HVEM in situ deformation of Al-Li-X alloys

Journal Article · Sun May 01 04:00:00 EDT 1983 · Scr. Metall.; (United States)

DOI:https://doi.org/10.1016/0036-9748(83)90394-0· OSTI ID:5400475

Crooks, R E; Kenik, E A; Starke, Jr, E A

Lithium additions to aluminum alloys increase both the strength and elastic modulus while decreasing the density, thereby resulting in very attractive combinations of properties. The commercial utilization of these alloys, however, has been hindered by a lack of adequate ductility at peak strength. Recent investigations have attributed the low ductility to intense, localized deformation. This is considered to be due to the promotion of planar slip by coherent, shearable, delta' (Al/sub 3/Li) precipitates and the presence of precipitate free zones (PFZ's) at high angle grain boundaries. An Al-Cu-Li-Mg-Zr alloy, produced by rapidly solidified powder processing, was found to exhibit ductility improvements over comparable, lithium-containing alloys. Thin foils prepared from bulk tensile samples were examined by transmission electron microscopy (TEM), and no evidence of localized deformation was found. These, however, were only successfully produced from the region of uniform elongation below the neck and were thus limited to approximately 4% plastic strain. In order to observe the deformation behavior under severe strain, an in situ deformation study was conducted in a high voltage electron microscope (HVEM). Several investigators have used in situ HVEM techniques to study ductile fracture processes. The advantages of HVEM versus TEM for this purpose include: thicker specimens (due to a lower energy exchange of the electrons), a lower specimen contamination rate and a negligible increase in specimen temperature. Two lithium-containing alloys which had been previously reported to demonstrate localized, planar slip were studied for comparison.

• Research Organization: Fracture and Fatigue Research Laboratory, Georgia Institute of Technology, Atlanta, GA 30332
• DOE Contract Number: W-7405-ENG-26
• OSTI ID: 5400475
• Journal Information: Scr. Metall.; (United States), Journal Name: Scr. Metall.; (United States) Vol. 17:5; ISSN SCRMB
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360103* -- Metals & Alloys-- Mechanical Properties
ALLOYS
ALUMINIUM ALLOYS
COMPARATIVE EVALUATIONS
COPPER ALLOYS
CRYSTAL STRUCTURE
DEFORMATION
DUCTILITY
ELECTRON MICROSCOPY
FLEXURAL STRENGTH
GRAIN BOUNDARIES
HARDENING
LITHIUM ALLOYS
MAGNESIUM ALLOYS
MATERIALS TESTING
MECHANICAL PROPERTIES
MECHANICAL TESTS
METALLURGY
MICROSCOPY
MICROSTRUCTURE
POWDER METALLURGY
PRECIPITATION HARDENING
SHEAR
TENSILE PROPERTIES
TESTING
TRANSMISSION ELECTRON MICROSCOPY
YOUNG MODULUS
ZIRCONIUM ALLOYS