共查询到20条相似文献,搜索用时 15 毫秒
1.
Osetsky Y. N. Bacon D. J. de Diego N. 《Metallurgical and Materials Transactions A》2002,33(13):777-782
Two types of intrinsic defect, i.e., vacancy and self-interstitial atom (SIA), are formed in metals during irradiation with energetic particles. The evolution
of defect population leads to significant changes in microstructure and causes a number of radiation-induced property changes.
Some phenomena, such as radiation growth of anisotropic materials, are due to anisotropy in the atomic mass transport by point
defects. Detailed information on atomic-scale mechanisms is, therefore, necessary to understand such phenomena. In this article,
we present results of a computer simulation study of mass transport via point defects in alpha-zirconium. The matrix of self-diffusion coefficients and activation energies for vacancy and SIA defects
have been obtained, and different methods of treatment of diffusion have been tested. Molecular dynamics (MD) shows that vacancy
diffusion is approximately isotropic in the temperature range studied (1050 to 1650 K), although some preference for basal-plane
diffusion was observed at the lower end of the range. The mechanism of interstitial diffusion changes from one-dimensional
(1-D) in a
direction at low temperature (<300 K) to two-dimensional (2-D) in the basal plane and, then, three-dimensional (3-D) at higher
temperatures.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
2.
Fernández J. R. Monti A. M. Pasianot R. C. 《Metallurgical and Materials Transactions A》2002,33(13):791-796
Minimum-energy structures for the symmetric
and
twin grain boundaries (GBs), as well as for two nonsymmetric GBs that exhibit dislocations, are obtained for the hcp structure
by computer modeling. Central force potentials constructed within the embedded-atom method are used to represent atomic interactions.
Vacancy-formation energies and entropies for different sites are calculated, and the properties of various vacancy jumps are
investigated. Unstable vacancy sites, located in the GB dislocation cores, are observed. The random-walk approach, combined
with simulation results, is applied to study tracer diffusion by a vacancy mechanism in the twin GBs; higher diffusivity values
than those for the lattice are obtained, in qualitative agreement with experiments. Correlation effects, taken into account
by the matrix method, determine the main features of GB diffusion to be contributed by jumps in a narrow region.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001 in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
3.
J. R. Fernández A. M. Monti R. C. Pasianot R. C. Pasianot 《Metallurgical and Materials Transactions A》2002,33(3):791-796
Minimum-energy structures for the symmetric (11
1) and (11
2) twin grain boundaries (GBs), as well as for two nonsymmetric GBs that exhibit dislocations, are obtained for the hcp structure
by computer modeling. Central force potentials constructed within the embedded-atom method are used to represent atomic interactions.
Vacancy-formation energies and entropies for different sites are calculated, and the properties of various vacancy jumps are
investigated. Unstable vacancy sites, located in the GB dislocation cores, are observed. The random-walk approach, combined
with simulation results, is applied to study tracer diffusion by a vacancy mechanism in the twin GBs; higher diffusivity values
than those for the lattice are obtained, in qualitative agreement with experiments. Correlation effects, taken into account
by the matrix method, determine the main features of GB diffusion to be contributed by jumps in a narrow region.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
4.
N. de Diego Y. N. Osetsky D. J. Bacon 《Metallurgical and Materials Transactions A》2002,33(3):783-789
Clusters of self-interstitial atoms (SIAs) formed in displacement cascades in metals irradiated with energetic particles play
an important role in microstructure evolution under irradiation. They have been studied in the fcc and bcc metals by atomic-scale
computer simulation, and in this article, we present the results of a similar study in a hexagonal close-packed (hcp) crystal.
Static and dynamic properties of clusters of up to 30 SIAs were studied using a many-body Finnis-Sinclair type interatomic
potential for Zr. The results show a qualitative similarity of some properties of clusters to those for cubic metals. In particular,
all clusters larger than four SIAs exhibit fast thermally activated one-dimensional (1-D) glide, which is in a 〈11
0〉 direction in the hcp lattice. Due to the structure of the hcp lattice, this mechanism leads to two-dimensional mass transport
in basal planes. Some clusters exhibit behavior peculiar to the hcp structure, for they can migrate two-dimensionally (2-D)
in the basal plane. The jump frequency, activation energy, and correlation factors of clusters have been estimated, and comparisons
drawn between the behavior of SIA clusters in different structures.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
5.
Manuel J. Iribarren Marina M. Iglesias Fanny Dyment 《Metallurgical and Materials Transactions A》2002,33(3):797-800
Diffusion parameters of Cr diffusion along the α/β interphase boundaries of a Zr-2.5 wt pct Nb alloy are presented. The conventional radiotracer technique combined with serial
sectioning of the samples was applied. In the Arrhenius plot, it is possible to consider only one straight line (with Q=133 kJ/mol for 615<T<953 K) or two zones (with Q=230 kJ/mol for 773<T<953 K and Q=77 kJ/mol for 615<T<773 K). An analysis is made of these results together with previous data concerning diffusion along short circuits paths
in α-Zr (grain boundaries) and Zr-2.5 wt pct Nb (interphase boundaries): Zr and Nb as the alloy component elements and Ni, Fe,
and Co as other relevant impurities. Different mechanisms are proposed: a vacancy mechanism for Zr and Nb and an interstitial-like
mechanism for the impurities, for both kind of boundaries. The influence on diffusion and the estimated values of the impurities
segregation in the α phase are discussed in the work.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
6.
Iribarren Manuel J. Iglesias Marina M. Dyment Fanny 《Metallurgical and Materials Transactions A》2002,33(13):797-800
Diffusion parameters of Cr diffusion along the α/β interphase boundaries of a Zr-2.5 wt pct Nb alloy are presented. The conventional
radiotracer technique combined with serial sectioning of the samples was applied. In the Arrhenius plot, it is possible to
consider only one straight line (with Q=133 kJ/mol for 615<T<953K) or two zones (with Q=230 kJ/mol for 773<T<953 K and Q=77 kJ/mol for 615<T<773 K). An analysis is made of these results together with previous data concerning diffusion along short circuits paths
in α-Zr (grain boundaries) and Zr-2.5 wt pct Nb (interphase boundaries): Zr and Nb as the alloy component elements and Ni,
Fe, and Co as other relevant impurities. Different mechanisms are proposed: a vacancy mechanism for Zr and Nb and an interstitial-like
mechanism for the impurities, for both kind of boundaries. The influence on diffusion and the estimated values of the impurities
segregation in the α phase are discussed in the work.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committe, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
7.
Deformation processes involving interfacial dislocation mechanisms in twin boundaries of hexagonal-close-packed (hcp) metals
are described. The topological properties of individual defects, namely their Burgers vectors, b, and step heights, h, are defined rigorously, and the magnitude of the diffusional flux of material required for motion of a defect along an interface
is expressed quantitatively in terms of b, h, and the material’s density. This framework enables interactions between defects to be treated and, in particular, enables
identification of processes that are conservative. Using these topological arguments, it is shown that sessile interfacial
defects in twins need not block further twinning and that the recently discovered Serra-Bacon (S—B) twinning mechanism is
conservative. The possible wider significance of the S—B-type mechanism that causes localized lateral growth of twins is also
considered briefly in the context of the deformation of hcp and martensitic materials.
This article is based on a presentation made in the symposium entitled “Defect Properties and mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Lousiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
8.
de Diego N. Osetsky Y. N. Bacon D. J. 《Metallurgical and Materials Transactions A》2002,33(13):783-789
Clusters of self-interstitial atoms (SIAs) formed in displacement cascades in metals irradiated with energetic particles play
an important role in microstructure evolution under irradiation. They have been studied in the fcc and bcc metals by atomic-scale
computer simulation, and in this article, we present the results of a similar study in a hexagonal close-packed (hcp) crystal.
Static and dynamic properties of clusters of up to 30 SIAs were studied using a many-body Finnis-Sinclair type interatomic
potential for Zr. The results show a qualitative similarity of some properties of clusters to those for cubic metals. In particular,
all clusters larger than four SIAs exhibit fast thermally activated one-dimensional (1-D) glide, which is in a <1120> direction
in the hcp lattice. Due to the structure of the hcp lattice, this mechanism leads to two-dimensional mass transport in basal
planes. Some clusters exhibit behavior peculiar to the hcp structure, for they can migrate two-dimensionally (2-D) in the
basal plane. The jump frequency, activation energy, and correlation factors of clusters have been estimated, and comparisons
drawn between the behavior of SIA clusters in different structures.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
9.
Bulk and grain boundary (GB) self-diffusion and substitutional solute diffusion in group IV hexagonal close-packed (hcp) metals
(α-Ti, α-Zr, and α-Hf) are reviewed. The recent results obtained on high-purity materials are shown to approach closely the
“intrinsic” diffusion characteristics. The enhancement effect of fast-diffusing impurities (such as Fe, Ni, or Co) is discussed
for both self-and substitutional bulk solute diffusion in terms of the interstitial solubility of the impurity atoms. In GB
self-diffusion, the impurity effect is found to be less dramatic. The results obtained on high-purity hop materials can be
interpreted in terms of intrinsically ‘normal’ vacancy-mediated GB diffusion, with the ratio of GB to volume diffusion activation
enthalpies of Q
gb
/Q ≈ 0.6. The GB self-diffusion in group IV hcp metals reveals distinct systematics. Bulk self-diffusion and fast interstitial
solute diffusion (Fe and Ni) in the hcp phase α
2-Ti3Al are reviewed. Interphase boundary diffusion of Ti in the unidirectional lamellar α
2/γ structure of the two-phase Ti48Al52 alloy is analyzed with respect to the phase boundary structure and GB self-diffusion in α
2-Ti3Al.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
10.
Deformation processes involving interfacial dislocation mechanisms in twin boundaries of hexagonal-close-packed (hcp) metals
are described. The topological properties of individual defects, namely their Burgers vectors, b, and step heights, h, are defined rigorously, and the magnitude of the diffusional flux of material required for motion of a defect along an interface
is expressed quantitatively in terms of b, h, and the material’s density. This framework enables interactions between defects to be treated and, in particular, enables
identification of processes that are conservative. Using these topological arguments, it is shown that sessile interfacial
defects in twins need not block further twinning and that the recently discovered Serra-Bacon (S-B) twinning mechanism is
conservative. The possible wider significance of the S-B-type mechanism that causes localized lateral growth of twins is also
considered briefly in the context of the deformation of hcp and martensitic materials.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
11.
Bulk and grain boundary (GB) self-diffusion and substitutional solute diffusion in group IV hexagonal close-packed (hcp) metals
(α-Ti, α-Zr, and α-Hf) are reviewed. The recent results obtained on high-purity materials are shown to approach closely the “intrinsic” diffusion
characteristics. The enhancement effect of fast-diffusing impurities (such as Fe, Ni, or Co) is discussed for both self- and
substitutional bulk solute diffusion in terms of the interstitial solubility of the impurity atoms. In GB self-diffusion,
the impurity effect is found to be less dramatic. The results obtained on high-purity hcp materials can be interpreted in
terms of intrinsically ‘normal’ vacancy-mediated GB diffusion, with the ratio of GB to volume diffusion activation enthalpies
of Q
gb
/Q ≈ 0.6. The GB self-diffusion in group IV hcp metals reveals distinct systematics. Bulk self-diffusion and fast interstitial
solute diffusion (Fe and Ni) in the hcp phase α
2-Ti3Al are reviewed. Interphase boundary diffusion of Ti in the unidirectional lamellar α
2/γ structure of the two-phase Ti48Al52 alloy is analyzed with respect to the phase boundary structure and GB self-diffusion in α
2-Ti3Al.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
12.
We report on studies of several hexagonal-close-packed (hcp) metals by Raman scattering techniques in the diamond anvil cell
for pressures up to 60 GPa. The pressure response of the observed transverse-optical (TO) zone-center phonon mode includes
positive pressure shifts as well as anomalies, such as mode softening in connection with phase transitions. It is shown that
the phonon frequencies and their pressure dependences are related to macroscopic elastic parameters. More general, these results
show that the measurement of Raman-active phonons provides a direct probe of bonding in metals, and agreement with theoretical
models gives additional confidence in ab initio techniques.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
13.
M. H. Yoo J. R. Morris K. M. Ho S. R. Agnew 《Metallurgical and Materials Transactions A》2002,33(3):813-822
A review is presented on the role of dislocation cores and planar faults in activating the nonbasal deformation modes, 〈c+a〉 pyramidal slip and deformation twinning, in hcp metals and alloys and in D019 intermetallic compounds. Material-specific mechanical behavior arises from a competition between altemate defect structures
that determine the deformation modes. We emphasize the importance of accurate atomistic modeling of these defects, going beyond
simple interatomic energy models. Recent results from both experiments and theory are summarized by discussing specific examples
of Ti and Mg single crystals; Ti-, Zr-, and Mg-base alloys; and Ti3Al ordered alloys. Remaining key issues and directions for future research are also discussed.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM and TMS committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic
& Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium
Committee. 相似文献
14.
The ductility of Mg alloys is limited due to a shortage of independent slip systems. In particular, c-axis compression cannot be accommodated by any of the easy slip or twinning modes. Basal-textured samples of pure Mg and
Mg-15 at. pct Li were examined for the presence of 〈c+a〉 dislocations by post-mortem transmission electron microscopy (TEM) after a small deformation, which forced the majority of grains to compress nearly
parallel to their c-axes. A higher density and more uniform distribution of 〈c+a〉 dislocations is found in the Li-containing alloy. Because the 1/3〈11
3〉 {11
} pyramidal slip mode offers five independent slip systems, it provides a satisfying explanation for the enhanced ductility
of α-solid solution Mg-Li alloys as compared to pure Mg. The issue of 〈c+a〉 dislocation dissociation and decomposition remains open from an experimental point of view. Theoretically, the most feasible
configuration is a collinear dissociation into two 1/2〈c+a〉 partial dislocations, with an intervening stacking fault on the glide plane. It is speculated that Li additions may lower
the fault’s energy and, thereby, increase the stability of this glissile configuration.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
15.
First-principles investigation of perfect and diffuse antiphase boundaries in HCP-based Ti-Al alloys
First-principles thermodynamic models based on the cluster expansion formalism, Monte Carlo simulations, and quantum-mechanical
total energy calculations are employed to compute short-range-order (SRO) parameters and diffuse-antiphase-boundary energies
in hcp-based α-Ti-Al alloys. Our calculations unambiguously reveal a substantial amount of SRO is present in α-Ti-6 Al and that, at typical processing temperatures and concentrations, the diffuse antiphase boundaries (DAPB) energies
associated with a single dislocation slip can reach 25 mJ/m2. We find very little anisotropy between the energies of DAPBs lying in the basal and prism planes. Perfect antiphase boundaries
in DO19-ordered Ti3Al are also investigated and their interfacial energies, interfacial stresses, and local displacements are calculated from
first principles through direct supercell calculations. Our results are discussed in light of mechanical property measurements
and deformation microstructure studies in α-Ti-Al alloys.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
16.
In the modeling of grain growth of isotropic, single-phase materials using three-dimensional (3-D) Monte Carlo (MC) Potts
algorithm, the theoretically expected grain growth exponent was obtained only in the late simulation stages. This article
addresses the grain growth simulated by a modified MC Potts model using simple cubic lattices. The grain growth kinetics was
analyzed both for the 3-D domain and for two-dimensional (2-D) cross sections. Regression analyses of the grain size data
averaged over time, multiple simulations runs, and three cross sections showed that both the Louat function and the log-normal
function can be fitted to the data. It was clearly observed that the lognormal function allows a better fit to the 3-D simulation
data, while the Louat function is more suited to the cross-sectional data. Furthermore, parabolic grain growth kinetics was
obtained both for the 3-D domain and for the cross sections, but the grain growth rates calculated for these cross sections
were smaller than that obtained for the 3-D domain.
This article is based on a presentation made in the symposium entitled “Three Dimensional Materials Science” during the 2003
MS&T ′03: Materials Science & Technology Conference 2003 in Chicago, Illinois, on November 11 & 12, 2003, under the auspices
of the ASM/MSCTS: Materials Science Critical Technology Sector Committee and the TMS/SMD: Structural Materials Division Committee. 相似文献
17.
David Basanta Mark A. Miodownik Elizabeth A. Holm Peter J. Bentley 《Metallurgical and Materials Transactions A》2005,36(7):1643-1652
The article describes work to bring together the topics of evolutionary computing and stereology and asks the reader to judge
whether such an approach can be genuinely useful or just represents a clever application of computer science. The problem
we address is that of constructing three-dimensional (3-D) microstructures from two-dimensional (2-D) micrographs. Our solution
is a computer program called MicroConstructor that evolves 3-D discrete computer microstructures, which are statistically
equivalent to the 2-D inputs in terms of the microstructural variables of interest. The core of Micro-Constructor is a genetic
algorithm that evolves the 3-D microstructure so that its stereological parameters match the 2-D data. MicroConstructor uses
a general method of pattern construction, the EmbryoCA, that does not require intervention from the user and is highly evolvable.
This article presents initial results from successful experiments to evolve 3-D two-phase microstructures from 2-D input microstructures.
The advantages and disadvantages of the method are discussed, and we conclude that the method, though delightfully elegant
and full of potential, has yet to prove itself capable of constructing 3-D microstructures that would interest experimentalists
and computer modelers.
This article is based on a presentation made in the symposium entitled “Three Dimensional Materials Science” during the 2003
MS&T ’03: Materials Science & Technology Conference 2003 in Chicago, Illinois, on November 11 & 12, 2003, under the auspices
of the ASM/MSCTS: Materials Science Critical Technology Sector Committee and the TMS/SMD: Structural Materials Division Committee. 相似文献
18.
W. S. Choi H. S. Ryoo S. K. Hwang M. H. Kim S. I. Kwun S. W. Chae 《Metallurgical and Materials Transactions A》2002,33(3):973-980
Pure polycrystalline Zr was deformed by equal channel angular pressing (ECAP), and the microstructural characteristics were
analyzed. By repeated alternating ECAP, it was possible to refine the grain size from 200 to 0.2 μm. Subsequent annealing heat treatment at 550 °C resulted in a grain growth of up to 6 μm. Mechanical twinning was an important deformation mechanism, particularly during the early stage of deformation. The most
active twinning system was identified as 85.2 deg {10
2}〈
011〉 tensile twinning, followed by 57.1 deg {10
1}〈
012〉 compressive twinning. Crystal texture as well as grain-boundary misorientation distribution of deformed Zr were analyzed
by X-ray diffraction (XRD) and electron backscattered diffraction (EBSD). The ECAP-deformed Zr showed a considerable difference
in the crystallographic attributes from those of cold-rolled Zr or Ti, in that texture and boundary misorientation-angle distribution
tend toward more even distribution with a slightly preferential distribution of boundaries of a 20 to 30 deg misorientation
angle. Furthermore, unlike the case of cold rolling, the crystal texture was not greatly altered by subsequent annealing heat
treatment. Overall, the present work suggests ECAP as a viable method to obtain significant grain refining in hexagonal close-packed
(hcp) metals.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
19.
Yoo M. H. Morris J. R. Ho K. M. Agnew S. R. 《Metallurgical and Materials Transactions A》2002,33(13):813-822
A review is presented on the role of dislocation cores and planar faults in activating the nonbasal deformation modes, <c + a> pyramidal slip and deformation twinning, in hcp metals and alloys and in D019 intermetallic compounds. Material-specific mechanical behavior arises from a competition between alternate defect structures
that determine the deformation modes. We emphasize the importance of accurate atomistic modeling of these defects, going beyond
simple interatomic energy models. Recent results from both experiments and theory are summarized by discussing specific examples
of Ti and Mg single crystals; Ti-, Zr-, and Mg-base alloys; and Ti3Al ordered alloys. Remaining key issues and directions for future research are also discussed.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans Louisiana, under the auspices of the following
ASM and TMS committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic
& Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium
Committee. 相似文献
20.
We report on studies of several hexagonal-close-packed (hcp) metals by Raman scattering techniques in the diamond anvil cell
for pressures up to 60 GPa. The pressure response of the observed transverse-optical (TO) zone-center phonon mode includes
positive pressure shifts as well as anomalies, such as mode softening in connection with phase transitions. It is shown that
the phonon frequencies and their pressure dependences are related to macroscopic elastic parameters. More general, these results
show that the measurement of Raman-active phonons provides a direct probe of bonding in metals, and agreement with theoretical
models gives additional confidence in ab initio techniques.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献