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Title: Deformation Mechanisms at Grain Boundaries in Polycrystals

Abstract

Grain boundaries (GBs) are important sources of deformation accommodation and strengthening in polycrystalline materials. Grain boundary sliding is a deformation mechanism that is known to activate at high temperatures, low strain rates, and for materials with small grain sizes. While crystalline slip has been extensively studied, investigations of grain boundary sliding has been mostly restricted to nanocrystalline materials, symmetric or synthetic GBs, and loading in high-temperature environments. This study is aimed at improving our understanding of the coupling between deformation mechanism relationships, namely between slip-GB interaction and grain boundary sliding, by means of a combined high-resolution experimental characterization in conjunction with multiscale modeling. The material of choice in the present study is high-purity aluminum with a through-the-specimen-thickness grain structure. Digital image correlation experiments are performed to measure 2D strains relative to the microstructural features. These experiments, performed at various load steps, can resolve individual slip bands and the onset of grain boundary sliding. Onset of grain boundary sliding is observed in the first loadstep (the first loadstep was collected just after macroscopic yield), which suggests that the mechanism is driven by high stress as opposed to only being active to accommodate large values of plastic strain. Further, grain boundary slidingmore » is observed in cases where slip impingement is present, as well as at boundaries that do not interact with obvious slip events. A temperature-dependent crystal plasticity model is used to study the constitutive response, which is then compared to full-field strain response experimentally obtained at the microscale-level. From this analysis, it is determined that a combination of the resolved shear stress at the grain boundary plane and boundary straightness form a set of criteria for predicting sliding propensity. Further, the GBs characterized from the experiments are exactly reproduced in a molecular dynamics framework as bicrystal systems, and the underlying atomistic scale mechanisms for pure sliding are studied. It is seen that GBs in the present study undergo sliding similar to a fluid-like flow. To study slip and sliding interaction, notches are introduced to facilitate dislocation emission and eventual interaction with the sliding GB. It was seen that slipGB interaction causes local increases in stress concentration, and a subsequent increase in the local sliding rate. These atomistic scale insights are used to inform a modified 3 crystal plasticity model with explicit GB elements and additional degrees of freedom to include GB sliding. The modified model results in improved predictions of deformation near the GBs than a conventional crystal plasticity model. These results improve the sophistication and accuracy of deformation modeling by establishing a set of criteria to describe the grain boundary sliding mechanism and help better predict micromechanical quantities near the grain boundaries.« less

Authors:
 [1];  [1]
  1. Purdue Univ., West Lafayette, IN (United States)
Publication Date:
Research Org.:
Purdue Univ., West Lafayette, IN (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division
OSTI Identifier:
1566034
Report Number(s):
DOE-Purdue-0014281-1
DOE Contract Number:  
SC0014281
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE

Citation Formats

Sangid, Michael D., and Venkataraman, Ajey. Deformation Mechanisms at Grain Boundaries in Polycrystals. United States: N. p., 2019. Web. doi:10.2172/1566034.
Sangid, Michael D., & Venkataraman, Ajey. Deformation Mechanisms at Grain Boundaries in Polycrystals. United States. https://doi.org/10.2172/1566034
Sangid, Michael D., and Venkataraman, Ajey. 2019. "Deformation Mechanisms at Grain Boundaries in Polycrystals". United States. https://doi.org/10.2172/1566034. https://www.osti.gov/servlets/purl/1566034.
@article{osti_1566034,
title = {Deformation Mechanisms at Grain Boundaries in Polycrystals},
author = {Sangid, Michael D. and Venkataraman, Ajey},
abstractNote = {Grain boundaries (GBs) are important sources of deformation accommodation and strengthening in polycrystalline materials. Grain boundary sliding is a deformation mechanism that is known to activate at high temperatures, low strain rates, and for materials with small grain sizes. While crystalline slip has been extensively studied, investigations of grain boundary sliding has been mostly restricted to nanocrystalline materials, symmetric or synthetic GBs, and loading in high-temperature environments. This study is aimed at improving our understanding of the coupling between deformation mechanism relationships, namely between slip-GB interaction and grain boundary sliding, by means of a combined high-resolution experimental characterization in conjunction with multiscale modeling. The material of choice in the present study is high-purity aluminum with a through-the-specimen-thickness grain structure. Digital image correlation experiments are performed to measure 2D strains relative to the microstructural features. These experiments, performed at various load steps, can resolve individual slip bands and the onset of grain boundary sliding. Onset of grain boundary sliding is observed in the first loadstep (the first loadstep was collected just after macroscopic yield), which suggests that the mechanism is driven by high stress as opposed to only being active to accommodate large values of plastic strain. Further, grain boundary sliding is observed in cases where slip impingement is present, as well as at boundaries that do not interact with obvious slip events. A temperature-dependent crystal plasticity model is used to study the constitutive response, which is then compared to full-field strain response experimentally obtained at the microscale-level. From this analysis, it is determined that a combination of the resolved shear stress at the grain boundary plane and boundary straightness form a set of criteria for predicting sliding propensity. Further, the GBs characterized from the experiments are exactly reproduced in a molecular dynamics framework as bicrystal systems, and the underlying atomistic scale mechanisms for pure sliding are studied. It is seen that GBs in the present study undergo sliding similar to a fluid-like flow. To study slip and sliding interaction, notches are introduced to facilitate dislocation emission and eventual interaction with the sliding GB. It was seen that slipGB interaction causes local increases in stress concentration, and a subsequent increase in the local sliding rate. These atomistic scale insights are used to inform a modified 3 crystal plasticity model with explicit GB elements and additional degrees of freedom to include GB sliding. The modified model results in improved predictions of deformation near the GBs than a conventional crystal plasticity model. These results improve the sophistication and accuracy of deformation modeling by establishing a set of criteria to describe the grain boundary sliding mechanism and help better predict micromechanical quantities near the grain boundaries.},
doi = {10.2172/1566034},
url = {https://www.osti.gov/biblio/1566034}, journal = {},
number = ,
volume = ,
place = {United States},
year = {2019},
month = {9}
}