Characterization of self-propagating formation reactions in Ni/Zr multilayered foils using reaction heats, velocities, and temperature-time profiles

摘要

We report on intermetallic formation reactions in vapor-deposited multilayered foils of Ni/Zr with 70 nm bilayers and overall atomic ratios of Ni:Zr, 2 Ni:Zr, and 7 Ni:2 Zr. The sequence of alloy phase formation and the stored energy is evaluated at slow heating rates (～1 K/s) using differential scanning calorimetry traces to 725 ℃. All three chemistries initially form a Ni-Zr amorphous phase which crystallizes first to the intermetallic NiZr. The heat of reaction to the final phase is 34-36 kJ/mol atom for all chemistries. Intermetallic formation reactions are also studied at rapid heating rates (greater than 10~5 K/s) in high temperature, self-propagating reactions which can be ignited in these foils by an electric spark. We find that reaction velocities and maximum reaction temperatures (T_(max)) are largely independent of foil chemistry at 0.6±0.1 m/s and 1220±50 K, respectively, and that the measured T_(max) is more than 200 K lower than predicted adiabatic temperatures (T_(ad)). The difference between T_(max) and T_(ad) is explained by the prediction that transformation to the final intermetallic phases occurs after T_(max) and results in the release of 20%-30% of the total heat of reaction and a delay in rapid cooling.