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Title: Plastic deformation in nanoindentation of tantalum: A new mechanism for prismatic loop formation

Journal Article · · Acta Materialia
 [1];  [2];  [3];  [4];  [1];  [1];  [1]
  1. Univ. of California, San Diego, CA (United States)
  2. Univ. Nacional de Cuyo, Mendoza (Argentina)
  3. Univ. Nacional de Cuyo, Mendoza (Argentina); CONICET, Mendoza (Argentina)
  4. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
+ Show Author Affiliations

Here, the mechanisms of deformation under a nanoindentation in tantalum, chosen as a model body-centered cubic (bcc) metal, are identified and quantified. Molecular dynamics (MD) simulations and indentation experiments are conducted for [1 0 0], [1 1 0] and [1 1 1] normals to surface orientations. The simulated plastic deformation proceeds by the formation of nanotwins, which rapidly evolve into shear dislocation loops. It is shown through a dislocation analysis that an elementary twin (three layers) is energetically favorable for a diameter below ~7 nm, at which point a shear loop comprising a perfect dislocation is formed. MD simulations show that shear loops expand into the material by the advancement of their edge components. Simultaneously with this advancement, screw components of the loop cross-slip and generate a cylindrical surface. When opposite segments approach, they eventually cancel by virtue of the attraction between them, forming a quasi-circular prismatic loop composed of edge dislocation segments. This “lasso”-like mechanism by which a shear loop transitions to a prismatic loop is identified for both [0 0 1] and [1 1 1] indentations. The prismatic loops advance into the material along $$\langle$$1 1 1$$\rangle$$ directions, transporting material away from the nucleation site. Analytical calculations supplement MD and experimental observations, and provide a framework for the improved understanding of the evolution of plastic deformation under a nanoindenter. Dislocation densities under the indenter are estimated experimentally (~1.2 × 1015 m-2), by MD (~7 × 1015 m-2) and through an analytical calculation (2.6–19 × 1015 m-2). Considering the assumptions and simplifications, this agreement is considered satisfactory. MD simulations also show expected changes in pile-up symmetry after unloading, compatible with crystal plasticity.

Research Organization:
Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Univ. of California, San Diego, CA (United States); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Organization:
USDOE National Nuclear Security Administration (NNSA); University of California; USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities Division
Grant/Contract Number:
AC52-07NA27344; 09-LR-06-118456-MEYM; PE-FG52-09NA-29043; PICT-PRH-0092; NA0002080; SeCTyP-UN Cuyo; 0092
OSTI ID:
1808763
Alternate ID(s):
OSTI ID: 1462255; OSTI ID: 1556483
Report Number(s):
LLNL-JRNL-824531; 1036748
Journal Information:
Acta Materialia, Vol. 78, Issue N/A; ISSN 1359-6454
Publisher:
ElsevierCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 118 works
Citation information provided by
Web of Science

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Cited By (13)

The physical and mechanical properties and local deformation micromechanisms in materials with different dependence of hardness on the depth of print journal September 2017
Shock wave propagation, plasticity, and void collapse in open-cell nanoporous Ta journal January 2018
Dislocation Interaction and V-Shaped Growth of the Distorted Structure During Nanoindentation of Cu20Ni20Al20Co20Fe20 (high-entropy alloy)-Coated Copper: A Molecular Dynamics Simulation-Based Study journal January 2019
Influence of defects on the shock Hugoniot of tantalum journal June 2019
Nanoindentation of Bi2Se3 Thin Films journal October 2018
Atomistic Studies of Nanoindentation—A Review of Recent Advances journal September 2017
Size of the Plastic Zone Produced by Nanoscratching journal December 2017
Nanoindentation of hcp metals: a comparative simulation study of the evolution of dislocation networks journal December 2015
Effect of subsurface voids on the nanoindentation of Fe crystals journal January 2020
Deducing density and strength of nanocrystalline Ta and diamond under extreme conditions from X-ray diffraction journal January 2019
Cyclic Indentation of Iron: A Comparison of Experimental and Atomistic Simulations journal May 2019
Investigation of Interaction between Dislocation Loop and Coherent Twin Boundary in BCC Ta Film during Nanoindentation journal November 2017
Molecular Dynamics Simulation on B3-GaN Thin Films under Nanoindentation journal October 2018

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Related Subjects

36 MATERIALS SCIENCE
plasma physics
nanoindentation
molecular dynamics
dislocations
shear loops
prismatic loops
77 NANOSCIENCE AND NANOTECHNOLOGY