等通道角挤压中纯铜的晶粒取向演变及织构起伏效应

Grain orientation evolution and texture fluctuation effect of pure copper during equal channel angular pressing

用XRD和EBSD对等通道角挤压(ECAP)过程中纯铜(99.9%)的晶粒取向变化进行研究,对挤压后的组织和晶粒取向变化机理进行分析。结果表明:纯铜经路径A挤压时,随着应变量的增大,晶粒在细化的同时原始〈101〉织构逐渐减弱,材料均匀性提高;从小角度向大角度晶界转变过程中,晶界取向差分布的峰值不断向大角度晶界的均值(40°)移动,逐渐呈现正态分布特征,取向差梯度逐渐减小;挤压过程中,织构的形成是动态过程,存在"织构起伏"效应,其强度和方向与材料的应变状态密切相关。认为"织构起伏"效应是材料晶体结构、晶界特征以及晶粒聚集状态在一定的温度和外力作用下的综合应变反映;材料内部新织构的产生与消失是晶群在受到外力作用后偏聚方向发生变化、内应力向相邻晶界传递的过程中,原来的聚集状态被破坏所致。

The polycrystalline samples of pure Cu（99.9%,mass fraction） were processed at room temperature by equal-channel angular pressing（ECAP）.The microstructure and its changing mechanism after ECAP were investigated by X-ray diffraction（XRD） and electron backscattered diffraction（EBSD）.The results indicate that when the pure copper is extruded by route A,with the increase of strain,the original 〈100〉 texture decreases coupled with the grains refinement,and the distribution uniformity of copper is improved.With the increase of the fraction of high-angle grain boundaries（HAGBs）,the peak of misorientation moves to the typical value（40°）,gradually becomes normal distribution,and the misorientation gradient decreases.The formation of texture shows a texture fluctuation effect when ECAP is a dynamic process,the direction and strength of which are closely related to the strain of the material.The texture fluctuation effect is the integrated reflection of crystal structure,grain boundary character,aggregation state at a certain temperature and under the action of forces.The external force acting on crystal class then makes the segregation orientation change,in the process of internal stress transmited on the neighboring grain boundaries,the aggregation state is broken,which cause the new texture of the material interior to vanish or appear.