Processing of titanium–titanium boride dual matrix composites

Discontinuously reinforced titanium (Ti)–titanium boride whisker (TiBw) composites are emerging as strong candidate materials for advanced applications within the automotive, aerospace and defense industries. Although increasing TiBw volume fraction has been shown to significantly improve the specific stiffness and wear resistance of titanium, it is usually on the expense of fracture toughness and ductility especially at high volume fractions of reinforcements. This paper discusses the feasibility of processing Ti–TiBw dual matrix composites that could overcome these shortcomings, by generating composite microstructures consisting of TiBw–Ti composite regions separated by a ductile Ti matrix. This microstructural design has been previously shown to impart unique combinations of properties for other composites. However, the design has never been applied to Ti–TiBw in situ generated composites which require the consideration of new processing steps and the complication of a high-temperature in situ transformation to form TiBw. Two high-temperature powder consolidation methods were investigated (pressure-less sintering and current-activated pressure assisted sintering (CAPAS)). Other aspects investigated include the use of two different boron sources (titanium di-boride (TiB2) and pure boron (B)) in addition to different composite particle sizes. Results show that pressure-less sintering was neither effective at completely forming TiBw, nor generating high-density products. Full conversion to TiBw was however attained using CAPAS generating high-density Ti–TiBw dual matrix composites.