INVESTIGADORES
BRINGA Eduardo Marcial
artículos
Título:
Growth and collapse of nanovoids in tantalum monocrystals
Autor/es:
Y. TANG; E.M. BRINGA; M.A. MEYERS
Revista:
ACTA MATERIALIA
Editorial:
PERGAMON-ELSEVIER SCIENCE LTD
Referencias:
Lugar: Amsterdam; Año: 2011 vol. 59 p. 1354 - 1372
ISSN:
1359-6454
Resumen:
The growth and collapse of nanoscale voids are investigated for tantalum
(a model body-centered cubic metal) under different stress states and
strain rates by molecular dynamics (MD). Three principal mechanisms
of deformation are identified and quantitatively evaluated: (i) shear
loop emission and subsequent expansion from the surface of the void;
(ii) cooperative shear loop emission from slip planes that are
parallel to the same 〈1 1 1〉 slip direction and their combination,
forming prismatic loops; (iii) twinning starting at the void surface.
The generation and evolution of these defects are found to be
functions of stress state and strain rate. Dislocations are found to
propagate preferably on {1 1 0} and {1 1 2} planes, with Burgers
vectors 1/2 〈1 1 1〉. The dislocation shear loops generated expand in a
crystallographic manner, and in hydrostatic tension and compression
generate prismatic loops that detach from the void. In uniaxial
tensile strain along [1 0 0], the extremities of the shear loops
remain attached to the void surface, a requisite for void growth. In
uniaxial compressive strain, the extremities of the shear loops can
also detach from the void surface. The difference in defect evolution
is explained by the equal resolved shear stress in the hydrostatic
loading case, in contrast with uniaxial strain loading. Nanotwins form
preferably upon both uniaxial tensile strain and hydrostatic stress
(in tension) and there is a slip-to-twinning transition as the strain
rate exceeds 108 s−1. A simplified constitutive
description is presented which explains the preponderance of twinning
over slip in tension beyond a critical strain rate. The formation of
both dislocations and twins is confirmed through laser compression
experiments, which provide strain rates (∼108 s−1)
comparable to MD. The dislocation velocities are determined by
tracking the edge component of the expanding loops and are found to be
subsonic even at extremely high stress and strain rates: 680 m s−1 for 108 s−1 and 1020 m s−1 for 109 s−1.