Formation mechanism of titanium silicide by mechanical alloying

The syntheses of five titanium silicides (Ti3Si, TiSi2, Ti5Si4, Ti5Si3, and TiSi) by mechanical alloying (MA) have been investigated. Rapid, self-propagating high temperature synthesis (SHS) reactions were involved in producing the last three materials during room temperature high-energy ball-milling of elemental powders. Such reactions appeared to occur through ignition by mechanical impact in the fine powder mixture formed after a critical milling period. From in-situ thermal analyses, each critical milling period for the formation of Ti5Si4, Ti5Si3, and TiSi was observed to be 22, 35.5 and 53.5 minutes, respectively. However, the formation of Ti3Si and TiSi2 did not occur even after 360 minutes of milling of as-received Ti and Si powder mixture, due to the lack of homogeneity of the powder mixture. Other ball-milling procedures were employed for the syntheses of Ti3Si and TiSi2 using different sizes of Si powder and milling medium materials. Ti3Si was synthesized by milling a Ti and 60 minutes premilled Si powder mixture for 240 minutes. α-TiSi2 and TiSi2 were produced by high energy partially stabilized zirconia (PSZ) ball-milling for 360 minutes in a steel vial followed by jar-milling of a Ti and 60 min premilled Si powder mixture for 48 hr. The formation of Ti3Si and TiSi2 occurs through a slow solid state diffusion reaction, and the product(s) and reactants coexist for a certain period of time. The formation of titanium silicides by MA and the reaction rate appeared to depend on the homogeneity of the powder mixture, milling medium materials, and heat of formation of the product involved.