THE AMORPHOUS-TO-GAMMA TRANSFORMATION IN ION-IMPLANTED AL2O3

Amorphous surface layers, free of implanted impurities, were produced on single crystal α-Al2O3 substrates by implantation at - 185 °C with 2 × 1016 Al/cm2 at 90 keV and 3 × 1016 O/cm2 at 55 keV. The response of these amorphous layers to post-implantation annealing in the temperature range from 700 to 800 ° C was investigated by in situ transmission electron microscopy (TEM) and conventional TEM of specimens annealed in bulk form. It was found that the amorphous Al2O3 transformed to the cubic transitional γ phase along an irregular front. The recrystallized material is columnar with the individual columns or domains being irregular in size and shape. The γ-Al2O3 is composed of two variants which are twin related and have the following orientation relationship with the substrate: 〈110〉)γ∥〈101̄0〉α and {111}γ∥{0001}α. The temperature-dependent velocity of the amorphous-to-γ transformation front was measured by in situ TEM. Assuming a thermally activated process, the activation energy has been determined from an Arrhenius plot of velocity versus T-1. These results are discussed in terms of possible rate controlling processes of the transformation. © 1990.