Doctoral Dissertations

Jingjing Qing

Keywords and Phrases

Austenite; Ductile Iron; Electron Microscopy; Solidification; Spheroidal Graphite Growth; Statistical Analysis

Abstract

"Evolutions of austenite and nodular/spheroidal graphite particles during solidifications of ductile irons were experimentally investigated. Spheroidal graphite particle and austenite dendrite were found nucleated independently in liquid. Austenite dendrite engulfed the spheroidal graphite particles after contact and an austenite shell formed around a spheroidal graphite particle. The graphite diameter at which the austenite shell closed around nodule was determined. Statistically determined graphite size distributions indicated multiple graphite nucleation events during solidification.

Structures in a graphite nodule varied depending on the growth stages of the nodule in ductile iron. Curved graphene layers appearing as faceted growth ledges swept circumferentially around the surface of a graphite nodule at early growth stages. Mismatches between the growth fronts created gaps which divided a nodule into radially oriented conical substructures (3-D). Columnar substructure was observed in the periphery of a nodule (formed during the intermediate growth stages) on its 2-D cross section. A columnar substructure consisted of parallel peripheral grains, with their c-axes approximately parallel. Graphene layers continued building up in individual conical substructure, and a graphite nodule increased its size accordingly.

Method for characterizing the crystal structures of graphite based on the selected area diffraction pattern was developed. Both hexagonal structure and rhombohedral structure were found in the spheroidal graphite particles. Possible crystallographic defects associated with hexagonal-rhombohedral structure transition were discussed. Schematic models for introducing tilt angles to the graphite lattice with basal plane tilt boundaries were constructed"--Abstract, page iv.

Advisor(s)

Richards, Von

Committee Member(s)

Van Aken, David C.
Lekakh, S. N. (Semen Naumovich)
Miller, F. Scott, 1956-
Medvedeva, Julia E.

Department(s)

Materials Science and Engineering

Degree Name

Ph. D. in Materials Science and Engineering

Sponsor(s)

Wolf Professorship of Metal Casting
Missouri University of Science and Technology. Department of Materials Science and Engineering

Publisher

Missouri University of Science and Technology

Publication Date

Spring 2016

Journal article titles appearing in thesis/dissertation

  • Chemical compositions (wt.%) of the iron alloys used in two heats
  • Chemical composition (wt.%) of ductile iron alloy studied
  • Chemical compositions (wt.%) of the iron alloys
  • Examples of changing stacking sequences by introducing partial dislocations

Pagination

xii, 140 pages

Note about bibliography

Includes bibliographic references.

Rights

© 2016 Jingjing Qing, All rights reserved.

Document Type

Dissertation - Open Access

File Type

text

Language

English

Subject Headings

Austenite
Iron alloys -- Ductility
Iron, Nodular

Thesis Number

T 10925

Electronic OCLC #

952598731

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