Simultaneous enhancements of strength, ductility, and toughness in a TiB reinforced titanium matrix composite

Abstract

In titanium matrix composites (TMCs), the enhancement in strength and specific stiffness with the addition of ceramic reinforcements often occurs with lowered ductility and fracture toughness. The latter is primarily due to the location of the reinforcement particles at the grain boundaries (GBs). In the current work, it is illustrated that it is possible to enhance the strength, ductility, and fracture initiation toughness (KQ) simultaneously if the particles are micron sized and predominantly present within the grains. For this purpose, TMCs (in which the majority of titanium monoboride (TiB) particles present intra-granularly) are synthesized using the powder metallurgy technique, and their microstructures and the uniaxial tensile properties, mode I fracture toughness, and fatigue crack growth behavior were evaluated. Interrupted uniaxial tensile tests reveal that the intragranular TiB particles enhance the strain hardening rate, by resisting the planar slip, which is otherwise dominant in the Ti matrix; the particles present at the GBs fracture prematurely and compromise the ductility and the toughness of the material. Such significant differences in the roles played by the inter- and intra-granular TiBs in determining the overall mechanical performance of the TMCs highlight the importance of microstructural design of them, especially on the location of reinforcements with respect to GBs.