In-situ synthesis of Ti matrix composite reinforced with dispersed Ti 5Si3 particles via spark plasma sintering

Abstract

In this work, Ti matrix composite reinforced with dispersed Ti 5Si3 particles was synthesized via spark plasma sintering starting with Ti and SiO2. Because reports on the equilibrium phase diagram show that there is a two phase region with O dissolved Ti, Ti(O), and Ti5Si3, Ti and small amount of SiO2 transform into Ti5Si3/Ti composite according to a reaction, Ti + SiO2 = Ti(O) + Ti5Si3. Initial amount of SiO2 and sintering temperature were varied in ranges of 2.5-15 mass% and 800-1200°C, respectively. Their dependence on microstructure, bulk density, fraction of spatial occupation and Vickers hardness was studied systematically. From microstructure observation, composition and temperature range to yield Ti5Si3/Ti composite was identified. At low temperature sintering, however, SiO2 remained inside the Ti 5Si3 envelope, indicating incompleteness of above reaction. A simple analysis was made on the phase transformation mechanism of Ti5Si3, supposing that the diffusion of Ti controls this process. Vickers hardness of the Ti5Si3/Ti composite increases with increase both in amount of SiO2 and temperature, but it is remarkably larger than that of commercial pure Ti. The bulk density and fraction of spatial occupation also increases with increase in temperature but decreases with increase in amount of SiO2. Taking into account the experimental and analytical results, microstructure formation and its effect on the properties are discussed briefly. © 2005 The Japan Institute of Metals.