INVESTIGADORES
TROIANI Horacio Esteban
artículos
Título:
High-resolution transmission electron microscopy study of small hexagonal precipitates produced during the dezincification of β-CuZn
Autor/es:
TROIANI; TOLLEY; AHLERS
Revista:
PHILOSOPHICAL MAGAZINE A
Editorial:
Taylor and Francis
Referencias:
Año: 2000 p. 1379 - 1391
ISSN:
0141-8610
Resumen:
The evaporation of Zn from β-phase Cu?Zn alloys produces a phase
transformation in the material. For low evaporation temperatures (450°C)
and short dezincification times (around 14 min) the phase
transformation is observed solely close to the sample surface. Two
phases are formed during this process: the fcc phase, expected at lower
Zn concentration, and a metastable phase with an approximately hexagonal
structure, which is not expected in principle. Previous transmission
electron microscopy studies have reported that this hexagonal structure
has a 4H stacking sequence and that the precipitates contain a high
density of stacking faults. In this paper the formation of hexagonal
precipitates is studied with high-resolution transmission electron
microscopy. It is shown that the precipitates do not have a homogeneous
structure. Different regions present different stacking sequences, which
on the average result in a diffraction pattern corresponding to a 4H
structure. The interface with the matrix appears as a relatively
extended region. The results indicate that the β phase transforms to a
hexagonal structure by a simple shuffle mechanism, a result not
previously observed. All results can be understood as a consequence of
the collapse of the high vibrational entropy due to the large amplitude
soft mode {110} 110 vibrations of the β phase.