Epitaxy in multilayer coatings of kappa-Al2O3

In this study, epitaxy in multilayer coatings of CVD kappa-Al2O3 was investigated by electron diffraction in transmission electron microscopy (TEM). The aim was to describe a general form of the orientation relationship between kappa-Al2O3 and the kappa-modification layers. The results from diffraction pattern analyses confirm that kappa-Al2O3 exhibits three twin-related domains, rotated 120 degrees around the c axis. On these kappa-grains, the grains in the kappa-modification layer grow epitaxially. These kappa-modification grains are f.c.c. and consist of two families of domain, rotated 180 degrees around <[(1)over bar 11]>, which is the growth direction. The next kappa-Al2O3 layer grows epitaxially on the kappa-modification layer domains. In this way, the same orientation relationship continues past each interface in the growth direction, through the remaining coating. The orientation relationships between all the domains of the two layers can be described as [GRAPHICS] The general form of these orientation relationships indicates that close-packed planes grow on close-packed planes, with f.c.c. close-packed directions parallel to the oxygen ion close-packed directions in alumina.