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1.
C. W. Lentz D. A. Koss M. G. Stout S. S. Hecker 《Metallurgical and Materials Transactions A》1983,14(12):2527-2533
The influence of internal hydrogen on the multiaxial stress-strain behavior of commercially pure titanium has been studied.
Thin-walled tubing specimens containing either 20 or 1070 ppm hydrogen have been tested at constant stress ratios in combined
tension and internal pressure. The addition of hydrogen lowers the yield strength for all loading paths but has no significant
effect on the strain hardening behavior at strains ε ≥ 0.02. Thus, the hydrogen embrittlement of titanium under plain strain
or equibiaxial loading is not a consequence of changes of flow behavior. The yielding behavior of this anisotropic material
is described well by Hill’s quadratic yield criterion. As measured mechanically and by pole figure analysis, the plastic anisotropy
changes with deformation in a manner which depends on stress state. Hill’s criterion and the associated flow rule do not describe
the multiaxial flow behavior well because of their inability to account for changes of texture which depend on multiaxial
stress path. Hence, a strain dependent, texture-induced strengthening effect in equibiaxial tension is observed, this effect
having the form of an enhanced strain hardening rate.
Formerly with Michigan Technological University 相似文献
2.
The effects of dilute additions of titanium up to 0.20 wt pct on the solubility of nitrogen in two complex Fe−Cr−Ni alloys
were examined over the temperature range 1450 to 1600°C. Sieverts' law was obeyed by all titanium-bearing alloys up to some
nitrogen pressure below one atmosphere. ‘Breaks’ in each solubility plot were observed that corresponded to the formation
of titanium nitride. Titanium additions were observed to lower the nitrogen solubility in each group of alloys. This effect
is opposite to that previously observed in pure iron. Calculated values of the solubility product (pct Ti) (pct N) for TiN
formation in each alloy increased with rising melt temperature. 相似文献
3.
Y. Torres J. J. Pavón I. Nieto J. A. Rodríguez 《Metallurgical and Materials Transactions B》2011,42(4):891-900
Commercially pure titanium (c.p. Ti) is one of the best metallic biomaterials for bone tissue replacement. However, one of
its main drawbacks, which compromises the service reliability of the implants, is the stress-shielding phenomenon (Young’s
modulus mismatch with respect to that one of the bone). Several previous works attempted to solve this problem. One alternative
to solve that problem has been the development of biocomposites implants and, more recently, the fabrication of titanium porous
implants. In this work, porous samples of c.p. Ti grade 4 were obtained using conventional powder metallurgy technique. The
influence of the processing parameters (compacting pressure and sintering temperature) on the microstructure features (size,
type, morphology, and percentage of porosity), as well as on the mechanical properties (compressive yield strength, and conventional
and dynamic Young’s modulus) were investigated. The results indicated that there is an increment in density, roundness of
pores, and mean free path between them as compacting pressure and/or sintering temperature is increased. The Young’s modulus
(conventional and dynamic) and yield strength showed the same behavior. Better stiffness results, in the central part of cylindrical
samples, were obtained for a uniaxial compression of 38.5 MPa using a sintering temperature of 1273 K and 1373 K (1000 °C
and 1100 °C). An evaluation of porosity and Young’s modulus along a cylindrical sample divided in three parts showed that
is possible to obtain a titanium sample with graded porosity that could be used to design implants. This approach opens a
new alternative to solve the bone resorption problems associated with the stress-shielding phenomenon. 相似文献
4.
O. N. Senkov M. Dubois J. J. Jonas 《Metallurgical and Materials Transactions A》1996,27(12):3963-3970
The elastic properties of a series of polycrystalline titanium-hydrogen alloys (containing up to 25 at. pct H) were measured
over the temperature range 20 °C to 1100 °C. The latter limits permitted investigation of adjacent parts of the α+δ, α, and
β phase fields. A laser ultrasonic technique was employed to measure the temperature and hydrogen-concentration dependencies
of the elastic constants. The room-temperature elastic properties of the alloys depended only slightly on hydrogen concentration,
remaining almost independent of the volume fraction of the δ hydride phase. In the α phase field, the addition of hydrogen
decreased the shear and Young’s moduli and increased the bulk modulus, Lamé constant, and Poisson’s ratio. The Young’s and
shear moduli decreased more rapidly with increasing temperature than in cubic phases. By contrast, Poisson’s ratio increased
with temperature. In the β phase field, the temperature dependence of the elastic constants was weak. However, alloying with
hydrogen increased the shear and Young’s moduli, decreased Poisson’s ratio, but did not appreciably affect the bulk modulus
and Lamé constant. The different effects of hydrogen on the elastic constants of alpha and beta titanium are interpreted in
terms of the influence of dissolved hydrogen on the stability of the hexagonal close-packed (hcp) and body-centered cubic
(bcc) lattices in the vicinity of the α-to-β transformation. The present results are also used to help account for the effect
of hydrogen concentration on the mechanical properties of Ti-H alloys. 相似文献
5.
Y. Morizane B. Ozturk Ph.D. R. J. Fruehan 《Metallurgical and Materials Transactions B》1999,30(1):29-43
Equilibrium studies between CaO-SiO2-10 pct MgO-Al2O3-TiO1.5-TiO2 slags, carbon-saturated iron, and a carbon monoxide atmosphere were performed at 1773 K to determine the activities of TiO1.5 and TiO2 in the slag. These thermodynamic parameters are required to predict the formation of titanium carbonitride in the blast furnace.
In order to calculate the activity of titanium oxide, the activity coefficient of titanium in carbon-saturated iron-carbon-titanium
alloys was determined by measuring the solubility of titanium in carbon-saturated iron in equilibrium with titanium carbide.
The solubility and the activity coefficient of titanium obtained were 1.3 pct and 0.023 relative to 1 wt pct titanium in liquid
iron or 0.0013 relative to pure solid titanium at 1773 K, respectively. Over the concentration range studied, the effect of
the TiO
x
content on its activity coefficient is small. In the slag system studied containing 35 to 50 pct CaO, 25 to 45 pct SiO2, 7 to 22 pct Al2O3, and 10 pct MgO, the activity coefficients of TiO1.5 and TiO2 relative to pure solid standard states range from 2.3 to 8.8 and from 0.1 to 0.3, respectively. Using thermodynamic data
obtained, the prediction of the formation of titanium carbonitride was made. Assuming hypothetical ‘TiO2,’ i.e., total titanium in the slag expressed as TiO2, and using the values of the activity coefficients of TiO1.5 and TiO2 determined, the equilibrium distribution of titanium between blast furnace-type slags and carbon-saturated iron was computed.
The value of [pct Ti]/(pct ‘TiO2’) ranges from 0.1 to 0.2. 相似文献
6.
M. Labudovic R. Kovacevic I. Kmecko T. I. Khan D. Blecic Z. Blecic 《Metallurgical and Materials Transactions A》1999,30(6):1597-1603
The surface modification of a Ti-6Al-4V alloy using a gas tungsten arc, as a heat source, was studied. The experimental results
show that the titanium alloy surface can be melted and nitrided using pure nitrogen or a nitrogen/argon mixture shielding
atmosphere. The resolidified surfaces are 0.9 to 1.2-mm thick and contain titanium nitride dendrites, α-titanium, and α″-titanium
(martensite). The average dendrite arm spacing is influenced by the electrode speed. Small titanium nitride dendrites are
homogeneously distributed in the resolidified surfaces. The microstructure and phase constitution in the resolidified surfaces
were determined and analyzed, and the mechanism of the formation of titanium nitrides is discussed. The results show that
the nitriding kinetics obey parabolic laws and are, therefore, controlled by nitrogen diffusion. The nitrogen-concentration
depth profiles, calculated using Fick’s second law of diffusion, are compared to experimental nitrogen depth profiles, showing
satisfactory agreement. 相似文献
7.
A survey of diffusion data of interstitial oxygen and of the substitutional elements aluminum and vanadium is presented for
alpha and beta titanium. It is based on a survey of literature. Oxygen is an important interstitial element in titanium alloys.
Oxygen’s large chemical affinity to titanium is indicated by Ti—O bond energy of 2.12 eV,1 comparable to the Ti—Ti bond energy of 2.56 eV.2 Oxygen is difficult to eliminate completely from titanium, and commercial titanium alloys usually contain from 0.10 to 0.20
wt pct oxygen. Oxygen significantly affects the mechanical properties of titanium alloys1,3 and is sometimes used as an alloying element. The effects of oxygen on phase transformation ,4,5,6 Youngs modulus,7,8 hardness,9,10 fracture toughness,11 and other mechanical properties12 have been amply documented. Aluminum and vanadium are the most frequently used substitutional alloying elements. Aluminum
is an alpha stabilizer and vanadium is a beta stabilizer.
An erratum to this article is available at . 相似文献
8.
W. T. Loomis J. W. Freeman D. L. Sponseller 《Metallurgical and Materials Transactions B》1972,3(4):989-1000
The influence of 1, 3, and 5 at. pct Mo on the γ’precipitate has been studied in experimental wrought nickel-base superalloys
containing about 14 at. pct Cr and 6-1/2, 9, or 12 at. pct Al, or 2 at. pct Al plus 4 at. pct Ti. Concentrations of all other
elements were quite low to limit the observed effects to those of molybdenum alone. Molybdenum markedly increases the γ’ solvus
temperature, as determined by the sensitive and relatively simple technique of differential thermal analysis; correspondingly,
the weight fraction of γ’ increases with molybdenum additions for a given aging treatment. Molybdenum dissolves extensively
in the γ’of the titanium-free alloys, but it dissolves to a considerably smaller extent in the γ’of the titanium-bearing alloys.
Molybdenum substitutes for chromium in y’, but does not alter the aluminum or titanium contents of this phase. Lattice parameters
of both the matrix and the γ’are increased markedly by molybdenum, in proportion to the molybdenum contents of these phases.
The resulting effects on lattice-parameter mismatch correlate rather well with observed γ’morphology, which tends to change
from spheroidal to cuboidal in titanium-free alloys, and from cuboidal to spheroidal in 2 at. pct Al-4 at. pct Ti alloys,
as molybdenum is added to these alloys.
J. W. Freeman was formerly Professor of Metallurgical Engineering, University of Michigan, Ann Arbor, Mich. (Deceased, November,
1970).
This paper is based upon a thesis submitted by W. T. Loomis in partial fulfillment of the requirements for the degree of Doctor
of Philosophy at the Horace H. Rackham School of Graduate Studies, The University of Michigan. 相似文献
9.
Zinc oxide and titanium dioxide powders mixed in an equimolar ratio are mechanically activated in a planetary ball mill and
sintered under nonisothermal and isothermal conditions. Nonisothermal sintering is studied using dilatometry and SEM. The
activation energy of sintering is determined using the method based on different heating rates and Dorn’s method as well.
The phase composition of the isothermally sintered samples is determined using x-ray powder diffraction.
Published in Poroshkovaya Metallurgiya, Vol. 47, No. 1–2 (459), pp. 55–62, 2008. 相似文献
10.
Hydrogen absorption and desorption often limits a material’s application. For titanium, hydrogen absorption kinetics determine
its suitability for tritium storage, tritium gettering, and vacuum pump applications. This study examines the absolute rate
theory energy surface which molecular hydrogen gas encounters as it is absorbed into alpha-phase titanium. This results in
useful new predictions for hydrogen absorption rates, desorption rates, and surface coverages on titanium. The only energy
surface which is consistent with observed activation and absorption enthalpies, while predicting all absorption/desorption
rate data, is found to contain a new activation barrier. Accuracy is within a factor of 3.6 for two surface preparations and
temperatures between 250 and 500 °C. 相似文献
11.
Masaaki Nakai Mitsuo Niinomi Takahiro Oneda 《Metallurgical and Materials Transactions A》2012,43(1):294-302
The improvement in fatigue strength, with maintenance of a low Young’s modulus, in a biomedical β-type titanium alloy, Ti–29Nb–13Ta–4.6Zr (TNTZ), by thermomechanical treatment was investigated. A short aging time at an
ω-phase-forming temperature combined with severe cold rolling was employed. A fine ω phase is observed in TNTZ subjected to this thermomechanical treatment. Because the rolling texture of β phase is formed by cold rolling, such as the ω phase may be preferentially oriented to a direction that is effective for inhibiting the increase in Young’s modulus. The
samples aged at 573 K (300 °C) for 3.6 ks and 10.8 ks after cold rolling exhibit a good balance between a high tensile strength
and low Young’s modulus. In the case of the sample aged for 3.6 ks, the tensile strength is improved, although the fatigue
strength is not improved significantly. Both the tensile strength and the fatigue strength of the sample aged for 10.8 ks
are improved. This fatigue strength is the highest among the TNTZ samples used in the current and in previous studies with
Young’s moduli less than 80 GPa. 相似文献
12.
R. E. Dutton S. Shamasundar S. L. Semiatin 《Metallurgical and Materials Transactions A》1995,26(8):2041-2051
Modeling of the consolidation of ceramic and metal powders by sintering, hot pressing, and hotisostatic pressing (HIP) was
conducted using a continuum yield function and associated-flow rule modified to incorporate microstructure effects such as
grain growth, pore size, and pore geometry. It was shown that consolidation behavior can be described over the entire range
of densities through two parameters, the stress intensification factor and Poisson’s ratio, which are readily measured using
uniaxial upset tests. Both parameters are functions of relative density, whose exact dependence varies from one material to
another. Furthermore, it was demonstrated that in sinter forging of ceramics, an “apparent” Poisson’s ratio depending on stress
level (relative to the sintering stress) gives a quantitative measure of the compctition between sintering and creep deformation.
The accuracy of the microstructure-sensitive yield function was established through finite-element modeling (FEM) simulations
of the isothermal sintering of a soda-lime glass, sinter forging of alumina, and die pressing of an alpha-two titanium aluminide
alloy. 相似文献
13.
The plastic flow of the commercial titanium material Ti-50A (0.5 at. pct Oeq) of 22 μm grain size was investigated over the temperature range of 600 to 1150 structure) and strain rates of 3 x 10-5 to 3 x 10-2 per s employing both constant strain rate and strain rate cycling tests. Dynamic strain aging occurred in the temperature
range of 600 to 850 (0.31 to 0.44Tm) with an activation energy of 50 kcal per mole derived from the start of serrations in the stress-strain curves, maxima in
strain hardening and minima in ductility. This value is in accord with that for the diffusion of oxygen in titanium. At temperatures
above 850 (0.46 to 0.59Tm) the data were very well represented by Weertman’s glide and climb high temperature creep mechanism, giving εskT/Dμb= 1.1 x 106 (σ/μ)4.55 withD = 1.0 x exp (- 57,800/RT). The value of 57.8 kcal per mole is in accord with available self-diffusion data for titanium. 相似文献
14.
Y. L. Hao R. Yang M. Niinomi D. Kuroda Y. L. Zhou K. Fukunaga A. Suzuki 《Metallurgical and Materials Transactions A》2003,34(4):1007-1012
Alloys for implant devices require improved strength but a reduced Young’s modulus, in order to become mechanically more compatible
with adjacent bone tissues. In this study, a new metastable β-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (wt pct), was subjected to aging treatment to produce different microstructures,
and the resulting mechanical properties, including the Young’s modulus, were measured. The Young’s modulus of this alloy is
found to be sensitive to microstructures generated by various heat treatments. For microstructures varying from (α + β) to (α + β + ω) and (β + ω), the Young’s modulus increases with an accompanying increase in tensile strength and hardness, but decreases in ductility.
The (β + ω) microstructure has a low strength, high modulus, and poor ductility and cannot be used for biomedical applications. For
an (α + β) microstructure, the volume fraction of the phases is shown to be the main factor that determines the mechanical properties. 相似文献
15.
Kiritkumar K. Shah Howard G. Nelson Donald L. Johnson Frank M. Hamaker 《Metallurgical and Materials Transactions A》1975,6(1):373-375
A generalized expression for the nonsteady state parameter, lag-time, has been obtained from Fick’s second law for gas-phase
transport through hollow, cylindrical membranes. This generalized expression is simplified for three limiting cases of practical
interest: 1) diffusion controlled transport, 2) phase boundary reaction control at the inlet surface, and 3) phase boundary
reaction control at the outlet surface. In all three cases the lagtime expressions were found to be inversely proportional
only to the diffusion coefficient and functionally dependent on the membrane radii. Finally, the lag-time expressions were
applied to experimentally obtained lag-time data for α-phase titanium and α-phase iron.
Formerly with NASA-Ames Research Center, Materials Science Branch. 相似文献
16.
A metallographic study has been made of the microstructures produced by room temperature deformation of 0.6mm thick commercially
pure titanium sheet metal in uniaxial, plane strain and biaxial tension. Deformation twinning becomes increasingly important
as the deformation mode changes from uniaxial through plane strain to equibiaxial tension, and is more significant for strain
transverse to the rolling direction than for strain in the longitudinal direction. In uniaxial tension, 1122 twins are dominant
in longitudinal straining, while 1012 twins dominate in transverse straining. In plane strain and equibiaxial straining, 1012
twinning is suppressed and largely replaced by 1122 twinning. The observed changes in twin occurrence and type are attributed
to the interaction of the imposed stress system and the crystallographic texture of the rolled sheet, which alters the distribution
of the grain basal-plane poles with respect to the operative stress axes. In uniaxial tension parallel to the longitudinal
direction, twins favored by ‘c’ axis compression are produced, while in the transverse direction twins favored by ‘c’ axis
tension appear. In plane strain and biaxial tension the dominant stress is through-thickness compression, which produces twins
favored by ‘c’ axis compression in nearly all cases. The alterations in twin orientation and numbers are associated with changes
in stress-strain behavior. As twin volume fraction increases and twins are aligned more closely to the principal stress axis,
the instantaneous work-hardening rate tends to stabilize at a nearly constant value over a large strain range.
Formerly Chief Metallurgist, The APV Company. 相似文献
17.
V. I. Ratnikov V. K. Prokudina A. F. Belikova N. V. Sachkova 《Russian Journal of Non-Ferrous Metals》2010,51(4):352-358
The experimental data of investigations of obtaining titanium powder from titanium sponge by self-propagating high-temperature
synthesis (SHS) hydration and its subsequent dehydration are presented. The properties of dehydrated titanium obtained under
optimal conditions are investigated. It is shown that, compared with its analogs, dehydrated titanium contains fewer impurities.
The shape of its particles is molten comminuted with nanodimensional structural elements in the form of cracks, channels,
incrustations, and layers with dimensions of 100–500 nm. Prolonged milling of starting titanium hydride to micrometer sizes
does not affect the surface morphology of nanostructured particles and leads to the contamination of the final dehydrated
titanium. The dispersity of the latter varies depending on the sponge sizes (−10 + 2 mm) to 20 μm. The results of a refined
calculation of the prime cost of SHS of titanium hydride and dehydrated titanium are presented. 相似文献
18.
C. G. Rhodes M. S. Vassiliou M. R. Mitchell R. A. Spurling 《Metallurgical and Materials Transactions A》1990,21(6):1589-1593
Explosive shock-wave consolidation has been used to fabricate a composite consisting of gamma phase titanium aluminide matrix
reinforced with paniculate silicon carbide. Although the consolidation process takes less than a microsecond to complete,
melting of the surfaces of the titanium aluminide powder particles results in a reaction with the silicon carbide. Titanium
suicide and titanium carbide form in the molten zone, depleting it of titanium to the extent that its final composition is
TiAl3. In addition, a second titanium suicide phase forms on the surfaces of the silicon carbide particles.
This paper is based on a presentation made in the symposium “Interfaces and Surfaces of Titanium Materials” presented at the
1988 TMS/AIME fall meeting in Chicago, Illinois, September 25–29, 1988, under the auspices of the TMS Titanium Committee. 相似文献
19.
Diffusion of cobalt,chromium, and titanium in Ni3Al 总被引:1,自引:0,他引:1
Y. Minamino S. B. Jung T. Yamane K. Hirao 《Metallurgical and Materials Transactions A》1992,23(10):2783-2790
Diffusion studies of cobalt, chromium, and titanium in Ni3Al (γ′) at temperatures between 1298 and 1573 K have been performed using diffusion couples of (Ni-24.2 at. pct Al/Ni-24.4
at. pct Al-2.91 at. pct Co), (Ni-24.2 at. pct Al/Ni-23.1 at. pct Al-2.84 at. pct Cr), and (Ni-24.2 at. pct Al/Ni-20.9 at.
pct Al-3.17 at. pct Ti). The diffusion profiles were measured by an electron probe microanalyzer, and the diffusion coefficients
of cobalt, chromium, and tita-nium in γ′ containing 24.2 at. pct Al were determined from those diffusion profiles by Hall’s
method. The temperature dependencies of their diffusion coefficients (m[su2]/s) are as follows: ~D(Co)
= (4.2 ± 1.2) × 1O-3exp {-325 ± 4 (kJ/mol)/RT} ~D(Cr) = (1.1 ± 0.3) × 10-1 exp {-366 ± 3 (kJ/mol)/RT} and D(Ti)
= (5.6 ± 3.1) × 101 exp {-468 ± 6 (kJ/mol)/RT} The values of activation energy increase in this order: cobalt, chromium, and titanium. These
activation energies are closely related to the substitution behavior of cobalt, chromium, and titanium atoms in the Ll2 lattice sites of γ′; the cobalt atoms occupying the face-centered sites in the Ll2 structure diffuse with the normal activation energy, whereas the titanium atoms oc-cupying the cubic corner sites diffuse
with a larger activation energy that includes the energy due to local disordering caused by the atomic jumps. The chromium
atoms which can occupy both sites diffuse with an activation energy similar to that of cobalt atoms. 相似文献
20.
An associated solution model is used to describe the thermodynamic properties of the liquid phase in the Pb−S system, where
the existence of ‘PbS’ species is assumed in addition to ‘Pb’ and ‘S’. The liquid is now considered as a pseudo-ternary solution
of ‘Pb’, ‘S’, and ‘PbS’ in which the concentrations of the species are related by an equilibrium constant. The thermodynamic
properties of the intermediate phase, PbS, are described by a point-defect model. The doubly ionized vacancies on the Pb and
the S sites are considered to be the dominant defects and the nonstoichiometry is caused by the excess of vacancies on either
site. The parameters of these models are obtained by simultaneous optimization of the available thermodynamic and phase equilibria
data. The Pb−S phase diagram is then calculated, using these thermodynamic models, and compared with the experimental data. 相似文献