含与不含晶界空穴的双晶体蠕变行为研究

Study on creep behavior of the bi-crystal with or without void in the grain boundary

基于晶体滑移理论,建立了各向异性镍基合金双晶体的蠕变本构模型和蠕变寿命预测模型,通过MARC用户子程序CRPLAW将上述本构模型进行了有限元实现,并对双晶体蠕变行为进行了计算分析,考虑了:(1)晶体取向的影响;(2)垂直、倾斜和平行于外载方向的三种位向晶界情况;(3)晶界处引进空间空穴的影响。结果表明,双晶体上特别是微空穴和晶界附近区域的蠕变应力应变呈现不同的变化规律,对此晶粒晶体取向和晶界位向有较大的影响;微空穴的存在削弱了双晶体的承载能力,显著地影响了双晶体蠕变持久寿命;相同条件下,垂直晶界对双晶体模型的蠕变损伤影响最为强烈,倾斜晶界次之,平行晶界最小;微空穴的生长与晶界位向和晶体取向有强烈的依赖关系,其中垂直晶界更有利于晶体滑移和微空穴生长。

Based on crystallographic theory, a creep constitutive relationship and a life predictive model have been presented. The crystallographic creep constitutive relationship has been implemented as an user subroutine ＂CRPLAW＂ to MACR. Bi-crystal models containing a void in the grain boundary and bicrystal model without void have been studied by the finite element method. Different loading directions have been studied in order to show the influence of relative direction of loading to grain boundary on the creep behavior of the bi-crystal. The numerical results of bi-crystal model show that there are a high stress gradient and stress concentration near the void and grain boundary. The existence of void has strong influence on creep durability life of the crystal. The stress distribution and creep strain characteristic are dependent on the crystallographic orientations of the two crystals and the grain boundary direction as well as the existence of void and loading directions. It is shown that loading direction perpendicular to the grain boundary has the highest creep the bi-crystal model with strain and creep damage, while that model with the loading direction parallel to the grain boundary has the minimum. The same conclusion is tenable to the growth of void.