Investigation of composite powder synthesis (Al2O3-WXSiY-WXBY) in aluminothermic combustion system (Al+B2O3+Si+WO3) using thermal analysis

Composites that are including silicide of tungsten and boride of tungsten intermetallic compound have properties such as high hardness, relatively good thermal shock, chemical stability and high strength at high temperature. The purpose of this investigation is evaluation of phase and microstructure of alumina base composite reinforced by boride and silicide of tungsten in three systems 1-Al+ Si+WO3, 2-Al+B2O3+WO3 and 3-Al+B2O3+Si+WO3 by combustion synthesis method in different thermal analysis experiments. In this study starting materials according to stoichiometric ratio were mixed by ball-milling under atmosphere of argon for 10 hours. The XRD results don’t show any new phase during ball-milling even up to 10 hours. Differential thermal analysis (DTA) and thermal gravity analysis (TGA) were conducted on different mixture of starting material. The results show a compact microstructure of WxBy (mostly WB) and WxSiy (mostly WSi2) as secondary phases in alumina matrix. There is a lower temperature for forming of tungsten silicide (WxSiy) compared with tungsten boride (WxBy). The presence of Si in the Al+B2O3+WO3 system facilitates the formation of tungsten borides. Tungsten boride grains are coarser and more elongated than silicide tungsten grains.