Characterization of the structure of TiB2/TiC composites prepared via mechanical alloying and subsequent pressureless sintering

Abstract

TiB2 and TiC ceramics are particularly attractive for high-temperature applications due to their high modulus, excellent refractory properties and chemical inertness. The high electrical and thermal conductivities of TiB2 and TiC also suggest the potential use of TiB2/TiC composites in high-performance electrolytic systems, such as cathodes for Hall–Heroult cells. However, TiB2/TiC composites are very difficult to fabricate by conventional sintering methods due to their high melting points (2980°C and 3067°C, respectively) and low self-diffusion coefficients. It has been found that ball milling may increase powders reactivity. This feature is associated to the reactants interface formation, increase of internal and surface energy as well as surface area, which all favor the subsequent sintering process.In this paper, dense TiB2/TiC composites were achieved by mechanical milling of Ti and B4C powder blends and subsequent pressureless sintering. X-ray diffraction analysis reflecting the evolution of the phases during milling showed that TiC formed within 18h of milling, earlier than TiB2. Transmission electron microscopy clearly indicated that the powders milled for 48h were composed of nano-sized TiC and TiB2 particles. The target products sintered using the 48h milled powder at 1750°C for 2h owned the optimum values of mechanical properties, such as higher hardness (92.1, HRA) , higher bending strength (459MPa) and fracture toughness (5.78MPa·m1/2). The target products showed relatively uniform microstructures and densities greater than 98% of the theoretical value. All the results are highly significant especially in terms of possibly commercializing the fabrication process.