共查询到20条相似文献,搜索用时 46 毫秒
1.
J. H. Zhu P. K. Liaw J. M. Corum H. E. McCoy Jr. 《Metallurgical and Materials Transactions A》1999,30(6):1569-1578
Mechanical behaviors at 538 °C, including tensile and creep properties, were investigated for both the Ti-6Al-4V alloy and
the Ti-6Al-4V composite reinforced with 10 wt pct TiC particulates fabricated by cold and hot isostatic pressing (CHIP). It
was shown that the yield strength (YS) and ultimate tensile strength (UTS) of the composite were greater than those of the
matrix alloy at the strain rates ranging from approximately 10−5 to 10−3 s−1. However, the elongation of the composite material was substantially lower than that of the matrix alloy. The creep resistance
of the composite was superior to that of the matrix alloy. The data of minimum creep strain rate vs applied stress for the composite can be fit to a power-law equation, and the stress exponent values of 5 and 8 were obtained
for applied stress ranges of 103 to 232 MPa and 232 to 379 MPa, respectively. The damage mechanisms were different for the
matrix alloy and the composite, as demonstrated by the scanning electron microscopy (SEM) observation of fracture surfaces
and the optical microscopy examination of the regions adjacent to the fracture surface. The tensile-tested matrix alloy showed
dimpled fracture, while the creep-tested matrix alloy exhibited preferentially interlath and intercolony cracking. The failure
of the tensile-tested and creep-tested composite material was controlled by the cleavage failure of the particulates, which
was followed by the ductile fracture of the matrix. 相似文献
2.
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
3.
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
4.
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
5.
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
6.
Megan Frary Christopher Schuh David C. Dunand 《Metallurgical and Materials Transactions A》2002,33(6):1669-1680
By thermally cycling through their transformation temperature range, coarse-grained polymorphic materials can be deformed
superplastically, owing to the emergence of transformation mismatch plasticity (or transformation superplasticity) as a deformation
mechanism. This mechanism is presently investigated under biaxial stress conditions during thermal cycling of unalloyed titanium,
Ti-6Al-4V, and their composites (Ti/10 vol. pct TiC
p
, Ti-6Al-4V/10 vol. pct TiC
p
, and Ti-6Al-4V/5 vol. pct TiB
w
). During gas-pressure dome bulging experiments, the dome height was measured as a function of forming time. Adapting existing
models of biaxial doming to the case of transformation superplasticity where the strain-rate sensitivity is unity, we verify
the operation of this deformation mechanism in all experimental materials and compare the biaxial results directly to new
uniaxial thermal cycling results on the same materials. Finally, existing thickness distribution models are compared with
experimentally measured profiles. 相似文献
7.
P. K. Brindley S. L. Draper J. I. Eldridge M. V. Nathal S. M. Arnold 《Metallurgical and Materials Transactions A》1992,23(9):2527-2540
The tensile stress-strain behavior and failure mechanisms of Ti-24Al-11Nb and a SiC/ Ti-24Al-11Nb composite with continuous
SCS-6 fibers oriented parallel to the loading direction have been examined over a range of temperatures from 23 °C to 815°C in air. Failure in Ti- 24Al-11Nb occurred at strains of approximately 4 pct soon after crack initiation at low tem- peratures.
Ductility increased with temperature up to a maximum of 20 pct elongation at 600 °C, as surface-initiated cracks did not propagate
readily at intermediate temperatures. At higher temperatures, the onset of grain boundary and interfacial void nucleation
limited ductility. Com- posite failure appeared to be controlled by fiber fracture at all temperatures; for practical en-
gineering purposes, composite failure occurred at 0.8 pct strain at all temperatures. At temperatures of 425 °C and less,
fiber fractures occurred at intervals along the lengths of the fibers and appeared to be cumulative, while at temperatures
of 650 °C and greater, fiber fractures were only observed locally to the fracture surfaces. The decreased radial residual
stresses, interfacial strengths, and matrix properties at 650 °C and 815 °C allowed the composite to unload at 0.8 pct strain,
due to fiber fractures, followed by a reloading in which fibers pulled out and the matrix failed, resulting in composite failure.
The decreasing residual stresses with increasing temper- ature determined from an elastic-plastic concentric cylinder model
were shown to affect the stress-strain response of the composite and were consistent with the measured decreasing inter- facial
shear stresses, the increased fiber pullout with temperature, and the circumferential de- bonding observed around the fibers
at higher temperatures. 相似文献
8.
Creep tests were conducted at 295 K on Ti-6 Al-4 V in the solution treated and aged (4 h at 815 K) condition, and in the as-welded
condition. Some aged specimens were tested after pre-straining. Creep stresses ranged from 40 to 90 pct of the aged material
yield strength. Results showed that creep was of the primary or transient kind in all cases, and was much greater in welded
than in aged material. In general, pre-strains reduced creep, although a strain larger than 10-3 was needed to do this at the highest creep stress. Activation areas A* were between 10 and 20 b2, and thus were similar to tensile results on titanium and its alloys. The microstructural rationale applied to Ti-5 Al-2.5
Sn in earlier work, based on the character of dislocation sources, proved successful in understanding the effects of prestrain
in this work.
Formerly with Sandia Laboratories, Livermore, Calif. 相似文献
9.
This study is concerned with the correlation of microstructure and abrasive and sliding wear resistance of (TiC,SiC)/Ti-6Al-4V
surface composites fabricated by high-energy electron-beam irradiation. The mixtures of TiC, SiC, Ti + SiC, or TiC+SiC powders
and CaF2 flux were deposited on a Ti-6Al-4V substrate, and then an electron beam was irradiated on these mixtures. The surface composite
layers of 1.2 to 2.1 mm in thickness were homogeneously formed without defects and contained a large amount (30 to 66 vol
pct) of hard precipitates such as TiC and Ti5Si3 in the martensitic matrix. This microstructural modification, including the formation of hard precipitates in the surface
composite layer, improved the hardness and abrasive wear resistance. Particularly in the surface composite fabricated with
TiC + SiC powders, the abrasive wear resistance was greatly enhanced to a level 25 times higher than that of the Ti alloy
substrate because of the precipitation of 66 vol pct of TiC and Ti5Si3 in the hardened martensitic matrix. During the sliding wear process, hard and coarse TiC and Ti5Si3 precipitates fell off from the matrix, and their wear debris worked as abrasive particles, thereby reducing the sliding wear
resistance. On the other hand, needle-shaped Ti5Si3 particles, which did not play a significant role in enhancing abrasive wear resistance, lowered the friction coefficient
and, accordingly, decelerated the sliding wear, because they played more of the role of solid lubricants than as abrasive
particles after they fell off from the matrix. These findings indicated that high-energy electron-beam irradiation was useful
for the development of Ti-based surface composites with improved abrasive and sliding wear resistance, although the abrasive
and sliding-wear data should be interpreted by different wear mechanisms. 相似文献
10.
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
11.
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
12.
Qiu Peikun Han Yuanfei Huang Guangfa Le Jianwen Lei Liming Xiao Lv Lu Weijie 《Metallurgical and Materials Transactions A》2020,51(5):2276-2290
Metallurgical and Materials Transactions A - TiB, TiC and La2O3 hybrid-reinforced Ti-6Al-4V matrix composites were fabricated by common casting and processed by the following forging and isothermal... 相似文献
13.
TiAl-based titanium aluminide alloys and their composites reinforced with ceramic particles are considered to be important
candidate materials for high-temperature structural applications. Laser-engineered net shaping (LENS) is a layered manufacturing
process, which involves laser processing fine powders into three-dimensional components directly from a computer-aided design
(CAD) model. In this work, the LENS process was employed to fabricate carbide-particle-reinforced titanium aluminide-matrix
composites using TiC and gas-atomized Ti-48Al-2Cr-2Nb powders as the feedstock materials. The composites deposited by the
LENS process were susceptible to solid-state cracking due to high thermal stresses. The microstructures of the laser-deposited
monolithic and composite titanium aluminide materials were characterized using light optical microscopy (LOM), scanning electron
microscopy (SEM), X-ray energy-dispersive spectroscopy (EDS) analysis, electron-probe microanalysis (EPMA), and X-ray diffraction
(XRD) techniques. Effects of the LENS processing parameters on the cracking susceptibility and microstructure were studied.
Crack-free deposits were fabricated by preheating the substrate to 450 °C to 500 °C during LENS processing. The fabricated
composite deposits exhibit a hardness of more than twice the value of the Ti-6Al-4V alloy. 相似文献
14.
Direct metal deposition (DMD) is a rapid laser-aided deposition method that can be used to manufacture near-net-shape components from their computer aided design (CAD) files. The method can be used to produce fully dense or porous metallic parts. The Ti-6Al-4V alloy is widely used as an implantable material mainly in the application of orthopedic prostheses because of its high strength, low elastic modulus, excellent corrosion resistance, and good biocompatibility. In the present study, Ti-6Al-4V scaffold has been fabricated by DMD technology for patient specific bone tissue engineering. Good geometry control and surface finish have been achieved. The structure and properties of the scaffolds were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and tension test. The microstructures of laser-deposited Ti-6Al-4V scaffolds are fine Widmanstätten in nature. The tensile and yield strengths of the as-deposited Ti-6Al-4V were 1163 ± 22 and 1105 ± 19 MPa, respectively, which are quite higher than the ASTM limits (896 and 827 MPa) for Ti-6Al-4V implants. However, the ductility of the as-deposited sample was very low (~4 pct), which is well below the ASTM limit (10 pct). After an additional heat treatment (sample annealed at 950 °C followed by furnace cooling), both strength (UTS ~ 1045 ± 16, and YS ~ 959 ± 12 MPa) and ductility (~10.5 ± 1 pct) become higher than ASTM limits for medical implants. 相似文献
15.
K. Muszka M. Lopez-Pedrosa K. Raszka M. Thomas W. M. Rainforth B. P. Wynne 《Metallurgical and Materials Transactions A》2014,45(13):5997-6007
The effect of forward and reverse torsion on flow behavior and microstructure evolution, particularly dynamic and static spheroidization, on Ti-6Al-4V with an alpha lamella colony microstructure was studied. Testing was undertaken sub beta transus [1088 K (815 °C)] at strain rates of either 0.05 or 0.5 s?1. Quantitative metallography and electron back scatter diffraction has identified that a critical monotonic strain (ε c) in the range of 0.3 to 0.6 is required to initiate rapid dynamic spheroidization of the alpha lamella. For material deformed to strains below ε c and then reversed to a zero net strain the orientation relationships between alpha colonies are close to ideal Burgers, enabling prior beta grains to be fully reconstructed. Material deformed to strains greater than ε c and reversed lose Burgers and no beta reconstruction is possible, suggesting ε c is the strain required to generate break-up of lamella. Static spheroidization is, however, sensitive to strain path around ε c. Annealing at 1088 K (815 °C) for 4 hours for material subjected to 0.25 forward + 0.25 forward strain produces 48 pct spheroidized grains while material with 0.25 forward + 0.25 reverse strain has 10 pct spheroidization. This is believed to be a direct consequence of different levels of the stored energy between these two strain paths. 相似文献
16.
Radhakrishna B. Bhat Seshacharyulu Tamirisakandala Daniel B. Miracle Vilupanur A. Ravi 《Metallurgical and Materials Transactions A》2005,36(3):845-857
The thermomechanical response of Ti-6Al-4V modified with 2.9 pct B produced by a blended powder metallurgy route was studied
with isothermal constant strain-rate hot compression tests in the temperature range 850 °C to 1200 °C and strain rate range
10−3 to 10 s−1. Detailed analyses of the flow stress data were conducted to identify various microstructural deformation and damage mechanisms
during hot working by applying available materials modeling techniques. In the α + β phase field, cavitation at the matrix/TiB interfaces and TiB particle fracture occurs at low strain rates (<10−1 s−1), while adiabatic shear banding also occurs at high strain rates. At low strain rates, the β phase deforms superplastically due to the stabilization of a fine grain size by the TiB particles. Grain boundary and matrix/TiB
interface sliding with simultaneous diffusional accommodation are observed to contribute to the β superplasticity. The deformation behavior at high strain rates in the β-phase field is similar to that of the α + β phase field, with microstructural manifestations of extensive cavitation at the matrix/TiB interfaces and TiB particle fracture. 相似文献
17.
Friction-stir (FS) processing was used to modify the coarse, fully lamellar microstructure of investment cast and hot isostatically
pressed (HIP’ed) Ti-6Al-4V. The effect of FS processing on mechanical properties was investigated using microtensile and four-point
bend fatigue testing. The tensile results showed a typical microstructure dependence where yield strength and ultimate tensile
strength both increased with decreasing slip length. Depending on the processing parameters, fatigue strength at 107 cycles was increased by 20 pct or 60 pct over that of the investment cast and HIP’ed base material. These improvements have
been verified with a statistically significant number of tests. The results have been discussed in terms of the resistance
of each microstructure fatigue crack initiation and small crack propagation. For comparison, a limited number of fatigue tests
was performed on α + β forged Ti-6Al-4V with varying primary α volume fraction and also on investment cast material heat treated to produce a bi-lamellar condition. 相似文献
18.
In this study, a newly developed duplex coating method incorporating plasma carhurization and CrN coating was applied to Ti-6AI-4V and its effects on the wear resistance and fatigue life were investigated. The carburized layer with approximately150μm in depth and CrN coating film with 7. 5 μm in thickness were fomled after duplex coating. Hard carbide particles such as TiC And V4C3 were formed in the carburized layer. XRD diffraction pattern analysis revealed that CrN film had predominant [111] and [200] textures. The hardness (Hv) was significantly improved up to ahout 1960 after duplex coating while the hardness value of original Ti-6Al-4V was 402. The threshold load for the modification and/or failure of CrN coating was measured to be 32 N using the acoustic emission technique. The wear resistance and fatigue life of duplex coated Ti-6Al-4V improved significantly compared to those of un-treated specimen. The enhanced wear resistance can be attributed to the excellent adhesion and improved hardness of CrN coating film for the duplex coated Ti-6Al-4V. The initiation of fatigue cracks is likely to be retarded by the presence of hard and strong layers on the surface, resulting in the enhanced fatigue life. 相似文献
19.
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
20.
This article presents the results of a combined experimental and theoretical study of the effects of loading rate (1, 10,
and 100 MPa√m · s−1) on the resistance-curve behavior and toughening in cast lamellar gamma-based titanium aluminides (Ti-48Al-2Cr-2Nb, Ti-45Al-2Mn-2Nb
+ 0.8 vol pct TiB2, and Ti-47Al-2Mn-2Nb + 0.8 vol pct TiB2). Note that compositions are quoted in at. pct unless stated otherwise. The fracture-initiation toughness and resistance-curve
behavior in Ti-48Al-2Cr-2Nb are shown to be similar at the three loading rates examined. In the case of the Mn-containing
alloys, stronger resistance-curve behavior is observed as the loading rate increases from 1 to 10 MPa√m · s−1. However, the fracture-initiation toughness and resistance-curve behavior of the Mn-containing alloys are similar at loading
rates of 10 and 100 MPa√m · s−1. The observed resistance-curve behavior is attributed largely to the role of ligament bridging and, to a lesser extent, to
the effects of cracktip plasticity. Small- and large-scale bridging models are also shown to predict the measured resistance
curves when the observed/measured bridging parameters and material properties are used in the micromechanical modeling of
crack bridging. The implications of the results are also discussed for the design of damage-tolerant gamma alloys and microstructures. 相似文献