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Title: Experimentally quantifying critical stresses associated with basal slip and twinning in magnesium using micro-pillars

Abstract

Basal slip and {01$$\bar{1}$$2} twinning are two major plastic deformation mechanisms in hexagonal closed-packed magnesium. Here in this paper, we quantify the critical stresses associated with basal slip and twinning in single-crystal and bi-crystal magnesium samples by performing in situ compression of micropillars with different diameters in a scanning electron microscope. The micropillars are designed to favor either slip or twinning under uniaxial compression. Compression tests imply a negligible size effect related to basal slip and twinning as pillar diameter is greater than 10 μm. The critical resolved shear stresses are deduced to be 29 MPa for twinning and 6 MPa for basal slip from a series of micropillar compression tests. Employing full-field elasto-visco-plastic simulations, we further interpret the experimental observations in terms of the local stress distribution associated with multiple twinning, twin nucleation, and twin growth. Our simulation results suggest that the twinning features being studied should not be close to the top surface of the micropillar because of local stress perturbations induced by the hard indenter.

Authors:
 [1]; ORCiD logo [1];  [1];  [1];  [2]; ORCiD logo [1]; ORCiD logo [1];  [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  2. Univ. of Nebraska, Lincoln, NE (United States). Dept. of Mechanical and Materials Engineering
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE Office of Science (SC). Basic Energy Sciences (BES) (SC-22); USDOE National Nuclear Security Administration (NNSA); National Science Foundation (NSF)
OSTI Identifier:
1364544
Report Number(s):
LA-UR-16-27007
Journal ID: ISSN 1359-6454
Grant/Contract Number:
AC52-06NA25396; W-7405-ENG-36
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Acta Materialia
Additional Journal Information:
Journal Volume: 135; Journal ID: ISSN 1359-6454
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; Magnesium; Micropillar compression; Basal slip; Twin

Citation Formats

Liu, Yue, Li, Nan, Mariyappan, Arul Kumar, Pathak, Siddhartha, Wang, Jian, Mccabe, Rodney James, Mara, Nathan Allan, and Tome, Carlos N. Experimentally quantifying critical stresses associated with basal slip and twinning in magnesium using micro-pillars. United States: N. p., 2017. Web. doi:10.1016/j.actamat.2017.06.008.
Liu, Yue, Li, Nan, Mariyappan, Arul Kumar, Pathak, Siddhartha, Wang, Jian, Mccabe, Rodney James, Mara, Nathan Allan, & Tome, Carlos N. Experimentally quantifying critical stresses associated with basal slip and twinning in magnesium using micro-pillars. United States. doi:10.1016/j.actamat.2017.06.008.
Liu, Yue, Li, Nan, Mariyappan, Arul Kumar, Pathak, Siddhartha, Wang, Jian, Mccabe, Rodney James, Mara, Nathan Allan, and Tome, Carlos N. 2017. "Experimentally quantifying critical stresses associated with basal slip and twinning in magnesium using micro-pillars". United States. doi:10.1016/j.actamat.2017.06.008.
@article{osti_1364544,
title = {Experimentally quantifying critical stresses associated with basal slip and twinning in magnesium using micro-pillars},
author = {Liu, Yue and Li, Nan and Mariyappan, Arul Kumar and Pathak, Siddhartha and Wang, Jian and Mccabe, Rodney James and Mara, Nathan Allan and Tome, Carlos N.},
abstractNote = {Basal slip and {01$\bar{1}$2} twinning are two major plastic deformation mechanisms in hexagonal closed-packed magnesium. Here in this paper, we quantify the critical stresses associated with basal slip and twinning in single-crystal and bi-crystal magnesium samples by performing in situ compression of micropillars with different diameters in a scanning electron microscope. The micropillars are designed to favor either slip or twinning under uniaxial compression. Compression tests imply a negligible size effect related to basal slip and twinning as pillar diameter is greater than 10 μm. The critical resolved shear stresses are deduced to be 29 MPa for twinning and 6 MPa for basal slip from a series of micropillar compression tests. Employing full-field elasto-visco-plastic simulations, we further interpret the experimental observations in terms of the local stress distribution associated with multiple twinning, twin nucleation, and twin growth. Our simulation results suggest that the twinning features being studied should not be close to the top surface of the micropillar because of local stress perturbations induced by the hard indenter.},
doi = {10.1016/j.actamat.2017.06.008},
journal = {Acta Materialia},
number = ,
volume = 135,
place = {United States},
year = 2017,
month = 6
}

Journal Article:
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  • Based on a new model for basal slip in sapphire developed in Part 1 of this series of papers, the formation of a basal twin is considered. It is shown that deformation twinning is a natural outgrowth of the present model of slip when the material is deformed in a particular regime of temperature and stress. The model is based on the glide of a leading partial dislocation on a basal slip plane and double-cross-slip to the next-but-one slip plane. The model predicts a Type-II twin.
  • The motion of partial dislocations in sapphire ({alpha}-Al{sub 2}O{sub 3}) is analyzed. Crystallographic arguments suggest that the basal slip plane should be a plane passing through the normally-vacant octahedral sites defined by the anion sublattice. This definition of the basal slip plane implies that half of the cations lying between two adjacent anion layers are above and the other half are below the slip plane. The stacking faults that would be created by the motion of a dissociated basal dislocation differs in structure and energy, depending on whether the partial is leading or trailing. Thus, the motion of a partialmore » in its favorable (lower energy) direction creates a stacking fault with a stacking /sequence in which the cations are in a localized twin symmetry, whereas the motion of a partial in its unfavorable (higher energy) direction is ``forbidden``.« less
  • A high resolution transmission electron microscopy (HRTEM) investigation of basal twins in sapphire ({alpha}-Al{sub 2}O{sub 3}) indicates that they are either Type-II or Type-I ``glide`` twins. These two types cannot be distinguished with the resolution of the HRTEM used in the present study. However, a Type-II twin is consistent with the model of basal twinning presented in the second paper of this series, with an AC{prime}BA{prime}CB{prime}/a{prime}bc{prime}ab{prime}c stacking sequence for the Al-O-Al layers along a direction perpendicular to the twin/matrix interface, and pair potential calculations suggest that Type-II interfaces have the lowest energy of all possible twin interfaces in sapphire. Anmore » overlap of the twin/matrix leads to Moire-like contrast features. This can also be explained with the proposed twinning mechanism.« less
  • Knowledge of the critical resolved shear stress (CRSS) values of different slip modes is important for accurately modeling plastic deformation of hexagonal materials. Here, we demonstrate that CRSS can be directly measured with an in-situ high energy X-ray diffraction microscopy (HEDM) experiment. A commercially pure Ti tensile specimen was deformed up to 2.6% strain. In-situ far-field HEDM experiments were carried out to track the evolution of crystallographic orientations, centers of masses, and stress states of 1153 grains in a material volume of 1.1mm×1mm×1mm. Predominant prismatic slip was identified in 18 grains, where the orientation change occurred primarily by rotation aroundmore » the c-axis during specimen deformation. By analyzing the resolved shear stress on individual slip systems, the estimated CRSS for prismatic slip is 96±18 MPa. Predominant basal slip was identified in 22 other grains, where the 2 orientation change occurred primarily by tilting the c-axis about an axis in the basal plane. The estimated CRSS for basal slip is 127±33 MPa. The ratio of CRSS basal/CRSS prismatic is in the range of 1.7-2.1. From indirect assessment, the CRSS for pyramidal < c+a > slip is likely greater than 240MPa. Lastly, grain size and free surface effects on the CRSS value in different grains are also examined.« less