【作者】 王亮兵；

【导师】 陈照峰； 张平则；

【作者基本信息】 南京航空航天大学 ， 材料学， 2009， 硕士

【摘要】 铱具有优异的高温抗氧化性能,是目前唯一能同时满足高温强度、高熔点和优异抗氧化性的贵金属,可作为难熔金属钼、铌和碳/碳复合材料抗氧化涂层。本研究采用双层辉光等离子表面合金化技术制备铱涂层,采用扫描电镜、X-射线衍射仪和光学显微镜等分析手段分析铱涂层的表面形貌和微观结构,并利用划痕仪、纳米压入和氧-乙炔焰烧蚀等测试手段对铱涂层进行性能表征。研究结果表明,工艺参数、基体对铱涂层的表面形貌,沉积速率,(220)晶面优先生长程度等都有较大影响。难熔金属与铱涂层之间结合较好,界面处存在一个两元素共存的共混区,共混区内,基体、涂层元素呈梯度分布;铱涂层呈柱状晶,生长方向垂直于基体表面。纳米压入研究表明,同种基体上铱涂层的应力状态均匀性较好,不同基体上涂层应力状态不同,从而导致涂层的表面硬度、弹性模量差异较大。烧蚀实验研究表明,烧蚀失效主要体现在基体氧化后蒸发,气体冲蚀铱涂层导致其起泡和脱落;铱涂层高温状态下由柱状晶转变为等轴晶导致晶界处有微孔出现;由于涂层未完全涂敷基体表面,基体有不同程度的氧化。本研究采用双层辉光等离子表面合金化技术首次制备铱涂层,研究发现利用该方法制备的涂层具有(220)晶面择优取向,并对这一现象从涂层晶粒间应变能密度方面进行了分析讨论;提出了铱涂层界面处共混区的概念,共混区内涂层元素、基体元素呈梯度分布,对共混区的形成过程进行了模型解释。更多还原

【Abstract】 Iridium has excellent properties of oxidation resistance and high strength at high temperature. In this dissertation, Iridium coatings were prepared on the surfaces of molybdenum, niobium and carbon/carbon substrates by double glow plasma technique. The microstructure and the morphology of the coatings were systematically investigated by scanning electron microscope, x-ray diffraction and microscope. The binding performance, mechanic property and quality parameters were measured by the scratch test measurement and nano-indendation, respectively. The ablation property of the Iridium coating was evaluated by oxy-acetylene torch in the temperature range of 1800~2000oC.The quality of the coating was related to the process parameters. The micromorphology, the deposition ratio and the (220) preferential growth orientation of the Iridium coating were determined by the process parameters and the substrates. The coating/substrate interface exhibited excellent adhesion with no evidence of delamination. A buffer layer, which combined the elements of the substrate and the target, presented between the coating and the substrate. The element concentration distributed gradiently along the depth of the buffer layer. The coating was composed of lots of columnar crystals which had embedded mode. The growth direction of these columnar crystals was perpendicular to the surface of the substrate. The mechanical properties of the coating were different for the different substrates. The difference of the stress state resulted from the deposition process and the thermal stress. One failure mode of the coating under oxy-acetylene torch at high temperature was the surface blistering for the oxidation of the substrate. Another failure model of the coating was the recrystallization from the column crystal to equiaxed grain that result in the micropore in the grain boundary. Because the substrates were not fully covered by the coating, the substrates were oxidized during ablation.Iridium coating was firstly prepared on the refractory materials by double glow plasma technique. There were two new phenomena in the experiment. The first was the (220) preferential growth orientation which was explained by the strain energy density between the grains. The second was the buffer layer between the coating and the substrate which was explained by sputtering and diffusion.更多还原