金属间化合物大晶粒超塑性变形机理

Superplasticty in Large-grained Intermetallics

在所研究的Fe3Al,Fe3Si,FeAl,Ni3Al,NiAl和TiAl等金属间化合物中均发现大晶粒超塑性。显微分析表明 ,超塑性变形过程中晶粒明显细化 ;电子背散射衍射 (EBSD)技术和透射电子显微学(TEM)分析表明 ,大晶粒金属间化合物超塑变形过程中形成了大量亚晶界网络 ,且随变形量增大 ,亚晶界不断吸收晶内滑动位错 ,使其位向差不断增大 ,从而逐渐演变成小角度和大角度晶界 ,即超塑性变形过程中产生了连续动态回复与再结晶 (CDRR)。高温塑性变形是通过位错的滑移和攀移进行的 ,而亚晶界的迁移、滑动和转动起到协调变形的作用 。

Superplastic behavior has been found in Fe 3Al, Fe 3Si, FeAl, Ni 3Al, NiAl and TiAl alloys with large grain sizes (>30～600μm). Metallographic examinations show that the average grain size of large-grained intermetallics decreases during superplastic deformation and a much finer grain size could be obtained after superplastic deformation. Electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM) observations show that there are great numbers of subgrain boundaries which form a network and among which the proportion of low and high angle boundaries increases with the increase of strain. The observed superplastic phenomenon is explained by continuously dynamic recovery and recrystallization (CDRR). During superplastic deformation, an unstable subgrain boundary network forms and these subboundaries are absorbing gliding dislocations and transform into low and high angle grain boundaries. A dislocation gliding and climbing process accommodated by subgrain boundary sliding, migration and rotation, enables the superplastic flow to proceed.