Microstructural evaluation and thermal oxidation behaviors of YSZ/NiCoCrAlYTa coatings deposited by different thermal techniques

In this paper, two coating techniques, the high velocity oxy-fuel (HVOF) and air plasma spray (APS) techniques, were used to deposit a bond coat of NiCoCrAlYTa on the Inconel 625 substrate, followed by applying a topcoat of yttria-stabilized zirconia (YSZ). The samples were preoxidized in an argon-controlled furnace at a temperature of 1000 °C for 12 and 24 h to characterize the microstructure of a thermally grown oxide (TGO) using the two coating techniques. The most suitable preoxidized samples were further tested for isothermal oxidation at 1000 °C for up to 120 h, and a hot corrosion test was performed at 1000 °C for up to 52 h or until spalling occurred. As-sprayed and oxidized samples prepared with different coating techniques were evaluated in terms of their microstructure using different characterization methods, such as field emission scanning electron microscopy (FESEM), variable pressure scanning electron microscopy (VPSEM), energy dispersive X-ray spectroscopy (EDS) equipped with energy dispersive X-ray and X-ray diffraction (XRD) analyses. In addition, the mechanical properties of these samples were evaluated using adhesion tests. The results show that the YSZ/NiCoCrAlYTa coating applied with the HVOF technique forms a more thin and continuous layer of TGO than that obtained when applying a YSZ/NiCoCrAlYTa coating using the APS technique, indicating that a severe brittle oxidation interface exists between the two layers. The results also indicate that the mechanical strength obtained from the adhesion test of the coated samples is observably affected by the oxidation behaviors obtained with the different deposition techniques chosen.     

Ta含量对NiCoCrAlY涂层性能的影响

采用真空雾化的方法制备了Ta含量为0、2%及5%的NiCoCrAlYTa合金粉末,利用超音速火焰喷涂制备了三种涂层,研究了Ta对合金粉末微观组织及物相的影响,绘制了1050℃条件下涂层的高温氧化动力学曲线,研究了500h氧化试验后涂层组织和β相的分布,初步探讨了Ta元素对改善涂层抗氧化性能的作用机理。研究结果表明:Ta通过提高MCrAlY体系抗氧化元素的溶质浓度,促进了氧化膜的形成,随着Ta含量的增加,涂层的内氧化程度降低,涂层抗氧化性能提高。但含Ta涂层在长时间氧化条件下会生成CrTaO_4、AlTaO_4等尖晶石类氧化物,且Ta的氧化物PBR值较大,对涂层的抗热震性能不利。     

氧化时间对 NiCoCrAlYTa 涂层 / 镍基高温合金界面 显微组织影响

采用真空等离子喷涂技术在 DD407 合金和 DD6 合金上制备了 NiCoCrAlYTa 涂层。 通过 SEM、 EDS 等方 法研究了 900 ℃ 不同氧化时间下经热处理后 NiCoCrAlYTa 涂层 /DD407 合金和 NiCoCrAlYTa 涂层 /DD6 合金的 界面组织。 结果表明， 随着氧化时间延长， NiCoCrAlYTa 涂层 /DD407 合金界面扩散层组织析出 σ 相， σ 相形状 发生明显变化， 并且界面扩散层厚度缓慢增加， 扩散系数为 13.32 μm/h； 随着氧化时间延长， NiCoCrAlYTa 涂层 /DD6 合金界面扩散层析出 TCP 相（σ 相和 μ 相） ， TCP 相形状未发生明显变化， 并且界面扩散层厚度缓慢增加， 扩散系数为 3.85 μm/h。     

涡轮叶片NiCoCrAlYTa涂层超声测厚

NiCoCrAlYTa涂层作为航空发动机高温部件的抗氧化涂层而得到广泛应用,涂层的厚度影响其抗氧化性能。利用超声波在涂层和基体间传播中的信号突变现象,采用小波变换技术分离出信号突变点和突变点间时间间隔,计算出涂层厚度,并应用于带有NiCoCrAlYTa涂层的涡轮叶片厚度测量,超声涂层厚度测量结果与金相解剖厚度测量数据进行对比,研究结果表明,使用的超声涂层厚度测量方法获得的涂层与金相法测厚数据基本接近,在平均厚度150μm,测量相对误差在5%以内。