【作者】 张忠礼；

【导师】 李德元；

【作者基本信息】 沈阳工业大学 ， 材料加工工程， 2007， 博士

【摘要】 高温氧化和热腐蚀是在高温环境下工作的设备及零件失效的主要原因。金属材料的抗氧化性能取决于该金属表面形成氧化膜的性质。Al是生成稳定、致密、保护性优良氧化膜的首选元素，Al合金化的Fe、Ni、Cu工程材料表现出很好的抗氧化和热腐蚀性能。由于材料的氧化与热腐蚀均由表面开始，本文通过采用电弧喷涂方法在钢铁和纯Cu基体表面施加Al或Al基合金涂层来提高材料的抗高温氧化及热腐蚀能力。为了研究高温条件下涂层与基体间原子的自扩散和互扩散机制，借助于电子显微镜（SEM）观察、电子探针（EPMA）以及X射线衍射分析等方法，分析了在加热过程中涂层的组织结构变化、铝化物扩散层的形成以及元素的扩散规律和相互影响，并运用有限元差分法计算了铁铝的互扩散系数。实验结果表明，在钢铁基体表面电弧喷涂的纯铝、铝青铜、FeCrAl涂层以及铝-铝青铜复合涂层体系、Al-FeCrAl复合涂层体系对基体的高温氧化防护都是有效的，尤其复合涂层体系的防护效果更佳。通过在CS₂实际生产现场的挂片试验证明了电弧喷涂的Al-FeCrAl复合涂层可以显著地增加灰铸铁的抗高温硫化腐蚀能力。在高温、高硫压和低氧压条件下，复合涂层中合金元素的相互扩散形成了FeCrAl金属间化合物，并且在涂层表面选择性氧化形成连续的Al₂O₃膜，因而具有很好的抗硫化能力。将表面喷涂纯铝涂层的钢铁试件高温加热时，在试件表面形成Fe₂Al₅铝化物层。形成铝化物层的厚度不但与加热温度和加热时间有关，还与热喷涂铝涂层的厚度有关。在700～1100℃加热温度范围内，铝涂层的厚度直接影响到扩散层的扩散层深度，涂层越厚，扩散层越深。在对纯铜基体表面喷铝扩散时也有类似于上述的影响规律，在800～900℃加热时，涂层中的铝向铜基体方向扩散，基体中的铜又反向扩散到涂层中，最后形成的铝化物扩散层由铜铝金属间化合物Cu₉Al₄和α-Cu固溶体两相组成。为研究铝化物内元素的扩散进程，利用MATLAB软件分别计算了800℃、900℃和1000℃加热条件下Fe₂Al₅相的互扩散系数。结果表明，Fe-Al互扩散系数随着铝浓度的增加而增大，800℃时的变化范围在10^-12～10^-11之间。900℃时在10^-11～10^-10之间。利用V. I. Dybkov经验公式建立了互扩散系数与形成铝化物层厚度的联系，计算获得的铝化物层厚度与实验测得数据接近，验证了所计算互扩散系数数值的合理性。更多还原

【Abstract】 Oxidation and hot corrosion are the main reasons of which the machines or parts used at elevated temperatures degrade. The oxidation resistance of metal materials mainly depends on the properties of the oxide formed on the metal surface. Aluminum is one of the best candidates since alumina film is stable, dense and continuous. Materials, such as steel, copper and nickel, alloyed with aluminum are good oxidation-resistant and hot-corrosion-resistant. It is well known that high-temperature oxidation and hot-corrosion take place on the surface of materials. In order to protect steel and copper parts used at elevated temperatures from oxidation and hot corrosion, arc-sprayed aluminum coatings and aluminum-based coatings were studied in this dissertation.To estimate the behaviors of the coatings at elevated temperature, some hot-corrosion tests and continuous oxidation kinetics tests were performed. By using scanning electron microscopy （SEM）, electron probe micro analyzer （EPMA） and X-Ray diffraction analyzer, the surface morphology of coatings and the microstructure of the diffusion layers formed in the coatings and substrates were examined. Also, the relationships between the process parameters, the composition of coating and the thickness of the diffusion layers were studied in this work. In addition, the interdiffusivities of the elements in aluminized layers were calculated by using finite element methods.The results of the experiments revealed that the arc sprayed single coatings of aluminum, aluminum bronze or FeCrAl and the composite coatings of aluminum/aluminum bronze or aluminum/FeCrAl could well protect the steel substrate from high-temperature oxidation, the composite coatings especially being better. The high-temperature sulphuration tests in situ gave a strong proof that aluminum/FeCrAl composite coatings provided a good preservation to gray iron substrate. Under the conditions of high sulphur and low oxygen atmosphere at elevated temperature, the interdiffusion of the elements in the composite coatings resulted in the formation of an intermetallic compound, AlCrFe₂. Therefore, the coatings were oxidation-resistant and sulphuration-resistant since there was a preservative alumina layer formed on their surface.When the specimens coated with aluminum were heated at high temperatures, an intermetallic compound, Fe₂Al₅, was formed on them, because of the interdiffusion of aluminum and iron atoms. It was found that the process parameters and the thickness of as-sprayed aluminum coating could greatly effect on the thickness of the diffused layers. The thicker the arc-sprayed aluminum coating, the thicker the diffusion layers at the temperatures ranging from 700—1100℃.It is much the same as steel that the thickness of diffusion layers was effected on by the thickness of as-sprayed aluminum coating on the copper substrate. There were two layers in the diffused region, the outer layer which originally was an as-sprayed aluminum coating was fomied by the diffusion of copper atoms into the coating upwards and the inner layer formed by the diffusion of aluminum atoms into copper substrate downwards. The results of X-ray diffraction and EDS analyses revealed that both layers consisted of CU₉Al₄ andα-copper solid solution.By using MATLAB software, the interdiffusivities of Fe₂Al₅ phase at temperatures of 800°C, 900°C and 1000°C were calculated to study the diffusing behaviours of elements in aluminid layers. The results of calculation revealed that the interdiffusion coefficients at 800°C increased with increasing of aluminum concentration in the diffusion layer, which ranged from 10^-12 to 10^-11. However, that at 900°C was from 10^-11’ to 10^-10, which was tens times more than that at 800°C under the same concentration conditions. By using V. I. Dybkov’s experimental formulation, which has relation with interdiffusion coefficients, the thickness of the aluminide was calculated. The calculated results did not have big difference with those from experiments so it proved indirectedly calculated interdiffusion coefficients to be reasonable.更多还原