基于位错运动的镍基单晶各向异性蠕变寿命预测

Anisotropic Creep Life Prediction of Nickel Based Single Crystal Based on Dislocation Movement

摘要:

镍基单晶高温合金特殊的两相结构使其具有各向异性的特征。本研究对三种不同取向的DD6镍基单晶高温合金进行了980℃下的蠕变试验，试验表明镍基单晶高温合金蠕变失效机理是材料内部微孔洞的萌生与微裂纹的扩展，其本质是由位错运动造成的。采用透射电镜(TEM)对蠕变初期[001]、[111]和[011]三种取向的单晶合金的位错形貌进行观测，发现其分别符合八面体滑移系开动、六面体滑移系开动与两滑移系同时开动的特征。针对上述微观现象，基于晶体塑性理论建立了考虑Orowan效应与位错阻碍效应的蠕变本构模型与蠕变损伤模型，并根据试验得到的蠕变曲线拟合了模型参数。该模型的有限元模拟结果与单晶材料的蠕变断口形貌相互印证，解释了单晶蠕变的各向异性的力学行为。

Abstract:

The special two-phase micro-structure of nickel-based single crystal superalloy makes it anisotropic. Creep tests of three different orientations of the single crystal superalloy DD6 were carried out under 980℃, indicated that the creep failure of superalloy is the initiation of micropores and the propagation of microcracks, which is caused by dislocation motion. Transmission electron microscopy (TEM) was used to observe the dislocation morphology of monocrystals in [001], [111] and [011] orientation at the initial stage of creep, found matching the characteristics of the octahedral sliding system activated, the hexahedral sliding system activated and the simultaneous motion of the two sliding systems respectively. Based on the crystal plasticity theory, the creep constitutive model and creep damage model?under variational stress conditions were established with Orowan effect and dislocation blocking effect considered, meanwhile, the model parameters were fitted according to the creep curve obtained from the test. Moreover, the finite element simulation results of the model and creep fracture morphology of monocrystalline materials mutually confirm and explain the anisotropic behavior of monocrystalline creep.