Shi Dongfeng, Zhang Jin
Light Alloy Research Institute, Central South University, Changsha 410083, China.
State Key Laboratory of High Performance and Complex Manufacturing, Central South University, Changsha 410083, China.
Materials (Basel). 2022 Aug 11;15(16):5510. doi: 10.3390/ma15165510.
This study investigated the twinning behavior with increasing compressive strain in rolled AZ31 alloy. With that purpose, a polycrystalline structure with an average grain size of 30 μm was utilized to perform the uniaxial compression tests. Microstructure evolution was traced by in situ electron backscattered diffraction (EBSD). Multiple primary twin variants and extension double twins were observed in the same grain. A comprehensive analysis of kernel average misorientation (KAM) and Schmid factor (SF) revealed that the nucleation of twins in one special grain is not only based on the SF criterion, but that it is also strongly influenced by surrounding grains. Moreover, the existing primary twins modified the inner and outer strain distribution close to the twin boundaries. With continued compression, the strain inside the primary twins stimulated the nucleation of double twins, while the strain in the matrixes facilitated twin growth. Therefore, the primary twin growth and the new nucleation of secondary twins could take place simultaneously in the same twinning system to meet the requirements of strain accommodation. Twinning behaviors are controlled by the combined effect of the Schmid factor, strain accommodation between surrounding grains, and variation in the local stress state. The local stress exceeded the critical resolved shear stress (CRSS), implying that twin nucleation is possible. Hence, the twinning process tends to be a response of the local stress rather than the applied stress.
本研究调查了轧制AZ31合金中孪晶行为随压缩应变增加的变化情况。为此，利用平均晶粒尺寸为30μm的多晶结构进行单轴压缩试验。通过原位电子背散射衍射（EBSD）追踪微观结构演变。在同一晶粒中观察到多个初生孪晶变体和延伸双孪晶。对晶核平均取向差（KAM）和施密德因子（SF）的综合分析表明，一个特殊晶粒中孪晶的形核不仅基于施密德因子准则，还受到周围晶粒的强烈影响。此外，现有的初生孪晶改变了孪晶界附近的内部和外部应变分布。随着压缩的继续，初生孪晶内部的应变促使双孪晶形核，而基体中的应变则促进孪晶生长。因此，初生孪晶生长和次生孪晶的新形核可以在同一孪晶系统中同时发生，以满足应变协调的要求。孪晶行为受施密德因子、周围晶粒间的应变协调以及局部应力状态变化的综合影响。局部应力超过临界分切应力（CRSS），这意味着孪晶形核是可能的。因此，孪晶过程倾向于对局部应力而非外加应力做出响应。
