Fabrication and characterization of graded impedance impactors for gas gun experiments from hot-pressed magnesium and polyethylene powders

A methodology is described for fabrication of compositionally graded metal/polymer structures to be used as light-gas gun impactors. Mixtures of Mg and polyethylene (PE) powders were layered into a stainless steel mold and uniaxially pressed to achieve a controlled composition gradient ranging from 5 to 100% PE. Monolithic pellets of each composition were evaluated by measurement of density and sound wave velocity. Both properties vary monotonically over most of the composition range. Graded impactors were characterized by ultrasonic C-scan and white light interferometry. A prototype impactor was launched into a stationary LiF target using a two-stage light-gas gun, and the resulting particle velocity was characterized via velocimetry. An impactor with 20 layers of differing composition produced smooth compression with a barely visible manifestation of the discrete layer structure. Fabrication of graded impactors by this technique is of significant interest for providing improved control of the pressure profile and impactor planarity in gas gun experiments.