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-prop agating high temperature synthesis (SHS) reactions were involved in produci ng the last three materials during room temperature high-energy ball-millin g of elemental powders. Such reactions appeared to occur through ignition b y mechanical impact in the fine powder mixture formed after a critical mill ing 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 n ot 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-m illing procedures were employed for the syntheses of Ti3Si and TiSi2 using different sizes of Si powder and milling medium materials. Ti3Si was synthe sized by milling a Ti and 60 minutes premilled Si powder mixture for 240 mi nutes. alpha -TiSi2 and TiSi2 were produced by high energy partially stabil ized zirconia (PSZ) ball-milling for 360 minutes in a steel vial followed b y 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 r eaction, and the product(s) and reactants coexist for a certain period of t ime. The formation of titanium silicides by MA and the reaction rate appear ed to depend on the homogeneity of the powder mixture, milling medium mater ials, and heat of formation of the product involved. (C) 2001 Kluwer Academ ic Publishers.