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The deformation of iodide titanium single crystals containing 200 to 250 ppm O, was studied in compression at temperatures from 25° to 800°C. Reduction of about 5 pct along thec axis was accommodated almost entirely by \(\left\{ {11\bar 22} \right\}\) twinning from 25° to 300°C, and above 400°C by \(\left\{ {10\bar 11} \right\}\) twinning in combination with c+a slip. The stress for \(\left\{ {11\bar 22} \right\}\) twinning increased with increasing temperature, and twin formation was accompanied by a load drop, while the stress for \(\left\{ {10\bar 11} \right\}\) twinning decreased with increasing temperature and twinning was not accompanied by a load drop. Crystals reduced normal to thec axis deformed by a combination of prism slip and \(\left\{ {10\bar 12} \right\}\) twinning at 25°C and by prism slip alone above 500°C. 相似文献
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Plastic deformation in a multifunctional Ti-Nb-Ta-Zr-O alloy 总被引:7,自引:0,他引:7
S. Kuramoto T. Furuta J. H. Hwang K. Nishino T. Saito 《Metallurgical and Materials Transactions A》2006,37(3):657-662
Mechanisms for plastic deformation in the newly developed Ti-24 at. pct (Ta + Nb + V)-(Zr,Hf)-O alloys (Gum Metal) were investigated
in relation to their unique properties. Transmission electron microscopy revealed that the microstructure after deformation
was characterized by highly distorted crystal images, which are accompanied by numerous “giant faults.” Such plastic behavior
implies that a large amount of elastic stain energy was stored discretely and hierarchically during cold working. Calculated
elastic constants of the Ti-X (Nb,Ta,Mo,V) binary systems predicted that Young’s modulus in 〈001〉 and shear moduli along some
directions including slip systems in a bcc crystal were extraordinary small. The low modulus not only well explains the highly
distorted microstructure observed in the cold-worked specimens, but also signifies that ideal shear strength of the developed
alloys is a very small value, which is close to the practical strength required for plastic deformation in the alloy. This
implies that the giant faults observed in the deformed specimen were formed without the aid of dislocation glide. 相似文献
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对BT25钛合金在温度为950~1 100 ℃,应变速率为0.001~10 s-1条件下的高温变形行为进行了研究,分析了热力学参数对流变应力和微观组织的影响,并以Arrhenius方程为基础,构建了本构方程,最后进行了验证.结果表明:BT25合金在相同温度和应变速率下变形,变形量越大,动态再结晶越充分并细化了晶粒.相同变形量,变形温度越低,应变速率越高,动态再结晶晶粒尺寸越细小;流变应力随应变速率的增加而增加,随变形温度的升高而减小;BT25合金在α+β两相区(950~1 010 ℃)Q=763.51 kJ/mol,β相区(1 040~1 100 ℃)Q=231.36 kJ/mol. 相似文献
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Coarsening behavior of an alpha-beta titanium alloy 总被引:1,自引:0,他引:1
Semiatin S. L. Kirby B. C. Salishchev G. A. 《Metallurgical and Materials Transactions A》2004,35(9):2809-2819
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Martin L. Green G. Y. Chin J. B. Vander Sande 《Metallurgical and Materials Transactions A》1977,8(2):353-361
This paper reports the results of the first detailed study of the room temperature mechanical behavior of a ternary ordered
alloy. Single crystals of Cu2MnAl were tested in both free and plane-strain compression. Optical and transmission electron microscopy results established
that the slip mode is {110} 〈111〉. The superlattice dislocations consist of two 1/2a
0 〈111⦔ partials separated by an APB of unsually high energy, unlike the case of isostructural Fe3Al. The initial work hardening rate θ in free compression varies from 78 MN/m2 for the single slip orientation to ∼1100 MN/m2 for [100] and [111] where multiple slip occurs. For plane-strain compression, the τ-γ curves are divided into two bands,
depending on the stability of the orientation during deformation. Thus the Taylor model which predicts a single band is disobeyed.
The work hardening results are interpreted in terms of strong latent hardening in Cu2MnAl. 相似文献
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Plastic-flow and microstructure evolution during hot deformation of a gamma titanium aluminide alloy 总被引:3,自引:0,他引:3
The hot workability of a near gamma titanium aluminide alloy, Ti-49.5Al-2.5Nb-1.1Mn, was assessed in both the cast and the
wrought conditions through a series of tension tests conducted over a wide range of strain rates (10−4 to 100 s−1) and temperatures (850 °C to 1377 °C). Tensile flow curves for both materials exhibited sharp peaks at low strain levels
followed by pronounced necking and flow localization at high strain levels. A phenomenological analysis of the strain rate
and temperature dependence of the peak stress data yielded an average value of the strain rate sensitivity equal to 0.21 and
an apparent activation energy of ∼411 kJ/mol. At low strain rates, the tensile ductility displayed a maximum at ∼ 1050 °C
to 1150 °C, whereas at high strain rates, a sharp transition from a brittle behavior at low temperatures to a ductile behavior
at high temperatures was noticed. Dynamic recrystallization of the gamma phase was the major softening mechanism controlling
the growth and coalescence of cavities and wedge cracks in specimens deformed at strain rates of 10−4 to 10−2 s−1 and temperatures varying from 950 °C to 1250 °C. The dynamically recrystallized grain size followed a power-law relationship
with the Zener-Hollomon parameter. Deformation at temperatures higher than 1270 °C led to the formation of randomly oriented
alpha laths within the gamma grains at low strain levels followed by their reorientation and evolution into fibrous structures
containing γ + α phases, resulting in excellent ductility even at high strain rates. 相似文献
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J. M. McNaney M. J. Edwards R. Becker K. T. Lorenz B. A. Remington 《Metallurgical and Materials Transactions A》2004,35(9):2625-2631
Recent development of a laser-based experimental platform allows loading materials to high pressures in the solid state while
controlling both strain rate and peak pressure. The drive utilizes momentum transfer from a plasma generated by the introduction
of a strong shock in a reservoir of low-Z material. This study looks at the response of a commercial aluminum alloy (6061-T6)
subjected to pressures of 18 and 40 GPa at strain rates of 107/s and 5 × 107/s, respectively. It was found that the depth of the crater formed on the sample surface is a good indicator of the general
yield behavior of the material and that a relatively simple strength model prevails under the loading conditions considered
here. Metallographic examination of recovered samples showed no evidence of shear-band formation or significant melting due
to plasma-surface interactions. Crystal plasticity-based calculations were used to assess the effects of material texture.
Lack of shear-band formation during the laser-based drive is rationalized by considering the strain gradient as compared to
grain size and texture.
This article is based on a presentation given in the symposium “Dynamic Deformation: Constitutive Modeling, Grain Size, and
Other Effects: In Honor of Prof. Ronald W. Armstrong,” March 2–6, 2003, at the 2003 TMS/ASM Annual Meeting, San Diego, California,
under the auspices of the TMS/ASM Joint Mechanical Behavior of Materials Committee. 相似文献
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The unusual occurrence of plastic deformation in an adult is described. 相似文献
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A. Garg S. V. Raj R. D. Noebe M. V. Nathal R. Darolia 《Metallurgical and Materials Transactions A》1998,29(1):179-189
Tensile samples from NiAl-Hf single crystals, having the same nominal composition and heat treated and creep tested under
identical conditions at 1144 K, were found to exhibit very different rupture lives and creep ductilities. A case study was
conducted on two samples with creep rupture lives of 343.6 and 37.0 hours (with corresponding creep ductilities of 12.3 and
39.9 pct, respectively) in order to find the causes of such a large variation in creep properties. Detailed microstructural
analyses using optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) indicated
that the sample with higher rupture life and lower ductility had deformed uniformly along the length of the gage section,
whereas the sample with lower rupture life and higher ductility (sample L) deformed by localized plastic deformation resulting
in shear failure. This shear failure was due to a plastic instability in sample L which was caused by the presence of a high
density of large Hf-rich interdendritic particles that were formed during casting of the single-crystal ingot but did not
go into solution during the homogenization heat treatment. The role of these particles in causing nonuniform deformation,
which led to strain localization and a premature failure in sample L, has been described in detail. 相似文献
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S. L. Semiatin M. W. Corbett P. N. Fagin G. A. Salishchev C. S. Lee 《Metallurgical and Materials Transactions A》2006,37(4):1125-1136
The dynamic-coarsening behavior of Ti-6Al-4V with an equiaxed α microstructure was established via isothermal hot-compression
testing of cylindrical samples cut from an ultra-fine-grain-size (UFG) billet. Compression experiments were conducted at 900
and 955 °C, strain rates between 10−4 and 1 s−1, and imposed true strains between 0 and 1.4. Following deformation, quantitative metallography revealed marked coarsening
of the primary α particles at low strain rates (10−4 and 10−3 s−1). The dynamic-coarsening rate followed rn
vs time kinetics, in which n was between 2 and 3, or behavior between those of bulk-diffusion and interface-reaction controlled.
An examination of the temperature and strain-rate dependence of theoretical coarsening rates, however, strongly suggested
that bulk diffusion (with n=3) was more important. The dynamic-coarsening behavior was also interpreted in the context of the observed plastic-flow behavior.
At low strain rates, high values of the strain-rate sensitivity (m>0.5) and the overall shape of log stress-log strain rate plots indicated that the majority of the imposed strain was accommodated
by grain-boundary sliding (gbs) and only a small amount via dislocation glide/climb processes. In addition, an analysis of
the flow hardening that accompanied dynamic coarsening indicated that the flow stress varied approximately linearly with the
α particle size, thus providing support for models based on gbs accommodation by dislocation activity in grain-mantle regions. 相似文献
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During hot extrusion, the microstructure and resultant mechanical properties of materials are subjected to considerable change
due to adiabatic local heat generation. In this work, strain, temperature distributions, and microstructural changes resulting
from the hot extrusion of Ti-6A1-4V alloy were studied using visioplasticity methods, thermal calculations, and optical microscopy.
The results were correlated to the microstructural behavior during hot deformation. Billets 62 mm in diameter were heated
to either 950 °C(α + β region) or 1100 °C(β region) and extruded at the extrusion ratios of either 6 or 12. Visioplasticity calculations show that, in the deformation
zone, strain is relatively high at the surface of the billet and gradually decreases with depth. Estimated strains of a bar
extruded at 950 °C with the extrusion ratio of 12 are 3.5 at the surface and 2.5 at the center, respectively. But the estimated
temperature at the surface is lower than that at the center. As a result, microstructures of the bar were bi-modal structure
at the surface and acicular transformed structure at the center. A bar extruded at 950 °C with an extrusion ratio of 6 had
all bi-modal microstructure. The strain distributions of bar extruded at 1100 °C were similar in nature to those at 950 °C.
M. ISHII formerly with Hikari Research and Development Laboratory. 相似文献
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The plastic flow kinetics of hafnium single crystals and polycrystals of a range of oxygen contents were investigated over
the temperature range of 77 to 873 K employing the technique of incrementally changing the temperature and strain rate. It
was found that τ*0 ≈ 2.4 x 10−3 μ0√Ci, where τ*0 is the effective CRSS extrapolated to 0K, μ0 the modulus at OK, and Ci the total interstitial content (0.05 to 1.16 at. pct). Using the theory of thermally activated
deformation, it is concluded that overcoming local interstitial obstacles is rate controlling over the temperature range of
77 to 750 K and that the obstacles are characterized by a Gibbs activation free energy δG at 0K and zero effective stress
of ∼1.7 eV (0.14 μ0b3). Results for single crystals and polycrystals are in agreement using a Taylor factor of 3.5 for the ratio of tensile to
shear stress.
W. R. Tyson is on leave from the Physics Department of Trent University, Peterborough, Ontario, Canada. 相似文献
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The high-temperature deformation and failure behavior of an orthorhombic titanium aluminide sheet alloy (fabricated by diffusion
bonding of six thin foils) was established by conducting uniaxial tension and plane-strain compression tests at 980 °C and
strain rates between 10−4 and 10−2 s−1. The stress-strain response was characterized by a peak stress at low strains followed by moderate flow softening. Values
of the strain-rate sensitivity index (m) were between 0.10 and 0.32, and the plastic anisotropy parameter (R) was of the order of 0.6 to 1.0. Cavity nucleation and growth were observed during tensile deformation at strain rates of
10−3 s−1 and higher. However, the combined effects of lowm, low cavity growth rateη, and flow softening were deduced to be the source of failure controlled by necking and flow localization rather than cavitation-induced
fracture prior to necking. 相似文献