154 research outputs found
Decomposition process in a FeAuPd alloy nanostructured by severe plastic deformation
The decomposition process mechanisms have been investigated in a Fe50Au25Pd25
(at.%) alloy processed by severe plastic deformation. Phases were characterized
by X-ray diffraction and microstructures were observed using transmission
electron microscopy. In the coarse grain alloy homogenized and aged at , the bcc \alpha-Fe and fcc AuPd phases nucleate in the fcc
supersaturated solid solution and grow by a discontinuous precipitation process
resulting in a typical lamellar structure. The grain size of the homogenized
FeAuPd alloy was reduced in a range of 50 to 100nm by high pressure torsion.
Aging at this nanostructure leads to the decomposition
of the solid solution into an equi-axed microstructure. The grain growth is
very limited during aging and the grain size remains under 100nm. The
combination of two phases with different crystallographic structures (bcc
\alpha-Fe and fcc AuPd) and of the nanoscaled grain size gives rise to a
significant hardening of the allo
Influence of severe plastic deformation on the precipitation hardening of a FeSiTi steel
The combined strengthening effects of grain refinement and high precipitated
volume fraction (~6at.%) on the mechanical properties of FeSiTi alloy subjected
to SPD processing prior to aging treatment were investigated by atom probe
tomography and scanning transmission electron microscopy. It was shown that the
refinement of the microstructure affects the precipitation kinetics and the
spatial distribution of the secondary hardening intermetallic phase, which was
observed to nucleate heterogeneously on dislocations and sub-grain boundaries.
It was revealed that alloys successively subjected to these two strengthening
mechanisms exhibit a lower increase in mechanical strength than a simple
estimation based on the summation of the two individual strengthening
mechanisms
The Hall-Petch effect as a manifestation of the general size effect
The experimental evidence for the Hall-Petch dependence of strength on the
inverse square-root of grain size is reviewed critically. Both the classic data
and more recent results are considered. While the data can be fitted to the
inverse square-root dependence excellently (but using two free fitting
parameters for each dataset), it is also consistent with a dependence on the
simple inverse of grain size (with one free fitting parameter for each
dataset). There have been difficulties, recognised for half-a-century, in
explaining the inverse square-root expression. A Bayesian analysis shows that
the data strongly supports the simple inverse expression proposed. Since this
expression derives from underlying theory, it is also more readily explicable.
It is concluded that the Hall-Petch effect is not to be explained by the
variety of theories found in the literature, but is a manifestation of, or
underlain by, the general size effect observed throughout micromechanics, due
to the inverse relationship between the stress required and the space available
for dislocation sources to operate.Comment: Paper presented at Plasticity 2014, The Bahama
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