Dynamic X-ray Diffraction to Study the Shock-induced α-ε Phase Transition in Iron

Recent advancements in coupling dynamic loading platforms with third generation light sources are providing new means to study materials at extreme conditions. Diagnostics such as X-ray diffraction (XRD) and X-ray phase contrast imaging (PCI) are being employed in-line with dynamic loading platforms for studying dynamic phenomena such as phase transitions, microstructural evolution, etc. Here we study the well-known polymorphic phase transformation (alpha-epsilon phase) in polycrystalline iron through front-surface plate impact experiments using dynamic X-ray diffraction techniques at the Dynamic Compression Sector at the Advanced Photon Source (APS) The impact stress state of the iron samples were measured using optical velocimetry techniques The window correction for Lexan (TM) was also investigated since this material was used as the impact surface and optical window in the experimental configuration described here, and has been shown to be useful as a window material for other dynamic XRD measurements. X-ray diffraction data show that at impact stresses near the known transition stress for polycrystalline iron (13 GPa), we begin to see evidence of the transition to the higher pressure epsilon phase (hcp). Although additional experiments are needed to observe the complete transformation to the epsilon-phase, this work provides the first XRD data for iron obtained in plate impact experiments that provide insight into this well-known transition.