Mesoscale finite element phase field modelling of liquid lithium corrosion of steels

液态锂被提议作为STEP聚变反应堆的冷却剂，因为它作为液态金属能够有效地去除热量，但还有一个额外的优势，即锂可以从中子相互作用中繁殖出氚。液态锂将接触的拟议材料之一是P91级钢。这些钢已广泛用于化石燃料和核工业，由于Cr的存在，它们具有合理的耐腐蚀/抗氧化性，但更重要的是在STEP要求的高温下具有高蠕变强度。P91牌号是铁素体-马氏体钢，具有高度复杂的组织，含有各种沉淀和夹杂物。众所周知，这些因素会影响钢的蠕变性能，但也可能在液态锂对钢的腐蚀中起作用。在帝国理工学院，我们最近在有限元相场法框架内开发了一个模型，该模型可以生成类似于腐蚀金属测量过程中实验观察到的极化曲线。这些模型将用于研究P91钢中发现的各种类型的单晶、双晶和嵌有单一第二相颗粒的晶粒，以评估哪些颗粒在Li存在时是关键的，并控制这些钢的腐蚀行为。这些模型将与将在UKAEA进行的P91钢在液态锂中的局部腐蚀实验并行开发。曾经为简单情况开发的模型也将尝试（根据实验数据的可用性）包括通过硬化的辐射损伤和这些钢中潜在的晶界化学偏析效应对液态锂腐蚀行为的影响。

Liquid lithium is a proposed coolant for the STEP fusion reactor because of its ability to remove heat efficiently, as a liquid metal, but with the added advantage that Li can breed tritium from neutron interactions. One of the proposed materials that the liquid lithium will be in contact with is grade P91 steels. These steels have been used extensively in the fossil fuels and nuclear industry and they have both reasonable corrosion/oxidation resistance due to the Cr present but more importantly have high creep strength at elevated temperatures required by STEP. P91 grades are ferritic-martensitic steels with a highly complex microstructure that contains a variety of both precipitates and inclusions. These are well known to influence the creep properties but are likely to have a role to play in the corrosion of the steel by liquid lithium. At Imperial we have recently been developing a model, within the finite element phase field method framework, that can generate polarisation curves similar to those observed experimentally during the measurements of corroding metals. These models will be developed to study single grain, bi-crystals and grains with a single second phase particle embedded, of the various types found in P91 steels, to assess which particles are critical in the presence of Li and control the corrosion behaviour of these steels. These models will be developed in parallel with the localised corrosion experiments that will take place at UKAEA of P91 steels in liquid lithium. The models once developed for simple cases will also attempt (subject to experimental data availability) to include the effect of radiation damage through hardening and potentially grain boundary chemical segregation effects in these steels on the corrosion behaviour in liquid Li.