAl3-Al复合涂层中的相结构发生了显著的变化。涂层内部由TiAl3相变为一层均匀致密的TiAl2相，外部由纯Al相原位转化为弥散分布 Al2O3 内氧化物的TiAl3相。涂层表面生成一层连续的保护性Al2O3膜。氧化直到1000 h，涂层的氧化产物仍以Al2O3为主，含有少量TiO2。没有检测到氧扩散进入TiAl2中间层及TiAl基体内。氧化过程中，TiAl3相与基体发生互扩散反应退化为TiAl2相，而TiAl2的生长速度为先快后慢。采用冷喷涂在γ-TiAl基合金上分别喷涂纯Al及Al-Al2O3混合粉末，然后在空气中720℃热扩散4h形成扩散态涂层。两种扩散态涂层均主要为致密的TiAl3相。不同的是，Al-Al2O3复合扩散涂层表面有Al2O3颗粒不连续地分布。950 ℃的恒温氧化试验表明两种扩散涂层均能有效地降低γ-TiAl的氧化速度。氧化动力学近似符合三段抛物线规律。在最终稳态阶段，纯Al扩散涂层的氧化速率常数Kp约为空白TiAl的1/3，而Al-Al2O3复合扩散涂层的Kp则约为空白TiAl的1/7。Al-Al2O3复合扩散涂层中不连续分布于表层的Al2O3颗粒被认为是其低氧化速率的主要因素。首先采用辉光等离子溅射沉积一层Cr膜，再冷喷涂Al-Ti混合涂层的方法，在γ-TiAl基合金上制备出Cr+Ti-Al复合涂层。然后经640 ℃，5 h及1000 ℃，5 h的两步热扩散处理后，形成由改性L12 型TiAl3外层及TiAl2内层组成的两层复合涂层。L12型TiAl3硬度约为DO22型TiAl3的一半。950 ℃的氧化实验表明含L12型TiAl3及TiAl2的两层复合涂层显著改善了TiAl基合金的抗氧化性能。涂层表面生成单一、连续致密的α-Al2O3膜。氧化过程中，L12型TiAl3层逐渐退化，TiAl2层逐渐扩大。氧化50 h后，L12型TiAl3层呈片状不连续散布于TiAl2层中。"
其他摘要	"TiAl intermetallic alloys are considered as potential materials for high-temperature applications, such as, parts in automotive and aero engines, due to their low density and their well-balanced mechanical properties. However, the limited ductility at room temperature and the insufficient oxidation resistance at temperatures above 800°C pose a bottleneck to successful applications. Applying surface coatings on TiAl alloys is an effective approach to enhance oxidation resistance. In this thesis, several different TiAl3 based coatings were produced on TiAl alloys by cold spray and subsequent interdiffusion treatment. Microstructure, microhardness and high temperature properties of the coatings were studied. Mechanism of formation of these coatings during heat treatment and degradation of the coatings during oxidation were investigated. The main results are as follows: A composite coating consisted of inner TiAl3 layer and out Al layer was prepared on TiAl alloy by cold spraying pure Al and subsequent heat treatment at 630 ℃ for 5 h. The phase structures of the coating changed significantly after oxidation at 950 ℃. The inner TiAl3 layer turned into a TiAl2 interlayer, while out Al layer in situ transformed into TiAl3 -matrix containing randomly dispersed internal alumina oxides. A continous and protective alumina scale formed on the surface of the coating. The formed oxides consisted of mainly Al2O3 and a little TiO2 after oxidation for 1000 h. No diffusion of oxygen could be detected beneath the TiAl2 interlayer or the TiAl substrate. TiAl3 reacted with TiAl substrate to form TiAl2 during oxidation. The growth rate of TiAl2 was rapid at the initial stage and then slowed down later. Pure Al and Al- Al2O3 mixture were deposited respectively onγ-TiAl alloy substrate by cold spray. Two diffusion coatings were produced on the surface of the substrate after interdiffusion treatment of the Al-sprayed and Al-Al2O3-sprayed specimens at 720 ℃ for 4 h in air. Both of these two diffusion coatings mainly composed of TiAl3 which exhibited good adhesion with the substrate, except that some Al2O3 particles distributed uncontinuously on the surface of Al-Al2O3 diffusion coating. Isothermal oxidation test at 950 ℃ indicated that both of the two diffusion coatings can dramatically reduce the oxidation rate of γ-TiAl. Approximate three parabolic stages of the oxidation were observed for these coatings. During the steady oxidation stage, the parabolic rate constant Kp of specimens with Al and Al-Al2O3 diffusion coatings can be reduced to about 1/3 and 1/7, respectively, as compared to that of bare TiAl. The result suggested that Al2O3 particles which dispersed uncontinuously on the surface of Al-Al2O3 diffusion coating was a major factor in the further improvement of the oxidation resistance. Cr-Ti-Al composite coating was prepared on γ-TiAl alloy by combining glow plasma sputtered Cr film with cold sprayed Al-Ti powder mixtures. The heat treatment performed on the as-deposited Cr-Ti-Al composite coating was carried out in two stages, first at 640 ℃ for 5 h and second at 1000 ℃ for 5 h. A laminate coating composed of out modified L12 type TiAl3 layer and inner TiAl2 layer was formed on the surface of the substrate after the interdiffusion treatment. The microhardness for L12 phase was about 1/2 of that for the DO22 type TiAl3. High temperature oxidation test at 950 ℃ indicated that the laminate coating which consisted of L12 outlayer and TiAl2 innerlayer could significantly improve the oxidation resistance of TiAl alloy. A continous and dense Al2O3 scale was formed on the outer surface of the coating. A gradual degradation of the L12 layer occurs simultaneously to an increase of the TiAl2 layer thickness during the oxidation. After oxidation for 50 h, L12 phase distributed in the form of tablets in the TiAl2 layer."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64400
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	杨婧. 冷喷涂制备TiAl3型高温防护涂层的研究[D]. 北京. 中国科学院金属研究所,2011.