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1.
Effects of microstructural morphology on quasi-static and dynamic deformation behavior of Ti-6Al-4V alloy 总被引:2,自引:0,他引:2
Dong-Geon Lee Sangho Kim Sunghak Lee Chong Soo Lee 《Metallurgical and Materials Transactions A》2001,32(2):315-324
The effects of microstructural morphology on quasi-static and dynamic deformation behavior of a Ti-6Al-4V alloy were investigated in this study. Quasi-static and dynamic torsional tests were conducted using a torsional Kolsky bar for Widmanstätten, equiaxed, and bimodal microstructures, which were processed by different heat treatments, and then, the test data were analyzed in relation to microstructures, tensile properties, and fracture mode. Quasi-static torsional properties showed a tendency similar to tensile properties and ductile fracture occurred in all three microstructures. Under dynamic torsional loading, maximum shear stress of the three microstructures was higher and fracture shear strain was lower than those under quasi-static loading, but the overall tendency was similar. In the Widmanstätten and equiaxed microstructures, adiabatic shear bands were found in the deformed region of the fractured specimens. The possibility of the adiabatic shear band formation under dynamic loading was quantitatively analyzed, depending on how plastic deformation energy was distributed to either void initiation or adiabatic shear banding. It was found to be most likely in the equiaxed microstructure, whereas it was least likely in the bimodal microstructure. 相似文献
2.
Dong-Geun Lee You Hwan Lee Sunghak Lee Chong Soo Lee Sun-Moo Hur 《Metallurgical and Materials Transactions A》2004,35(10):3103-3112
Effects of microstructural morphology on dynamic deformation behavior and ballistic impact properties of Ti-6Al-4V alloy plates
were investigated in this study. Dynamic torsional and ballistic impact tests were conducted on equiaxed and bimodal microstructures,
which were processed by different heat treatments, and then the test data were analyzed in relation to microstructures and
tensile properties. According to the dynamic torsional test data, maximum shear stress and fracture shear strain of the bimodal
microstructure were higher than those of the equiaxed microstructure, and the possibility of the adiabatic shear band formation
was more likely in the equiaxed microstructure than in the bimodal microstructure. In the ballistically impacted region of
the equiaxed microstructure, a number of adiabatic shear bands and cracks were observed to be formed along plastic flow lines,
and delamination occurred because of cracking along the flow lines or shear bands. In the case of the bimodal microstructure,
shear bands were found in limited areas near the penetrated surface without occurring delamination, and their number was smaller
than that of the equiaxed microstructure. Thus, ballistic performance of the bimodal microstructure was better than that of
the equiaxed microstructure, which was consistent with the dynamic torsional test results. 相似文献
3.
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
4.
5.
Yongjin Kim Sang Yong Shin Yang Gon Kim Nack J. Kim Sunghak Lee 《Metallurgical and Materials Transactions A》2010,41(8):1961-1972
This study aimed at investigating effects of strain rate and test temperature on deformation and fracture behavior of three
API X70 and X80 linepipe steels fabricated by varying alloying elements and hot-rolling conditions. Quasi-static and dynamic
torsional tests were conducted on these steels having different grain sizes and volume fractions of acicular ferrite and polygonal
ferrite, using a torsional Kolsky bar, and then the test data were compared via microstructures, tensile properties, and adiabatic shear band formation. The dynamic torsional test results indicated that
the steels rolled in the single-phase region had the higher maximum shear stress than the steel rolled in the two-phase region,
because their microstructures were composed mainly of acicular ferrites. Particularly in the API X80 steel rolled in the single-phase
region, increased dynamic torsional properties could be explained by the decrease in the overall effective grain size due
to the presence of acicular ferrite having smaller effective grain size. The possibility of the adiabatic shear band formation
at low temperatures was also analyzed by the energy required for void initiation and difference in effective grain size. 相似文献
6.
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
7.
Sunghak Lee Kyung-Mox Cho Chang Sun Lee Wung Yong Choo 《Metallurgical and Materials Transactions A》1993,24(10):2217-2224
This article presents a study of the microstructural development of the adiabatic shear band in an HY-100 steel. The steel
was deformed at a high strain rate by ballistic impact, and subsequent metallographic observations along with electron microscopy
were performed. A number of white- etched shear bands were found near the perforated region, and three typical microstructural
features of the adiabatic shear band were observed: elongated grain structure at the boundary between the shear band and matrix,
fine equiaxed grain structure with high dislocation densities in the middle of the shear band, and relatively coarse-grained
structure located between the above two structures. These microstructures might be formed in an extremely short time by the
combined effects of the large temperature rise and the highly localized deformation. Since very complex phenomena might occur
within the shear band, possible mechanisms, such as dynamic recovery and strain-induced dynamic phase transformation, are
suggested to explain the micro- structural development of the adiabatic shear band. 相似文献
8.
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
9.
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
10.
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
11.
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
12.
Seok Su Sohn Byeong-Joo Lee Sunghak Lee Jai-Hyun Kwak 《Metallurgical and Materials Transactions A》2014,45(12):5469-5485
In the present study, effects of Mn addition on cracking phenomenon occurring during cold rolling of ferritic light-weight steels were clarified in relation to microstructural modification involving κ-carbide, austenite, and martensite. Four steels were fabricated by varying Mn contents of 3 to 12 wt pct, and edge areas of steel sheets containing 6 to 9 wt pct Mn were cracked during the cold rolling. The steels were basically composed of ferrite and austenite in a band shape, but a considerable amount of κ-carbide or martensite existed in the steels containing 3 to 6 wt pct Mn. Microstructural observation of the deformed region of fractured tensile specimens revealed that cracks which were initiated at ferrite/martensite interfacial κ-carbides readily propagated along ferrite/martensite interfaces or into martensite areas in the steel containing 6 wt pct Mn, thereby leading to the center or edge cracking during the cold rolling. In the steel containing 9 wt pct Mn, edge cracks were found in the final stage of cold rolling because of the formation of martensite by the strain-induced austenite to martensite transformation, whereas they were hardly formed in the steel containing 12 wt pct Mn. To prevent or minimize the cracking, it was recommended that the formation of martensite during the cooling from the hot rolling temperature or during the cold rolling should be suppressed, which could be achieved by the enhancement of thermal or mechanical stability of austenite with decreasing austenite grain size or increasing contents of austenite stabilizers. 相似文献
13.
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
14.
Dong-Geun Lee You Hwan Lee Chong Soo Lee Sunghak Lee 《Metallurgical and Materials Transactions A》2005,36(3):741-748
The effects of the volume fraction of tempered martensite on the tensile and dynamic deformation properties of a Ti-6Al-4V
alloy having a bimodal microstructure were investigated in this study. Five microstructures having various tempered-martensite
volume fractions were obtained by varying heat-treatment conditions. Dynamic torsional tests were conducted on them using
a torsional Kolsky bar. The test data were analyzed in relation to microstructures, tensile properties, and adiabatic shear-band
formation. Under a dynamic loading condition, the maximum shear stress increased with increasing tempered-martensite volume
fraction, whereas the fracture shear strain decreased. Observation of the deformed area after the dynamic torsional test indicated
that a number of voids initiated mainly at α-phase/tempered-martensite interfaces, and that the number of voids increased with increasing martensite volume fraction.
Adiabatic shear bands of 6 to 10 μm in width were formed in the specimens having lower martensite volume fractions, while they were not formed in those having
higher martensite volume fractions. The possibility of adiabatic shear-band formation was explained by concepts of absorbed
deformation energy and void initiation. 相似文献
15.
The stable and unstable plastic flow of Ti-6Al-2Sn-4Zr-2Mo-0.1Si (Ti-6242) has been investigated at temperatures from 816
to 1010 °C (1500 to 1850 °F) and at strain rates from 0.001 to 10 s-1 in order to establish its hot forging characteristics. In hot, isothermal compression, Ti-6242 with an equiaxed a structure
deforms stably and has a flow stress which decreases with straining due to adiabatic heating. With a transformed-β microstructure,
unstable flow in hot compression is observed and concluded to arise from large degrees of flow softening caused by microstructural
modification during deformation and, to a small extent, by adiabatic heating. Both microstructures have a sharp dependence
of flow stress on temperature. Using the concepts of thermally-activated processes, it was shown analytically that this dependence
is related to the large strain-rate sensitivity of the flow stress exhibited by the alloy. From lateral sidepressing results,
the large dependence of flow stress on temperature was surmised to be a major factor leading to the shear bands occurring
in nonisothermal forging of the alloy. Shear bands were also observed in isothermal forging. A model was developed to define
the effect of material properties such as flow softening rate and strain-rate sensitivity on shear band development and was
applied successfully to predict the occurrence of shear bands in isothermal forging. 相似文献
16.
17.
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
18.
Effects of volume fraction of tempered martensite on dynamic deformation properties of a Ti-6Al-4V alloy having a bimodal microstructure 总被引:1,自引:0,他引:1
Dong-Geun Lee You Hwan Lee Chong Soo Lee Sunghak Lee 《Metallurgical and Materials Transactions A》2005,36(13):741-748
The effects of the volume fraction of tempered martensite on the tensile and dynamic deformation properties of a Ti-6Al-4V
alloy having a bimodal microstructure were investigated in this study. Five microstructures having various tempered-martensite
volume fractions were obtained by varying heat-treatment conditions. Dynamic torsional tests were conducted on them using
a torsional Kolsky bar. The test data were analyzed in relation to microstructures, tensile properties, and adiabatic shear-band
formation. Under a dynamic loading condition, the maximum shear stress increased with increasing tempered-martensite volume
fraction, whereas the fracture shear strain decreased. Observation of the deformed area after the dynamic torsional test indicated
that a number of voids initiated mainly at α-phase/tempered-martensite interfaces, and that the number of voids increased
with increasing martensite volume fraction. Adiabatic shear bands of 6 to 10 μm in width were formed in the specimens having
lower martensite volume fractions, while they were not formed in those having higher martensite volume fractions. The possibility
of adiabatic shear-band formation was explained by concepts of absorbed deformation energy and void initiation.
jointly appointed with the Materials Science and Engineering Department, Pohang University of Science and Technology 相似文献
19.
Microscopic observations are made of the shear band material in three different steels: (1) an AISI 1018 cold-rolled steel
(CRS), (2) a structural steel (HY-100), and (3) an AISI 4340 vacuum arc remelted (VAR) steel tempered to either of two hardnesses,
RHC 44 or 55. To produce the shear bands, specimens were subjected to large shear strains at relatively high strain rates,
≈103/s, resulting in essentially adiabatic deformation conditions. It was found that whenever the shear band led to fracture of
the specimen, the fracture occurred by a process of void nucleation and coalescence; no cleavage was observed on any fracture
surface, including the most brittle of the steels tested (RHC = 55). This is presumably due to the softening of the shear
band material that results from the local temperature rise occurring during dynamic deformation. Differences in shear band
behavior between the various microstructures are also described.
Formerly Research Assistant, Brown University 相似文献
20.
通过理化检测,对铆螺钢在冷镦时出现开裂现象的原因进行了分析.结果表明: 铆螺钢在冶炼和浇注过程中生成的复合夹杂物,造成其在冷镦过程中开裂的发生.通过调整连铸前的吹氩工艺和中间包的烘烤工艺,有效地避免了铆螺钢冷镦开裂现象的发生. 相似文献