COMBUSTION SYNTHESIS OF HFB2-AL COMPOSITES

Combustion synthesis (SHS) of HfB2-Al composite materials with a wide range of HfB2-to-Al ratios corresponding to either metal (Al) or ceram ic (HfB2) matrix was carried out with the emphasis on 60 and 70 vol pc t Al. The effects of composition and green density of pellets on the c ombustion characteristics were studied. Combustion temperature, wave v elocity, and reaction mode all changed drastically with composition an d green density. The combustion mechanisms were also studied using tem perature profile analysis. The combustion zone can be divided into pre flame and main reaction zones, and the width of the latter was much la rger than that of the former. It was also found that the combustion re action was initiated at the melting of the aluminum and consisted of a two-Step reaction sequence corresponding to the initial formation of Al3Hf and, subsequently, HfB2 compounds. The formation of Al3Hf trigge red the HfB2 formation according to the following reaction mechanism: Al3Hf + 2B --> HFB2 + 3Al.