Effects of Loading Rate Range on Mechanical and Microstructural Properties of Dynamically Compacted Iron Powder

In this paper, an attempt was made to investigate the effects of dynamic loading rate on the properties of iron powder with a focus on the microstructural characteristics of the compacted material. Dynamic compaction tests were performed using an instrumented die equipped with a load cell under the low loading rate ranging from 20 to 44 kN/ms in a drop hammer and the high loading rate ranging from 308 to 665 kN/ms in a one-stage light gas gun. Optical and scanning electron microscopes, diametric compression test, and Vickers hardness measurement were used to investigate microstructural and mechanical properties of the green compacts. The obtained results show that the range of loading rate completely changes the behavior of the powder by changing the number and velocity of the propagating stress waves. Comparison of the properties of specimens with equivalent density compacted under two ranges of loading rates indicates that the high range significantly increases the strength and hardness, distributes stress and porosity more uniformly, and reduces initiation and growth of inter-particle cracks as well as the compaction force required to achieve a specific density.