CREEP RESISTANCE OF CMSX-3 NICKEL-BASE SUPERALLOY SINGLE-CRYSTALS
CREEP RESISTANCE OF CMSX-3 NICKEL-BASE SUPERALLOY SINGLE-CRYSTALS
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DOI：
10.1016/0956-7151(92)90195-k
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发表时间：
1992-01-01
期刊：
影响因子：
--
通讯作者：
ARGON, AS
中科院分区：
文献类型：
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作者：
POLLOCK, TM;ARGON, AS
本文研究了取向镍基高温合金单晶的蠕变变形，以探讨影响高γ相含量高温合金蠕变抗力的因素。用体视电子显微术对蠕变产生的三维位错排列进行了详细的观察。在800-900 ℃的温度范围内，在552 MPa或更低的应力下，无位错的γ ′-沉淀物抵抗位错的剪切。结果，蠕变变形通过位错通过{111}面上的窄γ矩阵通道的强制弯曲而发生。在中等水平的温度和应力下，在初始蠕变开始之前，原始晶体中存在孕育期。孕育的出现，因为最初的位错饥饿的基体材料填充与蠕变位错从广泛的间距源的困难的过程。当新产生的位错渗透通过横截面时，孕育期结束，主蠕变开始。在初始蠕变中，加工硬化和任何类型的回复都不起重要作用。蠕变速率减慢，因为γ和γ '相之间的有利的初始热失配应力被蠕变流动释放。持续的蠕变导致位错的三维节点网络的建立。这种三维网络在稳态蠕变期间填充伽马矩阵通道，并在时间上实现准静态结构。原位退火实验表明，在850 ℃或更低的温度下，静态恢复在引起三维网络中的重排方面是无效的。在表观稳态蠕变过程中维持准稳态位错网络结构的运动学位错置换过程还不清楚，需要进一步研究。由于γ沉淀物的不可穿透性，位错通过强制奥罗万弯曲穿过γ基体，这是蠕变阻力的主要组成部分。此外，共格或半共格沉淀物的摩擦约束导致微结构中压力梯度的建立，这提供了承载能力。固溶强化的成分也较少。加工硬化相对来说并不重要。有限元分析表明，随着蠕变变形在基体中的累积，非变形沉淀物所受的应力越来越大。在稳态蠕变的后期阶段和第三蠕变期间，沉淀物中的应力上升到足够高的水平，从而通过从γ基体进入的位错引起γ ′颗粒的剪切。该材料的恢复阻力部分是由于非常低的有效扩散常数，另一部分是由于在γ基体中形成的三维位错网络用于中和γ和γ ′相之间的失配。
Creep deformation in oriented nickel base superalloy single crystals has been studied in an effort to assess the factors which contribute to the overall creep resistance of superalloys with high volume fractions of gamma'-phase. Detailed observations of three dimensional dislocation arrangements produced by creep have been made with the use of stereo electron microscopy. In the temperature range of 800-900-degrees-C at stresses of 552 MPa or lower, the dislocation-free gamma'-precipitates are resistant to shearing by dislocations. As a result, creep deformation occurs by forced bowing of dislocations through the narrow gamma-matrix channels on {111} planes. At moderate levels of temperature and stress there are incubation periods in virgin crystals prior to the onset of primary creep. The incubations arise because of the difficult process of filling the initially dislocation starved matrix material with creep dislocations from widely spaced sources. When the newly generated dislocations percolate through the cross section, incubation comes to an end and primary creep begins. In primary creep neither work hardening nor any type of recovery plays an important role. The creep rate decelerates because the favorable initial thermal misfit stresses between gamma and gamma'-phases are relieved by creep flow. Continued creep leads to a build-up of a three-dimensional nodal network of dislocations. This three-dimensional network fills the gamma-matrix channels during steady state creep and achieves a quasi-stationary structure in time. In situ annealing experiments show that static recovery is ineffective at causing rearrangements in the three-dimensional network at temperatures of 850-degrees-C or lower. The kinematical dislocation replacement processes which maintain the quasi-stationary dislocation network structures during apparent steady state creep are not understood and require further study. Because of the impenetrability of the gamma'-precipitates, dislocations move through the gamma-matrix by forced Orowan bowing, and this accounts for a major component of the creep resistance. In addition, the frictional constraint of the coherent or semi-coherent precipitates leads to the build-up of pressure gradients in the microstructure, and this provides load carrying capacity. There is also a smaller component of solid solution strengthening. Work hardening is comparatively unimportant. Finite element analysis shows that the non-deforming precipitates are increasingly stressed as creep deformation accumulates in the matrix. In the later stages of steady state creep and during tertiary creep the stresses in the precipitates rise to high enough levels to cause shearing of the gamma'-particles by dislocations entering from the gamma-matrix. The recovery resistance of the material is in part due to a very low effective diffusion constant and in another part due to the fact that the three-dimensional dislocation networks formed in the gamma-matrix serve to neutralize the misfit between the gamma and gamma'-phases.