COMBUSTION SYNTHESIS IN THE TI-C-NI-MO SYSTEM .2. ANALYSIS

Combustion-wave arrest experiments provide the means of greater unders tanding of the physical phenomena which occur during the propagation o f a combustion wave within a Ti-C-Ni-Mo powder mixture. The apparent a ctivation energy for the process (E approximate to 120 +/- 40 kJ/mol) and the observations reported in the companion article indicate that t he rate-limiting step in the reaction between Ti and C is the dissolut ion of C into the Ti-Ni-C melt. Temperature profile analysis indicates that the 2 mu m C flakes are completely consumed within approximately 0.2 seconds. The formation of TiCx spherules and their subsequent det achment is explained in terms of compressive stresses established in t he growing TICx layer on the C particle. The compressive stresses are estimated to exceed 1 GPa, and an energy balance analysis predicts the formation of spherules for layer thicknesses on the order of 1 mu m, consistent with the experimental results.