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1.
The influence of strain rate and environment on the fracture behavior of a two-phase TiAl-alloy, Ti-47Al-2.6Nb-2(Cr + V),
heat-treated to a nearly fully lamellar microstructure has been studied by performing conventional tensile, compression, and
fracture toughness tests in air, argon, and vacuum at 25 °C and 800 °C. Both tensile and compression tests were conducted
at strain rates of 1 × 10−3 and 1 × 10−5 s−1, and fracture toughness tests were performed under displacement rates of 0.25 to 2.5 mm/min. In addition,in situ fracture toughness tests were conducted at slow rates both in vacuum and in air. The results indicated that both strain rate
and environment affected the tensile stress-strain behavior and ductility and the fracture resistance of the TiAl-alloy at
800 °C. In contrast, neither the tensile ductility nor the fracture toughness was significantly affected by the environment
at ambient temperature. For compression in air, the stress-strain behavior was insensitive to both strain rate and test temperature
within the conditions tested. Studies of fracture surfaces revealed that low tensile ductility in this alloy at ambient temperature
is associated with the tendency to delaminate alongγ/γ andγ/α
2 interfaces.
formerly with Metcut-Materials Research Group, Wright-Patterson AFB, Dayton, OH 45433-0511 相似文献
2.
The effect of loading rate on the strength and deformation characteristics of tensile tested smoothed round bar specimens and on linear-elastic and elastic-plastic fracture toughness values was investigated. Test materials were a high toughness melt of the fine-grained structural steel 20 MnMoNi 5 5 and two model materials of reduced toughness. The strain rate was varied between ?? = 10?3 and 103 s?1 in the tensile tests, the loading rate between K? = 1 and 2 · 106 MPam1/2 s?1 in the fracture toughness tests. The true-stress true-strain curve is shifted to higher stresses with increasing strain rate. A reduction of the deformation characteristics was only observed in cases of extremely reduced toughness. However, no brittle fracture at nominal stresses below yield was found in the tensile tests with smoothed specimens. Contrary to that all fracture mechanics tests showed a reduction of the crack initiation toughness with increasing loading rate K?. 相似文献
3.
Influence of microstructure on crack-tip micromechanics and fracture behaviors of a two-phase TiAl alloy 总被引:4,自引:0,他引:4
The tensile deformation, crack-tip micromechanics, and fracture behaviors of a two-phase (γ + α2) gamma titanium aluminide alloy, Ti-47Al-2.6Nb-2(Cr+V), heat-treated for the microstructure of either fine duplex (gamma
+ lamellar) or predominantly lamellar microstructure were studied in the 25 °C to 800 °C range.In situ tensile and fracture toughness tests were performed in vacuum using a high-temperature loading stage in a scanning electron
microscope (SEM), while conventional tensile tests were performed in air. The results revealed strong influences of microstructure
on the crack-tip deformation, quasi-static crack growth, and the fracture initiation behaviors in the alloy. Intergranular
fracture and cleavage were the dominant fracture mechanisms in the duplex microstructure material, whose fracture remained
brittle at temperatures up to 600 °C. In contrast, the nearly fully lamellar microstructure resulted in a relatively high
crack growth resistance in the 25 °C to 800 °C range, with interface delamination, translamellar fracture, and decohesion
of colony boundaries being the main fracture processes. The higher fracture resistance exhibited by the lamellar microstructure
can be attributed, at least partly, to toughening by shear ligaments formed as the result of mismatched crack planes in the
process zone. 相似文献
4.
G. Babu Viswanathan Michael J. Mills Vijay K. Vasudevan 《Metallurgical and Materials Transactions A》2003,34(10):2113-2127
The effects of microstructure on the tensile properties and deformation behavior of a binary Ti-48Al gamma titanium aluminide
were studied. Tensile-mechanical properties of samples with microstructures ranging from near γ to duplex to fine grained, near- and fully-lamellar were determined at a range of temperatures, and the deformation structures
in these characterized by transmission electron microscopy (TEM). Microstructure was observed to exert a strong influence
on the tensile properties, with the grain size and lamellar volume fraction playing connected, but complex, roles. Acoustic
emission response monitored during the tensile test revealed spikes whose amplitude and frequency increased with an increase
in the volume fraction of lamellar grains in the microstructure. Analysis of failed samples suggested that microcracking was
the main factor responsible for the spikes, with twinning providing a minor contribution in the near-lamellar materials. The
most important factor that controls ductility of these alloys is grain size. The ductility, yield stress, and work-hardening
rate of the binary Ti-48Al alloy exhibit maximum values between 0.50 and 0.60 volume fraction of the lamellar constituent.
The high work-hardening rate, which is associated with the low mobility of dislocations, is the likely cause of low ductility
of these alloys. In the near-γ and duplex structures, slip by motion of 1/2<110] unit dislocations and twinning are the prevalent deformation modes at room
temperature (RT), whereas twinning is more common in the near- and fully-lamellar structures. The occurrence of twinning is
largely dictated by the Schmid factor. The 1/2<110] unit dislocations are prevalent even for grain orientations for which
the Schmid factor is higher for <101] superdislocations, though the latter are observed in favorably oriented grains. The
activity of both of these systems is responsible for the higher ductility at ambient temperatures compared with Al-rich single-phase
γ alloys. A higher twin density is observed in lamellar grains, but their propagation depends on the orientation and geometry
of the individual γ lamellae. The increase in ductility at high temperatures correlates with increased activity of 1/2<110] dislocations (including
their climb motion) and twin thickening. The role of microstructural variables on strength, ductility, and fracture are discussed.
This article is based on a presentation made in the symposium entitled “Fundamentals of Structural Intermetallics,” presented
at the 2002 TMS Annual Meeting, February 21–27, 2002, in Seattle, Washington, under the auspices of the ASM and TMS Joint
Committee on Mechanical Behavior of Materials. 相似文献
5.
Room-temperature deformation behavior of directionally solidified multiphase Ni-Fe-Al alloys 总被引:1,自引:0,他引:1
Directionally solidified (DS) β + (γ + γ′) Ni-Fe-Al alloys have been used to investigate the effect of a ductile second phase on the room-temperature mechanical behavior
of a brittle 〈001〉-oriented β (B2) phase. The ductile phase in the composite consisted of a fine distribution of ordered γ′ precipitates in a γ (fcc) matrix. Three microstructures were studied: 100 pct lamellar/rod, lamellar + proeutectic β, and discontinuous γ. The β matrix in the latter two microstructures contained fine-scale bcc precipitates formed due to spinodal decomposition. Room-temperature
tensile ductilities as high as 12 pct and fracture toughness (K
Q
) of 30.4 MPa √m were observed in the 100 pct lamellar/rod microstructure. Observations of slip traces and dislocation substructures
indicated that a substantial portion of the ductility was a result of slip transfer from the ductile phase to the brittle
matrix. This slip transfer was facilitated by the Kurdjumov-Sachs (KS) orientation relationship between the two phases and
the strong interphase interface which showed no decohesion during deformation. In microstructures which show higher values
of tensile ductility and fracture toughness, 〈100〉 slip was seen in the β phase, whereas 〈111〉 slip was seen in the β phase in the microstructure which showed limited ductility. The high ductility and toughness are explained in terms of increased
mobile dislocation density afforded by interface constraint. The effect of extrinsic toughening mechanisms on enhancing the
ductility or toughness is secondary to that of slip transfer. 相似文献
6.
J. H. Zhu P. K. Liaw J. M. Corum H. E. McCoy Jr. 《Metallurgical and Materials Transactions A》1999,30(6):1569-1578
Mechanical behaviors at 538 °C, including tensile and creep properties, were investigated for both the Ti-6Al-4V alloy and
the Ti-6Al-4V composite reinforced with 10 wt pct TiC particulates fabricated by cold and hot isostatic pressing (CHIP). It
was shown that the yield strength (YS) and ultimate tensile strength (UTS) of the composite were greater than those of the
matrix alloy at the strain rates ranging from approximately 10−5 to 10−3 s−1. However, the elongation of the composite material was substantially lower than that of the matrix alloy. The creep resistance
of the composite was superior to that of the matrix alloy. The data of minimum creep strain rate vs applied stress for the composite can be fit to a power-law equation, and the stress exponent values of 5 and 8 were obtained
for applied stress ranges of 103 to 232 MPa and 232 to 379 MPa, respectively. The damage mechanisms were different for the
matrix alloy and the composite, as demonstrated by the scanning electron microscopy (SEM) observation of fracture surfaces
and the optical microscopy examination of the regions adjacent to the fracture surface. The tensile-tested matrix alloy showed
dimpled fracture, while the creep-tested matrix alloy exhibited preferentially interlath and intercolony cracking. The failure
of the tensile-tested and creep-tested composite material was controlled by the cleavage failure of the particulates, which
was followed by the ductile fracture of the matrix. 相似文献
7.
Plastic deformation and fracture of binary TiAl-base alloys 总被引:4,自引:0,他引:4
The mechanical behavior of binary TiAl alloys containing 46 to 60 at. pct Al has been studied in bulk materials preparedvia rapid solidification processing. Bending and tensile tests were carried out at room temperature as a function of Al concentration.
A few alloys were also tested from liquid nitrogen temperature to ∼ 1000°C. Deformation substructures were studied by analytical
transmission electron microscopy and fracture modes by scanning electron microscopy (SEM). It was found that both microstructure
and composition strongly affect the mechanical behavior of TiAl-base alloys. A duplex structure, which contains both primary
y grains and transformedγ/α
2 lamellar grains, is more deformable than a single-phase or a fully transformed structure. The highest plasticities are observed
in duplex alloys containing 48–50 at. pct Al after heat treatment in the center of theγ + α phase field. The deformation of these duplex alloys is facilitated by 1/2[110] slip and {111} twinning, but very limited
superdislocation slip occurs. The twin deformation is suggested to result from a lowered stacking fault energy due to oxygen
depletion or an intrinsic change in chemical bonding. Other factors, such as grain size and grain boundary chemistry and structure,
are important from a fracture point of view. The results on the deformation and fracture modes as a function of test temperature
are also discussed. 相似文献
8.
Yasuhiro Maehara 《Metallurgical and Materials Transactions A》1991,22(5):1083-1091
Effects of prior thermomechanical treatments on the superplasticity of a 25 wt pct Cr-7 wt pct Ni-3 wt pct Mo-0.14 wt pct
N δ/γ duplex stainless steel have been studied by means of hot tensile testing with constant crosshead speeds. The objective
is to increase the strain rate suitable for superplasticity. The strain rate is found to be markedly increased by a special
prior treatment,i.e., solution treatment at temperatures in the δ single-phase region with subsequent heavy cold-rolling. In hot tensile tests
at 1273 K, elongations greater than 1000 and 300 pct were observed at initial strain rates (έ) of 10−3 to 10−1 s−1 and 1 x 100 s−1, respectively. The results for strain rates 〈10−1 s−1 can be explained in terms of a structural superplastic effect due to grain refinement. In the case of έ 〉 10−1 s−1, transformation superplastic effects due to γ-phase precipitation from the σ-ferrite matrix are also important, especially
in the early stages of deformation. In the equiaxedδ/γ microduplex structures during stable superplastic deformation, there exists a mixture of two different structures,i.e., dislocated and recovered/ recrystallized δ grains with a homogeneous dispersion of dislocation-free γ particles. This result
shows that dynamic recrystallization ofδ grains occurs locally and intermittently due to the dispersion of relatively hardγ particles. The apparent average grain growth rate during deformation is small compared to static grain growth, because grain
refinement due to dynamic recrystallization reduces the superplasticity-enhanced grain growth. 相似文献
9.
Minwoo Jeon Jae-Hyun Lee Ta Kwan Woo Sangshik Kim 《Metallurgical and Materials Transactions A》2011,42(4):974-985
Nimonic 263 has been developed for the improved ductility in welded assemblies and is a candidate material for gas turbine
combustor and transition pieces along with its good weldability and mechanical properties at room and elevated temperatures.
In this study, the tensile behavior of an as-welded Nimonic 263 specimen at room temperature and 1053 K (780 °C) was examined
in conjunction with microstructural evolution during welding and postweld heat treatment (PWHT). With the welding and the
PWHT, the yield strength (YS), ultimate tensile strength (UTS), and tensile elongation of Nimonic 263 varied in a complex
manner. It was observed that the PWHT of resolutionization at 1423 K (1150 °C) for 2 hours gave the highest YS and UTS values,
whereas the tensile elongation was the lowest, at both testing temperatures. With increasing resolutionization time, the YS
and UTS tended to decrease along with the increase in tensile ductility. The tensile behaviors of as-welded Nimonic 263 specimens
was affected by several factors, including grain size, residual stress, possible microsegregation of γ′ forming elements, a tendency for interdendritic or intergranular fracture and a morphological change in both M23C6 and MC type carbides, depending on the testing temperature and the PWHT. The complex changes in tensile properties of Nimonic
263 with welding and PWHT at room temperature and 1053 K (780 °C) were discussed based on the micrographic and fractographic
observations. 相似文献
10.
The environment-assisted cracking behavior of a Fe3Al intermetallic in an air moisture environment was studied. At room temperature, tensile ductility was found to be increased
with strain rate, from 10.1 pct at 1×10−6 s−1 to 14.3 pct at 2 × 10−3 s−1. When tensile tests were done in heat-treated mineral oil on specimens that have been heated in the oil for 4 hours at 200°C,
ductility was found to be recovered. These results suggest the existence of hydrogen embrittlement. Shear ligaments, which
are ligament-like structures connected between microcracks, were observed on the tensile specimens. They undergo ductile fracture
by shearing and enhance fracture toughness. This toughness enhancement (represented byJ
l
) was estimated by a micromechanical model. The values of the unknown parameters, which are the average ligament length
, the area fractionV
l
, and the work-to-fractureτ
1
γ
1, were obtained from scanning electron microscopy (SEM) observation. The total fracture toughnessK
c
andJ
l
were reduced toward a slower strain rate. The experimental fracture toughness,K
Q
, was found to be increased with strain rate, from 35 MPa
at 2.54×10−5 mm·s−1 to 47 MPa
at 2.54×10−2 mm·s−1. The fact that strain rate has a similar effect onK
Q
andK
c
verifies the importance of shear ligament in determining fracture toughness of the alloy. With the presence of hydrogen,
length and work-to-fracture of the shear ligament were reduced. The toughening effect caused by shear ligament was reduced,
and the alloy would behave in a brittle manner. 相似文献
11.
The stress-strain response of polycrystalline, γ-quenched U-7.5 wt pct Nb-2.5 wt pct Zr alloy was studied as a function of
strain rate and compared to equilibrium stress-strain tests performed by allowing the strain to reach a maximum value at incrementally
increasing stresses. Equilibrium stress-strain tests were also performed on prestressed samples. Sheet tensile specimens were
held at various states of strain in an X-ray diffractometer to determine crystal structural changes during deformation. Prestressed
tensile bars were sectioned and examined metallographically and with the X-ray diffractometer. Two linear regions were observed
in the equilibrium stress-strain tests: a low stress region with a slope of 5.3 to 5.5 x 106 psi, and a region above 40,000 psi with a slope of 3.3 x 106 psi. Finite strain rates tended to increase both slopes. The diffractometer experiments yielded plots of lattice parameter
vs strain which showed a shift from a bcc structure of the γs phase, to a bct structure of the γ0 phase between 1 and 3 pct deformation. It is postulated that this is a thermoelastic martensite transformation. A semiempirical
equation was developed which describes the equilibrium stress-strain behavior of this alloy in terms of a stress induced phase
transformation. 相似文献
12.
H. Couque R. J. Asaro J. Duffy S. H. Lee 《Metallurgical and Materials Transactions A》1988,19(9):2179-2206
An investigation was conducted into the effects of temperature, loading rate, and various micro-structural parameters on the
initiation of plane strain fracture of a plain carbon AISI 1020 steel. Ferrite and prior austenite grain sizes were chosen
as the principal microstructural features to be in-vestigated. The microstructural variations were accomplished by changing
the austenitizing tempera-ture and by altering the cooling rate during normalization. Fracture toughness tests were conducted
using precracked notched round bars loaded in tension to produce two stress intensity rates,viz.,K
1 = 1 MPa √m s-1 andK
1
= 2 × 106 MPa √m s-1. In addition, Charpy impact tests along with quasistatic and high rate plasticity tests were conducted. The plasticity tests
were done in torsion at shear strain rates of
. Testing temperatures covered the range from -150 °C to 150 °C which encompassed fracture initiation modes involving transgranular
cleavage to fully ductile fracture. Micromechanical processes involved in void and cleavage micro-crack formation were identified
and quantified. For these purposes notched round tensile tests and subsequent metallographic observations along with TEM and
SEM observations of the plane strain fracture toughness specimens were performed. The experimental results and quantitative
micro-modeling using simple fracture models provide a means of correlating both quasistatic and dynamic fracture toughness
with microstructures. 相似文献
13.
Directionally solidified (DS) β+(γ+γ′) Ni−Fe−Al alloys have been used to investigate the effect of a ductile second phase
on the room-temperature mechanical behavior of a brittle 〈001〉-oriented β (B2) phase. The ductile phase in the composite consisted
of a fine distribution of ordered γ′ precipitates in a γ (fcc) matrix. Three microstructures were studied: 100 pct lamellar/rod,
lamellar+proeutectic β, and discontinuous γ. The β matrix in the latter two microstructures contained fine-scale bcc precipitates
formed due to spinodal decomposition. Room-temperature tensile ductilities as high as 12 pct and fracture toughness (K
Q) of 30.4 MPa
were observed in the 100 pct lamellar/rod microstructure. Observations of slip traces and dislocation substructures indicated
that a substantial portion of the ductility was a result of slip transfer from the ductile phase to the brittle matrix. This
slip transfer was facilitated by the Kurdjumov-Sachs (KS) orientation relationship between the two phases and the strong interphase
interface which showed no decohesion during deformation. In microstructures which show higher values of tensile ductility
and fracture toughness, 〈100〉 slip was seen in the β phase, whereas 〈111〉 slip was seen in the β phase in the microstructure
which showed limited ductility. The high ductility and toughness are explained in terms of increased mobile dislocation density
afforded by interface constraint. The effect of extrinsic toughening mechanisms on enhancing the ductility or toughness is
secondary to that of slip transfer.
A. MISRA, formerly Graduate Student, Department of Materials Science and Engineering, University of Michigan is Research Associate 相似文献
14.
The kinetics of dynamic spheroidization of the lamellar microstructure and the associated flow-softening behavior during isothermal,
constant-strain-rate deformation of a gamma titanium aluminide alloy were investigated, with special emphasis on the role
of the prior-alpha grain/colony size. For this purpose, fully lamellar microstructures with prior-alpha grain sizes between
80 and 900 μm were developed in a Ti-45.5Al-2Nb-2Cr alloy using a special forging and heat-treatment schedule. Isothermal hot compression
tests were conducted at 1093 °C and strain rates of 0.001, 0.1, and 1.0 s−1 on specimens with different grain sizes. The flow curves from these tests showed a very strong dependence of peak flow stress
and flow-softening rate on grain size; both parameters increased with alpha grain/colony size. Microstructures of the upset
test specimens revealed the presence of fine, equiaxed grains of γ + α
2 + β phases resulting from the dynamic spheroidization process that initiated at and proceeded inward from the prior-alpha grain/colony
boundaries. The grain interiors displayed evidence of microkinking of the lamellae. The frequency and severity of kinking
increased with strain, but were also strongly dependent on the local orientation of lamellae with respect to the compression
axis. The kinetics of dynamic spheroidization were found to increase as the strain rate decreased for a given alpha grain
size and to decrease with increasing alpha grain size at a given strain rate. The breakdown of the lamellar structure during
hot deformation occurred through a combination of events, including shear localization along grain/colony boundaries, microbuckling
of the lamellae, and the formation of equiaxed particles of γ + β
2 + α
2 on grain/colony boundaries and in zones of localized high deformation within the microbuckled regions. 相似文献
15.
Effects of temperature and strain rate on tensile properties and activation energy for dynamic strain aging in alloy 625 总被引:1,自引:0,他引:1
Vani Shankar M. Valsan K. Bhanu Sankara Rao S. L. Mannan 《Metallurgical and Materials Transactions A》2004,35(10):3129-3139
Alloy 625 ammonia cracker tubes were service exposed for 60,000 hours at 873 K. These were then subjected to a solution-annealing
treatment at 1473 K for 0.5 hours. The effects of temperature and strain rate on the tensile properties of the solution-annealed
alloy were examined in the temperature range of 300 to 1023 K, employing the strain rates in the range of 3×10−5 s−1 to 3×10−3 s−1. At intermediate temperatures (523 to 923 K), various manifestations of dynamic strain aging (DSA) such as serrated flow,
peaks, and plateaus in the variations of yield strength (YS) and ultimate tensile strength (UTS) and work-hardening rate with
temperature were observed. The activation energy for serrated flow (Q) was determined by employing various methodologies for T<823 K, where a normal Portevien-Le Chatelier effect (PLE) was observed. The value of Q was found to be independent of the method employed. The average Q value of 98 kJ/mol was found to be in agreement with that for Mo migration in a Ni matrix. At elevated temperatures (T≥823 K), type-C serrations and an inverse PLE was noticed. The decrease in uniform elongation beyond 873 K for 3×10−5 s−1 and 3×10−3 s−1 and beyond 923 K for 3×10−4 s−1 strain rates seen in this alloy has been ascribed to reduction in ductility due to precipitation of carbides and δ phase on the grain boundaries. 相似文献
16.
Y. Umakoshi H. Y. Yasuda T. Nakano K. Ikeda 《Metallurgical and Materials Transactions A》1998,29(3):943-950
The temperature and orientation dependence of cyclic deformation, fatigue life, and fracture behavior in TiAl polysynthetically
twinned (PST) crystals were investigated, focusing on the change of plastic strain energy and deformation mode in the γ domains. Stress-controlled fatigue tests were performed at 1 or 10 Hz using the same stress amplitude in tension and compression
(R=−1) over a temperature range from −196 °C to 700 °C. The fatigue strength at ϕ=45 deg (ϕ being the angle between the loading axis and lamellar planes) decreased monotonically with increasing temperature. At ϕ=0 deg, the fatigue strength was high up to 500 °C, but the fatigue life decreased rapidly above 600 °C because of dynamic
recovery and interlamellar separation. The plastic strain energy-stress amplitude curves in specimens fatigued with ϕ=45 deg increased monotonically with stress amplitude for all temperatures and for higher temperatures with ϕ=0 deg. At 25 °C and −196 °C with ϕ=0 deg, three regions in the plastic strain energy-stress amplitude curves were observed. This anomalous change in the plastic
strain energy at lower temperatures was due to a transition in primary deformation mode between twinning and slip by ordinary
dislocations in some domain orientations.
This article is based on a presentation made in the symposium “Fundamentals of Gamma Titanium Aluminides,” presented at the
TMS Annual Meeting, February 10–12, 1997, Orlando, Florida, under the auspices of the ASM/MSD Flow & Fracture and Phase Transformations
Committees. 相似文献
17.
The hard-orientated polysynthetically twinned (PST) crystal with the lamellar plates oriented parallel to the compression
axis was deformed at 1150 K under the applied stress of 158 to 316 MPa. Microstructural changes were examined quantitatively
for the PST crystal during creep deformation. In the as-grown PST crystal of the present study, proportions of α
2/γ, true twin, pseudotwin, and 120 deg rotational fault interfaces were 12, 59, 12, and 17 pct, respectively. After creep deformation,
lamellar coarsening by dissolution of α
2 lamellae and migration of γ/γ interfaces were observed. The acceleration of creep rate after the minimum strain rate in the creep curve was attributed
to the lamellar coarsening and destruction of lamellar structure during the creep deformation. Thirty-two percent of α
2/γ interfaces, 51 pct of true twin interfaces, 74 pct of pseudotwin interfaces, and 80 pct of 120 deg rotational faults disappeared
after 4 pct creep strain at 1150 K. The α
2/γ interface was more stable than γ/γ interfaces during the creep deformation. The pseudotwin interface and 120 deg rotational fault were less thermally stable
than the true twin interface for γ/γ interfaces.
This article is based on a presentation made in the symposium entitled “Fundamentals of Structural Intermetallics,” presented
at the 2002 TMS Annual Meeting, February 21–27, 2002, in Seattle, Washington, under the auspices of the ASM and TMS Joint
Committee on Mechanical Behavior of Materials. 相似文献
18.
P. Mallikarjuna Rao S. S. Bhattacharya 《Transactions of the Indian Institute of Metals》2009,62(1):41-48
The hot deformation characteristics of AISI 316LN stainless steel were studied in the temperature range of 1123–1323 K and
strain rate range of 10−4–10−1s−1 by carrying out tensile tests. The flow stress, ultimate tensile stress and percentage elongation were found to be strongly
dependent on the temperature and strain rate. The critical strain required for the initiation of dynamic recrystallisation
and peak strain were determined at each condition and their variation with temperature and strain rate studied. The deformation
behavior was analyzed using a generic model for high temperature deformation and deformation parameters were computed. The
variation of the true activation energy with strain for rate controlled high temperature tensile deformation was obtained.
Microstructural studies were carried out on tested samples and the results of all the above studies are presented. 相似文献
19.
The low cycle deformation saturation stress in Ferrovac-E a-iron was studied using diametral plastic strain (0.001 ≤ Δεdp/2 ≤ 0.0135) as the control variable. Increasing strain rate (6 × 10•5 s•1 • 4 × 10•3 s•1) and decreasing temperature (295 to 173 K) increased the saturation stress levels. The cyclic work hardening coefficient
decreased from 0.18 at 295 K to 0.10 at 173 K, which is consistent with previous studies of monotonie deformation. The temperature
dependence of both the saturation stress and the strain rate sensitivity, as measured during cyclic deformation, were similar
to that measured during monotonic tensile tests. The temperature dependence of the dislocation velocity indexm* was in good agreement with published values from high cycle fatigue and monotonie tensile tests. Thus the same deformation
mechanisms are believed to occur in both monotonie and large plastic cyclic deformation (Δεdp/2 ≥ 0.001) of a-iron. 相似文献
20.
T. Tsuyumu Y. Kaneno H. Inoue T. Takasugi 《Metallurgical and Materials Transactions A》2003,34(3):645-655
By using isothermally forged TiAl-based intermetallic alloys, various microstructures (of γ-grain, duplex, dual-phase, and fully lamellar microstructures) were prepared. These TiAl-based intermetallic alloys were
tensile tested in vacuum and air as functions of strain rate and temperature to investigate microstructural effects on the
moisture-induced embrittlement. All the intermetallic alloys with different microstructures showed different levels of reduced
tensile stress (or elongation) in air at room temperature. The reduction in tensile stress (or elongation) due to testing
in air diminishes as the testing temperature (or strain-rate) increases. From the fracture stress-temperature curves, it was
found that the γ-grain microstructure was the most resistant to the moisture-induced embrittlement, and the dual-phase microstructure was
the most susceptible to the moisture-induced embrittlement. Also, the moisture-induced embrittlement of the TiAl-based intermetallic
alloys with a fully lamellar microstructure depends on the lamellar spacing and is reduced with decreasing lamellar spacing.
The possible reasons for the observed microstructural effect on the moisture-induced embrittlement were discussed, in association
with hydrogen behavior and properties in the constituent phases and at some interfaces. 相似文献