Influence of Pressing Parameters on the Microstructure of PBX 9501

Abstract

Microstructural features, such as defects, crystal morphology, and crystal size distribution can dramatically affect the ignition sensitivity, performance, and mechanical properties of energetic materials. While these features can be characterized for the raw material, little is known about how they are altered during pressing. For example, in the preparation of a consolidated charge of PBX 9501, variables such as ultimate pressure, number of pressing cycles, dwell time, or rest time are varied in order to achieve nominal density of 1.830 g/cc. Although this density is met, differences in pressing parameters can lead to variations in microstructure between samples. To evaluate the effect of pressing parameters on the microstructure, three cylinders of PBX 9501 have been pressed at 5 kpsi, 15 kpsi, and 30 kpsi, using a 100 Ton heated steel die press. Polarized light microscopy (PLM) images taken at 144 locations within each cylinder show differences in porosity, crystal size and size distribution between cylinders and at different locations within the same cylinder. Scanning electron microscopy (SEM) further verifies increased fracture and rubblization of HMX during pressing.