Oxide scale formation on Al containing Ni–Cr‐based high temperature alloys during application as flame tube material in recirculation oil burners
Oxide scale formation on Al containing Ni–Cr‐based high temperature alloys during application as flame tube material in recirculation oil burners
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循环油燃烧器火焰管材料中含铝镍铬基高温合金氧化皮的形成
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发表时间：
2008
期刊：
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通讯作者：
J. Mayer
中科院分区：
文献类型：
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作者：
H. Ackermann;G. Teneva;H. Köhne;K. Lucka;S. Richter;J. Mayer
火焰管是采用火焰管稳燃概念的燃烧器的重要功能部件。在典型的燃烧条件下，火焰管的材料暴露于高温（≥900 °C）和燃烧气体的腐蚀侵蚀。此外，由于燃烧器通常间歇地操作，材料遭受极端的温度和气氛变化。对于火焰管，期望寿命约为8000小时。主要使用金属高温材料。本工作的范围是在应用条件下和最高材料温度超过900 ° C时测试用作管材的替代高温合金。奥氏体镍铬基合金（601、602 CA、617和693）的耐腐蚀性已在燃烧器试验台中进行了研究，材料最高温度为950和1000 °C，暴露时间为50至3000 h。合金的铬含量为20至30重量%，铝含量为1至3.4重量%。通过电子显微探针分析合金样品的金相横截面，获得有关表面区域氧化物的微观结构和组成以及暴露时间期间变化的信息。这项研究的重点是观察到的合金元素铝的氧化皮的发展和合金的寿命上的具体影响。在500 h暴露时间后，在合金表面形成氧化铬皮，氧化铝主要沿沿着晶界在下面形成。对于铝含量较低的合金，铝氧化物形成开放的网络而不是封闭的层。对于铝含量最高的合金（693合金），50 h后在表面发现了两种不同的特征显微组织：一种是表面晶粒被氧化铬覆盖，其余晶粒表面完全被氧化铝包围;在另一种情况下，氧化铝在氧化铬氧化皮的正下方形成一层薄层。经过500小时的暴露时间后，观察到显着较薄的氧化铬皮和大量的内部氧化铬。甚至在500 h后开始发生灾难性腐蚀，形成内部氧化物和氮化铝。这将表明，合金693的早期击穿是链接到铝氧化物作为一个障碍，限制铬从合金基体向表面的扩散。在燃烧器中给定的极端温度变化的条件下，其部分上的氧化铝层不提供腐蚀保护。
The flame tube is an important functional component of burners using the concept of the flame tube stabilised combustion. Under typical combustion conditions the material of the flame tube is exposed to high temperatures (≥900 °C) and to corrosion attack by the combustion gases. Furthermore as the burners are generally operated intermittently, the material suffers from extreme temperature and atmosphere changes. For flame tubes, a lifetime of approximately 8000 h is desired. Predominantly metallic high temperature materials are used. The scope of the present work was to test—under application conditions and for maximum material temperatures exceeding 900 °C—alternative high temperature alloys for use as tube material. The corrosion resistance of the austenitic Ni–Cr‐based alloys (601, 602 CA, 617 and 693) has been investigated in a burner rig at maximum material temperatures of 950 and 1000 °C and with exposure times from 50 to 3000 h. The chromium content of the alloys was between 20 and 30 wt% and that of aluminium between 1 and 3.4 wt%. Metallographic cross‐sections of samples of the alloys were analysed by electron microprobe yielding information about the microstructure and composition of the oxides in the surface zone and variations during exposure time. This study focuses on the observed specific effects of the alloying element aluminium on the development of the oxide scale and on the lifetime of the alloys. At the alloy surface after 500 h exposure time a chromium oxide scale had formed with aluminium oxides underneath predominantly along grain boundaries. For the alloys with the lower aluminium content, the aluminium oxides built up an open network but not a closed layer. For the alloy with the highest aluminium content (alloy 693) after 50 h two different characteristic microstructures at the surface were found. In one case, the grains at the surface were covered with chromium oxide on top and the remaining grain surface was completely enclosed by aluminium oxides. In the other case, the aluminium oxide formed a thin layer directly below the chromium oxide scale. After 500 h exposure time, a significantly thinner chromium oxide scale and massive internal chromium oxides were observed. Catastrophic corrosion, formation of internal oxides and aluminium nitrides started even after 500 h. It will be demonstrated that the early breakdown of alloy 693 is linked to the aluminium oxides which act as a barrier constricting the diffusion of chromium from the alloy matrix towards the surface. Under the conditions of extreme temperature changes given in the burner the aluminium oxide layer on its part did not provide corrosion protection.