Modeling non-basal deformation modes in Mg-Y and other Mg-RE alloys

Bibliographic Details
Main Author:	Buey, Daniel
Language:	English
Published:	The Ohio State University / OhioLINK 2018
Subjects:	Materials Science Magnesium automotive industry aerospace industry materials science
Online Access:	http://rave.ohiolink.edu/etdc/view?acc_num=osu1532081086077038

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spelling	ndltd-OhioLink-oai-etd.ohiolink.edu-osu15320810860770382021-08-03T07:07:43Z Modeling non-basal deformation modes in Mg-Y and other Mg-RE alloys Buey, Daniel Materials Science Magnesium automotive industry aerospace industry materials science Magnesium has a phenomenal specific strength, making it ideal for use in the automotive and aerospace industries, but its poor room temperature ductility limits its use to cast parts. The poor ductility is a result of the highly anisotropic plastic deformation response of the HCP crystal system. The Peierls stress for non-basal deformation modes is several times larger than for basal slip, in some cases as much as an order of magnitude larger. As a result of this discrepancy, non-basal deformation modes are unlikely to be activated during arbitrary loading in a polycrystalline sample. The ultimate goals of this study are to examine the deformation modes to gain a better understanding of the mechanisms involved with ductile failure in Mg, and to provide a mechanistic explanation for the improvement in ductility seen with the addition of rare earth (RE) solutes.To that end, we first model the cross-slip behavior of screw (c + a) dislocations between first- and second-order pyramidal planes. In addition to determining the core energy and the critical resolved shear stress (CRSS) for the dislocations, we also identify a metastable compact, undissociated dislocation core as a possible transition state for cross slip between pyramidal I and pyramidal II planes.Next we calculate the interaction energy between a (c + a) edge dislocation and a solute substituted on some atomic site near the dislocation, and then use the calculated interaction energy to apply a solid solution strengthening model to determine the change in the CRSS for the glide of edge $\ca$ dislocations along the pyramidal II plane. We also calculated the change in CRSS for the basal dislocation and compared. From the solutes effect on the CRSS values, we find that the addition of yttrium solutes is not expected to prevent (c + a) slip as hard as it prevented basal slip, effectively increasing (c + a) activation relative to basal. The other major result from this study is that we show how the direct substitution of solutes into the dislocation cell causes the dislocation to shift, sometimes significantly changing its geometry, and necessitating a modification to the method used to determine the interaction energy.Finally, we do the same thing for the twinning dislocation. In this case, the interaction energies were calculated using an approximation that scales the directly calculated interaction energy map of one solute to another solute based on smaller, more manageable calculations. We find that like the (c + a) dislocation, the addition of Y solutes makes glide of the twinning dislocation easier. However, it is possible that the strengthening effect on the twinning dislocation could be underestimated (possibly due to a change in defect geometry that we do not consider), or the strengthening effect on basal slip is overestimated. This study also indicated that the solutes considered may be expected to cause changes in geometry in the defect structures they are put into, necessitating directly calculated interaction energies for this geometry in order to accurately predict the strengthening effect. 2018-11-06 English text The Ohio State University / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=osu1532081086077038 http://rave.ohiolink.edu/etdc/view?acc_num=osu1532081086077038 unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.
collection	NDLTD
language	English
sources	NDLTD
topic	Materials Science Magnesium automotive industry aerospace industry materials science
spellingShingle	Materials Science Magnesium automotive industry aerospace industry materials science Buey, Daniel Modeling non-basal deformation modes in Mg-Y and other Mg-RE alloys
author	Buey, Daniel
author_facet	Buey, Daniel
author_sort	Buey, Daniel
title	Modeling non-basal deformation modes in Mg-Y and other Mg-RE alloys
title_short	Modeling non-basal deformation modes in Mg-Y and other Mg-RE alloys
title_full	Modeling non-basal deformation modes in Mg-Y and other Mg-RE alloys
title_fullStr	Modeling non-basal deformation modes in Mg-Y and other Mg-RE alloys
title_full_unstemmed	Modeling non-basal deformation modes in Mg-Y and other Mg-RE alloys
title_sort	modeling non-basal deformation modes in mg-y and other mg-re alloys
publisher	The Ohio State University / OhioLINK
publishDate	2018
url	http://rave.ohiolink.edu/etdc/view?acc_num=osu1532081086077038
work_keys_str_mv	AT bueydaniel modelingnonbasaldeformationmodesinmgyandothermgrealloys
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Modeling non-basal deformation modes in Mg-Y and other Mg-RE alloys

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