大晶粒单相Ni-48Al金属间化合物超塑性变形过程中的组织演化

MICROSTRUCTURAL EVOLUTION DURING SUPERPLASTIC DEFORMATION IN LARGE-GRAINED SINGLE PHASE Ni-48Al INTERMETALLICS

原始平均晶粒尺寸约为200μm的单相Ni-48Al金属间化合物在温度为1025—1100℃、应变速率为1.25×10^(-4)—2.00~10^(-3)s^(-1)范围内呈现超塑性。在1100℃、应变速率为1.125×10^(-3)s^(-1)时,最大延伸率可达188.2％。金相分析表明,超塑性变形过程中晶粒明显细化;电子背散射衍射分析(EBSD)和透射电子显微术(TEM)观察表明,超塑变形过程中形成了大量亚晶界网络,且随变形量增大,亚晶界及小角晶界比例不断增加。亚晶界由位错墙和位错网络构成,不稳定的亚晶界在超塑性变形过程中不断吸收晶内滑移和攀移位错,亚晶界位错密度不断增加,取向差不断增大。伴随亚晶界的滑移和迁移及亚晶的转动,部分亚晶界转变为小角度晶界,并进而转变为大角度晶界,即在超塑性变形过程中发生了连续动态回复与再结晶(CDRR)。

Superplastic deformation has been found in large-grained Ni-48Al intermetallics with grain size of 200 mum. Metallographic examination shows that the average grain size of the tested material decreases during superplastic deformation and much finer grains could be obtained after superplastic deformation. TEM and EBSD show that there are great numbers of subgrain boundaries and the proportion of subgrain and low angle boundaries increases with the increase of strain. During superplastic deformation an unstable subgrain network forms, which absorbs gliding and climbing dislocations and transforms into low and high angle grain boundaries accommodated by subgrain boundary sliding, migration and rotation. The observed superplastic phenomenon was explained by continuously dynamic recovery and recrystallization.