Deformation microstructures in titanium sheet metal |
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Authors: | S Mullins B M Patchett |
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Affiliation: | (1) The APV Company, Crawley, 10 2QB West Sussex, RH, England;(2) Dept. of Mineral Engineering, The University of Alberta, T6G 2G6 Edmonton, Alberta, Canada |
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Abstract: | A metallographic study has been made of the microstructures produced by room temperature deformation of 0.6mm thick commercially
pure titanium sheet metal in uniaxial, plane strain and biaxial tension. Deformation twinning becomes increasingly important
as the deformation mode changes from uniaxial through plane strain to equibiaxial tension, and is more significant for strain
transverse to the rolling direction than for strain in the longitudinal direction. In uniaxial tension, 1122 twins are dominant
in longitudinal straining, while 1012 twins dominate in transverse straining. In plane strain and equibiaxial straining, 1012
twinning is suppressed and largely replaced by 1122 twinning. The observed changes in twin occurrence and type are attributed
to the interaction of the imposed stress system and the crystallographic texture of the rolled sheet, which alters the distribution
of the grain basal-plane poles with respect to the operative stress axes. In uniaxial tension parallel to the longitudinal
direction, twins favored by ‘c’ axis compression are produced, while in the transverse direction twins favored by ‘c’ axis
tension appear. In plane strain and biaxial tension the dominant stress is through-thickness compression, which produces twins
favored by ‘c’ axis compression in nearly all cases. The alterations in twin orientation and numbers are associated with changes
in stress-strain behavior. As twin volume fraction increases and twins are aligned more closely to the principal stress axis,
the instantaneous work-hardening rate tends to stabilize at a nearly constant value over a large strain range.
Formerly Chief Metallurgist, The APV Company. |
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