Oxidation of nickel superalloys for aero-engine applications

镍高温合金因其在高温下具有优异的机械强度而被用于航空发动机。热生长的氧化物会削弱合金，然而，如果精心设计，这些氧化物是合金抵御腐蚀的第一道防线。氧化物可以通过钝化表面和防止进一步的反应来保护合金。为此，氧化物需要是连续的、无孔的，并且能很好地附着在基材上。这为优化合金成分以改善氧化垢留下了很大的空间。你的博士项目的目的是通过添加有针对性的合金来优化成分，以创造一种强氧化物。特别是，微量Si的作用已被证明可以促进在表面上形成连续的氧化铝保护层。这层氧化铝比通常形成的铬基或镍基尖晶石更具保护性。然而，有一个最佳的硅量，超过这个量，对合金的氧化和脆相的沉淀都是有害的，导致微观结构不稳定。氧化层中的硅已被证明与钽直接相互作用，尽管尚未对该主题进行过系统的研究，其机制也未得到很好的理解

Nickel superalloys are used in aero-engines due to their outstanding mechanical strength up to high temperatures. Thermally grown oxides can weaken the alloys, however, when carefully designed, these oxides are the alloy's first line of defence against corrosion. Oxides can protect alloys by passivating the surface and preventing further reactions. For this, oxides need to be continuous, non-porous and adhere well to the substrate. This leaves plenty of scope for the optimization of alloy composition to improve the oxide scale. The aim of your PhD project is to optimize the composition to create a strong oxide through targeted alloying additions. In particular, the effect of trace amounts of Si have been shown to promote the formation of a continuous, protective layer of alumina on the surface. This layer of alumina is more protective than the chromia or nickel-based spinels that normally form. However, there is an optimal amount of silicon beyond which the effect will be deleterious both for oxidation and for the precipitation of embrittling phases within the alloy, causing microstructural instability. Silicon in the oxide scale has been shown to interact directly with tantalum, though no systematic study on the topic has ever been performed and the mechanisms are not well understood