330 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
Microstructure and mechanical properties of Pb-4%Sb alloy processed by equal channel angular pressing
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
Structure and microstructure evolution of Al-Mg-Si alloy processed by equal-channel angular pressing
An ultrafine grained Al–Mg–Si alloy was prepared by severe plastic deformation using the equal-channel angular pressing (ECAP) method. Samples were ECAPed through a die with an inner angle of F = 90° and outer arc of curvature of ¿ = 37° from 1 to 12 ECAP passes at room temperature following route Bc. To analyze the evolution of the microstructure at increasing ECAP passes, X-ray diffraction and electron backscatter diffraction analyses were carried out. The results revealed two distinct processing regimes, namely (i) from 1 to 5 passes, the microstructure evolved from elongated grains and sub-grains to a rather equiaxed array of ultrafine grains and (ii) from 5 to 12 passes where no change in the morphology and average grain size was noticed. In the overall behavior, the boundary misorientation angle and the fraction of high-angle boundaries increase rapidly up to 5 passes and at a lower rate from 5 to 12 passes. The crystallite size decreased down to about 45 nm with the increase in deformation. The influence of deformation on precipitate evolution in the Al–Mg–Si alloy was also studied by differential scanning calorimetry. A significant decrease in the peak temperature associated to the 50% of recrystallization was observed at increasing ECAP passes.Peer ReviewedPreprin
New Deformation Twinning Mechanism Generates Zero Macroscopic Strain In Nanocrystalline Metals
Macroscopic strain was hitherto considered a necessary corollary of deformation twinning in coarse-grained metals. Recently, twinning has been found to be a preeminent deformation mechanism in nanocrystalline face-centered-cubic (fcc) metals with medium-to-high stacking fault energies. Here we report a surprising discovery that the vast majority of deformation twins in nanocrystalline Al, Ni, and Cu, contrary to popular belief, yield zero net macroscopic strain. We propose a new twinning mechanism, random activation of partials, to explain this unusual phenomenon. The random activation of partials mechanism appears to be the most plausible mechanism and may be unique to nanocrystalline fcc metals with implications for their deformation behavior and mechanical properties
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