Negative creep of nickel-based superalloys

镍基合金在600°C左右的中温下观察到“负蠕变”现象。在这种情况下，样本收缩-0.04%至-0.07%。这种效应在没有任何外部载荷和低应力的情况下都会发生。在文献中发现了各种解释，这些解释通常是高度具体的，并且仅对一种特殊合金或载荷条件有效。在拟议的项目中，正在采取一种新的办法。假设制定，估计占负蠕变。可能的假设是碳含量（非常缓慢的碳化物形成或转化），晶粒粗化，元素在各个阶段或紧密排列的域中的再分配。对于这些假设中的每一个，熔化特殊的合金，使得仅改变在假设中研究的参数。负蠕变本身和微观结构的变化模型合金的效果进行了比较与各自的起始合金。这导致四个实验任务：熔化的模型合金;暴露测试与确定的长度变化;蠕变选定的合金;和深入研究的微观结构与组成的测定与高空间分辨率。目的是量化假设及其对负蠕变的影响，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.