Microstructural characterization and mechanical behavior of Cu-Sn frangible bullets

The microstructure and mechanical behavior of commercially available, frangible bullets were evaluated. The projectiles were manufactured by compressing blended powders of copper and tin to shape followed by a low temperature heat treatment. The microstructure consisted of minor phase clusters (Cu3Sn, Cu6Sn5, and un-reacted Sn) heterogeneously distributed throughout a copper matrix. Approximately 5% porosity was encased within these clusters. Morphological development of the Cu-Sn intermetallic compounds was discussed with respect to observations in solder literature. A tight statistical dispersion in Rockwell hardness measurements indicated that the non-uniform microstructure of the bullets did not affect the overall mechanical behavior of the individual projectile. This information will be used in finite element models developed to predict the impact performance of frangible bullets with soft body armor.