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1.
The present study is concerned with a correlation between dynamic deformation properties obtained from the dynamic Kolsky
bar test with the adiabatic shear banding behavior developed in Al-Li alloys upon ballistic impact, and then with the ballistic
performance. The selected materials were a 2090 Al-Li alloy, a WELDALITE 049 alloy, and a 7039 Al alloy, to allow a comparative
study of different strengths and microstructures. After the ballistic impact testing, the amount and the distribution of adiabatic
shear bands were examined using optical and scanning electron microscopes. In the front side of the impacted area, many thin
delaminated sheets and a large amount of fragmentation were observed in the 2090 alloy and the WELDALITE alloy, respectively.
Near the impacted region, a large amount of plastic flow also existed, and adiabatic shear bands were hardly observed in the
2090 and the WELDALITE alloys, whereas they easily formed in the 7039 alloy. Since adiabatic shear bands usually deteriorate
the impact resistance of target materials, the ballistic performance of each alloy was discussed by comparing the adiabatic
shear banding behavior with microstructure, strength level, and dynamic torsional properties. 相似文献
2.
《Acta Metallurgica Materialia》1990,38(11):2309-2326
Cryogenic strength-toughness relationships for advanced aluminum-lithium alloys 2090, 8090, 8091 and 2091 are examined as a function of microstructure, plate orientation and wrought-product form (plate vs sheet), with specific emphasis on the underlying micro-mechanisms associated with crack advance. It is found that, with decrease in temperature from 298 K to 77 and 4 K, strength, tensile elongation and strain-hardening exponent are increased for all alloy chemistries, microstructures and product forms; however, the longitudinal (L-T, T-L) fracture toughness may increase or decrease depending upon the prevailing microscopic mechanism (microvoid coalescence vs transgranular shear) and macroscopic mode (plane strain vs plane stress) of fracture. In general, alloy microstructures that exhibit changes in either the fracture mechanism or mode at low temperatures show a decrease in L-T toughness. Conversely, when the fracture mechanism is unchanged between ambient and 4 K, observed variations in toughness with temperature are a strong function of the degree of local stress-triaxiality that develops at the crack tip. In very thin sheets, where the fracture mode remains one of plane stress (“slant” fracture), the elevation in toughness at low temperatures is associated with the concurrent increase in tensile strength and ductility; conversely, in thick plate, the increased occurrence of through-thickness delaminations (due to the weak short-transverse properties) at low temperatures locally promotes plane-stress conditions, thereby enhancing toughness by relaxing triaxial constraint. In sheets of intermediate thickness, however, the absence of such through-thickness delaminations permits the expected transition from plane-stress to plane-strain conditions, with the result that the toughness now decreases with reduction in temperature. 相似文献
3.
J. Glazer S. L. Verzasconi R. R. Sawtell J. W. Morris 《Metallurgical and Materials Transactions A》1987,18(10):1695-1701
The cryogenic mechanical properties of aluminum-lithium alloys are of interest because these alloys are attractive candidate
materials for cryogenic tankage. Previous work indicates that the strength-toughness relationship for alloy 2090-T81 (Al-2.7Cu-2.2Li-0.12Zr
by weight) improves significantly as temperature decreases. The subject of this investigation is the mechanism of this improvement.
Deformation behavior was studied since the fracture morphology did not change with temperature. Tensile failures in 2090-T81
and -T4 occur at plastic instability. In contrast, in the binary aluminum-lithium alloy studied here they occur well before
plastic instability. For all three materials, the strain hardening rate in the longitudinal direction increases as temperature
decreases. This increase is associated with an improvement in tensile elongation at low temperatures. In alloy 2090-T4, these
results correlate with a decrease in planar slip at low temperatures. The improved toughness at low temperatures is believed
to be due to increased stable deformation prior to fracture. 相似文献
4.
Effect of tungsten particle shape on dynamic deformation and fracture behavior of tungsten heavy alloys 总被引:1,自引:0,他引:1
Dong-Kuk Kim Sunghak Lee Heungsub Song 《Metallurgical and Materials Transactions A》1998,29(3):1057-1069
The effect of the tungsten particle shape on the dynamic deformation and fracture behavior of tungsten heavy alloys was investigated.
Dynamic torsional tests were conducted using a torsional Kolsky bar for five alloys, one of which was fabricated by the double-cycled
sintering process, and then the test data were compared via microstructures, mechanical properties, adiabatic shear banding, and fracture mode. The dynamic torsional test results indicated
that in the double-sintered tungsten alloy whose tungsten particles were very coarse and irregularly shaped, cleavage fracture
occurred in the central area of the gage section with little shear deformation, whereas shear deformation was concentrated
in the central area of the gage section in the other alloys. The deformation and fracture behavior of the double-sintered
alloy correlated well with the observation of the impacted penetrator specimen and the in situ fracture test results, i.e., microcrack initiation at coarse tungsten particles and cleavage crack propagation through tungsten particles. These findings
suggested that the cleavage fracture mode would be beneficial for the self-sharpening effect, and, thus, the improvement of
the penetration performance of the double-sintered tungsten heavy alloy would be expected. 相似文献
5.
Dong-Kuk Kim Sunghak Lee Heung-Sub Song 《Metallurgical and Materials Transactions A》1998,29(13):1057-1069
The effect of the tungsten particle shape on the dynamic deformation and fracture behavior of tungsten heavy alloys was investigated.
Dynamic torsional tests were conducted using a torsional Kolsky bar for five alloys, one of which was fabricated by the double-cycled
sintering process, and then the test data were compared via microstructures, mechanical properties, adiabatic shear banding, and fracture mode. The dynamic torsional test results indicated
that in the double-sintered tungsten alloy whose tungsten particles were very coarse and irregularly shaped, cleavage fracture
occurred in the central area of the gage section with little shear deformation, whereas shear deformation was concentrated
in the central area of the gage section in the other alloys. The deformation and fracture behavior of the double-sintered
alloy correlated well with the observation of the impacted penetrator specimen and the in situ fracture test results, i.e., microcrack initiation at coarse tungsten particles and cleavage crack propagation through tungsten particles. These findings
suggested that the cleavage fracture mode would be beneficial for the self-sharpening effect, and, thus, the improvement of
the penetration performance of the double-sintered tungsten heavy alloy would be expected. 相似文献
6.
J. W. Kirby D. J. Borich D. E. Mikkola 《Metallurgical and Materials Transactions B》1973,4(4):1129-1132
The disappearance of stacking faults in filings of α-Cu-Ge alloys (5.6, 6.7, 7.7, and 8.5 at. pct Ge) prepared at various
deformation temperatures has been studied with X-ray diffraction. The faults anneal out in two stages, the second of which
is diffusion controlled. The time necessary to anneal out all of the faults depends on both alloy composition and deformation
temperature. The dependence of the number of faults on the deformation temperature has also been determined. 相似文献
7.
采用等温压缩试验,在变形温度为600~1050 ℃、应变速率为0.002~0.2 s-1的条件下,研究了粉末冶金Ti-47.5Al-2.5V-1.0Cr合金的高温压缩性能与高温变形行为.结果表明:合金在高温压缩变形时,屈服强度随变形温度的升高、应变速率的降低而降低,塑性趋于升高.合金在高温塑性变形时,峰值流变应力、应变速率和变形温度之间较好地满足双曲正弦函数形式修正的Arrhenius关系,说明其变形受热激活控制.在800~1050℃/0.002~0.2 s-1范围内,合金应变敏感系数m为0.152,高温变形激活能Q为376kJ·mol-1. 相似文献
8.
变形温度对ULCB钢动态再结晶的影响 总被引:1,自引:0,他引:1
取得800 MPa级和900 MPa级ULCB钢,在1100~850℃进行单道次变形的热模拟试验,变形量为40%,应变速率为2 s-1。将应力-应变变化特征和显微组织观察相结合,分析研究变形温度对ULCB钢奥氏体动态再结晶的影响规律。结果表明,温度低于950℃时以形变硬化和动态回复为主,奥氏体形变再结晶主要发生在1000℃以上的高温变形中;奥氏体再结晶百分数随变形温度升高而增加,在1050℃变形后奥氏体再结晶百分数约40%,在1100℃变形后则发生完全再结晶。 相似文献
9.
The deformation behavior of a rapidly solidified Al-8.9Fe-6.9Ce (wt pct) alloy was studied in the temperature range of 250
°C to 350 °C and stress range of 20 to 175 MPa. The stress exponents and activation energies suggest that the alloy exhibits
a pronounced diffusional creep regime with a transition to power law creep behavior at stresses beyond 60 MPa. Comparing these
data with those obtained earlier for an Al-8.8Fe-3.7Ce alloy, it was found that in the diffusional creep regime, the Ce content
had no effect on the creep rate. However, in the power law creep regime, a strong dependence on the precipitate spacing, as
predicted by the structureinvariant creep law,[5] was observed. The higher volume fraction of precipitates in the Al-8.9Fe6.9Ce alloy causes a decrease in the power law creep
rates by a factor of 5.
Formerly Graduate Student.
Formerly Assistant Professor, University of Illinois at Urbana-Champaign. 相似文献
10.
A study of high temperature plastic deformation has been undertaken on alloys of V-18 at. pct Ga and V-23 at. pct Ga. The
materials were prepared by arc melting, homogenizing, and transformation annealing, resulting in polycrystalline A15 structure.
Through compression testing and load-relaxation testing, plastic deformation has been studied over a strain rate range from
10-6 to 10-2/s and a temperature range from 1000 to 1300 °C. Flow stress decreases with increased temperature and decreased strain rate.
Stress-strain rate relations may be fitted with a power law creep expression. The flow stress is influenced by the length
of the 1150 °C transformation anneal; longer anneals result in a decrease in flow stresses projected from load relaxation
testing. Analysis of compressive yield strength data places the activation energy for A15 V-Ga creep roughly in the 400 kJ/mol
range. 相似文献
11.
Effect of size and shape of tungsten particles on dynamic torsional properties in tungsten heavy alloys 总被引:3,自引:0,他引:3
Dong-Kuk Kim Sunghak Lee Heung-Sub Song 《Metallurgical and Materials Transactions A》1999,30(5):1261-1273
The effect of the size and shape of tungsten particles on dynamic torsional properties in tungsten heavy alloys was investigated.
Dynamic torsional tests were conducted on seven tungsten alloy specimens, four of which were fabricated by repeated sintering,
using a torsional Kolsky bar, and then the test results were compared via microstructure, mechanical properties, adiabatic shear banding, and deformation and fracture mode. The size of tungsten particles
and their hardness were increased as sintering temperature and time were increased, thereby deteriorating fracture toughness.
The dynamic torsional test results indicated that in the specimens whose tungsten particles were coarse and irregularly shaped,
cleavage fracture occurred predominantly with little shear deformation, whereas shear deformation was concentrated into the
center of the gage section in the conventionally fabricated specimens. The deformation and fracture behavior of the specimens
having coarse tungsten particles correlated well with the observation of the in situ fracture test results, i.e., cleavage crack initiation and propagation. These findings suggested that there would be an appropriate tungsten particle
size because the cleavage fracture mode would be beneficial for the “self-sharpening” of the tungsten heavy alloys. 相似文献
12.
Effect of phase composition and hydrogen level on the deformation behavior of titanium-hydrogen alloys 总被引:4,自引:0,他引:4
Compression tests were carried out on a series of titanium-hydrogen alloys (containing up to 31 at. pct H) over the temperature
range 500 °C to 1000 °C within the α, α + β, and β phase fields. The effect of hydrogen content was studied on the flow stress,
rate of work hardening, and mechanical anisotropy. Hydrogen in solid solution produces significant softening of the α phase
and (α + β) phase mixture, while it induces hardening of the β phase. The occurrence of strain softening was detected in the
(α + β) phase field as well, the extent of which depends on temperature, strain rate, and hydrogen concentration. The work
required to deform the Ti-H alloys is sensitive to the hydrogen concentration and has the lowest value at interstitial levels
that correspond to the (α + β)/β phase boundary at the temperature of interest. 相似文献
13.
Effect of surface carburization on dynamic deformation and fracture of tungsten heavy alloys 总被引:1,自引:0,他引:1
Sug-Woo Jung Suk-Joong L. Kang Dong-Kuk Kim Sunghak Lee Joon-Woong Noh 《Metallurgical and Materials Transactions A》1999,30(8):2027-2035
Effects of surface carburization on dynamic deformation and fracture behavior of tungsten heavy alloys were investigated in
order to improve the penetration performance. Dynamic torsional tests using a torsional Kolsky bar were conducted on four
specimens, three of which were carburized by the case carburization process. The test data were then compared with hardness,
Charpy impact energy, adiabatic shear banding, deformation and fracture mode, and penetration performance. With increasing
carburization temperature and time, surface hardness increased, but impact energy decreased. The dynamic torsional test results
indicated that for the carburized tungsten specimens, cleavage fracture occurred in the center of the gage section with little
shear deformation, whereas shear deformation was concentrated at the center of the gage section for the conventionally processed
specimen without carburization. The deformation and fracture behavior of the carburized specimens correlated well with the
observation of the impacted penetrator specimens, i.e., microcrack initiation at tungsten particles and cleavage crack propagation. Since the cleavage fracture mode is thought
to be beneficial for self-sharpening, these findings suggest the beneficial effect of the surface carburization on the penetration
performance. 相似文献
14.
15.
《Acta Metallurgica Materialia》1992,40(11):3075-3083
16.
17.
J. M. Papazian R. L. Schulte P. N. Adler 《Metallurgical and Materials Transactions A》1986,17(4):635-643
The loss of lithium from the near surface region during heat treatment of two commercial aluminum-lithium alloys was studied
using a nuclear reaction analysis technique. A finely collimated 2.5 MeV beam of3He ions was used to stimulate the7Li(3He,p)9Be reaction in samples of BAACo 8090 and 8091 alloys heat treated for 1, 4, and 16 hours at 500 °C. The emitted protons were
detected as a cross section of the sample was traversed through the beam, thereby determining the lithium content as a function
of distance from the external surface. Suitable calibration and control samples were used to validate the technique. The lithium
concentration data were fit with assumed concentration profiles calculated from diffusion equations and modified for the particular
experimental configuration employed. Extensive lithium depletion was found in both alloys, and the concentration profiles
were found to be accurately predicted by the diffusion calculations. For heat treatment in either wet or dry air, the depth
of lithium loss was the same, and can be approximately given as x = 1.5 √Dt. When heat treated in an argon atmosphere, the
depth of lithium loss was reduced. The lithium loss appeared to be limited by the diffusive flux of lithium to the surface
of the sample in wet and dry air, but was limited by other factors in argon. Porosity was observed in the lithium depleted
region; this was ascribed to the accumulation of vacancies generated by the unequal fluxes of aluminum and lithium atoms. 相似文献
18.
The flow properties of β-phase Zr-Mo alloys were investigated by means of compression testing in a nominally pure (10 ppm
O2) argon atmosphere. Experiments were carried out in the strain rate range 10-1 to 10-5 s-1 and from 900 to 1000°C. The stress-strain curves were unusual in that they exhibited a continuous decrease in flow stress
with strain, after little or no work hardening. A further unusual feature of the data was that the flow stress in interrupted
tests increased with delay time in all the alloys. By contrast, crystal bar Zr, tested under the same atmosphere, exhibited
neither flow softening nor significant interruption hardening, but deformed in a conventional manner. The results obtained
from X-ray investigations, as well as from interrupted tests and from tests carried out in a more purified atmosphere, indicated
that the occurrence of both interruption hardening and flow softening was associated with the formation of an oxygen stabilized
a-layer on the outer surface of the β-sample. Growth of the hard α-layer during annealing produces strengthening while its
decrease in volume during deformation produces softening. A model, based on the assumption that the hard α-phase shares the
load applied to the sample, was developed, and its predictions agree satisfactorily with the experimental observations. The
extreme sensitivity of Zr-Mo alloys to trace amounts of oxygen is attributed to the presence of liquid molybdenum oxides in
the surface scale, which leads to rapid oxygen transport. The stress sensitivity of the strain rate in these alloys decreases
from 4.0 to 3.4 as the molybdenum concentration is increased from 0 to 6 pct, for both the yield and the steady-state regimes
of flow. The alloy flow stress increases with molybdenum concentration approximately as C0.4, and it is apparent that the molybdenum atoms do not act as individual obstacles to flow, but are likely to lead to strengthening
by indirect means. 相似文献
19.
Effect of prestrain and deformation temperature on the recrystallization behavior of steels microalloyed with niobium 总被引:1,自引:0,他引:1
The evolution of microstructure during the hot working of steels microalloyed with Nb is governed by the recrystallization
kinetics of austenite and the recrystallization-precipitation interaction. The present study focuses on the effects of prestrain
and deformation temperature on the rectrystallization behavior in these steels. The extent of recrystallization is characterized
by a softening parameter calculated from a series of interrupted plane strain compression tests carried out at different deformation
temperatures and strain levels. The results indicate that at low temperatures, softening is caused by static recovery, while
at higher temperatures, static recrystallization is the predominant mechanism. The recrystallization-stop temperature (T
5pct) and the recrystallization-limit temperature (T
95pct), marking the beginning and end of recrystallization, respectively, are determined as a function of strain. In order to achieve
a homogeneous microstructure, finish rolling should be carried out outside the window of partial recrystallization (T
5pct<T<T
95pct), as determined in this study. The Nb(CN) precipitation kinetics have been calculated using a model proposed in an earlier
work, and these results are used to estimate the precipitate pinning force under the given processing conditions. Based on
these estimations, a criterion has been proposed to predict the onset of recrystallization. The predicted results are found
to be in reasonably good agreement with the experimental measurements. 相似文献