轻质结构材料表面激光熔覆耐高温、隔热涂层研究

发布时间：2018-06-09 21:44

本文选题：轻质结构材料 + 激光熔覆　；参考：《大连理工大学》2016年硕士论文

【摘要】：钛合金和SiC纤维复合材料以其低密度、高比强、耐高温等优异性能而广泛应用于高超声速飞行器热端部件,但随着高超声速飞行器飞行速度的不断提升使得高温热端部件的服役条件面临更加严苛的要求。为改善钛合金在极高温度下使用抗高温氧化性能不足和SiC纤维复合材料换热系数低极高温度下易烧损的情形,通过在钛合金和SiC纤维复合材料表面制备具有可耐极高温度和隔热性能的涂层将具备重要的工程价值。本文利用激光熔覆技术在TC4钛合金表面制备了不同Ti添加量的Nb-Al-Ti高温合金涂层。利用X射线衍射仪、扫描电子显微镜、电子探针等现代微观检测技术以及显微硬度计、热重分析仪等性能检测设备,系统分析了Ti添加量对涂层微观组织及性能的影响规律。同时利用等离子喷涂技术在SiC纤维复合材料表面制备了不同CeO2添加量的CeO2/Y2O3-ZrO2的隔热涂层,并对涂层表面进行了激光上釉处理。利用以上微观分析技术及高级傅里叶红外变换光谱仪、隔热性能测试装置等性能检测设备,系统分析CeO2添加量对涂层组织形貌及性能的影响规律。铌合金以其高熔点、低密度、高温强度大等特点,成为了替代镍基、钴基高温合金及铝系中间合金极有潜力的高温结构材料之一,且通过合金化的方法加入Ti、Al等元素显著改善了铌合金的抗高温氧化性能。研究表明,随着Ti添加量的增加合金涂层依次形成了β-(Nb,Ti)树枝晶+枝晶间Nb3Al和β-(Nb,Ti)树枝晶+枝晶间NbsAl+Nb1Al组织,且β-(Nb,Ti)树枝晶的含量随Ti添加量的增加逐渐降低,而Nb3Al的含量先增加后降低再增加,当Ti添加量超过23.0 at.%时,涂层中开始出现Nb2Al相,并随Ti添加量的增加而增加。当Ti添加量达到37.0 at.%时,Nb3Al的生长形态发生了变化。合金涂层的显微硬度随着Ti添加量的增加逐渐增加,受金属间化合物数量和微观偏析等因素的影响,当Ti添加量为23.0 at.%时涂层具有最佳的抗高温氧化性能。(6%～8%Y203)-Zr02热障涂层材料以低热导率、高热膨胀系数等性能广泛应用于航空航天领域热端部件,通过向涂层中加入不同含量的CeO2以期提升ZrO2高温下的稳定性进而提升涂层服役温度。结果表明,随着CeO2添加量的增加,喷涂态涂层中四方相ZrO2的含量逐渐增加,涂层表面孔隙及微观裂纹数量减少,致密度提高；经激光上釉处理后消除了表面的孔洞和裂纹,表面呈现均匀平整的玻璃状,且随着CeO2添加量的增加表面柱状晶的尺寸逐渐减小。通过隔热性能试验表明,添加CeO2的涂层具有比传统热障涂层更好的隔热性能,且随着CeO2添加量的增加,涂层隔热性能呈现增加的趋势。
[Abstract]:Titanium alloy and sic fiber composites are widely used in the hot end parts of hypersonic aircraft due to their low density, high ratio, high temperature resistance and other excellent properties. However, with the increasing flight speed of hypersonic vehicles, the service conditions of the components at high temperature and hot end are facing more stringent requirements. In order to improve the low oxidation resistance of titanium alloy at very high temperature and the low heat transfer coefficient of sic fiber composites, the heat transfer coefficient of sic fiber composites is easy to burn at very high temperature. It is of great engineering value to prepare coatings on the surface of titanium alloy and sic fiber composites which can withstand extremely high temperature and heat insulation. In this paper, Nb-Al-Ti superalloy coatings with different amounts of Ti were prepared on the surface of TC4 titanium alloy by laser cladding technique. The effects of Ti addition on the microstructure and properties of coatings were systematically analyzed by means of X-ray diffractometer, scanning electron microscope, electron probe, microhardness tester and thermogravimetric analyzer. At the same time, the thermal insulation coating of CEO _ 2 / Y _ 2O _ 3-ZrO _ 2 with different amount of CEO _ 2 was prepared on sic fiber composite surface by plasma spraying technology, and the coating surface was glazed by laser. The effects of CeO2 addition on the microstructure and properties of the coatings were systematically analyzed by means of the above micro-analysis techniques, advanced Fourier transform spectrometer and thermal insulation testing equipment. Because of its high melting point, low density and high strength at high temperature, niobium alloy has become one of the most potential high-temperature structural materials instead of nickel base, cobalt base superalloy and aluminum master alloy. The oxidation resistance of niobium alloy was improved by alloying tial and other elements. The results show that the structure of Nb3Al and Nb1Al between dendritic dendrite and NbsAl Nb1Al among dendritic dendrites are formed with the increase of Ti content, and the content of NbsAl Nb1Al) dendritic grains decreases with the increase of Ti content, and the content of NbsAl Nb1Al in dendritic coatings decreases with the increase of Ti content, and the content of NbsAl Nb1Al in dendritic dendrites decreases with the increase of Ti content. However, the content of NB _ 3AL increased first and then decreased, and then increased. When Ti content exceeded 23.0 at.%, the NB _ 2AL phase began to appear in the coating and increased with the increase of Ti content. The growth morphology of NB _ 3AL was changed when Ti content reached 37.0 at.%. The microhardness of the alloy coating increases with the increase of Ti content, which is affected by the number of intermetallic compounds and microsegregation. When Ti content is 23. 0 at.%, the coating has the best oxidation resistance at high temperature. Y203-Zr02 thermal barrier coating material has been widely used in aerospace hot end parts with low thermal conductivity and high thermal expansion coefficient. By adding different amounts of CeO2 to the coating to improve the stability of ZrO _ 2 at high temperature and then to raise the service temperature of the coating. The results show that the content of tetragonal phase ZrO _ 2 in sprayed coating increases with the increase of CEO _ 2 content, the number of pores and micro-cracks on the coating surface decreases and the density increases, and the holes and cracks on the surface are eliminated after laser glazing. The surface is flat glass and the size of the columnar crystal decreases with the increase of CeO2 content. The results of thermal insulation test show that the coating with CeO2 has better thermal insulation performance than the traditional thermal barrier coating, and the thermal insulation performance of the coating increases with the increase of the amount of CeO2.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TG174.4

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