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1.
Transformation Superplasticity of Cast Titanium and Ti-6Al-4V 总被引:1,自引:0,他引:1
Qizhen Li Edward Y. Chen Douglas R. Bice David C. Dunand 《Metallurgical and Materials Transactions A》2007,38(1):44-53
Samples of unalloyed titanium and Ti-6Al-4V with a cast, coarse-grain structure were subjected to simultaneous mechanical
loading and thermal cycling about their transformation range to assess their capability for transformation superplasticity.
Under uniaxial tensile loading, high elongations to failure (511 pct for titanium, and 265 pct for Ti-6Al-4V) and an average
strain-rate sensitivity exponent of unity are observed. Samples previously deformed superplastically to a strain of 100 pct
show no significant degradation in room-temperature mechanical properties as compared to the undeformed state. Biaxial dome
bulging tests confirm that transformation superplasticity is activated under thermal cycling and faster than creep deformation.
The cast, coarse-grained titanium and Ti-6Al-4V have similar transformation-superplasticity characteristics as wrought or
powder-metallurgy materials with finer grains. This may enable superplastic forming of titanium objects directly after the
casting step, thus bypassing the complicated and costly thermomechanical processing steps needed to achieve fine-grain superplasticity.
相似文献
David C. Dunand (Professor)Email: |
2.
J. S. Marte T. F. Zahrah S. L. Kampe 《Metallurgical and Materials Transactions A》2004,35(5):1603-1611
A series of in-situ, deformation-processed metal matrix composites were produced by direct powder extrusion of blended constituents. The resulting
composites are comprised of a metallic Ti-6Al-4V matrix containing dispersed and co-deformed discontinuously reinforced-intermetallic
matrix composite (DR-IMC) reinforcements. The DR-IMCs are comprised of discontinuous TiB2 particulate within a titanium trialuminide or near-γ Ti-47Al matrix. Thus, an example of a resulting composite would be Ti-6Al-4V+40 vol pct (Al3Ti+30 vol pct TiB2) or Ti-6Al-4V+40 vol pct (Ti-47Al+40 vol pct TiB2), with the DR-IMCs having an aligned, high aspect ratio morphology as a consequence of deformation processing. The degree
to which both constituents deform during extrusion has been examined using systematic variations in the percentage of TiB2 within the DR-IMC, and by varying the percentage of DR-IMC within the metal matrix. In the former instance, variation of
the TiB2 percentage effects variations in relative flow behavior; while in the latter, varying the percentage of DR-IMC within the
metallic matrix effects changes in strain distribution among components. The results indicate that successful co-deformation
processing can occur within certain ranges of relative flow stress; however, the extent of commensurate flow will be limited
by the constituents’ inherent capacity to plastically deform. 相似文献
3.
C G. Rhodes A. K. Ghosh R. A. Spurling 《Metallurgical and Materials Transactions A》1987,18(12):2151-2156
Ti-6Al-4V-2Ni is being considered as a composite matrix material because of its potential for a lower consolidation temperature
and reduced reaction product formation compared with conventional Ti-6A1-4V. Stress/strain-rate measurements of Ti-6Al-4V-2Ni
in sheet form provided data for calculation of diffusion bonding parameters required for efficient consolidation. These data
were used as consolidation parameters for fabrication of SiC (SCS-6) reinforced Ti-6Al-4V-2Ni. The composite with 10.5 vol
pct SiC exhibits room temperature tensile strength approximately 80 pct of that observed for conventional Ti-6Al-4V/SiC having
35 to 40 vol pct SiC. Scanning and transmission electron microscopy revealed that the fiber-matrix reaction zone is roughly
one-half the thickness of that found in SiC-reinforced Ti -6A1-4V, and that it consists of TiC and Ti5Si3. Nickel does not enter into the reaction zone products, but rather promotes the formation of Ti2Ni in the matrix. 相似文献
4.
Y. G. Ko C. S. Lee D. H. Shin S. L. Semiatin 《Metallurgical and Materials Transactions A》2006,37(2):381-391
The low-temperature superplasticity of ultra-fine-grained (UFG) Ti-6Al-4V was established as a function of temperature and
strain rate. The equiaxed-alpha grain size of the starting material was reduced from 11 to 0.3 μm (without a change in volume
fraction) by imposing an effective strain of ∼4 via isothermal, equal-channel angular pressing (ECAP) at 873 K. The ultrafine microstructure so produced was relatively stable
during annealing at temperatures up to 873 K. Uniaxial tension and load-relaxation tests were conducted for both the starting
(coarse-grained (CG)) and UFG materials at temperatures of 873 to 973 K and strain rates of 5 × 10−5 to 10−2 s−1. The tension tests revealed that the UFG structure exhibited considerably higher elongations compared to those of the CG
specimens at the same temperature and strain rate. A total elongation of 474 pct was obtained for the UFG alloy at 973 K and
10−4 s−1. This fact strongly indicated that low-temperature superplasticity could be achieved using an UFG structure through an enhancement
of grain-boundary sliding in addition to strain hardening. The deformation mechanisms underlying the low-temperature superplasticity
of UFG Ti-6Al-4V were also elucidated by the load-relaxation tests and accompanying interpretation based on inelastic deformation
theory. 相似文献
5.
Bing Ye Marc R. Matsen David C. Dunand 《Metallurgical and Materials Transactions A》2012,43(1):381-390
A powder-level, finite-element model is created to describe densification, as a function of applied stress during uniaxial
hot pressing, of CP-Ti and Ti-6Al-4V powders with spherical or spheroidal shapes for various packing geometries. Two cases
are considered: (1) isothermal densification (in the α- or β-fields of CP-Ti and in the β-field of Ti-6Al-4V) where power-law creep dominates and (2) thermal cycling densification (across the α/β-phase transformation of Ti-6Al-4V) where transformation mismatch plasticity controls deformation at low stresses. Reasonable
agreement is achieved between numerical results and previously published experimental measurements and continuum modeling
predictions. 相似文献
6.
E. Frás A. Janas S. Wierzbiński H. F. Lopez 《Metallurgical and Materials Transactions A》2002,33(12):3831-3838
The deformation behavior of TiC particulate-reinforced aluminum composites (Al-TiC
p
) was investigated in this work using pure aluminum as the reference matrix material. Uniaxial compression tests were carried
out at 293 and 623 K and at two strain rates (3.7×10−4 and 3.7×10−3 s−1). Yield strengths of up to 127 MPa were found in composites containing 10 vol pct TiC particulates, which were almost 4 times
the yield strength of pure Al. In addition, at 623 K, relatively small reductions in yield strength were found, suggesting
that this property was rather insensitive to temperature for the temperatures investigated in this work. Nevertheless, at
623 K, increasing the rate of straining from 3.7×10−4 s−1 to 3.7×10−3 s−1 lowered the yield strength, particularly in 10 vol pct TiC
p
-Al composites. Two stages of work hardening were identified in pure Al and a 10 vol pct TiC
p
composite during plastic flow through the modified version of the Hollomon equation (σ = Kɛ
n ± Δ). In particular, the work-hardening exponents found in pure Al shifted from high to low values as the extent of plastic
strain was increased while the opposite was true for the 10 vol pct TiC
p
composite. Finally, at 623 K, dynamic recovery mechanisms became dominant at plastic strain levels >0.2 in 10 vol pct TiC
p
-Al composites, with the effect being minor at room temperature. 相似文献
7.
Jun Cheol Oh Sunghak Lee Mikhail G. Golkovski 《Metallurgical and Materials Transactions A》2001,32(12):2995-3005
This study is concerned with the microstructural analysis and improvement of the hardness and wear resistance of Ti-6Al-4V
surface-alloyed materials fabricated by a high-energy electron beam. The mixtures of TiC, TiN, or TiC + TiN powders and CaF2 flux were deposited on a Ti-6Al-4V substrate, and then the electron beam was irradiated on these mixtures. In the specimens
processed with a flux addition, the surface-alloyed layers of 1 mm in thickness were homogeneously formed without defects
and contained a large amount (over 30 vol pct) of precipitates such as TiC, TiN, (Ti
x
Al1−x
)N, and Ti(C
x
N1−x
) in the martensitic or N-rich acicular α-Ti matrix. This microstructural modification, including the formation of hard precipitates and hardened matrices in the surface-alloyed
layers, improved the hardness and wear resistance. Particularly in the surface-alloyed material fabricated by the deposition
of TiN powders, the wear resistance was greatly enhanced to a level 10 times higher than that of the Ti alloy substrate. These
findings suggested that surface alloying using high-energy electron-beam irradiation was economical and useful for the development
of titanium-based surface-alloyed materials with improved hardness and wear resistance. 相似文献
8.
The correlation of microstructure with the hardness and wear resistance of (TiC,SiC)/Ti-6Al-4V surface composites fabricated
by high-energy electron-beam irradiation was investigated in this study. The mixtures of TiC, SiC, or TiC + SiC powders and
CaF2 flux were placed on a Ti-6Al-4V substrate, and then an electron beam was irradiated on these mixtures using an electron-beam
accelerator. The surface composite layers of 1.2 to 2.1 mm in thickness were formed without defects and contained a large
amount (up to 66 vol pct) of precipitates such as TiC and Ti5Si3 in the martensitic matrix. This microstructural modification, including the formation of hard precipitates and a hardened
matrix in the surface composite layer, improved the hardness and wear resistance. Particularly in the surface composite fabricated
with TiC + SiC powders, the wear resistance was greatly enhanced to a level 25 times higher than that of the Ti alloy substrate,
because 66 vol pct of TiC and Ti5Si3 was precipitated homogeneously in the hardened martensitic matrix. These findings suggested that high-energy electron-beam
irradiation was useful for the development of Ti-based surface composites with improved hardness and wear properties. 相似文献
9.
Jun Cheol Oh Chang Sup Lee Sunghak Lee 《Metallurgical and Materials Transactions A》2002,33(10):3173-3185
Correlation of microstructure with the hardness, wear resistance, and fracture toughness of two-layered VC/Ti-6Al-4V surface
composites fabricated by high-energy electron-beam irradiation was investigated in this study. A mixture of VC powders and
CaF2 flux was deposited on a Ti-6Al-4V substrate, and then an electron beam was irradiated on these powder mixtures to fabricate
an one-layered surface composite. A two-layered surface composite was fabricated by irradiating an electron-beam again onto
the powder mixture deposited on the one-layered surface composite. The composite layers of 1.2 to 1.5 mm in thickness were
homogeneously formed without defects and contained a large amount (25 to 40 vol pct) of carbides in the martensitic or β-Ti matrix. This microstructural modification, including the formation of hard carbides and hardened matrix, improved the
hardness and wear resistance. Particularly in the two-layered surface composite containing more carbides, the wear resistance
was greatly enhanced to a level 7 times higher than that of the Ti-6Al-4V substrate. In-situ observation of the fracture process showed that microcracks were initiated at carbides and propagated along these microcracked
carbides and that shear bands were formed in the matrix between these microcracks. In the two-layered surface composite, numerous
microcracks were initiated at many carbides and then rapidly propagated along them, thereby lowering the fracture toughness. 相似文献
10.
11.
M.?D.?S.?Pirzada F.?H.? Froes S.?N.?Patankar 《Metallurgical and Materials Transactions A》2004,35(6):1899-1903
Synthesis of nanocrystalline Ti-6Al-4V was explored using mechanochemical processing. The reaction mixture was comprised of
CaH2, Mg powder, anhydrous AlCl3, anhydrous VCl3, and TiCl4. The milled powder (reaction product) primarily consisted of nanocrystalline alloy hydride having a composition (Ti-6Al-4V)H1.942, along with MgCl2 and CaCl2 as by-products. Aqueous solutions of nitric acid, sulfuric acid, and 1 pct sodium sulfite were found to be very effective
in leaching of the chlorides from the milled powder. The (Ti-6Al-4V)H1.942 on dehydrogenation at 375°C resulted in nanocrystalline Ti-6Al-4V alloy powder. 相似文献
12.
A. J. Wagoner Johnson K. S. Kumar C. L. Briant 《Metallurgical and Materials Transactions A》2003,34(9):1869-1877
The compressive behavior at room temperature of Ti-6Al-4V/TiC composites was examined at strain rates from 0.1 to 1000 s−1. As little as 1 vol pct TiC particulates provided greater than a 20 pct increase in strength over that of the monolithic
Ti-6Al-4V, while further additions of TiC did not provide proportional benefits. Microstructural examination before and after
compression testing was instrumental in understanding the relative importance of the primary strengthening mechanism in the
composites as compared to the monolithic material. A comparison of the various possible mechanisms clearly showed that the
dominant mechanism was due to carbon in solid solution. At low strain rates, the failure process consisted of a progression
of damage in the matrix and at particle-matrix boundaries, while at high strain rates, failure occurred along adiabatic shear
bands. The composites had a greater susceptibility to adiabatic shear-band formation than did the monolithic material. 相似文献
13.
Kwangjun Euh Jongmin Lee Sunghak Lee 《Metallurgical and Materials Transactions A》2001,32(10):2499-2508
The present study is concerned with the fabrication and microstructural analysis of boride/Ti-6Al-4V surface-alloyed materials
using the irradiation of a high-energy electron beam. Mixtures of TiB2 or MoB powders and CaF2 flux were placed on a Ti-6Al-4V alloy substrate and subsequently irradiated using a high-energy electron beam. Specimens
processed with a flux mixing ratio of 40 wt pct showed that the melted region of 1.1 to 1.5 mm in thickness was homogeneously
formed without defects and contained a large amount of titanium borides (TiB). The formation of TiB in the melted region greatly
improved the Vickers hardness, high-temperature Vickers hardness, and wear resistance to levels 2 or 3 three times higher
than the those for the Ti alloy substrate. Also, the addition of MoB powders into the mixtures made possible the fabrication
of surface-alloyed materials with various properties by controlling the kind, size, and volume fraction of TiB and the characteristics
of the matrix. These findings suggested that surface alloying using high-energy electron-beam irradiation was economical and
useful for the development of boride/Ti-6Al-4V surface-alloyed materials with improved properties. 相似文献
14.
T. K. Roy R. Balasubramaniam A. Ghosh 《Metallurgical and Materials Transactions A》1996,27(12):3993-4002
The oxidation behavior of Ti-25Al, Ti-24Al-15Nb, and Ti-25Al-11Nb (at. pct) titanium aluminides was studied in dry oxygen
at atmospheric pressure in the temperature range 1000 to 1300 K for 4 to 6 hours by thermogravimetry. The oxidation products
were characterized by X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive X-ray (EDX) analysis.
Although some departures from the parabolic rate law were found, the analysis of data revealed that the parabolic rate law
was a more reliable basis for interpretation of results as compared to the empirical power law. Parabolic rate constants (k
p
) for Ti-24Al-15Nb and Ti-25Al-11Nb were almost the same at the same temperature. However, k
p
values for Ti-25Al were 2 to 8 times larger than niobium-containing alloys except at 1000 K, where k
p
values for all three alloys were approximately the same. The effective activation energy (Q
eff) was 289 kJ/mole for Ti-25Al in the range of 1000 to 1300 K, while in the case of Ti-24Al-15Nb and Ti-25Al-11Nb,Q
eff values were 329 and 330 kJ/mole, respectively, in the range of 1100 to 1300 K. In general, the scales on Ti-25Al were porous
and exhibited significant spallation above 1100 K. The scales were thinner, compact, and adherent for niobium-containing alloys.
The scales formed on these alloys were predominantly composed of TiO2, while Al2O3 was also present as a minor constituent. The superior oxidation resistance of the niobium-containing alloys has been attributed
to the doping effect of niobium in TiO2. 相似文献
15.
16.
The effect of alloying additions on the superplastic properties of Ti-6 pct Al-4 pct V 总被引:1,自引:0,他引:1
The superplastic deformation properties of Ti-6 pct Al-4 pct V and modified alloys containing 1/4 pct, 1/2 pct, 1 pct, and
2 pct of either cobalt or nickel have been investigated in the temperature range 950 to 750 °C. The results show that both
cobalt and nickel modified alloys have reduced flow stresses, in comparison with Ti-6 pct Al-4 pct V, the reductions being
particularly marked at the lower temperatures and lower strain rates. The results are shown to be consistent with an isostress
model for the deformation of (α + β) two-phase alloys in which the varying β volume fractions and differing diffusivities
of titanium, cobalt, or nickel in the β phase are taken into account. 相似文献
17.
G. Wang P. Shi M. Qi F. X. Chen D. Z. Yang J. J. Xu 《Metallurgical and Materials Transactions A》1998,29(6):1741-1747
The objective of this article is to characterize the sliding wear behavior of a 30 vol pct Ti50Ni25Cu25 particulate-reinforced aluminum matrix composite under dry conditions. The transformation temperatures of Ti50Ni25Cu25 particles were measured before and after the compounding procedure by the differential scanning calorimeter (DSC) method.
The wear tests were carried out on a pin-on-disc machine. A 10 vol pct SiC particulate-reinforced composite and pure aluminum
were chosen as the comparison specimens. The results indicate that Al-30 vol pct Ti50Ni25Cu25 composites exhibit higher wear resistance than their unreinforced matrices and are comparable with Al-10 vol pct SiC composites
in this experiment. A self-adaptive mechanism that contributes to the wear resistance of an Al-30 vol pct Ti50Ni25Cu25 composite is proposed. Scanning electron microscopy (SEM) and energy diffraction spectrum (EDS) examinations were carried
out to investigate the wear mechanism and interface reactions. The results indicate that the interfacial reaction is a predominant
factor in determining the wear behavior of the Ti50Ni25Cu25/Al composite. 相似文献
18.
W. O. Soboyejo J. Dipasquale F. Ye C. Mercer T. S. Srivatsan D. G. Konitzer 《Metallurgical and Materials Transactions A》1999,30(4):1025-1038
This article presents the results of a study of the fatigue and fracture behavior of a damage-tolerant Nb-12Al-44Ti-1.5Mo
alloy. This partially ordered B2 + orthorhombic intermetallic alloy is shown to have attractive combinations of room-temperature
ductility (11 to 14 pct), fracture toughness (60 to 92 MPa√m), and comparable fatigue crack growth resistance to IN718, Ti-6Al-4V,
and pure Nb at room temperature. The studies show that tensile deformation in the Nb-12Al-44Ti-1.5Mo alloy involves localized
plastic deformation (microplasticity via slip-band formation) which initiates at stress levels that are significantly below the uniaxial yield stress (∼9.6 pct of
the 0.2 pct offset yield strength (YS)). The onset of bulk yielding is shown to correspond to the spread of microplasticity
completely across the gage sections of the tensile specimen. Fatigue crack initiation is also postulated to occur by the accumulation
of microplasticity (coarsening of slip bands). Subsequent fatigue crack growth then occurs by the “unzipping” of cracks along
slip bands that form ahead of the dominant crack tip. The proposed mechanism of fatigue crack growth is analogous to the unzipping
crack growth mechanism that was suggested originally by Neumann for crack growth in single-crystal copper. Slower near-threshold
fatigue crack growth rates at 750 °C are attributed to the shielding effects of oxide-induced crack closure. The fatigue and
fracture behavior are also compared to those of pure Nb and emerging high-temperature niobium-based intermetallics. 相似文献
19.
Chang Sup Lee Jun Cheol Oh Sunghak Lee 《Metallurgical and Materials Transactions A》2003,34(7):1461-1471
The objective of this study is to investigate microstructure, hardness, and wear properties of three kinds of (TiC,TiB)/Ti-6Al-4V
surface-alloyed materials fabricated by high-energy electron-beam irradiation. The mixtures of Ti+C, TiC+TiB2, and Ti+B4C powders and CaF2 flux were deposited on a Ti-6A1-4V substrate, and then high-energy electron beam was irradiated on these mixtures. The surface-alloyed
layers of 0.9 to 1.6 mm in thickness were homogeneously formed, and contained a large amount (30 to 44 vol. pct) of hard precipitates
such as TiC and TiB in the martensitic matrix. This microstructural modification improved the hardness and wear resistance
of the surface-alloyed layer 2 times and 6 to 9 times, respectively, greater than that of the substrate. Particularly, the
surface-alloyed material fabricated with Ti+B4C powders had a larger volume fraction of TiB and TiC homogeneously distributed in the martensitic matrix, and thus showed
the best hardness and wear resistance. These findings suggested that the surface-alloying using high-energy electron-beam
irradiation was economical and useful for the development of titanium-base surface-alloyed materials with improved hardness
and wear properties. 相似文献
20.
Kaveh Edalati Zenji Horita Hiroshi Fujiwara Kei Ameyama 《Metallurgical and Materials Transactions A》2010,41(13):3308-3317
Pure Ti (99.5 pct) powders after processing with ball milling (BM) were consolidated to disc-shaped samples with 10-mm diameter
and 0.8-mm thickness at room temperature using high-pressure torsion (HPT). A relative density as high as 99.9 pct, high bending
and tensile strengths of 2.55 to 3.45 and 1.35 GPa, respectively, and a moderate ductility of 8 pct with an ultrafine grained
structure are achieved after cold consolidation with HPT, which exceed those of hot consolidation methods. X-ray diffraction
(XRD) analysis showed that a phase transformation occurs from α phase to ω phase during HPT under a pressure of 6 GPa as in bulk pure Ti, whereas no phase transformation is detected after processing
with BM alone. It was confirmed that the strength and ductility are improved by a combined application of BM and HPT when
compared with other severe plastic deformation methods applied to Ti and Ti-6 pct Al-4 pct V, so that no alloying elements
are required for the achievement of a comparable strength and ductility. 相似文献