Probing the lattice structure of dynamically compressed and released single crystal iron through the alpha to epsilon phase transition
Experiments using broadband Laue x-ray diffraction (XRD) were used to examine the lattice structure of dynamically compressed [100]-oriented single crystal iron samples at the Dynamic Compression Sector at the Advanced Photon Source. These experiments used 1~$$\mu$$m thick iron single crystal samples sandwiched between a polyimide ablator and a polycarbonate window. A 100~J, 10~ns duration laser pulse incident on the polyimide ablator was used to shock compress the iron samples to initial stresses greater than 25~GPa, exceeding the $$\sim$$13~GPa alpha (body-centered-cubic or bcc structure) to epsilon (hexagonal-close-packed or hcp structure) phase transition stress. XRD measurements were performed at various times relative to the shock wave entering the iron sample: early times <$$\sim$$150~ps while the initial shock waves propagated through the iron; intermediate times after the iron equilibrated with the ablator and window reaching a plateau stress state (12~GPa or 17~GPa) lasting several nanoseconds; and late times during uniaxial strain release. The early time measurements show that in less than $$\sim$$150~ps the high-pressure hcp phase is relaxed with a $c/a$ ratio of 1.61, contrary to previous laser shock experiments where a $c/a$ ratio of 1.7 was inferred. In the plateau stress state and partially released states, XRD measurements showed that the hcp structure retained a $c/a$ ratio of 1.61 with no observable changes in microstructure. Upon stress release at $$\sim$$1~GPa/ns release rate, the reverse phase transition (hcp to bcc) to the original single crystal orientation (implying a transformation memory effect) was observed to go to completion somewhere between 13 GPa and 11 GPa, indicating little stress hysteresis under rapid uniaxial strain release. A similar memory effect for the reverse hcp to bcc transformation has been previously observed under hydrostatic compression. However, the bcc/hcp orientation relationships differ somewhat between dynamic and static compression experiments, implying that the transformation pathway under uniaxial dynamic strain differs from the Burgers mechanism.
- Research Organization:
- Washington State Univ., Pullman, WA (United States). Inst. for Shock Physics
- Sponsoring Organization:
- USDOE National Nuclear Security Administration (NNSA), Office of Defense Programs (DP)
- Grant/Contract Number:
- NA0003957; NA0003900; AC02-06CH11357
- OSTI ID:
- 1778969
- Alternate ID(s):
- OSTI ID: 1773950; OSTI ID: 1781786
- Journal Information:
- Journal of Applied Physics, Vol. 129, Issue 13; ISSN 0021-8979
- Publisher:
- American Institute of Physics (AIP)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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