Long-term behaviour of Nb and Cr nitrides nanostructured coatings under steam at 650 °C. Mechanistic considerations
Long-term behaviour of Nb and Cr nitrides nanostructured coatings under steam at 650 °C. Mechanistic considerations
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DOI：
10.1016/j.jallcom.2017.12.288
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发表时间：
2018-03-30
影响因子：
6.2
通讯作者：
Muelas, R.
中科院分区：
文献类型：
--
作者：
Aguero, A.;Juez-Lorenzo, M.;Muelas, R.
蒸汽发电厂在超临界条件下运行的需求越来越大，即温度超过600摄氏度。在这些条件下，抗蠕变的铁素体钢氧化，因此需要涂层以持久。物理气相沉积，特别是高功率脉冲磁控溅射沉积的Cr/Nb比为2.45的CrN/NbN纳米级多层涂层在暴露于650 ℃的纯蒸汽环境中长达2000小时时表现出优异的性能。然而，Nb在提供保护方面的作用尚不清楚。为了研究这类涂层的长期性能以及确定Nb对其抗氧化性的影响，对Cr/Nb比为1.16的CrN/NbN涂层进行了12，650小时的研究。该涂层是硬的、良好粘附的并且耐环境腐蚀，这是待施加在涡轮机叶片上的涂层特别需要的性质。涂层还保护P92在650 ℃下不被蒸汽氧化，然而涂层生长缺陷显著影响抗氧化性。长时间暴露可以研究此类陶瓷涂层提供的保护/降解机制。结果表明，由于基体缺陷引起的涂层缺陷的存在，导致氧化物结核的生长。此外，较高Nb的CrN/NbN涂层缓慢氧化，在12，650 h后在很大程度上消耗涂层。因此，形成了含有Cr和Nb的保护性氧化物，至少在测试持续时间内保持良好地附着于基材，并防止基材被蒸汽进一步氧化。有趣的是，沉积涂层中存在的薄空隙通过形成富Cr氧化物而自愈，富Cr氧化物阻止蒸汽到达基材。(c)2017爱思唯尔B. V.保留所有权利。
There is an increasing demand for steam power plants to operate in super-critical conditions i.e. temperatures in excess of 600 degrees C. Under these conditions creep resistant ferritic steels oxidize and therefore require coatings in order to last. Physical vapor deposition and especially High Power Impulse Magnetron Sputtering deposited CrN/NbN nano-scale multilayer coatings with a 2.45 Cr/Nb ratio showed excellent performance when exposed to 650 degrees C in pure steam environment up to 2000 h. However the role of Nb in offering protection is unclear. In order to study the long term behaviour of this type of coatings as well as to determine the influence of Nb on their oxidation resistance, a CrN/NbN coating with a 1.16 Cr/Nb ratio was studied for 12,650 h. The coating is hard, well adhered and resistant to environmental corrosion, which are properties required in particular for coatings to be applied on turbine blades. The coating also protects P92 from steam oxidation at 650 degrees C, however coating growth defects influence significantly the oxidation resistance. The long-time exposure allowed to study the protection/degradation mechanisms provided by this type of ceramic coatings. It was found that oxide nodules grow due to the presence of coating defect originated from substrate defects. Moreover, the higher Nb CrN/NbN coating slowly oxidizes, consuming the coating to a large extent after 12,650 h. As a result, protective oxides containing Cr and Nb are developed, remaining well attached to the substrate for at least the test duration, and preventing further substrate oxidation by steam. Interestingly, thin voids present in the as deposited coating self-heal by forming Cr rich oxides, which block steam to reach the substrate. (c) 2017 Elsevier B.V. All rights reserved.