Cyclic Constitutive Relation and Creep-Fatigue Life of Directionally Solidified Superalloy

高温低周疲劳试验10min。对MAR-M247定向凝固高温合金在1173K下进行了拉伸和无保持试验。疲劳强度与弹性模量的各向异性密切相关，因此考虑了各晶内弹性模量的各向异性，进行了三维有限元分析。得到的主要结论如下：1.对DS轴0度试件疲劳强度最大，45度试件疲劳强度最小，90度试件疲劳强度中等。对于蠕变-疲劳强度，这个顺序没有改变。由于试件取向的不同，疲劳强度的差异归因于施加的应力的不同。45度试件的应力最大，0度试件最小，90度试件次之。应力幅值的差异是由于弹性模量的各向异性造成的。提出了一种考虑弹性模数各向异性的简单寿命预测方法。在有限元分析中，确定了由5个柱状晶组成的DS板的弹性柔度矩阵，其中每个晶具有立方各向异性。用Reuss平均和Voigt平均计算了弹性柔度矩阵。用这两种平均法得到的弹性柔度矩阵与有限元分析的结果吻合较好，从而可以用简单的平均法准确地估计出柔度矩阵。分析证明DS板具有正交各向异性柔度矩阵。

High temperature low cycle fatigue tests with 10 min. tension and no hold-times were carried out for Mar-M247 directionally solidified (DS) superalloy at 1173 K.The fatigue strength had a close connection to the anisotropy of the elastic modulus so that the three dimensional finite element analyses were made taking account of the anisotropy of elastic modulus in each grain. The main conclusions obtained are as follows:1. The fatigue strength of the 0 degree specimen to the DS axis exhibited the maximum fatigue strength, the 45 degree specimen the minimum strength and 90 degree specimen the intermediate fatigue strength. For the creep-fatigue strength this order was not changed.2. The difference in the fatigue strength due to the orientation of the specimen was attributed to the difference in the applied stress. The 45 degree specimen yielded the largest stress, the 0 degree specimen the smallest and the 90 degree specimen the intermediate. The difference in the stress amplitude was resulted from the anisotropy of the elastic modulus. The simple life prediction method, which takes account of the anisotropy of the elastic modulus, was developed.3. The elastic compliance matrix of the DS plate which was composed of five columnar grains was determined in the finite element analysis, where each grain was assumed to have the anisotropy of the cubic system. The elastic compliance matrix by Reuss and Voigt averages was also calculated. The elastic compliance matrix by the two averages agrees well with that in the finite element analysis, so that the matrix can be accurately estimated by the simple averaging methods. The analysis proved that the DS plate had the orthotropic compliance matrix.