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Enhancement of the rafting in Ni-based superalloys by controlling elastic misfit

通过控制弹性失配增强镍基高温合金的漂流

基本信息

批准号：
13650758
负责人：
TANAKA Katsushi
金额：
$ 2.24万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

项目摘要

The elastic energies associated with the formation of raft structure of Ni-based superalloys has already been calculated and discussed by Nabarro et al. However, this involves an uncertain part about the method of approximation. Our calculation in the framework of purely elastic regime concerning a macroscopic shape deformation indicates that their conclusion is wrong owing to its method of approximation. Our calculation also leads the normal raft always forms regardless to the sign of the lattice misfit and external stress. This result does not agree with the experimental results and indicates that the mechanism of rafting cannot be explained by the calculation in the framework of purely elastic regime.When creep dislocations are induced before rafting, our calculation indicates that the dislocations can creep into so called normal channels but cannot creep into parallel channels. This anisotropic behavior of the motion of creep dislocations changes the spherical symmetry of the lattice misfit into the tetragonal symmetry which makes the morphology of raft as experimentally observed.The driving force for rafting in the framework of elastic regime is very small in comparison with other thermodynamic energies. So, it is difficult to explain the mechanism of rafting only by the elastic interactions. That in the framework of elastic-plastic regime where creep dislocations are taken into account is quite large and mainly depends on the lattice misfit. We conclude that the dominant factor for the choice of morphology of rafting and the elastic misfit is the secondary factor.

Nabarro等人已经计算和讨论了与镍基高温合金筏状结构形成有关的弹性能，但是，这涉及到近似方法的不确定部分。我们在纯弹性框架下对宏观形状变形的计算表明，由于其近似方法，他们的结论是错误的。计算结果还表明，无论网格错配和外应力的大小如何，筏板总是能正常成形。这一结果与实验结果不符，表明在纯弹性范围内的计算不能解释筏化机制，当筏化前诱发蠕变位错时，位错可以蠕变进入所谓的正常通道，但不能蠕变进入平行通道。蠕变位错运动的这种各向异性行为使晶格失配的球对称性转变为四方对称性，使得筏形结构与实验观察到的一致。在弹性区，筏形结构的驱动力与其它热力学能相比很小。因此，仅用弹性相互作用很难解释漂流的机理。在考虑蠕变位错的弹塑性体系中，位错的位错密度很大，主要取决于晶格失配度。我们得出结论，漂流形态的选择和弹性失配的主导因素是次要因素。