EBSD技术分析大晶粒NiAl合金高温塑性变形组织演变与CSL特征晶界分布

EBSD ANALYSES OF THE MICROSTRUCTURAL EVOLUTION AND CSL CHARACTERISTIC GRAIN BOUNDARY OF COARSE-GRAINED NiAl ALLOY DURING PLASTIC DEFORMATION

采用EBSD分析了1075℃和初始应变速率为8.75×10^(-4)s^(-1)条件下大晶粒NiAl合金高温塑性变形过程中的组织演变与重位点阵(CSL)特征晶界分布。变形前大晶粒NiAl合金以大角度晶界为主,小角度晶界比例极低。在高温塑性变形过程中,取向差5°以下的小角度晶界不断产生。随变形量的增大,新形成的小角度晶界取向差增加、转变为取向差较大的6°—15°小角度晶界,进而转变为15°以上的大角度晶界。小角度晶界的产生速率与转变为大角度晶界的速率趋向动态平衡。小角度晶界向较大角度晶界不断转变导致晶粒显著细化。CSL特征晶界分析表明,大晶粒NiAl合金高温塑性变形过程中,CSL晶界分布发生改变,将对合金室温力学性能产生影响。

The microstructural evolution and the coincidence site lattice （CSL） characteristic grain boundary of coarse grained NiAl alloy during plastic deformation at 1075℃with the initial strain rate of 8.75×10^-4s^-1 were studied using EBSD technique. Before deformation most grain boundaries are high angle boundaries, in which several particular angles are predominant, but low angle grain boundaries with misorientation less than 5° occurred successively during deformation. With the increase of the deformation, the misorientations of the newly formed low angle grain boundaries increase, and grain boundaries with larger misorientation between 6°-15° are formed, and finally high angle grain boundaries with misorientation larger than 15° are formed. There exists a dynamic equilibrium between the formation rate of new low angle grain boundaries and the rate of changing into higher-angle grain boundaries. Turning of low angle into higher angle grain boundaries results in the refinement of grains. The results also show that plastic deformation can change the CSL characteristic grain boundaries of the coarse-grained NiAl, which may improve mechanical properties of the alloy at room temperature.