Crystallographic Orientation and Chemical Composition Dependence of Creep and High Temperature Fatigue Strength of Single Crystals of Ni-Base Superalloys.

本研究的目的是研究不同化学成分的镍基高温合金单晶屈服强度、蠕变强度和疲劳强度的取向依赖关系，并为实际应用展示具有优异性能的合金。1)材料：三种镍基高温合金，1)Al-Ti-Ta型，2)Al-Ti-V型，3)Al-Si型。2)拉伸试验：对三种合金的单晶进行室温高达1000℃的拉伸试验。研究了证明应力和CRSS的取向依赖性。在700℃左右，[001]取向的强度在三种合金中最高。在900和1000 C时，合金2和3在[001]取向强度最高，而合金1在[115]和[014]取向强度最高。3)蠕变强度：对合金1和合金2进行蠕变试验。选取了5种低指数的典型取向作为初始拉伸取向。测试温度为700 ~ 9000℃。在7000℃时，合金1和合金2中[001]取向的断裂时间最长。在9000℃时，[113]或[111]的破裂时间比[001]长。如果在相同的测试条件下进行比较，合金1的断裂时间比合金2长。4)高温疲劳：采用取向为[001]、[011]、[111]的合金1，在7000℃的温度下进行高周疲劳试验。施加应力的形式是一个完全反对称的三角形形式的张力。频率为5Hz。三个方向的S-N曲线相似。因此，发现疲劳强度的取向依赖性很小。结论：根据以往的研究，[001]取向是最强的取向。然而，在本研究中，得到了不同的结果，即屈服强度、蠕变强度和疲劳强度的取向依赖关系不同。在相同试验条件下，合金1的屈服强度和蠕变强度均高于合金2。少

A. The purpose of the present studyThe purpose of the present study is to examine the orientation dependence of yield, creep and fatigue strengths of single crystals of Ni-base superalloys with different chemical compositions, and to show the alloy with excellent properties for practical use.B. Procedures and results of the present study1) Materials: Three kinds of Ni-base superalloys, 1) Al-Ti-Ta type, 2) Al-Ti-V type, 3) Al-Si type.2) Tensile tests: Single crystals of the three kinds of alloys were subjected to tensile tests at room temperature up to 1000ﾟC. Orientation dependences of proof stress and CRSS were examined. Around 700ﾟC, the [001] orientation had the highest strength in three kinds of alloys. At 900ﾟC and 1000ﾟC, the alloys 2 and 3 had the highest strength in the [001], while the alloy 1 exhibited the highest strength in the [115] and [014] orientations.3) Creep strength: The alloys 1 and 2 were subjected to creep tests. Typical five orientations with low indices were s … More elected as the initial tensile orientations. Testing temperatures were 700ﾟC and 9000ﾟC. At 7000ﾟC, the [001] exhibited the longest rupture times compared with those of the other orientations in both the alloys 1 and 2. At 9000ﾟC, however, the [113] or [111] showed longer rupture times than the [001]. The alloy 1 had longer rupture times compared with the alloy 2, if compared in the same testing conditions.4) High temperature fatigue: The high cycle fatigue tests were performed at 7000ﾟC using the alloy 1 with the orientations of [001], [011] and [111]. The form of applied stress was a perfectly antisymmetric triangular form in tension.The frequency was 5Hz. The S-N curves of the three orientations were resembled each other. Thus, it was found that the orientation dependence of fatigue strength is small.C. Conclusions: According to the previous studies, it has been reported that the [001] orientation is the strongest orientation. In the present study, however, the different results have been obtained, i.e. the orientation dependence of yield strength, that of creep strength and that of fatigue strength were different each other. In both the yield strength and creep strength, the alloy 1 exhibited higher strengths compared with the alloy 2 in the same testing condition. Less