From nanocrystalline to amorphous structure in beryllium-based coatings

The material properties of vapor deposited coatings are sensitive to the growth morphology and microstructure. For certain applications it is desirable to deposit Be-rich coatings that are homogeneous, isotropic, dense, mechanically strong, and smooth. One way to develop this set of properties is to refine the grain size in these deposits to the nanoscale range. In this study, the compositional effects of Cu, Fe, and B additions on the microstructure of Be coatings have been characterized with transmission electron microscopy. Fe and B additions are found to have a dominant affect on grain refinement. Furthermore, an amorphous Be-B phase is found in deposits having compositions in excess of 11 at.% B. Nanoindentation was used to assess the mechanical properties of the coatings. The measured hardness values are correlated with the grain size and compositions of the coatings. The presence of amorphous Be-B phases is found to decrease the coating hardness.