Title page for ETD etd-213172849731471


Type of Document Dissertation
Author Panova, Julia B.
Author's Email Address julia@vision.mse.vt.edu
URN etd-213172849731471
Title Mechanisms of Deformation and Fracture in TiAl: An Atomistic Simulation Study
Degree PhD
Department Materials Science and Engineering
Advisory Committee
Advisor Name Title
Aning, Alexander O. Committee Member
Curtin, William A. Jr. Committee Member
Kampe, Stephen L. Committee Member
Reynolds, William T. Jr. Committee Member
Keywords
  • atomistic simulations
  • dislocations
  • cracks
  • intermetallics
  • ductility
Date of Defense 1997-05-15
Availability unrestricted
Abstract

The intermetallic compound TiAl possesses

a unique complex of properties that include

sufficiently low material density, high values

of the strength-to-ductility ratio, high

elastic moduli, high oxidation resistance,

low creep rate, and improved fatigue

characteristics. These properties make TiAl

alloys very attractive, particularly for

structural applications for aerospace and

aeronautic industries, where, at certain

temperatures, they might be capable of

replacing heavy nickel-based superalloys.

However, so far applications of TiAl alloys

have been limited by their poor ductility.

Many of the recent studies have focused

on the source of this limited ductility and on

methods to improve this property. It has

been found out experimentally that the

strength and ductility of $gamma$-TiAl

alloys can be affected by many different

parameters, including alloy stoichiometry,

heat treatment, deformation temperature,

impurity content, grain size, and ternary

element additions. In this thesis we present

the results of our computer simulations of

deformation and fracture in TiAl. In

contrast to many previous studies our

simulations include the interaction of the

crack with point defects in the lattice. We

use the molecular statics technique with

atomic interactions described in terms of

the embedded atom method. We simulate

the crack propagation along (100), (001),

(110) and (111) planes in TiAl. The

cleavage along (100) and (001) planes

shows purely brittle behavior, whereas the

cleavage along (110) and (111) planes is

accompanied by extensive dislocation

emission. Our studies of the crack

interaction with point defects reveal that

vacancies and antisites near the crack tip

can influence the amount of plastic

deformation. Another important

observation is that the antisite formation

energy near the crack tip is generally lower

than in the perfect lattice. This observation

suggests the formation of relatively

disordered zones near the crack tip at high

temperatures, and leads us to a formulation

of a new mechanism of a brittle-to-ductile

transition in TiAl.

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