The role of molybdenum in suppressing cold dwell fatigue in titanium alloys

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Title: The role of molybdenum in suppressing cold dwell fatigue in titanium alloys
Authors: Ready, AJ
Haynes, PD
Grabowski, B
Rugg, D
Sutton, AP
Item Type: Journal Article
Abstract: We test a hypothesis to explain why Ti-6242 is susceptible to cold dwell fatigue, whereas Ti-6246 is not. The hypothesis is that in Ti-6246 substitutional Mo-atoms in $\alpha$-Ti grains trap vacancies thereby limiting creep relaxation. In Ti-6242 this creep relaxation enhances the loading of grains unfavourably oriented for slip and they subsequently fracture. Using density functional theory to calculate formation and binding energies between Mo-atoms and vacancies we find no support for the hypothesis. In the light of this result, and experimental observations of the microstructures in these alloys, we agree with the recent suggestion [J. Qiu, {\it et al.}, Metall. Mater. Trans. A {\bf 45}, 6075 (2014)] that Ti-6246 has a much smaller susceptibility to cold dwell fatigue because it has a smaller grain size and a more homogeneous distribution of grain orientations. We propose that the reduction of the susceptibility to cold dwell fatigue of Ti-6242 at temperatures above about 200~$^\circ$C is due to the activation of $\langle \mathbf{c} + \mathbf{a} \rangle$ slip in `hard' grains, which reduces the loading of grain boundaries.
Issue Date: 5-Jul-2017
Date of Acceptance: 6-Jun-2017
ISSN: 1364-5021
Publisher: Royal Society, The
Journal / Book Title: Proceedings of the Royal Society A: Mathematical, Physical & Engineering Sciences
Volume: 473
Issue: 2203
Copyright Statement: © 2017 The Author(s) Published by the Royal Society. All rights reserved.
Sponsor/Funder: Engineering and Physical Sciences Research Council
Funder's Grant Number: EP/L015579/1
Keywords: 01 Mathematical Sciences
02 Physical Sciences
09 Engineering
Publication Status: Published
Article Number: 20170189
Appears in Collections:Condensed Matter Theory
Faculty of Natural Sciences

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