Effect of titanium on solidification microstructure of Al-16%B4C composites

Abstract

Aluminum boron carbide particulate reinforced composites have found new applications in nuclear industry due to their special capability to capture neutrons. Recently, Alcan successfully developed a liquid metal mixing process to fabricate Al-B4C metal matrix composite instead of powder metallurgical technology. In the process, titanium is added into the composites to control interactions between boron carbide particulates and aluminum matrix. To understand the effects of titanium on the composites, the solidification microstructure of Al-16%B4C without or with titanium was examined by optical and electron microscopes. The results show that titanium can improve the uniformity of the particulate distribution within aluminum matrix if the titanium content in the composites is more than 0.5%. Furthermore, it is found that the layer with rich titanium on the surface of the particulates can limit the formation of AlB2 type compounds, which may greatly deteriorate the fluidity of the composites. In addition, it is also found that the amount of the reaction products in the composites increases with the increase of holding time. However, the rate of the increase is mitigated by the increase of the content of titanium in the composites. Besides, a procedure was proposed and implemented for the evaluation of uniformity of particulate distribution within aluminum matrix.