Equal-Channel-Angular Processing (ECAP) of Materials: Experiment and Theory

277 Pages·2016·10.5 MB·English

by  Grigoreta Mihaela Stoica

UUnniivveerrssiittyy ooff TTeennnneesssseeee,, KKnnooxxvviillllee
TTRRAACCEE:: TTeennnneesssseeee RReesseeaarrcchh aanndd CCrreeaattiivvee
EExxcchhaannggee
Doctoral Dissertations Graduate School
5-2007
EEqquuaall--CChhaannnneell--AAnngguullaarr PPrroocceessssiinngg ((EECCAAPP)) ooff MMaatteerriiaallss::
EExxppeerriimmeenntt aanndd TThheeoorryy
Grigoreta Mihaela Stoica
University of Tennessee - Knoxville
Follow this and additional works at: https://trace.tennessee.edu/utk_graddiss
Part of the Materials Science and Engineering Commons
RReeccoommmmeennddeedd CCiittaattiioonn
Stoica, Grigoreta Mihaela, "Equal-Channel-Angular Processing (ECAP) of Materials: Experiment and
Theory. " PhD diss., University of Tennessee, 2007.
https://trace.tennessee.edu/utk_graddiss/310
This Dissertation is brought to you for free and open access by the Graduate School at TRACE: Tennessee
Research and Creative Exchange. It has been accepted for inclusion in Doctoral Dissertations by an authorized
administrator of TRACE: Tennessee Research and Creative Exchange. For more information, please contact
[email protected].
To the Graduate Council:
I am submitting herewith a dissertation written by Grigoreta Mihaela Stoica entitled "Equal-
Channel-Angular Processing (ECAP) of Materials: Experiment and Theory." I have examined the
final electronic copy of this dissertation for form and content and recommend that it be
accepted in partial fulfillment of the requirements for the degree of Doctor of Philosophy, with a
major in Materials Science and Engineering.
Peter K. Liaw, Major Professor
We have read this dissertation and recommend its acceptance:
Joseph E. Spruiell, Hahn Choo, John D. Landes
Accepted for the Council:
Carolyn R. Hodges
Vice Provost and Dean of the Graduate School
(Original signatures are on file with official student records.)
To the Graduate Council:

I am submitting herewith a dissertation written by Grigoreta Mihaela Stoica entitled
′′Equal-Channel-Angular Processing (ECAP) of Materials: Experiment and Theory.′′ I
have examined the final electronic copy of this dissertation for form and content, and
recommend that it be accepted in partial fulfillment of the requirements for the degree of
Doctor of Philosophy, with a major in Materials Science and Engineering.

Peter K. Liaw
________________
Major Professor

We have read this dissertation
and recommend its acceptance:

Joseph E. Spruiell
___________________________

Hahn Choo
___________________________

John D. Landes
____________________________

Accepted for the Council

Carolyn Hodges
________________________
Dean of the Graduate School

(Original signatures are on file with official student records.)
Equal-Channel-Angular Processing
(ECAP)
of Materials: Experiment and Theory

A Dissertation
Presented for the
Doctor of Philosophy
Degree
The University of Tennessee, Knoxville

Grigoreta Mihaela Stoica
May 2007
Copyright © 2007 by Grigoreta Mihaela Stoica
All rights reserved.

ii
This work is dedicated

To my husband, who gave me everything: love,

children, and permanent support;

To my children, who are my pride;

To my Romanian and American friends, who really

care about me, and are so patient and kind;

To my entire family, who is the reason for everything

that happens to me.

iii
ACKNOWLEDGEMENTS
I am the most grateful to the committee members: Prof. Peter K. Liaw, Prof. Joseph E.
Spruiell, Prof. Hahn Choo, and Prof. John D. Landes, for their agreement to be part of
the present research effort. Prof. Raymond A. Buchanan, in your memory, we work hard
to continue your and Prof. P. K. Liaw′s initiative in the field of the severe plastic
deformation of metals. Foremost, I express to you, Prof. Liaw, my thanks for the constant
support, the tremendous energy, and excellent guidance in my graduate career and
beyond the school borders. My sincere gratitudes for the remarkable lectures, discussions,
and advices are directed to Prof. Joseph E. Spruiell. To Prof. Hahn Choo and Prof. John
D. Landes I address my special thanks for their interest in my project, and for their kind
suggestions and support. I had a fruitful learning experience working together with Dr.
Lijia Chen. I thank you, Jerry-Liang Wu, for your dedication and passion; you are an
admirable colleague and a perseverant researcher. Thank you, HH-Hao Hsiang Liao for
sharing your enthusiasm for the ECAP project. Here is the place to thank my lab mates,
Dr. George-Gongyao Wang, Mr. Robert Mc Daniels, Ms. Mary Qiao, and Ms. Carol
Winn for our work together. I thank you, Dr. Yandong Wang and Dr. Victor-Guojiang
Fan for the interesting discussions and help. I’m happy to say a word of gratitude to
Lanlan Huang, to Prof. B. Huang and Dr. Y. Liu for the tremendous help and interest in
the ECAP project. I owe my special appreciations to Dr. Louis-Yulin Lu and Julia Sun,
to Dr. Hongbo Tian and Jing He, to Dr. Bing Yang, to Fengxiao Liu, to Dr. Mark
Morrison and Dr. Bill Peters, to Ms. Brandice Green, Dr. Rejanah Steward and Ms.
Sujing Xie. Thank you for being such good friends and partners for work and discussions.
iv
Routinely, a miracle happened when entering the mechanical shop, lead by Mr. Douglas
E. Fielden. Special thanks to you, Prof. Fielden, and to your team, Mr. Larry A. Smith
and Mr. Dan Hackworth for your permanent help, innovative ideas, and professionalism.
And thank you, Mr. Gregory L. Jones, Mr. Michael R. Neal, and Mr. Stephen A. Stiner
for your constant help. This is an opportunity for me to thank the staff of the Materials
Science and Engineering Department at UT, wonderfully represented by Ms. Carla
Lawrence, Ms. Sandy P. Maples, Ms. Roberta L. Campbell, Ms. Carolyn S. Nelson, Ms.
Patricia A. Houser, Mr. W. Frank Holiway, and Mr. Randall D. Stooksbury. All of them
consistently help me on everyday basis. I have a heart-felt admiration for Prof. George
Pharr, a perfect teacher and educator. All of the above are again so many reasons to
always remember the days we worked together at UT.
Thank you, Dr. Andrew E. Payzant, for your competent help and cooperation, including
the provision of kind comments and suggestions during our work on Mg textures. The
collaboration with Dr. Cam Hubbard, Dr. Roberta Peascoe, Dr. Thomas Watkins, Dr.
Claudia J. Rawn, and Dr. Laura Riester at HTML-ORNL was essential for the present
work. I am very grateful to you all. Many thanks are addressed to Dr. Sean R. Agnew for
the extensive and passionate collaboration on the ECAP project. I’m very thankful to
Prof. Terrence G. Langdon, who produced the first ECAP billet I ever saw. Thank you,
Dr. Cheng Xu, for providing the ECAP-ed billets for our research on Al-alloys. I thank
you, Dr. Don A. Carpenter and Dr. Sven Vogel, for the delicate orientation-imaging
microscopy and neutron measurements performed on our Mg-samples.
v
I would like to express my special thanks and appreciations for the financial support from
(1) the University of Tennessee Scholarly Activities Research Incentive Fund (SARIF)
with Dr. K. Walker as the Program Director; (2) the Southeastern Universities Research
Association (SURA) with Dr. T. E. Hutchinson and Dr. G. Gruzalski as the Program
Coordinators; (3) National Science Foundation - Combined Research-Curriculum
Development Program (CRCD), under EEC-9527527, with Ms. M. Poats as the Program
Director; (4) National Science Foundation - Integrative Graduate Education and Research
Training Program (IGERT), under DGE-9987548, with Dr. C. J. Van Hartesveldt, Dr. D.
Dutta, Dr. W. Jennings, Dr. L. Goldberg, and Dr. L. Clesceri as the Program Directors,
and (5) National Science Foundation - International Materials Institutes (IMI) Program,
under DMR-0231320 with Dr. C. Huber as the Program Director, and support from the
Assistant Secretary for the Energy Efficiency and Renewable Energy, Office of
FreedomCAR and Vehicle Technologies, as part of the Material Science and Technology
User Program, Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the
U.S. Department of Energy under contract number DE-AC05-00OR22725, and the NSF
at the University of Southern California, under Grant DMR-02343331. The use of the
Advanced Photon Source was supported by the U. S. Department of Energy, Office of
Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
We address special thanks to the Centroid Corporation of Howard, Pennsylvania, for
the donated software on the Computerized Numerical Controlled (CNC) milling
machine functioning at UT, which was essential in solving the difficulty and accuracy
requirements for the sample preparation.

vi
ABSTRACT
Equal Channel-Angular Processing (ECAP), as a severe plastic deformation of metals
and composites, is analyzed both theoretically - to describe the ECAP macromechanics -
and experimentally - to obtain ultrafine-grained materials with new thermo-mechanical
properties - with a focus on hexagonal-closed-packed (HCP) structures such as Mg alloys.
Due to their obvious similarity to ECAP, the slip-line–field theories developed for
orthogonal cutting are applied to the ECAP deformation for predicting the shear-strain
spatial heterogeneities. A theoretical model for predicting the plastic-deformation zone
in an ECAP-ed billet with a free surface is provided, and is validated experimentally. A
shear-strain-mapping procedure was developed by decomposing the large deformation
process into fine steps, and, by analyzing the partially-deformed billets, the strain maps
captured the spatio-temporal evolutions of the ECAP-induced plastic shear strains. This
approach was later generalized for studying the local behavior of different material
parameters, such as textures (texture mapping).
The mechanical testing of the as-received and ECAP-deformed Mg-alloys (ZK60 and
AZ31) was performed in monotonic and cyclic tests, for three loading orientations. The
ECAP-ed samples demonstrate: (a) a good grain refinement from 50 - 70 μm down to 2.5
- 7 μm), (b) a superplastic ZK60 alloy, with an elongation to failure of 371 % at 3500C
and the strain rate of 10-2 s-1, and (c) a longer fatigue life for the AZ31 alloy, relative to
the as-received material.
The starting and ECAP-deformed materials were characterized by optical microscopy, X-
ray diffraction using both soft and hard X-rays, and neutron diffraction. The grain sizes,
vii