Aligned nanocrystalline fragmentation of mullite under shock loading

Transmission electron microscopy (TEM) and X-ray diffraction (XRD) observations of shock-loaded mullite ceramics was reported. The XRD pattern of the recovered sample that experienced a pressure below the phase transition pressure is identical to that of the mullite crystal at ambient conditions. The samples recovered from pressures above the phase transition pressure show XRD patterns consisting of weak mullites and a broad amorphous halo centered at 2θ=28.5°. The TEM image of the 29 GPa sample and 49 GPa shows no quantity of amorphous structure but some distortion contrast due to strain induced by plastic deformation. The nanofragmentation of mullite by shock induced amorphization indicate the possibility of controlling dynamic deformation and fragmentation by means of shock-induced phase transformations and careful selection of the initial nanostructure.