Effect of hydrogen from steam on external and internal oxidation processes of Fe- and Ni-base alloys

蒸汽中的氢气对铁基和镍基合金的外部和内部氧化过程的影响

• 批准号: 390545697
• 负责人: Professor Dr. Reinhard Dörner
• 金额: --
• 依托单位: Department of Mechanical Engineering and Materials Science
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/390545697?language=en
• 关键词: Effect; hydrogen; steam; external; internal

Metallic materials for high-temperatures rely on the formation oxide scales for protection from the environment. The critical alloy chromium or aluminium concentration required to achieve formation of a protective surface scale is known to be affected by the presence of water vapour. A high number of investigations have revealed that the mechanisms responsible for this technologically important effect differ between various alloys. Recenttudies indicate that, in the higher temperature range, hydrogen present in the gas or released by the reaction of water vapour with the metal surface affects the selective oxidation of the protective-scale-forming element. This may be attributed to a direct effect of hydrogen on the internal oxidation process and/or growth rate of the transient, non-protective oxide. For the latter (Fe-rich oxides in the case of Fe-Cr base alloys and Ni-rich oxides in the case of Ni-Cr(-Al) base alloys) may be related to hydrogen doping of the oxide lattice or molecular transport of gaseous species (water vapour and/or hydrogen) through the scale. One major drawback in elucidating the underlying mechanisms has been the ability to acquire a depth-resolved quantitative analysis of hydrogen in the surface scale and in the internal oxidation zone. In the proposed project the effect of water vapour on protective scale formation at temperatures around 900°C will be studied using three model alloy systems, FeCr- and NiCr-base and NiCrAl alloys. For this purpose in-situ determination of oxidation kinetics will be combined with microstructural characterization using SEM, EDX/WDX, TEM, XRD and depth profiling by SNMS and GDOES. The alloy compositions will be chosen in such a way that the effect of water vapour on internal oxidation kinetics can be studied with or without presence of an external oxide scale of the base elements Fe or Ni, respectively. Additionally, the effect of gas composition on the conditions for protective chromia- or alumina-scale formation will be determined and correlated with the effect of water vapour on internal oxide formation. Emphasis will be put on using a new approach for depth-resolved detection of hydrogen in the outer oxide layer, the internal oxidation zone and the unaffected alloy. For this purpose NRA and PIXE analysis in well-defined sputter craters produced by GDOES will be utilized. For excluding possible effects of background hydrogen signals, some of the exposures will be carried out in gases containing D2 and/or D2O rather than H2 and/or H2O. For elucidating contributions of molecular transport of gaseous species via microdefects induced by oxide growth stresses, in-situ studies using acoustic emission will also be employed. A modelling approach will be developed to modify existing oxidation theories to account for the presence of water vapour and/or hydrogen on the conditions for obtaining protective external scale formation in case of FeCr-, NiCr- and NiCrAl-base high temperature alloys.

金属材料在高温下依靠氧化皮的形成来保护其免受环境的影响。已知形成保护性表面氧化皮所需的临界合金铬或铝浓度受水蒸气存在的影响。大量的研究表明，这种技术上重要的影响的机制在各种合金之间是不同的。最近的研究表明，在较高的温度范围内，存在于气体中的氢或通过水蒸气与金属表面反应释放的氢影响保护性结垢形成元素的选择性氧化。这可归因于氢对瞬态非保护性氧化物的内氧化过程和/或生长速率的直接影响。对于后者（在Fe-Cr基合金的情况下的富Fe氧化物和在Ni-Cr（-Al）基合金的情况下的富Ni氧化物），可能与氧化物晶格的氢掺杂或气态物质（水蒸气和/或氢）通过氧化皮的分子输运有关。在阐明潜在的机制的一个主要缺点是能够获得一个深度分辨的定量分析氢的表面尺度和内部氧化区。在拟议的项目中，将使用三种模型合金系统，FeCr基和NiCr基以及NiCrAl合金，研究在900°C左右的温度下水蒸气对保护性水垢形成的影响。为此，氧化动力学的原位测定将与使用SEM、EDX/WDX、TEM、XRD的微观结构表征以及SNMS和GDOES的深度剖析相结合。选择合金成分时，应使水蒸气对内氧化动力学的影响可以分别在有或没有基体元素Fe或Ni的外部氧化皮的情况下进行研究。此外，将确定气体成分对保护性氧化铬或氧化铝垢形成条件的影响，并将其与水蒸气对内部氧化物形成的影响相关联。重点将放在使用一种新的方法，深度分辨检测氢的外氧化层，内氧化区和未受影响的合金。为此，将利用GDOES产生的明确溅射坑中的NRA和PIXE分析。为了排除背景氢信号的可能影响，一些暴露将在含有D2和/或D2 O而不是H2和/或H2O的气体中进行。为了阐明通过氧化物生长应力引起的微缺陷的气体物种的分子输运的贡献，使用声发射的原位研究也将被采用。将开发一种建模方法来修改现有的氧化理论，以考虑到在FeCr-，NiCr-和NiCrAl-基高温合金的情况下获得保护性外部氧化皮形成的条件下水蒸气和/或氢的存在。