Shock-loading meteoritic b.c.c. metal above the pressure transition: Remanent-magnetization stability and microstructure |
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| Authors: | Peter Wasilewski |
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| Institution: | Astrochemistry Branch, Laboratory for Extraterrestrial Physics, Goddard Space Flight Center, Greenbelt, Md. U.S.A. |
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| Abstract: | Three discrete levels of remanent-magnetization stability with associated microhardness and microstructural detail are recognized in meteoritic b.c.c. metal (α or kamacite) which has been shock loaded to peak pressures in excess of that required for the first-order crystallographic transformation. The first level () with moderately high magnetic stability is associated with shock transformation hardening in the absence of significant thermal effects. The second level () with low magnetic stability is characterized by decreasing hardness, finely structured metal, and minor recrystallization — evidence of thermal effect notably recovery. The third level () with the highest magnetic stability has hardness values characteristic of an alloy quenched from ～ 1,000°C. There is extensive fine-scale recrystallization and some areas have the appearance of massive martensite. The first level is associated with shock transition remagnetization i.e., simply a consequence of the ? (antiferromagnetic) → α (ferromagnetic) reversal. The second and third regions contain a thermal component. |
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