Investigation of shock-induced reaction behavior of as-blended and ball-milled Ni+Ti powder mixtures using time-resolved stress measurements

The shock-compression response of as-blended and ball-milled elemental Ni and Ti powder mixtures is investigated in this study. An $80\text{-}\mathrm{mm}$ diameter single-stage gas-gun was employed to perform time-resolved measurements using piezoelectric stress gauges to monitor the stress wave profiles at the front (input) and back (propagated) surfaces of the $\sim 50\%$ dense $\mathrm{Ni}+\mathrm{Ti}$ powder mixture compacts. Shock-compression experiments performed on as-blended $\mathrm{Ni}+\mathrm{Ti}$ powder mixtures in the range of $522\mathrm{m}∕\mathrm{s}\text{to}1046\mathrm{m}∕\mathrm{s}$ impact velocities, showed characteristics of powder densification at measured input stress of $1.12\mathrm{GPa}$ , and shock-induced chemical reaction indicated by volume expansion and wave speed increase at measured input stress of $3.2\mathrm{GPa}$ . Ball-milled powder mixtures also showed similar evidence of shock-induced chemical reaction at stresses exceeding $3\mathrm{GPa}$ , with the degree of expansion depending on the energy release associated with the reaction in the powder mixtures ball-milled for various times. The measured high-pressure expanded state was observed to correspond to that calculated using a thermodynamic “ballotechnic” model for shock-induced formation of reaction products in as-blended and ball-milled powder mixtures. The results of instrumented experiments provide clear evidence of shock-induced chemical reactions occurring in $\mathrm{Ni}+\mathrm{Ti}$ powder mixtures (following densification at stresses exceeding the crush strength) as evidenced by increased shock velocity and generation of an expanded state of products resulting from the associated heat of reaction.