基于EBSD技术的P91钢蠕变过程中小角度晶界演化行为表征

在620℃、145 MPa条件下对给定的P91钢进行高温蠕变持久与间断试验,采用电子背散射衍射(EBSD)技术研究其在蠕变过程中小角度晶界的演化行为。通过引入EBSD图像中的取向差分布来表征小角度晶界处(0.5~5°)的边界位错密度,分析了边界位错密度在蠕变过程中与小角度边界的数量、塑性应变以及内部微观组织演化之间的关系。此外,通过改变EBSD像素点与像素点之间的计算步长,探讨了步长选择对边界位错密度计算结果的影响。结果表明,小角度晶界处的位错密度在蠕变过程中先迅速上升,在最小蠕变率处达到极值后缓慢下降,直到最后基本保持不变;同时,EBSD的计算步长越小,得到的位错密度值越准确。

Characterization of Small-angle Grain Boundary Evolution During Creep of P91 Steel Using EBSD Technique

The high-temperature creep and interrupted creep tests of P91 steel were carried out under the stress of 145 MPa at 620 ℃.The evolution of small-angle grain boundary during creep was investigated by electron backscatter diffraction (EBSD)tech-nique.Meanwhile,the misorientation distribution in the EBSD image was introduced to characterize the dislocation density of small-angle grain boundary with the misorientation of adjacent grains from 0.5°to 5°.By these methods,the relationships between the boundary dislocation density,the number of small-angle grain boundaries,plastic strain,and internal microstructure evolution were discussed during creep.Besides,the influence of calculation step size on the boundary dislocation density was analyzed in detail.The results manifested that the dislocation density at the small-angle boundaries increased rapidly from the primary creep to the beginning of the secondary creep.Then,it reached a peak when the creep rate was minimum.Afterwards,it decreased slowly and then re-mained constant until the creep rupture.Moreover,it indicated that the smaller the step size of EBSD,the more accurate the disloca-tion density value can be obtained.