Negative creep of nickel-based superalloys

镍基合金在600℃左右的中温下观察到了“负蠕变”现象。在这种情况下，样品收缩了-0.04%到-0.07%。这种效应在没有任何外部载荷和低应力的两种情况下都会发生。在文献中可以找到各种解释，这些解释通常是高度具体的，并且只适用于一种特殊的合金或加载条件。在拟议的项目中，正在采取一种新的方法。提出了一些假设，估计这些假设可以解释负蠕变。可能的假设是碳含量(碳化物形成或转化非常缓慢)，晶粒粗化，元素在不同相或紧密排列的区域中的重新分布。对于这些假设中的每一个，都熔化了特殊的合金，因此只改变了那个参数，这在假设中进行了研究。将模型合金的负蠕变本身和组织变化的影响与相应的初始合金进行了比较。这导致了四项实验任务：熔化模型合金；暴露试验，确定长度变化；选定合金的蠕变；以及深入研究微观结构，确定高空间分辨率的成分。其目的是量化假设及其各自对负蠕变的影响，或在必要时反驳。

The phenomenon of "negative creep" is observed for nickel-based alloys at medium temperatures around 600°C. In this case a sample contracts by -0.04% to -0.07%. This effect occurs in both cases without any external load and at low stresses. In literature various explanations are found which are often highly specific and only valid for one special alloy or loading condition. In the proposed project, a new approach is being pursued. Hypotheses are formulated, which are estimated to account for the negative creep. Possible hypotheses are the carbon content (very slow carbide-formation or -conversion), grain coarsening, redistribution of elements in various phases or close arranged domains. For each of these hypotheses special alloys are melted, so that only that parameter is changed, which is investigated in the hypothesis. The effect of negative creep itself and microstructural changes in the model alloys are compared with the respective starting alloy. This results in four experimental tasks: melting of the model alloys; exposure tests with determination of the length-changes; creep of selected alloys; and intensive studies of the microstructure with the determination of composition with a high spatial resolution. The aim is to quantify the hypotheses and their respective impact on the negative creep or disprove if necessary.