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1.
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
2.
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
3.
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
4.
Y. N. Osetsky D. J. Bacon N. de Diego 《Metallurgical and Materials Transactions A》2002,33(3):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 basalplane
diffusion was observed at the lower end of the range. The mechanism of interstitial diffusion changes from one-dimensional
(1-D) in a 〈11
0〉 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
5.
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
6.
The boundary structure of {10
1}, {10
2}, {11
1} and, {11
2} twins in hexagonal-close-packed (hcp) metals and the interaction of crystal dislocations with the first two twin types
have been studied previously using atomic-scale computer simulation. The interaction of crystal dislocations with {11
1} and {11
2} twin boundaries is described here and compared with the results for {10
1} and {10
2} twins. These four twins are found to create barriers to the motion of crystal dislocations gliding on the basal plane,
and the strength of the barrier depends in a relatively complex manner on crystallographic parameters and details of the atomic
structures of the interfaces. In some circumstances, crystal dislocations can be transmitted through the twin boundary, thereby
creating twinning dislocations.
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
7.
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
8.
K. T. Ramesh 《Metallurgical and Materials Transactions A》2002,33(3):927-935
A substantial amount of work has been performed on the effect of high rates of loading on the deformation and failure of fcc
and bcc metals. In contrast, the influence of high strain rates and temperature on the flow stress of hcp metals has received
relatively little attention, and the modes of dynamic failure of these materials are poorly characterized. The low symmetry
of these materials and the development of twinning lead to a particularly rich set of potential mechanisms for deformation
and failure at high rates. This article reviews results of high-strain-rate deformation and dynamic failure studies on hcp
metals, with a focus on titanium, Ti-6Al-4V, and hafnium. Strain rates as high as 105
s
−1 are considered, and observations of adiabatic shear localization and subsequent failure are 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 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.
Choi W. S. Ryoo H. S. Hwang S. K. Kwun S. I. Chae S. W. 《Metallurgical and Materials Transactions A》2002,33(13):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
tensile twinning, followed by 57.1 deg
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
10.
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
11.
Twins as barriers to basal slip in hexagonal-close-packed metals 总被引:2,自引:0,他引:2
The boundary structure of
,
,
, and
twins in hexagonal-close-packed (hcp) metals and the interaction of crystal dislocations with the first two twin types have
been studied previously using atomic-scale computer simulation. The interaction of crystal dislocations with
and
twin boundaries is described here and compared with the results for
and
twins. These four twins are found to create barriers to the motion of crystal dislocations gliding on the basal plane, and
the strength of the barrier depends in a relatively complex manner on crystallographic parameters and details of the atomic
structures of the interfaces. In some circumstances, crystal dislocations can be transmitted through the twin boundary, thereby
creating twinning dislocations.
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.
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
14.
Atomic-scale modeling of dislocations and related properties in the hexagonal-close-packed metals 总被引:3,自引:0,他引:3
Metals with the hcp crystal structure have a wide variety of mechanical and physical properties, and understanding the links
between atomic processes, microstructure, and properties can open the way for new applications. Computer modeling can provide
much of the information required. This article reviews recent progress in atomic-scale computer simulation in three important
areas. The first is the core structure of dislocations responsible for the primary slip modes, where modeling has revealed
the variety of core states that can arise in pure, elemental metals and ordered alloys. While most research has successfully
employed many-body, central-force interatomic potentials, they are inadequate for metals which have an unfilled d-electron
band, such as α-Ti and α-Zr, and the resulting noncentral character of the atomic bonding is shown to have subtle yet significant effects on dislocation
properties. Deformation twinning is an important process in plasticity of the hcp metals, and modeling has been used to investigate
the factors that control the structure and mobility of twinning dislocations. Furthermore, simulation shows that twinning
dislocations are actually generated, in some cases, following the interaction of crystal dislocations with twin boundaries;
this can lead to the very mobile boundaries observed experimentally. The final area concerns the nature and properties of
the defects created by radiation damage. Computer simulation has been used to determine the number and arrangement of defects
produced in primary, displacement-cascade damage in several hcp metals. The number is similar to that found in cubic metals
and is considerably smaller than that expected from earlier models. Many self-interstitial atoms cluster in cascades to form
highly glissile dislocation loops, and, so, contribute to two-dimensional material transport in damage evolution.
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.
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
16.
Ando Shinji Gotoh Takushi Tonda Hideki 《Metallurgical and Materials Transactions A》2002,33(13):823-829
The core structures of 〈c+a〉 dislocations in hexagonal-close-packed (hcp) metals have been investigated by molecular dynamics (MD) simulation using a
Lennard-Jones-type pair potential. The 〈c+a〉 edge dislocation has two types of core at 0 K; one is a perfect dislocation (type A), and the other has two 1/2 〈c+a〉 partials (type B). Type A transforms to type B by abruptly increasing temperature from 0 K to 293 K, while type B is stable
in temperature range from 0 K to 293 K. In contrast, type A extends parallel to (0001) at 30 K, and this extended core is
still stable at 293 K. These results suggest that the 〈c+a〉 edge dislocation glides on the
as two 1/2 〈c+a〉 partial dislocations and becomes sessile, due to changes of the core structure. The 〈c+a〉 screw dislocation spreads over two
planes at 0 K. The core transforms into a unsymmetrical structure at 293 K, which is spread over
and
, and core spreading occurs parallel to
at 1000 K. A critical strain to move screw dislocations depends on the sense of shear strain. The dependence of the yield
stress on the shear direction can be explained in terms of these core structures.
This article is based on a presentation made in the symposium entitled “Dect 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
17.
Shinji Ando Hideki Tonda Takushi Gotoh 《Metallurgical and Materials Transactions A》2002,33(3):823-829
The core structures of 〈c+a〉 dislocations in hexagonal-close-packed (hcp) metals have been investigated by molecular dynamics (MD) simulation using a
Lennard-Jones-type pair potential. The 〈c + a〉 edge dislocation has two types of core at 0 K; one is a perfect dislocation
(type A), and the other has two 1/2 〈c+a〉 partials (type B). Type A transforms to type B by abruptly increasing temperature from 0 K to 293 K, while type B is stable
in temperature range from 0 K to 293 K. In contrast, type A extends parallel to (0001) at 30 K, and this extended core is
still stable at 293 K. These results suggest that the 〈c+a〉 edge dislocation glides on the {11
2} as two 1/2 〈c+a〉 partial dislocations and becomes sessile due to changes of the core structure. The 〈c+a〉 screw dislocation spreads over two {10
1} planes at 0 K. The core transforms into a unsymmetrical structure at 293 K, which is spread over {11
2} and {10
1}, and core spreading occurs parallel to {11
2} at 1000 K. A critical strain to move screw dislocations depends on the sense of shear strain. The dependence of the yield
stress on the shear direction can be explained in terms of these core 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
18.
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
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.
Conventional α(hcp) and α(hcp)/β(bcc) titanium alloys exhibit significant primary creep strains at room temperature and at
stresses well below their macroscopic yield strength. It has been previously reported in various materials systems that repeated
unloading during primary creep testing may either accelerate or retard the accumulation of creep strains. These effects have
been demonstrated to depend on both microstructure and the applied stress. This article demonstrates that significant room-temperature
recovery occurs in technologically relevant titanium alloys. These recovery mechanisms are manifested as a dramatic increase
in creep rates (by several orders of magnitude) upon the introduction of individual unloading events, ranging from 1 minute
to 365 days, during primary creep tests. Significant increases in both creep rate and the total accumulated creep strain were
observed in polycrystalline single α-phase Ti-6Al, polycrystalline α/β Ti-6Al-2Sn-4Zr-2Mo-0.1Si, and individual α/β colonies
of Ti-6242. Based on transmission electron microscopy (TEM) studies of the active deformation mechanisms, it is proposed that
the presence of significant stress concentrations within the α phase of these materials, in the form of dislocation pileups,
is a prerequisite for significant room-temperature recovery.
M.F. SAVAGE, formerly with the Department of Materials Science and Engineering, The Ohio State University Columbus, OH.
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