The $TiB_2/TiC$ composites have been fabricated by directed reaction of molten titanium with boron carbide particulates. The effect of nickel in molten titanium on the directed reaction of titanium with boron carbide has been studied. And the effect of reaction temperature on the microstructure of $TiB_2/TiC$ composites has been studied, also.
Directed reaction was performed in the range of 1600℃ to 1800℃ in argon atmosphere after laying titanium(+X nickel) preform on the boron carbide preform in graphite crucible.
Reaction between molten titanium and boron carbide occurred and resulted in the formation of dense $TiB_2/TiC$ composites. But reaction between pure titanium and boron carbide occurred at only their interface and could not move forward $B_4C$ preform. This phenomenon is believed to result from the formation of protective $TiB_2/TiC$ layer. Nickel added in the titanium promoted the reaction rate between titanium and boron carbide. It is thought that nickel changes the viscosity and/or wettability of molten titanium in the channels to promote reaction rate.
Microstructural gradient appeared through all the specimens fabricated by this process and its degree increased with reaction tempertature.
Microstructural gradient led to gradient of mechanical properties, eg. flexural strength, fracture toughness, and microhardness. Mechanical properties of this material was excellent and included values for room temperature flexural strengh of 900-1100MPa, fracture toughness of 8-13$MPa\cdotm^{1/2}$, and microhardness of 2000-2300kg/㎟.