Title: The role of deviatoric stress and dislocations on the α to ω phase transformation in Ti

Abstract

Under extreme conditions, α-Ti becomes unstable and transforms either into β-Ti at high temperature or into ω-Ti at high pressure. In what concerns the α to ω phase transformation (PT), there has been a wide range of experimentally reported transition pressures from approximately 2 to 15 GPa at room temperature. Deviatoric stresses and internal defects are often assumed to be the root cause of this variation. Here, in this study, these postulates are revisited using both continuum mechanics and molecular dynamics (MD) simulations. First, a simple continuum model, assuming linear elasticity and isotropic plasticity, is developed to describe the effects of applied stress and dislocations on the stability of an ω nucleus in an infinite α domain. Second, a new MD simulation method is developed to generate an ω nucleus in the α domain utilizing the displacement field identified from the topological analysis. Results from MD simulations show that despite the fact that phase diagrams typically delineate the limits between two phases in terms of only P and T, deviatoric stress promotes the α to ω phase transformation by reducing the critical radius above which an ω nucleus is stable. Furthermore, the required deviatoric stress to nucleate and stabilize a nanoscale ω nucleus is likely emanating from the internal stress of defects such as dislocations. The MD-informed micromechanics models are used to identify favorable configurations where dislocations help favor the α to ω transformation. These configurations show that the interaction with a basal or prismatic dislocation reduces the critical radius of a ω nucleus by about 10 or 16 %, respectively. In addition, prismatic edge dislocations are found to promote the growth of ω nucleus when interacting with the ($$\bar{1}$$$$\bar{1}$$20)_α//(0001)_ω interface. Importantly, a simple model of the arrival of dislocation at an ω nucleus suggests that PT does not necessarily require a pile-up to be present but could alternatively be mediated by a constant rapid flow of dislocations.

Authors:

Dang, Khanh Quoc  ^[1];

• Search DOE PAGES for author "Dang, Khanh Quoc"
• Search DOE PAGES for ORCID "0000-0002-9686-4270"

Tomé, Carlos N.  ^[1];

• Search DOE PAGES for author "Tomé, Carlos N."
• Search DOE PAGES for ORCID "0000-0003-3405-0500"

Capolungo, Laurent  ^[1]

• Search DOE PAGES for author "Capolungo, Laurent"
• Search DOE PAGES for ORCID "0000-0001-8079-7790"

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+ Show Author Affiliations

1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Publication Date:

Tue Nov 22 00:00:00 EST 2022

Research Org.:

Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:

1902096

Alternate Identifier(s):

OSTI ID: 1961277

Report Number(s):

LA-UR-22-25264
Journal ID: ISSN 1359-6454

Grant/Contract Number:  

89233218CNA000001; FWP 06SCPE401

Resource Type:

Accepted Manuscript

Journal Name:

Acta Materialia

Additional Journal Information:

Journal Volume: 244; Journal ID: ISSN 1359-6454

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; Phase transformation; α-Ti; HCP; ω-Ti; Molecular dynamics simulations