【摘要】 采用籽晶法制备偏离<111>取向不同角度的镍基单晶高温合金试样。研究了合金在760℃、650 MPa下小角偏离对蠕变性能的影响。结果表明,<111>取向附近合金的蠕变性能具有显著的小角偏离敏感性。偏离角度较小的<111>取向合金试样的蠕变寿命最长,蠕变过程中位错主要分布在γ通道内,随着取向偏离度增加,合金的蠕变寿命显著下降。且沿着[-111]-[011]边界偏离时蠕变寿命相对于沿着[-111]-[001]边界偏离下降更快。近<111>取向合金都表现出了较弱的加工硬化,但沿着[-111]-[001]边界偏离的样品,其初期蠕变速率相对较低,对应着较长的蠕变孕育期。进一步分析表明,[-111]-[011]边界对应着{111}<110>滑移系的共面双滑移取向,在蠕变初期就产生较高的蠕变速率,随着取向偏离度增加{111}<112>滑移系的Schmid因子迅速增加,蠕变寿命显著下降。而沿着[-111]-[001]边界偏离试样蠕变孕育期的产生则是由于占主导地位的滑移系数量下降且具有相对较低的{111}<110>滑移系Schmid因子,导致位错无法在γ通道内迅速增殖并分解产生<112>位错,延缓了初期蠕变阶段的产生。更多还原

【Abstract】 Single crystal nickel-based superalloys have been widely used in high temperature structural materials applications including blade parts of aero-engines and gas turbines due to their excellent mechanical properties in service. Although commercial single crystal superalloy blades are in [001] orientation, misorientation deviations are inevitable in industrial productions and work blades frequently have to endure complex stress states caused by their complicated shapes and temperature gradients. Therefore, it is of great significance to study the creep behavior of single crystal superalloys with different orientations for the design of engine blades. The anisotropic creep properties of a nickel-based single crystal superalloy with different orientations near <111> were investigated under 760 ℃ and 650 MPa. It is found that specimens with the smallest deviation from <111> orientation exhibit best creep strength because of the relatively low Schmid factors of both {111}<110> and {111}<112> slip systems. With the increase of-orientation deviate from [111] to [011], creep properties decrease more significantly compared with the de--viation from [111] to [001]. All samples deviate from <111> within 20° exhibit poor strain hardening. While-orientations toward [111]-[001] boundary have a distinct incubation creep stage with relatively low initial creep rate. Further dislocations and lattice rotation analysis showed that the dominant slip systems are{111}<110> for specimens with minimum deviations. The stress is almost uniformly distributed in three γmatrix channels, which lead to a homogeneous deformation behavior. As the orientation deviation increases, {111}<112> slip systems begin to play a leading role during creep process. While the generation of <112> dislocations is closely related to the reaction and decomposition of <110> dislocations. Speci--mens on [111]-[011] boundary have coplanar double slips for {111}<110> slip systems resulting in a high initial creep rate and poor strain harding. Meanwhile, Schmid factors of {111}<112> slip systems increase-rapidly with the increase of orientation deviation from [111] to [011], which lead to a significantly degrada--tion on creep properties. While as for orientations along [111]-[001] boundary, Schmid factors increase in a relatively gentle way with the number of dominant slip systems reduced from 6 to 2. Multiplication of dislocations and the formation of <112> dislocation ribbons are impeded, resulting in a comparatively long incubation creep stage.更多还原