To reduce the pollution emission from vehicles, an improvement on the combustion process is expected, leading to increased exhaust gas temperature. As a result, the development of new materials for an exhaust manifold used at higher temperatures is required. A cost-effective cast iron exhaust manifold treated by aluminising pack cementation was developed in the present work to combat the high temperature corrosion. Its kinetics under cyclic oxidation in N₂–12%O₂–10%H₂O at 850 °C was parabolic with the rate constant (k_p) of 5.66 × 10⁻¹² g² cm^–4 s^–1, about two orders of magnitude lower than that of the bare cast iron, which indicated the protectiveness of the applied coating. These results relate to the protective alumina formation for the aluminised cast iron and the formation of the less protective iron oxides for the bare cast iron after oxidation, as evidenced by the XRD and Raman spectroscopy results. The addition of 10% water vapour to N₂–12%O₂ thickened the aluminide layer from 344 μm for the sample oxidised in dry atmosphere to 409 μm for the sample oxidised humidified one. It accelerated the oxidation rate of the aluminised cast iron as the k_p value increased by 8.5 times, and also increased the hardness of the aluminised surface, as it was 364 HV for the sample exposed to dry atmosphere and 420 HV for the sample exposed to humidified one. The latter result implied the possibility of the hydrogen dissolution into the metal surface. The roles of hydroxyl ion and dissolved hydrogen on the oxidation and evolution of the aluminide layer after exposure to water vapour were proposed.

中文翻译：

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排气歧管用铝化物涂层铸铁的高温腐蚀行为

为了减少车辆的污染排放，期望改善燃烧过程，从而导致废气温度升高。结果，需要开发用于高温下的排气歧管的新材料。在目前的工作中，开发了一种具有成本效益的铸铝排气歧管，该组件通过渗铝包胶结处理来应对高温腐蚀。在850°C的N ₂ –12％O ₂ –10％H ₂ O中，其循环氧化动力学是抛物线形的，速率常数（k _p）为5.66×10 ^-12 g ² cm ^–4 s ^–1比裸露的铸铁低约两个数量级，这表明所施加的涂层具有保护性。这些结果与铝化铸铁的保护性氧化铝的形成以及氧化后裸露铸铁的保护性较小的氧化铁的形成有关，如XRD和拉曼光谱结果所证明的那样。在N ₂ –12％O _2中添加10％的水蒸气会使铝化物层的厚度从在干燥气氛中氧化的样品的344μm增至对于氧化湿的样品的409μm。随着k _p的增加，它加快了渗铝铸铁的氧化速度。值增加了8.5倍，并且还增加了镀铝表面的硬度，因为暴露在干燥气氛中的样品为364 HV，暴露于湿润的样品为420 HV。后者的结果暗示了氢溶解到金属表面中的可能性。提出了氢氧离子和溶解氢在暴露于水蒸气后对铝化物层的氧化和析出的作用。