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1.
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
2.
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
3.
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
4.
Dong-Kuk Kim Sunghak Lee Ho Jin Ryu Soon Hyunghong Joon-Woong Noh 《Metallurgical and Materials Transactions A》2000,31(10):2475-2489
In this study, tungsten heavy alloy specimens were fabricated by mechanical alloying (MA), and their dynamic torsional properties
and penetration performance were investigated. Dynamic torsional tests were conducted on the specimens fabricated with different
sintering temperatures after MA, and then the test data were compared with those of a conventionally processed specimen. Refinement
of tungsten particles was obtained after MA, but contiguity was seriously increased, thereby leading to low ductility and
impact energy. Specimens in which both particle size and contiguity were simultaneously reduced by MA and two-step sintering
and those having higher matrix fraction by partial MA were successfully fabricated. The dynamic test results indicated that
the formation of adiabatic shear bands was expected because of the plastic localization at the central area of the gage section.
Upon highspeed impact testing of these specimens, self-sharpening was promoted by the adiabatic shear band formation, but
their penetration performance did not improve since much of kinetic energy of the penetrators was consumed for the microcrack
formation due to interfacial debonding and cleavage fracture of tungsten particles. In order to improve penetration performance
as well as to achieve selfsharpening by applying MA, conditions of MA and sintering process should be established so that
alloy densification, particle refinement, and contiguity reduction can be simultaneously achieved. 相似文献
5.
Dynamic deformation behavior of an oxide-dispersed tungsten heavy alloy fabricated by mechanical alloying 总被引:14,自引:0,他引:14
Sanghyun Park Dong-Kuk Kim Sunghak Lee Dong-Kuk Kim Ho Jin Ryu Soon Hyung Hong Ho Jin Ryu 《Metallurgical and Materials Transactions A》2001,32(8):2011-2020
The objective of this study is to investigate the dynamic deformation and fracture behavior of an oxide-dispersed (OD) tungsten
heavy alloy fabricated by mechanical alloying (MA). The tungsten alloy was processed by adding 0.1 wt pct Y2O3 powders during MA, in order to form fine oxides at triple junctions of tungsten particles or at tungsten/matrix interfaces.
Dynamic torsion tests were conducted for this alloy, and the test data were compared with those of a conventional liquid-phase
sintered (LPS) specimen. A refinement in tungsten particle size could be obtained after MA and multistep heat treatment without
an increase in the interfacial area fraction between tungsten particles. The dynamic test results indicated that interfacial
debonding between tungsten particles occurred over broad deformed areas in this alloy, suggesting the possibility of adiabatic
shear-band formation. Also, oxide dispersion was effective in promoting interfacial debonding, since the fine oxides acted
as initiation sites for interfacial debonding. These findings suggest that the idea of forming fine oxides would be useful
for improving self-sharpening and penetration performance in tungsten heavy alloys. 相似文献
6.
7.
The effects of martensite morphology and volume fraction on the quasi-static and dynamic deformation behavior of dual-phase
steels were investigated in this study. Quasi-static and dynamic torsional tests were conducted using a torsional Kolsky bar
for four steel specimens, which had different martensite morphology and volume fraction, and then the test data were compared
via microstructures, tensile properties, and fracture mode. In the intermediate quenched (IQ) steel specimens, very fine fibrous
martensites were well distributed in the ferrite matrix, but bulky martensites were mixed with ferrites in the step quenched
(SQ) specimens. Quasi-static torsional properties were similar to tensile properties, and fracture occurred in a ductile mode
in IQ specimens, whereas cleavage fracture was predominated in SQ specimens. Under a dynamic loading condition, the fracture
mode of SQ specimens was changed from cleavage to ductile fracture, whereas IQ specimens had a ductile fracture mode, irrespective
of loading rate. These phenomena were analyzed using a shear lag model, phase continuity, and the thermal softening effect
of martensite. 相似文献
8.
Yang Gon Kim Byoungchul Hwang Sunghak Lee Woo Gyeom Kim Dong Hyuk Shin 《Metallurgical and Materials Transactions A》2005,36(11):2947-2955
In the present study, ultrafine-grained microstructures of a conventional 5083 aluminum alloy were fabricated by equal-channel
angular pressing, and their dynamic deformation and fracture behavior were investigated. Dynamic torsional tests were conducted
on four aluminum alloy specimens using a torsional Kolsky bar, and then the test data were analyzed in relation to microstructures,
tensile properties, and adiabatic shear-banding behavior. The equal-channel angular-pressed (ECAP) specimens consisted of
ultrafine grains and contained a considerable amount of second-phase particles, which were refined and distributed homogeneously
in the matrix as the equal-channel angular pressing pass number increased. The dynamic torsional test results indicated that
the maximum shear stress increased, while the fracture shear strain remained constant, with increasing equal-channel angular
pressing pass number. Observation of the deformed area beneath the dynamically fractured surface showed that a number of voids
initiated mainly at second-phase particle/matrix interfaces and that the number of voids increased with increasing pass number.
Adiabatic shear bands of 200 to <300 μm in width were formed in the as-extruded and 1-pass ECAP specimens having coarser particles, whereas they were hardly formed
in the four-pass and eight-pass ECAP specimens having finer particles. The possibility of adiabatic shear-band formation was
explained by concepts of absorbed deformation energy and void initiation. 相似文献
9.
Dong-Geun Lee Sunghak Lee Chong Soo Lee Sunmoo Hur 《Metallurgical and Materials Transactions A》2003,34(11):2541-2548
The effects of microstructural factors on the quasi-static tensile and dynamic torsional deformation behaviors in Ti-6Al-4V alloys with Widmanstätten structures were investigated in this study. Dynamic torsional tests were conducted using a torsional Kolsky bar for five Widmanstätten structures, in which microstructural parameters such as colony size and α lamellar spacing were varied by heat treatments, and then the test data were analyzed in relation to microstructures, tensile properties, and fracture mode. Under dynamic torsional loading, maximum shear stress was largely dependent on colony size, whereas shear strain at the maximum shear stress point was on colony size as well as α lamellar spacing. Adiabatic shear bands were found in the deformed area of the fractured torsional specimens, and their width was smallest in the structure whose colony size and α lamellar spacing were both large. The possibility of the adiabatic shear band formation was quantitatively analyzed in relation to microstructural factors. It was the highest in the coarse Widmanstätten structure, which was confirmed by the theoretical critical shear strain (υ c ) condition for the adiabatic shear band formation. 相似文献
10.
Effects of tungsten fiber on failure mode of zr-based bulk metallic glassy composite 总被引:1,自引:0,他引:1
H. Zhang Z. F. Zhang Z. G. Wang H. F. Zhang Q. S. Zang K. Q. Qiu 《Metallurgical and Materials Transactions A》2006,37(8):2459-2469
The authors systematically investigated the effects of tungsten fiber on failure mode as well as deformation and fracture
mechanisms in tungsten fiber-reinforced Zr41.25Ti13.75Ni10Cu12.5Be22.5 bulk metallic glassy composite under uniaxial compression at room and high temperatures. At room temperature, the failure
mode of the composite changes from shear fracture to longitudinal splitting failure with increasing fiber volume fraction.
Similar to the observations in monolithic metallic glasses, the shear fracture angle of the composite is approximately equal
to 39∼40 deg, indicating that the Mohr-Coulomb criterion is suitable to give the critical shear fracture condition of the
composite. When the compression tests were performed below the glass transition temperature of Zr41.25Ti13.75Ni10Cu12.5Be22.5 metallic glassT
g, the deformation behavior of the composite strongly depends on the strain rates and the test temperature, which is quite
similar to the deformation behavior of monolithic metallic glasses in the supercooled liquid region. The corresponding failure
mode of the composite changes from shear or splitting fracture to bending failure with decreasing strain rate or increasing
test temperature. The failure modes at the temperature nearT
g are mainly controlled by the metallic glass matrix due to the decrease in its viscosity at high temperature. Based on these
multiple failure modes, the effects of test temperature and tungsten fiber volume fraction on deformation and fracture mechanisms
are summarized. 相似文献
11.
Dynamic deformation behavior of ultrafine-grained low-carbon steels fabricated by equal-channel angular pressing 总被引:1,自引:0,他引:1
Byoungchul Hwang Yang Gon Kim Han Sang Lee Sunghak Lee Byoung Doo Ahn Dong Hyuk Shin Chang Gil Lee 《Metallurgical and Materials Transactions A》2005,36(2):389-397
The dynamic deformation behavior of ultrafine-grained low-carbon steels fabricated by equal-channel angular pressing (ECAP)
was investigated in this study. Dynamic torsional tests, using a torsional Kolsky bar, were conducted on four steel specimens,
two of which were annealed at 480 °C after ECAP, and then the test data were compared in terms of microstructures, tensile
properties, and adiabatic shear-band formation. The equal-channel angular pressed specimen consisted of very fine, equiaxed
grains of 0.2 to 0.3 μm in size, which were slightly coarsened after annealing. The dynamic torsional test results indicated that maximum shear
stress decreased with increasing annealing time, whereas fracture shear strain increased. Some adiabatic shear bands were
observed at the gage center of the dynamically deformed torsional specimen. Their width was smaller in the equal-channel angular
pressed specimen than in the 1-hour-annealed specimen, but they were not found in the 24-hour-annealed specimen. Ultrafine,
equiaxed grains of 0.05 to 0.2 μm in size were formed inside the adiabatic shear band, and their boundaries had characteristics of high-angle grain boundaries.
These phenomena were explained by dynamic recrystallization due to a highly localized plastic strain and temperature rise
during dynamic deformation. 相似文献
12.
《粉末冶金学》2013,56(4):175-178
AbstractW–Ni–Fe heavy alloy tensile specimens were sintered at 1450°C for various times up to 44h. The W content varied between 90 and 96 wt-%, and the Ni to Fe weight ratio was 1:1. The specimens are fully densified after 15 min to 1 h of sintering and show high strength and ductility. During the tension test, cracks are formed at the interface between tungsten grains when the grain deformation reaches critical levels. The number of these intergranular cracks increases with deformation until the specimens fracture. When the specimens are over-sintered for 4 and 8 h, large irregular pores are formed with a sharp decrease of strength and ductility. Upon further sintering, the porosity decreases again with a recovery of the mechanical properties. The results demonstrate that small amounts of porosity, even 1 or 2%, can cause drastic reduction of the mechanical properties in tungsten heavy alloys. 相似文献
13.
Controlled processing of heavy alloys containing 88 to 97 pct W resulted in high sintered densities and excellent bonding
between the tungsten grains and matrix. For these alloys, deformation and fracture behavior were studiedvia slow strain rate tensile testing at room temperature. The flow stress increased and the fracture strain decreased with increasing
tungsten content. The tradeoff between strength and ductility resulted in a maximum in the ultimate tensile strength at 93
pct W. Microstructure variations, notably grain size, explain sintering temperature and time effects on the properties. During
tensile testing, cracks formed on the surface of the specimens at tungsten-tungsten grain boundaries. The crack density increased
with plastic strain and tungsten content. The surface cracks, though initially blunted by the matrix, eventually increased
in density until catastrophic failure occurred. An empirical failure criterion was developed relating fracture to a critical
value of the surface crack tip separation distance. Application of the model explains the effects of microstructural variables
on tensile properties.
Formerly Graduate Research Assistant at Rensselaer Polytechnic Institute. 相似文献
14.
V. N. Chuvil’deev A. V. Nokhrin G. V. Baranov M. S. Boldin A. V. Moskvicheva N. V. Sakharov D. N. Kotkov Yu. G. Lopatin V. Yu. Belov Yu. V. Blagoveshchenskii N. A. Kozlova D. A. Konychev N. V. Isaeva 《Russian Metallurgy (Metally)》2014,2014(3):215-228
The structure and mechanical properties of nano- and ultradispersed mechanically activated heavy W-Ni-Fe and W-Ni-Fe-Co tungsten alloys (VNZh and VNZhK alloys, respectively) are studied. Mechanically activated nano- and ultradispersed charge powders are sintered by free sintering (thermally activated) and spark plasma sintering. The dependence of the density of the alloys made of the mechanically activated powders on the sintering temperature is found to have a nonmonotonic character with a maximum corresponding to the optimum sintering temperature. It is shown that an increase in the mechanical activation time and the acceleration of the milling bodies during mechanical activation lead to a decrease in the alloy particle size and the formation of nonequilibrium solid solutions and are accompanied by a decrease in the optimum sintering temperature of heavy tungsten alloys. Ultrahigh-strength tungsten alloys the mechanical properties of which are substantially higher than those of standard coarse-grained analogs are fabricated due to the optimization of the conditions of ball milling and high-rate spark plasma sintering of W-Ni-Fe powders. 相似文献
15.
Chang Gil Lee Ki Jong Kim Sunghak Lee Kyungmox Cho 《Metallurgical and Materials Transactions A》1998,29(2):469-476
The objective of the present study is to investigate the effect of test temperature on the dynamic torsional deformation behavior
of two Al-Li alloys, i.e., 2090 and 8090 alloys. Dynamic torsional tests were conducted using a torsional Kolsky bar at room temperature and a low
temperature (−196 °C), and the torsionally deformed regions and the fracture surfaces of the tested specimens were examined.
The dynamic properties of the two Al-Li alloys at the low temperature were improved, owing to the modification of the deformation
behavior. The dynamic deformation behavior at room temperature was dominated by intergranular cracks due to planar slips and
by crack propagation along the grain boundaries. At the low temperature, plastic deformation proceeded more homogeneously
as planar slip was prevented. These results indicated that the overall deformation mode of both the Al-Li alloys changed from
planar slip to homogeneous deformation with decreasing temperature, resulting in the improvement of cryogenic properties under
dynamic torsional loading. 相似文献
16.
Jung G. Lee Dong-Geun Lee Sunghak Lee Nack J. Kim 《Metallurgical and Materials Transactions A》2004,35(12):3753-3761
In this study, Zr-Ti-Cu-Ni-Be bulk metallic glass (BMG) alloys containing a small amount of crystalline phase particles were
fabricated by strip casting, and their improvement of mechanical properties and fracture toughness was explained by direct
observation of the microfracture process. The compressive and fracture toughness test results indicated that strength, strain
to failure, and fracture toughness of the strip-cast BMG alloy containing coarse crystalline particles were higher than those
of the as-cast monolithic BMG alloy or the strip-cast BMG alloy containing fine crystalline particles. From in-situ microfracture observations, the improvement of overall mechanical properties of the strip-cast BMG alloy containing coarse
crystalline particles could be interpreted by taking consideration of both the existence of coarse crystalline particles and
the role of the particles to block crack propagation and to form multiple shear bands. Such property improvement suggests
new applicability of the strip-cast BMG alloys containing coarse crystalline particles, which can work as toughening and strengthening
reinforcements, to structures and components requiring excellent mechanical properties. 相似文献
17.
Han Sang Lee Byoungchul Hwang Sunghak Lee Chang Gil Lee Sung-Joon Kim 《Metallurgical and Materials Transactions A》2004,35(8):2371-2382
The effects of martensite morphology and tempering on the quasistatic and dynamic deformation behavior of dual-phase steels
were investigated in this study. Dynamic torsional tests were conducted on six steel specimens, which had different martensite
morphologies and tempering conditions, using a torsional Kolsky bar, and then the test data were compared via microstructures, tensile properties, and fracture mode. Bulky martensites were mixed with ferrites in the step-quenched (SQ)
specimens, but small martensites were well distributed in the ferrite matrix in the intermediate-annealed (IA) specimens.
Under a dynamic loading condition, the fracture mode of the SQ specimens was changed from cleavage to ductile fracture as
the tempering temperature increased, whereas the IA specimens showed a ductile fracture mode, irrespective of tempering. These
phenomena were analyzed in terms of a rule of mixtures applied to composites, microstructural variation, martensite softening
and carbon diffusion due to tempering, and adiabatic shear-band formation. 相似文献
18.
19.
Sug-Woo Jung Suk-Joong L. Kang Sunghak Lee Eun-Pyokim Joon-Woong Noh Woon-Hyung Baek 《Metallurgical and Materials Transactions A》2002,33(4):1213-1219
A carburization technique using a Cr powder layer has been developed to control the diffusion depth of carbon in W-Ni-Fe heavy
alloys. The aged heavy alloy samples were covered with a Cr powder layer of about 1-mm thickness and then packed with carbon
black powder. The packed samples were heat-treated at 1150 °C for 10 minutes in H2 and then for 50 minutes in N2. The carburization treatment resulted in the formation of Cr7C3 and Fe3W3C around the tungsten grains from the sample surface with a thickness of 40 to 50 μm. This carburized layer was much thinner than that formed without a Cr powder layer under the same experimental conditions.
With the surface carburization, the surface hardness increased by ∼75 pct, from 508 to 888 VHN, and the impact energy decreased
by ∼31 pct, from 123 to 85 J. After the carburization treatment, the main fracture behavior in a dynamic torsional test changed
from smearing of the matrix to cleavage of the tungsten grains. A high-speed impact test showed that the surface carburization
of penetrators induced the formation of many cracks around the penetrator surface, enhanced the self-sharpening, and improved
the penetration performance. It appears that the developed technique provides an easy method of carburization without serious
deterioration of the toughness of the material. 相似文献
20.
K. E. Knipling G. Zeman J. S. Marte S. M. Kelly S. L. Kampe 《Metallurgical and Materials Transactions A》2004,35(9):2821-2828
A series of Ni-Fe alloys containing various levels of tungsten in solid solution have been prepared as a means to assess the
influence of solid solution strengthening on the mechanical behavior of monolithic 70Ni-30Fe. In particular, 70Ni-30Fe alloys
plus equilibrium concentrations of tungsten in solid solution nominally correspond to the compositions associated with the
matrix-only portion of certain tungsten heavy alloys, that is, alloys comprised of a high volume fraction of nominally pure
tungsten particles embedded within a minority Ni-Fe-W based matrix. The study shows that the working solubility of tungsten
within the 70Ni-30Fe base composition increases slightly with temperature, from approximately 21 wt pct at room temperature
to approximately 23 wt pct at 1400 °C. Increasing the level of tungsten in solid solution leads to increases in room-temperature
yield strength, tensile strength, and ductility. In contrast, the deformation characteristics of the alloys, as quantified
by the power-law work-hardening exponent, n, and the strain-rate-sensitivity exponent, m, show little variation with tungsten solute concentration. 相似文献