Doctoral Dissertations

Author

Jiye Wang

Abstract

"Friction stir welding (FSW) of Ti-6Al-4V alloy, nickel-based and iron-based oxide dispersion strengthened (ODS) alloys (MA754 and MA956) has been studied. The main aspects covered include tool evaluation, microstructural evolution, mechanical properties, and correlation between processing, microstructure and mechanical properties. Tool performance study was carried out for Ti-6Al-4V alloy with refractory tools made of W-1.1%La₂O₃ and two different grades of WC-Co based materials. The results showed that tool degradation can be attributed to mechanical and chemical interaction with processed material. The nature of tool-workpiece interaction was tool material dependent and influenced the resultant microstructure and weld quality in the stirred zone.

FSW resulted in refined grain structure in ODS alloys by dynamic recrystallization mechanism. A critical finding was 'strain induced dispersoid agglomeration'. For Ti-6Al-4V alloy, transformed ß microstructure formed composed of fine acicular α phase (~500 nm in thickness). The fine grain structure facilitated globularization during tensile deformation at 625 ºC.

Mechanical properties were correlated with microstructure in FSW materials. Improved mechanical properties were observed for ODS alloys due to grain refinement. An effort was made to predict room temperature yield strength for MA956 alloy with strengthening contribution analysis. On the other hand, at high temperature, degradation of creep properties was observed in MA754 alloy. Analysis of MA754 alloy with three grain structures (as-received, FSW and post-weld annealed conditions) revealed that the loss in creep strength of FSW MA754 was attributed to refined grain size and agglomerated dispersoid size"--Abstract, page iv.

Advisor(s)

Mishra, Rajiv S.

Committee Member(s)

Miller, F. Scott, 1956-
Kohser, Ronald A.
Newkirk, Joseph William
Dharani, Lokeswarappa R.

Department(s)

Materials Science and Engineering

Degree Name

Ph. D. in Metallurgical Engineering

Sponsor(s)

Boeing Company
Rolls-Royce plc
United States. Department of Energy

Publisher

Missouri University of Science and Technology

Publication Date

Fall 2012

Journal article titles appearing in thesis/dissertation

  • Tool evaluation in friction stir welding of Ti alloys
  • A preliminary study of deformation behavior of friction stir welded Ti-6Al-4V
  • Microstructure and mechanical properties of friction stir welded oxide dispersion strengthened alloy
  • Microstructural evolution and mechanical properties of friction stir welded ODS alloy MA754
  • An evaluation of creep behavior in friction stir welded MA754 alloy

Pagination

xii, 117 pages

Note about bibliography

Includes bibliographical references.

Rights

© 2012 Jiye Wang, All rights reserved.

Document Type

Dissertation - Restricted Access

File Type

text

Language

English

Library of Congress Subject Headings

Friction stir welding
Heat resistant materials -- Testing
Alloys -- Microstructure
Alloys -- Thermal fatigue

Thesis Number

T 10237

Print OCLC #

862971961

Electronic OCLC #

909399420

Link to Catalog Record

Electronic access to the full-text of this document is restricted to Missouri S&T users. Otherwise, request this publication directly from Missouri S&T Library or contact your local library.

http://laurel.lso.missouri.edu:80/record=b10158007~S5

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