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1.
Equal-channel angular extrusion of beryllium 总被引:1,自引:0,他引:1
R. D. Field C. T. Necker K. T. Hartwig J. F. Bingert S. R. Agnew 《Metallurgical and Materials Transactions A》2002,33(3):965-972
The equal-channel angular extrusion (ECAE) technique has been applied to a powder metallurgy (P/M) source Be alloy. Extrusions
have been successfully completed on Ni-canned billets of Be at approximately 425 °C. No cracking was observed in the billets,
and significant grain refinement was achieved. In this article, microstructural features and dislocation structures are discussed
for a single-pass extrusion, including evidence of 〈c〉 and 〈c+a〉 dislocations. Significant crystallographic texture developed during ECAE, which is discussed in terms of this unique deformation
processing technique and the underlying physical processes which sustain the deformation.
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.
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
3.
Williams J. C. Baggerly R. G. Paton N. E. 《Metallurgical and Materials Transactions A》2002,33(13):837-850
Single crystals of Ti-Al alloys containing 1.4, 2.9, 5, and 6.6 pct Al (by weight) were oriented for <a> slip on either basal or prism planes or loaded parallel along the c-axis to enforce a nonbasal deformation mode. Most of the tests were conducted in compression and temperatures between 77
and 1000 K. Trace analysis of prepolished surfaces enabled identification of the twin or slip systems primarily responsible
for deformation. Increasing the deformation temperature, Al content, or both, acted to inhibit secondary twin and slip systems,
thereby increasing the tendency toward strain accommodation by a single slip system having the highest resolved stress. In
the crystals oriented for basal slip transitions from twinning to multiple slip and, finally, to basal slip occurred with
increasing temprature in the lower-Al-content alloys, whereas for Ti-6.6 pct Al, only basal slip was observed at all temperatures
tested. A comparison of the critically resolved shear stress (CRSS) values for basal and prism slip as a function of Al content
shows that prism slip is favored at room temperature in pure Ti, but the stress to activate these two systems becomes essentially
equal in the Ti-6.6 pct Al crystals over a wide range of temperatures.
Compression tests on crystals oriented so that the load was applied parallel to the c-axis showed extensive twinning in lower Al concentrations and <c+a> slip at higher Al concentrations, with a mixture of <c+a> slip and twinning at intermediate compositions. A few tests also were conducted in tension, with the load applied parallel
to the c-axis. In these cases, twinning was observed, and the resolved shear for plastic deformation by twinning was much lower that
that, for <c+a> slip observed in compression loading.
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 and 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.
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
5.
The ductility of Mg alloys is limited due to a shortage of independent slip systems. In particular, c-axis compression cannot be accomodated by any of the easy slip or twinning modes. Basaltextured 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
pyramidal slip mode coffers 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 dissocation 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 Committe, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
6.
J. C. Williams R. G. Baggerly N. E. Paton 《Metallurgical and Materials Transactions A》2002,33(3):837-850
Single crystals of Ti-Al alloys containing 1.4, 2.9, 5, and 6.6 pct Al (by weight) were oriented for 〈a〉 slip on either basal or prism planes or loaded parallel along the c-axis to enforce a nonbasal deformation mode. Most of the tests were conducted in compression and at temperatures between
77 and 1000 K. Trace analysis of prepolished surfaces enabled identification of the twin or slip systems primarily responsible
for deformation. Increasing the deformation temperature, Al content, or both, acted to inhibit secondary twin and slip systems,
thereby increasing the tendency toward strain accommodation by a single slip system having the highest resolved stress. In
the crystals oriented for basal slip, transitions from twinning to multiple slip and, finally, to basal slip occurred with
increasing temperature in the lower-Al-content alloys, whereas for Ti-6.6 pct Al, only basal slip was observed at all temperatures
tested. A comparison of the critically resolved shear stress (CRSS) values for basal and prism slip as a function of Al content
shows that prism slip is favored at room temperature in pure Ti, but the stress to activate these two systems becomes essentially
equal in the Ti-6.6 pct Al crystals over a wide range of temperatures.
Compression tests on crystals oriented so that the load was applied parallel to the c-axis showed extensive twinning in lower Al concentrations and 〈c+a〉 slip at higher Al concentrations, with a mixture of 〈c+a〉 slip and twinning at intermediate compositions. A few tests also were conducted in tension, with the load applied parallel
to the c-axis. In these cases, twinning was observed, and the resolved shear for plastic deformation by twinning was much lower that
that for 〈c+a〉 slip observed in compression loading.
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 and 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.
Determination of dislocation densities in HCP metals from X-ray diffraction line-broadening analysis
Griffiths M. Sage D. Holt R. A. Tome C. N. 《Metallurgical and Materials Transactions A》2002,33(13):859-865
X-Ray diffraction (XRD) line-broadening analysis has been performed on highly textured Zr-2.5Nb specimens which had been deformed
in tensile tests to produce well-controlled dislocation structures. An iterative deconvolution method has been applied to
extract the broadening function for the material, using as standards, a Zr single crystal and a 0 pct deformed specimen. In
both cases, for specific tensile tests, a significant contribution to the basal line braodening was observed, which was clearly
not directly related to the dislocation structure generated by the deformation, i.e., so-called c-component dislocations having a component of their Burgers vectors perpendicular to the basal plane. Calculations showed
that the extent of basal line broadening cannot be attributed to the secondary effect of strain from a-type dislocations, i.e., dislocations with Burgers vectors parallel with the basal plane. It is concluded that most of the line broadening observed
was the result of intergranular strain distributions. These distributions are most prominent for grains oriented with their
c-axes perpendicular to the tensile-deformation axis and resulted in basal-plane line broadening even when there were few,
if any, c-component dislocations present.
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 and 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.
Determination of dislocation densities in HCP metals from X-ray diffraction line-broadening analysis
M. Griffiths D. Sage R. A. Holt C. N. Tome 《Metallurgical and Materials Transactions A》2002,33(3):859-865
X-Ray diffraction (XRD) line-broadening analysis has been performed on highly textured Zr-2.5Nb specimens which had been deformed
in tensile tests to produce well-controlled dislocation structures. An iterative deconvolution method has been applied to
extract the broadening function for the material, using as standards, a Zr single crystal and a 0 pct deformed specimen. In
both cases, for specific tensile tests, a significant contribution to the basal line broadening was observed, which was clearly
not directly related to the dislocation structure generated by the deformation, i.e., so-called c-component dislocations having a component of their Burgers vectors perpendicular to the basal plane. Calculations showed
that the extent of basal line broadening cannot be attributed to the secondary effect of strain from a-type dislocations, i.e., dislocations with Burgers vectors parallel with the basal plane. It is concluded that most of the line broadening observed
was the result of intergranular strain distributions. These distributions are most prominent for grains oriented with their
c-axes perpendicular to the tensile-deformation axis and resulted in basal-plane line broadening even when there were few,
if any, c-component dislocations present.
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 and 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.
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
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, 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
11.
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
12.
J. R. Bingert T. A. Mason G. C. Kaschner G. T. Gray III P. J. Maudlin 《Metallurgical and Materials Transactions A》2002,33(3):955-963
The response of polycrystalline α-zirconium to various deformation conditions was investigated through electron backscattered diffraction (EBSD) characterization.
The range of deformation conditions included quasi-static compression and tension at room and cryogenic temperatures, along
with a Taylor cylinder impact experiment. The resultant data provided spatial resolution of individual with system activity
as a function of the progression of deformation. Over 300 deformation twins were analyzed to identify the type of twin system
and active variant, along with the Schmid factor in the parent orientation. These data supplied information on the distribution
of Schmid factor and variant rank as a function of twin system and deformation condition. Results showed significant deviation
from a maximum Schmid factor activation criterion and suggest deformation twinning is greatly affected by local internal stress
heterogeneities and the sense of the applied stress.
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.
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
14.
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
15.
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
16.
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
17.
Bingert J. F. Mason T. A. Kaschner G. C. Maudlin P. J. Gray G. T. 《Metallurgical and Materials Transactions A》2002,33(13):955-963
The response of polycrystalline α-zirconium to various deformation conditions was investigated through electron backscattered
diffraction (EBSD) characterization. The range of deformation conditions included quasi-static compression and tension at
room and cryogenic temperatures, along with a Taylor cylinder impact experiment. The resultant data provided spatial resolution
of individual twin system activity as a function of the progression of deformation. Over 300 deformation twins were analyzed
to identify the type of twin system and active variant, along with the Schmid factor in the parent orientation. These data
supplied information on the distribution of Schmid factor and variant rank as a function of twin system and deformation condition.
Results showed significant deviation from a maximum Schmid factor activation criterion and suggest deformation twinning is
greatly affected by local internal stress heterogeneities and the sense of the applied stress.
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.
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
19.
Effect of deformation route on microstructural development in aluminum processed by equal channel angular extrusion 总被引:3,自引:0,他引:3
Pei-Ling Sun Po-We Kao Chih-Pu Chang 《Metallurgical and Materials Transactions A》2004,35(4):1359-1368
Aluminum has been deformed by equal channel angular extrusion (ECAE) to obtain submicron-grained structures under different
deformation routes. The deformation routes were varied by rotating billets through 0, 90, and 180 deg between each extrusion
pass, and were designated as route A, BC, and C, respectively. Based on quantitative microstructural analysis, the effectiveness of the deformation route is shown
to depend upon the different definition used. The order of effectiveness is (a) A > BC > C for both 90 and 120 deg dies, in terms of the generation of high-angle grain boundaries (HAGBs); (b) BC > C > A for both 90 and 120 deg dies, in terms of the formation of equiaxed shape of grains; and (c) BC > A > C for 90 deg die and BC ∼ A > C for 120 die, in terms of reducing grain size. It is suggested that the generation of HAGBs can be related to the
accumulation of nonredundant strain, while the shape and orientation of grains may be linked to the shearing patterns of the
deformation route. 相似文献