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1.
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
2.
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.
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.
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
4.
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
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.
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
7.
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
8.
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
9.
The microstructural changes during the α→ FeAl, FeAl → Fe3Al, and α→ Fe3Al transitions were studied by transmission electron microscopy. The ordering of ferromagnetic α was observed to occur in
a classical manner by the nucleation and growth of particles of the FeAl or Fe3Al type phases. However, the ordering of paramagnetic α to FeAl and paramagnetic FeAl to Fe3Al occurred by a mechanism which showed many of the characteristics expected of a second or higher degree transition. These
included critical point fluctuations in the degree of long-range order which also appeared to be greater in the vicinity of
antiphase domain boundaries. The FeAl phase was also observed to partially disorder in the initial stages of the FeAl → α
+ FeAl transition and this effect appears to account for the anomalous magnetic behavior of some FeAl alloys. 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.
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
13.
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
14.
15.
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
16.
17.
Creep processes in magnesium alloys and their composites 总被引:1,自引:0,他引:1
V. Sklenička M. Pahutová K. Kuchařová M. Svoboda T. G. Langdon 《Metallurgical and Materials Transactions A》2002,33(3):883-889
A comparison is made between the creep characteristics of two squeeze-cast magnesium alloys (AZ 91 and QE 22) reinforced with
20 vol pct Al2O3 short fibers and the unreinforced AZ 91 and QE 22 matrix alloys. The results show the creep resistance of the reinforced
materials is considerably improved by comparison with the unreinforced matrix alloys. It is suggested that creep strengthening
in these short-fiber composites arises primarily from the existence of a threshold stress and the effect of load transfer.
By testing samples to failure, it is demonstrated that the unreinforced and reinforced materials exhibit similar times to
failure at the higher stress levels. A detailed microstructural investigation by transmission electron microscopy (TEM) reveals
no substantial changes in matrix microstructure due to the presence of the reinforcement. This suggests that direct composite
strengthening dominates over indirect effects.
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.
Creep processes in magnesium alloys and their composites 总被引:1,自引:0,他引:1
Sklenička V. Pahutová M. Kuchařová K. Svoboda M. Langdon T. G. 《Metallurgical and Materials Transactions A》2002,33(13):883-889
A comparison is made between the creep characteristics of two squeeze-cast magnesium alloys (AZ 91 and QE 22) reinforced with
20 vol pct Al2O3 short fibers and the unreinforced AZ 91 and QE 22 matrix alloys. The results show the creep resistance of the reinforced
materials is considerably improved by comparison with the unreinforced matrix alloys. It is suggested that creep strengthening
in these short-fiber composites arises primarily from the existence of a threshold stress and the effect of load transfer.
By testing samples to failure, it is demonstrated that the unreinforced and reinforced materials exhibit similar times to
failure at the higher stress levels. A detailed microstructural investigation by transmission electron microscopy (TEM) reveals
no substantial changes in matrix microstructure due to the presence of the reinforcement. This suggests that direct composite
strengthening dominates over indirect effects.
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.
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
20.
Creep strength of magnesium-based alloys 总被引:5,自引:0,他引:5
Maruyama Kouichi Suzuki Mayumi Sato Hiroyuki 《Metallurgical and Materials Transactions A》2002,33(13):875-882
The high-temperature creep resistance of magnesium alloys was discussed, with special reference to Mg-Al and Mg-Y alloys.
Mg-Al solid-solution alloys are superior to Al-Mg solid-solution alloys in terms of creep resistance. This is attributed to
the high internal stress typical of an hcp structure having only two independent basal slip systems. Although magnesium has
a smaller shear modulus than aluminum, the inherent creep resistance of Mg alloys is better than that of Al alloys. The creep
resistance of Mg alloys is improved substantially by the addition of Y. Solid-solution hardening is the principal mechanism
of the strengthening, but the details of the mechanism have not been elucidated yet. Forest dislocation hardening in concentrated
alloys and dynamic precipitation in a Mg-2.4 pct Y alloy also contribute to the strengthening. An addition of a very small
amount of Zn raises the dislocation density and significantly improves the creep resistance of Mg-Y 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