The critical recrystallization strain of δ-plutonium

• Published in: Scripta materialia 2001-06, Vol.44 (12), p.2815-2820
• Main Authors: LASHLEY, J. C, STOUT, M. G, PEREYRA, R. A, BLAU, M. S, EMBURY, J. D
• Format: Article
• Language: English
• Subjects: Applied sciences; Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization; Cold working, work hardening; annealing, quenching, tempering, recovery, and recrystallization; textures; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Metals. Metallurgy; Physics; Treatment of materials and its effects on microstructure and properties
• ISSN: 1359-6462; 1872-8456
• DOI: 10.1016/S1359-6462(01)00979-4

Theoretical physics research efforts require single crystals of plutonium metal and plutonium alloys. However, it is not feasible to grow single crystals of plutonium from the melt, using a classical approach, because pure plutonium exhibits six allotropes between room temperature and the liquid phase. One phase of interest, the fcc delta -phase, is thermodynamically stable over the temperature range 319 deg C to 451 deg C. Small additions of gallium or aluminum help retain the delta -phase to room temperature. Even with the gallium addition, this alloy experiences a phase transformation while cooling to room temperature. Consequently, this phase transformation makes crystal growth using classical solidification techniques extremely difficult, and we elected to pursue a solid-state strain-anneal technique. In the current work a deformation gradient was established within a delta -plutonium specimen, which was then subjected to an isothermal anneal. Disks of material were deformed using biaxial punch stretching to different dome heights. It was found by deforming commercial purity aluminum sheets that the punch stretching produced a deformation gradient giving a 15% strain difference in a single specimen. This deformation gradient was determined through circle grid measurements. The punch-stretched disks were 25 mm in diameter resulting in a shallow strain gradient despite the 15% strain difference. Thus, this particular deformation technique results in a large volume of material at a particular strain, producing ample material at the critical strain in which large grains could grow.