Microstructural Characterization of Shock Recovered AD995 Alumina

The present work was initiated to characterize the crystallographic and microstructural changes in shock recovered specimens of AD995 alumina subjected to shock induced stress between 4 and 8 GPa, below and above its HEL, i.e., 6.7 GPa. The AD995 was recovered intact, but containing macroscopic cracks, when shocked to 4 GPa, a stress well below the HEL. The AD995 specimen recovered from the plate impact test at a stress (7.8 GPa) above the HEL showed visual evidence of extensive macroscopic damage and fragmentation. The AD995 specimen recovered from the 6 GPa impact test showed evidence of localized plastic deformation and the presence of dislocations primarily in the vicinity of grain boundaries. However, the AD995 specimen recovered from the 8 GPa test exhibited deformation twins. The aforementioned change in the shock induced plastic behavior/deformation and failure in AD995 below and above the HEL was simultaneously associated with a change in the fracture behavior of AD995, from intergranular fracture below the HEL to intragranular cleavage fracture above the HEL.