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1.
Shogo Komura Zenji Horita Minoru Furukawa Minoru Nemoto Terence G. Langdon 《Metallurgical and Materials Transactions A》2001,32(13):707-716
An Al-3 pct Mg-0.2 pct Sc alloy was fabricated by casting and subjected to equal-channel angular pressing to reduce the grain
size to ∼0.2 μm. Very high tensile elongations were achieved in this alloy at temperatures over the range from 573 to 723
K, with elongations up to >2000 pct at temperatures of 673 and 723 K and strain rates at and above 10−2 s−1. By contrast, samples of the same alloy subjected to cold rolling (CR) yielded elongations to failure of <400 pct at 673
K. An analysis of the experimental data for the equal-channel angular (ECA)—pressed samples shows consistency with conventional
superplasticity including an activation energy for superplastic flow which is within the range anticipated for grain boundary
diffusion in pure Al and interdiffusion in Al−Mg solid solution alloys.
MINORU NEMOTO, formerly Professor, Department of Materials Science and Engineering, Faculty of Engineering, Kyushu University. 相似文献
2.
Patrick B. Berbon Terence G. Langdon Nikolai K. Tsenev Ruslan Z. Valiev Minoru Furukawa Zenji Horita Minoru Nemoto 《Metallurgical and Materials Transactions A》1998,29(9):2237-2243
Ultrafine grain sizes were introduced into samples of an Al-3 pct Mg solid solution alloy and a cast Al-Mg-Li-Zr alloy using
the process of equal-channel angular (ECA) pressing. The Al-3 pct Mg alloy exhibited a grain size of ∼0.23 μm after pressing
at room temperature to a strain of ∼4, but there was significant grain growth when the pressed material was heated to temperatures
above ∼450 K. The Al-Mg-Li-Zr alloy exhibited a grain size of ∼1.2 μm, and the microstructure was heterogeneous after pressing
to a strain of ∼4 at 673 K and homogeneous after pressing to a strain of ∼8 at 673 K with an additional strain of ∼4 at 473
K. The heterogeneous material exhibited superplastic-like flow, but the homogeneous material exhibited high-strain-rate superplasticity
with an elongation of >1000 pct at 623 K at a strain rate of 10−2 s−1. It is concluded that a homogeneous microstructure is required, and therefore a high pressing strain, in order to attain
high-strain-rate superplasticity (HSR SP) in ultrafine-grained materials.
This article is based on a presentation made in the symposium “Mechanical Behavior of Bulk Nanocrystalline Solids,” presented
at the 1997 Fall TMS Meeting and Materials Week, September 14–18, 1997, in Indianapolis, Indiana, under the auspices of the
Mechanical Metallurgy (SMD), Powder Materials (MDMD), and Chemistry and Physics of Materials (EMPMD/SMD) Committees. 相似文献
3.
Kiyoshi Matsubara Yuichi Miyahara Zenji Horita Terence G. Langdon 《Metallurgical and Materials Transactions A》2004,35(6):1735-1744
Experiments were conducted to evaluate the utility of a new processing procedure developed for Mg-based alloys in which samples
are subjected to a two-step processing route of extrusion followed by equal-channel angular pressing (designated as EX-ECAP).
The experiments were conducted using a Mg-0.6 wt pct Zr alloy and, for comparison purposes, samples of pure Mg. It is shown
that the potential for successfully using ECAP increases in both materials when adopting the EX-ECAP procedure. For the Mg-Zr
alloy, the use of EX-ECAP produces a grain size of ∼1.4 μm when the pressing is undertaken at 573 K. By contrast, using EX-ECAP with pure Mg at 573 K produces a grain size of ∼26
μm. Tensile testing of the Mg-Zr alloy at 523 and 573 K after processing by EX-ECAP revealed the occurrence of significantly
enhanced ductilities with maximum elongations of ∼300 to 400 pct. 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.
Dong Hyuk Shin Duck-Young Hwang Yong-Jun Oh Kyung-Tae Park 《Metallurgical and Materials Transactions A》2004,35(3):825-837
Tensile tests were carried out at temperatures of 673 to 773 K and strain rates of 1×10−3 to 1 s−1 on an ultrafine-grained (UFG) 5083 Al alloy containing 0.2 wt pct Sc fabricated by equal-channel angular pressing, in order
to examine its high-strain-rate superplastic characteristics. The mechanical data for the alloy at 723 and 773 K exhibited
a sigmoidal behavior in a double logarithmic plot of the maximum true stress vs true strain rate. The strain-rate sensitivity was 0.25 to 0.3 in the low-(
<5×10−3 s−1) and high- (
>5×10−2 s−1) strain-rate regions, and ∼0.5 in the intermediate-strain-rate region (5×10−3 s−1<
<5 × 10−2 s−1). The maximum elongation to failure of ∼740 pct was obtained at 1×10−2 s−1 and 773 K. By contrast, no sigmoidal behavior was observed at 673 K. Instead, the strain-rate sensitivity of 0.3 was measured
in both intermediate-and low-strain-rate regions, but it was about 0.25 in the high-strain-rate region. High-strain-rate superplasticity
(HSRS) in the intermediate-strain-rate region at 723 and 773 K was dominated by grain-boundary sliding (GBS) associated with
continuous recrystallization and preservation of fine recrystallized grains by second-phase particles. However, the activation
energy for HSRS of the present alloy was lower than that predicted for any standard high-temperature deformation mechanism.
The low activation energy was likely the result of the not-fully equilibrated microstructure due to the prior severe plastic
deformation (SPD). For 673 K, the mechanical data and the microstructural examination revealed that viscous glide was a dominant
deformation mechanism in the intermediate- and low-strain-rate regions. Deformation in the high-strain-rate region at all
testing temperatures was attributed to dislocation breakaway from solute atmospheres. 相似文献
6.
Superplastic behavior and microstructure evolution in a commercial Al-Mg-Sc alloy subjected to intense plastic straining 总被引:1,自引:0,他引:1
F. Musin R. Kaibyshev Y. Motohashi G. Itoh 《Metallurgical and Materials Transactions A》2004,35(8):2383-2392
A commercial Al-6 pct Mg-0.3 pct Sc-0.3 pct Mn alloy subjected to equal-channel angular extrusion (ECAE) at 325 °C to a total
strain of about 16 resulted in an average grain size of about 1 μm. Superplastic properties and microstructural evolution
of the alloy were studied in tension at strain rates ranging from 1.4 × 10−5 to 1.4 s−1 in the temperature interval 250 °C to 500 °C. It was shown that this alloy exhibited superior superplastic properties in
the wide temperature range 250 °C to 500 °C at strain rates higher than 10−2 s−1. The highest elongation to failure of 2000 pct was attained at a temperature of 450 °C and an initial strain rate of 5.6
× 10−2 s−1 with the corresponding strain rate sensitivity coefficient of 0.46. An increase in temperature from 250 °C to 500 °C resulted
in a shift of the optimal strain rate for superplasticity, at which highest ductility appeared, to higher strain rates. Superior
superplastic properties of the commercial Al-Mg-Sc alloy are attributed to high stability of ultrafine grain structure under
static annealing and superplastic deformation at T ≤ 450 °C. Two different fracture mechanisms were revealed. At temperatures higher than 300 °C or strain rates less than 10−1 s−1, failure took place in a brittle manner almost without necking, and cavitation played a major role in the failure. In contrast,
at low temperatures or high strain rates, fracture occurred in a ductile manner by localized necking. The results suggest
that the development of ultrafine-grained structure in the commercial Al-Mg-Sc alloy enables superplastic deformation at high
strain rates and low temperatures, making the process of superplastic forming commercially attractive for the fabrication
of high-volume components. 相似文献
7.
Equal-channel angular pressing of commercial aluminum alloys: Grain refinement, thermal stability and tensile properties 总被引:15,自引:0,他引:15
Zenji Horita Takayoshi Fujinami Minoru Nemoto Terence G. Langdon 《Metallurgical and Materials Transactions A》2000,31(3):691-701
Using equal-channel angular (ECA) pressing at room temperature, the grain sizes of six different commercial aluminum-based
alloys (1100, 2024, 3004, 5083, 6061, and 7075) were reduced to within the submicrometer range. These grains were reasonably
stable up to annealing temperatures of ∼200 °C and the submicrometer grains were retained in the 2024 and 7075 alloys to annealing
temperatures of 300 °C. Tensile testing after ECA pressing through a single pass, equivalent to the introduction of a strain
of ∼1, showed there is a significant increase in the values of the 0.2 pct proof stress and the ultimate tensile stress (UTS)
for each alloy with a corresponding reduction in the elongations to failure. It is demonstrated that the magnitudes of these
stresses scale with the square root of the Mg content in each alloy. Similar values for the proof stresses and the UTS were
attained at the same equivalent strains in samples subjected to cold rolling, but the elongations to failure were higher after
ECA pressing to equivalent strains >1 because of the introduction of a very small grain size. Detailed results for the 1100
and 3004 alloys show good agreement with the standard Hall-Petch relationship. 相似文献
8.
Influence of pressing speed on microstructural development in equal-channel angular pressing 总被引:8,自引:0,他引:8
Patrick B. Berbon Minoru Furukawa Zenji Horita Minoru Nemoto Terence G. Langdon 《Metallurgical and Materials Transactions A》1999,30(8):1989-1997
The influence of pressing speed in equal-channel angular (ECA) pressing was investigated using samples of pure Al and an Al-1
pct Mg alloy and a range of pressing speeds from ∼10−2 to ∼10 mm s−1. The results show that the speed of pressing has no significant influence on the equilibrium grain size, at least over the
range used in these experiments. Thus, the equilibrium grain sizes were ∼1.2 μm for pure Al and ∼0.5 μm for the Al-1 pct Mg alloy for all pressing conditions. However, it is shown that the nature of the microstructure is dependent
on the pressing speed, because recovery occurs more easily at the slower speeds, so that the microstructure is then more equilibrated.
There is also indirect evidence for the advent of frictional effects when the cross-sectional dimensions of the samples are
at or below ∼5 mm. 相似文献
9.
Kyung-Tae Park Duck-Young Hwang Si-Young Chang Dong Hyuk Shin 《Metallurgical and Materials Transactions A》2002,33(9):2859-2867
A submicrometer-grained structure was introduced in a commercial 5083 Al alloy by imposing an effective strain of ∼8 through
equal channel angular pressing. In order to examine the low-temperature superplastic behavior, the as-equal channel angular
pressed (as-ECAP) samples were tensile tested in the strain rate range of 10−5 to 10−2 s−1 at temperatures of 498 to 548 K corresponding to 0.58 to 0.65 T
m, where T
m is the incipient melting point. The mechanical data of the alloy at 498 and 548 K exhibited a sigmoidal behavior in a double
logarithmic plot of the maximum true stress vs true strain rate. The strain rate sensitivity was 0.1 to 0.2 in the low- and high-strain rate regions and 0.4 in the intermediate-strain
rate region, indicating the potential for superplasticity. At 523 K, instead of the sigmoidal behavior, a strain rate sensitivity
of 0.4 was maintained to low strain rates. A maximum elongation of 315 pct was obtained at 548 K and 5×10−4 s−1. The activation energy for deformation in the intermediate-strain rate region was estimated as 63 kJ/mol. Low-temperature
superplasticity of the ultrafine grained 5083 Al alloy was attributed to grain boundary sliding that is rate-controlled by
grain boundary diffusion, with a low activation energy associated with nonequilibrium grain boundaries. Cavity stringers parallel
to the tensile axis were developed during deformation, and the failure occurred in a quasi-brittle manner with moderately
diffusive necking. 相似文献
10.
The elevated temperature deformation characteristics of a rapidly solidified Al-8.4 wt pct Fe-3.6 wt pct Ce alloy have been
investigated. Constant true strain rate compression tests were performed between 523 and 823 K at strain rates ranging from
10−6 to 10−3 s−1. At temperatures below approximately 723 K, the alloy is significantly stronger than oxide dispersion strengthened (ODS)
aluminum. However, at higher temperatures, the strength of the Al-Fe-Ce alloy falls rapidly with increasing temperature while
ODS aluminum exhibits an apparent threshold stress. It is shown that particle coarsening cannot fully account for the reduction
in strength of the Al-Fe-Ce alloy at elevated temperatures. The true activation energy for deformation of the Al-Fe-Ce alloy
at temperatures between 723 and 773 K is significantly greater than that for self-diffusion in the matrix. This is unlike
the behavior of ODS alloys, which contain nondeformable particles and exhibit true activation energies close to that for self-diffusion
in the matrix. Since abnormally high true activation energies for deformation are also exhibited by materials containing deformable
particles, such as γ′ strengthened superalloys, it is concluded that elevated temperature deformation in ythe Al-Fe-Ce alloy involves deformation
of both the matrix and the precipitates. The loss of strength of the Al-Fe-Ce alloy appears to be related to a reduction in
strength of at least some of the second phase particles at temperatures above 723 K.
Formerly Research Assistant, Department of Materials Science and Engineering, Stanford University. 相似文献
11.
Yuichi Miyahara Kiyoshi Matsubara Zenji Horita Terence G. Langdon 《Metallurgical and Materials Transactions A》2005,36(7):1705-1711
The extrusion/equal channel angular pressing (EX-ECAP) processing procedure, in which magnesium-based alloys are subjected
to extrusion followed by ECAP, was applied to a Mg-7.5 pct Al-0.2 pct Zr alloy prepared by casting. Microstructural inspection
showed the EX-ECAP process was effective in reducing the grain size from ∼21 μm after extrusion to an as-pressed grain size of ∼0.8 μm. It is shown through static annealing that these ultrafine grains are reasonably stable up to 473 K, but grain growth occurs
at higher temperatures. Tensile specimens were cut from the billets prepared by EX-ECAP and testing showed these specimens
exhibited superplasticity at relatively low temperatures with maximum elongations up to >700 pct. By processing through EX-ECAP
to a higher imposed strain and thereby increasing the area fraction of high-angle boundaries, it is demonstrated that there
is a potential for achieving high-strain-rate superplasticity.
This article is based on a presentation made at the Symposium entitled “Phase Transformations and Deformation in Magnesium
Alloys,” which occurred during the Spring TMS meeting, March 14–18, 2004, in Charlotte, NC, under the auspices of the ASM-MSCTS
Phase Transformations Committee. 相似文献
12.
H. N. Azari G. S. Murty G. S. Upadhyaya 《Metallurgical and Materials Transactions A》1994,25(10):2153-2160
The superplastic behavior of thermomechanically treated P/M 7091 aluminum alloy was assessed in the temperature range of 573
to 773 K. The thermomechanical treatment (TMT) comprised of three steps of solution treatment, overaging, and warm rolling.
There are large η-phase (MgZn2) precipitate particles of average size of 1.30 μm in the overaged condition. The warm-rolled alloy undergoes continuous recrystallization
at the test temperatures of 573 and 623 K, exhibiting a maximum tensile elongation of 450 pct at 573 K and a strain rate of
8 × 10−5 s−1. The precipitate particles play a major role in the process of continuous recrystallization. For a given volume fraction
of precipitate particles and constant amount of warm rolling (in the course of TMT), an optimum precipitate particle size
is expected to maximize the rate of continuous recrystallization and render the finest recrystallized grain size. The warm-rolled
alloy undergoes static recrystallization at temperatures above 673 K. The grain growth accompanying the deformation at these
test temperatures limits the tensile ductility to a lower value. Irrespective of the test temperature and strain rate, the
specimens undergo extensive cavitation when deformed at elevated temperatures. 相似文献
13.
Characterization of superplastic deformation behavior of a fine grain 5083 Al alloy sheet 总被引:3,自引:0,他引:3
R. Verma P. A. Friedman A. K. Ghosh S. Kim C. Kim 《Metallurgical and Materials Transactions A》1996,27(7):1889-1898
Superplastic deformation behavior of a fine grain 5083 Al sheet (Al-4.2 pct Mg-0.7 pct Mn, trade name FORMALL 545) has been
investigated under uniaxial tension over the temperature range of 500 °C to 565 °C. Strain rate sensitivity values >0.3 were
observed over a strain rate range of 3 × 10−5 s−1 to 1 × 10−2 s−1, with a maximum value of 0.65 at 5 × 10−4 s−1 and 565 °C. Tensile elongations at constant strain rate exceeded 400 pct; elongations in the range of 500 to 600 pct were
obtained under constant crosshead speed and variable strain rates. A short but rapid prestraining step, prior to a slower
superplastic strain rate, provided enhanced tensile elongation at all temperatures. Under the two-step schedule, a maximum
tensile elongation of 600 pct was obtained at 550 °C, which was regarded as the optimum superplastic temperature under this
condition. Dynamic and static grain growth were examined as functions of time and strain rate. It was observed that the dynamic
grain growth rate was appreciably higher than the static growth rate and that the dynamic growth rate based on time was more
rapid at the higher strain rate. Cavitation occurred during superplastic flow in this alloy and was a strong function of strain
rate and temperature. The degree of cavitation was minimized by superimposition of a 5.5 MPa hydrostatic pressure during deformation,
which produced a tensile elongation of 671 pct at 525 °C.
R. VERMA, formerly Visiting Scientist, Department of Materials Science and Engineering, University of Michigan 相似文献
14.
T. R. McNelley E. W. Lee M. E. Mills 《Metallurgical and Materials Transactions A》1986,17(6):1035-1041
Superplastic elongations in excess of 400 pct have been observed in tension testing at 573 K (300 °C) and strain rate έ= 2 × 10-3 s-1 for a thermomechanically processed Al-10.2 pct Mg-0.52 pct Mn alloy. The thermomechanical processing consists of solution
treatment and hot working, followed by extensive warm rolling at 573 K (300 °C), a temperature below the solvus for Mg in
the alloy. This processing results in a fine subgrain structure in conjunction with refined and homogeneously distributed
β(Al8Mg5) and MnAl6 precipitates. This structure does not statically recrystallize when annealed at 573 K (300 °C) but appears to recrystallize
continuously during deformation at such a temperature and the resulting fine grain structure deforms with minimal cavitation.
At temperatures above the Mg-solvus,e.g., 673 K (400 °C), recrystallization and growth occur readily resulting in rela tively coarser structures which deform superplastically
but with extensive grain boundary sliding and cavitation.
Formerly in Materials Group, Mechanical Engineering, Naval Postgraduate School
Formerly Graduate Student in Mechanical Engineering, Naval Postgraduate School 相似文献
15.
Roberto B. Figueiredo Terence G. Langdon 《Metallurgical and Materials Transactions A》2014,45(8):3197-3204
Experiments show that the magnesium AZ31 (Mg-3 pct Al-1 pct Zn) alloy exhibits excellent superplastic properties at 623 K (350 °C) after processing by equal-channel angular pressing using a die with a channel angle of 135 deg and a range of decreasing processing temperatures from 473 K to 413 K (200 °C to 140 °C). A maximum elongation to failure of ~1200 pct was achieved in this alloy at a tensile strain rate of 1.0 × 10?4 s?1. Microstructural inspection showed evidence for cavity formation and grain growth during tensile testing with the grain growth leading to significant strain hardening. An examination of the experimental data shows that grain boundary sliding is dominant during superplastic flow. Furthermore, a comprehensive review of the present results and extensive published data for the AZ31 alloy shows the exponent of the inverse grain size is given by p ≈ 2 which is consistent with grain boundary sliding as the rate-controlling flow mechanism. 相似文献
16.
Transition of dominant diffusion process during superplastic deformation in AZ61 magnesium alloys 总被引:2,自引:0,他引:2
The superplastic behavior of the AZ61 magnesium alloy sheet, processed by one-step hot extrusion and possessing medium grain
sizes of ∼12 μm, has been investigated over the temperature range of 523 to 673 K. The highest superplastic elongation of
920 pct was obtained at 623 K and a deformation rate of 1×10−4 s−1. In the lower and higher strain rate regimes, with apparent m values of ∼0.45 and ∼0.25, respectively, grain-boundary sliding (GBS) and dislocation creep appeared to dominate the deformation,
consistent with the scanning electron microscopy (SEM) examination. The SEM examination also revealed that individual GBS
started to operate from the very initial deformation stage in the strain rate range with m∼0.45, which was attributed to the relatively high fraction (88 pct) of high-angle boundaries. The analyses of the superplastic
data over 523 to 673 K and 5×10−5 to 1×10−3 s−1 revealed a true stress exponent of ∼2, and the activation energy was close to that for grain-boundary and lattice diffusion
of magnesium at 523 to 573 K and 573 to 673 K, respectively. The transition temperature of activation energy is ∼573 K, which
is attributed to the change in the dominant diffusion process from grain-boundary diffusion to lattice diffusion. It is demonstrated
that the effective diffusion coefficient is a valid parameter to characterize the superplastic behavior and the dominant diffusion
process. 相似文献
17.
R. G. Davies 《Metallurgical and Materials Transactions A》1979,10(1):113-118
A study has been made of the influence of up to 2 pct Si and 0.42 pct P upon the strength and ductility of ferrites over a
wide grain size range; the grain size was varied fromd
−1/2 mm−1/2 = 4 to 14. Although the ductility decreased with increasing strength for all the alloys, the 2 pct Si alloy had the best
combination of strength and ductility. The ferrites containing 2 pct Si and 0.2 pct P had greater uniform elongations than
conventional HSLA steels at the same tensile strength; it is thought that the ductility of the ferrites is enhanced by the
presence of Si while the ductility of conventional HSLA steels is reduced by the presence of carbide precipitates. With the
theory for a composite of two ductile phases and the results for the fine-grained alloyed ferrites, the change in uniform
elongation as a function of tensile strength was predicted for dual-phase (martensite plus ferrite) steels. Good agreement
was found between the prediction and experimental results for dual-phase steels containing up to 0.2 pct P or 2 pct Si; the
2 pct Si alloy had the best combination of strength and ductility of all dual-phase steels so far reported. This study again
emphasizes the importance of the high strength, high ductility ferrite in controlling the properties of dual-phase steels. 相似文献
18.
The deformation behavior of an extruded Ni-30 (at. pct) Al−20Fe−0.05Zr intermetallic alloy was studied in the temperature
range of 300 to 1300 K under initial tensile strain rates varying between about 10−6 and 2×10−3 s−1 and in constant load compression creep between 1073 and 1300 K. The deformation microstructures of the fractured specimens
were characterized by transmission electron microscopy (TEM). Three deformation regimes were observed: Region I consisted
of an athermal regime of low tensile ductility (less than 0.3 pct) occurring between 400 and 673 K, where the substructure
consisted of slip bands in a few grains. Exponential creep was dominant in region II between 673 and 1073 K, where the substructure
changed from a mixture of dislocation tangles, loops, and dipoles at 673 K to a microstructure consisting of subgrains and
dislocation tangles at 973 K. The tensile ductility was generally about 2.0 to 2.5 pct below 980 K in this region. A significant
improvement in tensile ductility was observed in region III, which occurred between 1073 and 1300 K. An analysis of the data
suggests that viscous glide creep with a stress exponent,n, of about 3 and high-temperature dislocation climb withn≈4.5 where the two dominant creep mechanisms in this region depending on stress and temperature. The average activation energy
for deformation in this region was about 310±30 kJ mol−1 for both processes. In this case, a transition from viscous glide creep to dislocation climb occurred when σ/E<1.7×10−4, where σ is the applied stress andE is the Young’s modulus. 相似文献
19.
An AA6082 alloy was subjected to eight passes of equal channel angular pressing at 100 °C, resulting in an ultrafine grain
size of 0.2 to 0.4 μm. The tensile deformation behavior of the material was studied over the temperature range of 100 °C to 350 °C and strain
rate range of 10−4 to 10−1 s−1. The evolution of microstructure under tensile deformation was investigated by analyzing both the deformation relief on the
specimen surface and the dislocation structure. While extensive microshear banding was found at the lower temperatures of
100 °C to 150 °C, deformation at higher temperatures was characterized by cooperative grain boundary sliding and the development
of a bimodal microstructure. Dislocation glide was identified as the main deformation mechanism within coarse grains, whereas
no dislocation activity was apparent in the ultrafine grains. 相似文献
20.
Minoru Furukawa Patrick B. Berbon Terence G. Langdon Zenji Horita Minoru Nemoto Nikolai K. Tsenev Ruslan Z. Valiev 《Metallurgical and Materials Transactions A》1998,29(1):169-177
Experiments were conducted to determine the age-hardening characteristics and the mechanical properties of an Al-5.5 pct Mg-2.2
pct Li-0.12 pct Zr alloy processed by equal-channel angular (ECA) pressing to give a very fine grain size of ∼1.2 μm. The results show that peak aging occurs more rapidly when the grain size is very fine, and this effect is interpreted in
terms of the higher volume of precipitate-free zones in the fine-grained material. Mechanical testing demonstrates that the
ECA-pressed material exhibits high strength and good ductility at room temperature compared to conventional Al alloys containing
Li. Elongations of up to ∼550 pct may be achieved at an elevated temperature of 603 K in the ECA-pressed condition, thereby
confirming that, in this condition, the alloy may be a suitable candidate material for use in superplastic forming operations. 相似文献