Heterogeneous shock energy deposition in shock wave consolidation of metal powders.

摘要

Shock wave consolidation of powder is a high deformation rate process in which a shock wave generated by an explosive or a colliding projectile rapidly densifies and bonds together the powder particles into a solid compact. The deposition of the shock energy during this process is highly inhomogeneous on the powder particle scale. Evidence of the extent and pattern of the energy deposition was provided by recovery experiments performed using a crystalline metallic glass forming alloy, and analyzed using a heat flow model. The energy deposited during the shock wave passage was best modeled as deposited partly into the particle bulk and partly onto particle surfaces. To investigate this inhomogeneity, and the powder parameters which influence it, a propellant driven gas gun was designed, built and utilized. The planarity of the shock waves produced using the targets designed for the gun was established. Powder - powder thermocouples were impacted with powders of varying sizes to establish the effect of particle size on energy deposition. Small particles in contact with large ones were inferred to absorb the greater fraction of shock energy. Hardened and unhardened steel powder was shocked to investigate the effect of particle hardness on energy distribution. The recovered compacts were not measurably affected by the initial hardness. Compaction experiments were performed on a Ni based super-alloy and on a SiC reinforced Ti matrix composite to test some of the practical applications of the process and the target designs developed. Superior tensile properties were observed in the shock consolidated and heat treated Ni based 718 alloy. The SiC reinforced composite was recovered in the intended net shape with no macro-cracks in the compact body, but with fractured SiC particles.