Optimizing Grain Boundary Complexions to Produce Dense Pressure-Less Sintered Boron Carbide (B4C)

Abstract

Abstract : The goal of this seedling grant was to explore the possible existence and role of grain boundary complexions in the sintering of boron carbide by two means. First, we have developed a novel processing strategy, which exploits the use of a chemical (dopant) gradient in order to facilitate the ease of identification and characterization of grain boundary complexions. Second, we have characterized commercially prepared samples in which different dopants led to significant differences in grain growth behavior (abnormal versus abnormal). The results of this study determined that sintering and grain growth in boron carbide is highly sensitive to dopant chemistry and amount. The chemical gradient model experiment revealed that yttria can readily activate complexion transitions in boron carbide. Alumina promotes abnormal grain growth in boron carbide by activating a grain boundary complexion transition from type I (sub monolayer adsorption) to type lit (multilayer adsorption). The use of multiple dopants is effective in stabilizing grain boundary complexion type tin boron carbide and in preventing abnormal grain growth. Further work on the identification and control of grain boundary complexions in boron carbide is highly recommended.