Shear localization and chemical reaction in Ti–Si and Nb–Si powder mixtures: Thermochemical analysis

Abstract

Chemical reactions in Ti–Si and Nb–Si powder mixtures were initiated in regions of high plastic strain induced by high-strain-rate deformation. These regions of high localized plastic strain had thicknesses of 10–25 μm and a characteristic spacing of 600–1000 μm. Scaling up of the experiments revealed a shear-band spacing that is constant and dictated by material and deformation parameters. The generation of heat due to plastic deformation and chemical reaction is treated in a one-dimensional calculation. The calculations are in qualitative agreement with experimental results: shear bands can serve as ignition regions for the propagation of the reaction throughout the entire specimen for Ti–Si, whereas in the Nb–Si system (that has a much lower enthalpy of reaction), the reaction is always localized in the shear bands. These results enable the estimation of a reaction time in the Ti–Si mixture (∼10 ms) and of a critical global strain required for the complete reaction to take place (εeff=0.38). This is a new regime of reaction, intermediate between combustion synthesis and shock compression synthesis.