In December I performed some Vicker’s hardness test on the last series of composite samples (with submicron AlN reinforcement). It turned out that they have considerably lower hardness than the previous series (with ~1 micron AlN) – about 250 HV. The worse mechanical properties may origin from the tendency of fine AlN particles to form agglomerates.
I also calculated a matrix grain size distribution of this series of composites on the basis of TEM bright field micrographs analysis.