SHOCK-WAVE INITIATION OF THE TI5SI3 REACTION IN ELEMENTAL POWDERS

Elemental powder mixes were subjected to plane wave shock processing w hich reduced the initial porosity to essentially zero. Two powder mixe s in a 5:3 Ti:Si atomic ratio were used: -325 mesh Ti and Si (<45 mu m ), and -100 mesh Ti and Si (<150 mu m) with shock pressures up to 7.3 GPa and shock energies up to 671 J/g. Shock pressures were calculated using hugoniot parameters for porous elemental powder mixtures and sho ck energies were taken to be the work done by the shock (P Delta V/2). Shock energy thresholds for complete reaction of the elemental powder s were found which depend upon powder particle size and the initial po rosity of the powder. The threshold energy for the larger powder mix w as found to be similar to 8O% larger than that for the smaller powder. A decrease in initial porosity from 0.49 to 0.40 caused an increase i n threshold shock energy of about 75% for both powders. At shock energ ies slightly below the threshold energy, evidence for the reaction of solid Ti and liquid Si was observed in small isolated regions. These r egions contained spherical micronodules with the composition of TiSi2 in Si. The results are compared to those of previous studies reported in the literature, and mechanisms for reaction initiation and the obse rved threshold values are proposed. (C) 1997 American Institute of Phy sics.