Title: Hydrogen segregation to inclined ^{Σ3 < 110 >}twin grain boundaries in nickel

Abstract

Low-mobility twin grain boundaries dominate the microstructure of grain boundary-engineered materials and are critical to understanding their plastic deformation behaviour. The presence of solutes, such as hydrogen, has a profound effect on the thermodynamic stability of the grain boundaries. This work examines the case of a Σ3 grain boundary at inclinations from 0° ≤ Φ ≤ 90°. The angle Φ corresponds to the rotation of the Σ3 (1 1 1) < 1 1 0 > (coherent) into the Σ3 (1 1 2) < 1 1 0 > (lateral) twin boundary. To this end, atomistic models of inclined grain boundaries, utilising empirical potentials, are used to elucidate the finite-temperature boundary structure while grand canonical Monte Carlo models are applied to determine the degree of hydrogen segregation. In order to understand the boundary structure and segregation behaviour of hydrogen, the structural unit description of inclined twin grain boundaries is found to provide insight into explaining the observed variation of excess enthalpy and excess hydrogen concentration on inclination angle, but the explanatory power is limited by how the enthalpy of segregation is affected by hydrogen concentration. At higher concentrations, the grain boundaries undergo a defaceting transition. In order to develop a more completemore » mesoscale model of the interfacial behaviour, an analytical model of boundary energy and hydrogen segregation that relies on modelling the boundary as arrays of discrete 1/3 < 1 1 1 > disconnections is constructed. Lastly, the complex interaction of boundary reconstruction and concentration-dependent segregation behaviour exhibited by inclined twin grain boundaries limits the range of applicability of such an analytical model and illustrates the fundamental limitations for a structural unit model description of segregation in lower stacking fault energy materials.« less

Authors:

O’Brien, Christopher J. ^[1]; Foiles, Stephen M. ^[1]

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1. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

Publication Date:

2016-08-04

Research Org.:

Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:

1343269

Report Number(s):

SAND-2016-12892J
Journal ID: ISSN 1478-6435; 650389

Grant/Contract Number:  

AC04-94AL85000

Resource Type:

Journal Article: Accepted Manuscript

Journal Name:

Philosophical Magazine (2003, Print)

Additional Journal Information:

Journal Volume: 96; Journal Issue: 26; Journal ID: ISSN 1478-6435

Publisher:

Taylor & Francis

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; twinning; grain boundary structure; nickel; hydrogen in metals; embrittlement; molecular dynamics; Monte Carlo; structural unit model