共查询到20条相似文献,搜索用时 31 毫秒
1.
Preet M. Singh John J. Lewandowski 《Metallurgical and Materials Transactions A》1993,24(11):2531-2543
The effects of heat-treatment, matrix microstructure, and reinforcement size on the evolution of damage, in the form of SiCp cracking, during uniaxial tension testing of an aluminum-alloy based composite have been determined. A powder metallurgy
Al-Zn-Mg-Cu alloy reinforced with 15 vol pct of either 5 or 13 μm average size SiCp was heat treated to solution annealed (SA), underaged (UA), and overaged (OA) conditions. The SA treatment exhibited lower
yield strength and higher ductility for both particulate sizes compared to the UA and OA conditions. The evolution of damage,
in the form of SiCp fracture, was monitored quantitatively using metallography and changes in modulus on sequentially strained specimens. It
is shown that the evolution of SiCp fracture is very dependent on particulate size, matrix aging condition, and the details of the matrix-reinforcement interfacial
regions. SiCp fracture was exhibited by the UA and OA treatment over a range of strains, while a preference for failure near the SiCp/matrix interfaces and in the matrix was exhibited in the OA material. While thepercentage of cracked SiCp at each global strain typically was equal or somewhat lower in the material reinforced with 5 μm average size SiCp, theabsolute number of cracked SiCp was always higher at each global stress and strain in the material containing 5 μm average size SiCp, for each heat treatment. Damage(e.g., voids) in the matrix and near the SiCp/matrix interfaces was additionally observed, although its extent was highly matrix and particle-size dependent. It was always
observed that increases in stress (and strain) produced a larger amount of fractured SiCp. However, neither a global stress-based nor a global strain-based model was sufficient in converging the amount of SiCp fractured for all heat treatments and particle sizes tested. 相似文献
2.
Dong H. Shin Ki S. Kim Dong W. Kum Soo W. Nam 《Metallurgical and Materials Transactions A》1990,21(10):2729-2737
Thermomechanical processes were developed which give fine grain sizes of 6 and 8 μm in the 7475 Al alloy. Superplastic properties
of this material were evaluated in the temperature range of 400 °C to 545 °C over the strain-rate range of 2.8 x 10-4 to 2.8 X 10-2 s-1. The maximum ductility exhibited by the alloy was approximately 2000 pct, and optimum superplasticity was achieved at a strain
rate of 2.8 X 10-3 s-1 which is higher by an order of magnitude than other 7475 Al alloys. This result is attributed to the presence of fine dispersoids
which maintain the fine grain size at high homologous temperatures. The flow stress and strain-rate sensitivity strongly depend
on the grain size. The superplastic 7475 Al alloy has strain-rate sensitivities of 0.67 (6 μm) and 0.5 (13 μm) and an activation
energy which is similar to the one for grain boundary diffusion of aluminum. Microstructural investigation after superplastic
tests revealed zones free of dispersoid particles at grain boundaries primarily normal to the tensile direction. These dispersoidfree
zones (DFZs) appear even after 100 pct elongation and are occasionally as large as 5 μm across. This result demonstrates the
importance of diffusional flow in superplastic deformation of the fine-grained 7475 Al alloy especially at low elongations. 相似文献
3.
4.
Z. Y. Ma R. S. Mishra M. W. Mahoney R. Grimes 《Metallurgical and Materials Transactions A》2005,36(6):1447-1458
The effect of friction stir processing on the superplastic behavior of extruded Al-4Mg-1Zr was examined at 350 °C to 600 °C
and at initial strain rates of 1×10−3 to 1 s−1. A combination of a fine grain size of 1.5 μm and high-angle grain boundaries in the friction stir-processed (FSP) alloy led to considerably enhanced superplastic ductility,
much-reduced flow stress, and a shift to a higher optimum strain rate and lower optimum temperature. The as-extruded alloy
exhibited the highest superplastic ductility of 1015 pct at 580 °C and an initial strain rate of 1×10−2s−1, whereas a maximum elongation of 1280 pct was obtained at 525 °C and an initial strain rate of 1×10−1s−1 for the FSP alloy. The FSP alloy exhibited enhanced superplastic deformation kinetics compared to that predicted by the constitutive
relationship for superplasticity in fine-grained aluminum alloys. A possible origin for enhanced superplastic deformation
kinetics in the FSP condition is proposed. 相似文献
5.
Preet M. Singh John J. Lewandowski 《Metallurgical and Materials Transactions A》1995,26(11):2911-2921
The effects of reinforcement additions and heat treatment on the evolution of the Poisson ratio were determined for a 7xxx
aluminum alloy reinforced with 15 vol pct SiCp, a 2xxx alloy with 20 pct SiCp, and a 2014 alloy with 15 pct A12O3. The Poisson ratio of the monolithic alloy was 0.31 to 0.32 in the elastic regime. At the onset of the plastic regime, the
Poisson ratio of the monolithic materials rose rapidly to about 0.45 and then gradually increased to 0.47 by 3.5 pct strain.
For discontinuously reinforced aluminum (DRA) materials, the Poisson ratio in the elastic regime was considerably lower than
that exhibited by the matrix alloy, while the magnitude of the difference was dependent upon the type, volume fraction, and
elastic properties of the reinforcement. In addition, th evolution of the Poisson ratio for DRA material depends upon heat
treatment and level of strain due to damage evolution(e.g., SiCp cracking, matrix failure,etc.) which accompanies straining in these materials. Both the magnitude and extent of change in the Poisson ratio with increasing
strain in the composite is rationalized by the accumulation of damage which accompanies increasing strain. 相似文献
6.
J. A. Jiménez G. González-Doncel P. Acosta O. A. Ruano 《Metallurgical and Materials Transactions A》1994,25(6):1241-1248
The high-temperature deformation behavior of two ultrahigh boron steels containing 2.2 pct and 4.9 pct B was investigated.
Both alloys were processedvia powder metallurgy involving gas atomization and hot isostatic pressing (hipping) at various temperatures. After hipping at
700 °C, the Fe-2.2 pct B alloy showed a fine microstructure consisting of l-μm grains and small elongated borides (less than 1μm) . At 1100 °C, a coarser microstructure with rounded borides was formed. This alloy was superplastic at 850 °C with stress
exponents of about two and tensile elongations as high as 435 pct. The microstructure of the Fe-4.9 pct B alloy was similar
to that of the Fe-2.2 pct B alloy showing, in addition, coarse borides. This alloy also showed low stress exponent values
but lacked high tensile elongation (less than 65 pct), which was attributed to the presence of stress accumulation at the
interface between the matrix and the large borides. A change in the activation energy value at theα-γ transformation temperature was seen in the Fe-2.2 pct B alloy. The plastic flow data were in agreement with grain boundary
sliding and slip creep models.
J.A. JIMéNEZ, Postdoctoral Fellow, formerly with Centro Nacional de Investigaciones Metalurgicas, C.S.I.C. 相似文献
7.
Al-SiC
p
composite and Al-SiC
p
-C
p
hybrid composite coatings were produced by plasma spraying of premixed powders onto A356 alloy substrates. Four composite
coatings, Al+20 vol pct SiC
p
, Al+20 vol pct SiC
p
+C
p
, Al+40 vol pct SiC
p
, and Al+40 vol pct SiC
p
+C
p
, were obtained. The dry sliding wear behavior of these coatings and pure aluminum have been studied at a sliding velocity
of 1 m/s in the applied-load range of 25 to 150 N (corresponding to a normal stress of 0.5 to 3 MPa). The composite coatings
had a significantly improved wear resistance over pure Al. The composite coatings with a higher SiC
p
content of 40 vol pct exhibited superior wear resistance than those with a lower SiC
p
content of 20 vol pct. The presence of graphite particles had different influences on the wear resistance, depending on the
applied load. At lower loads, graphite improved the wear resistance considerably. At higher loads, the wear resistance of
the hybrid composite coatings was similar to that of the composite coatings without graphite particles. At lower loads, an
oxidative wear mechanism was dominant. At higher loads, delamination was a major wear mechanism. Graphite particles did not
change their wear mechanism at the same applied loads. 相似文献
8.
G. M. Ludtka R. E. Oakes Gail Mackiewicz-Ludtka R. L. Bridges J. L. Griffith 《Metallurgical and Materials Transactions A》1993,24(2):379-388
A uranium-6 niobium alloy was shown to exhibit superplasticity. A thermomechanical processing (TMP) sequence was used to develop
the ultrafine grain size essential for superplastic behavior. Strain-rate sensitivity, maximum elongation, and flow curve
data indicated that this alloy is superplastic above the monotectoid temperature (647 °C) in the equilibrium γ1, single-phase, temperature regime. The existence of superplasticity in the single-phase temperature regime was explained
by the presence of metastable γ2 at these higher temperatures. Sluggish niobium diffusion and the resultant slow dissolution kinetics were shown to be responsible
for this anomalous “single-phase” superplastic behavior. An engineering elongation of 658 pct was obtained at 685 °C for a
constant true strain rate of 2.5 × 10-4 s-1 which required an initial flow stress of only 2.8 MPa. A grain growth kinetic study, along with flow curve information, has
also shown that superplastic forming (SPF) must be completed within 2 hours at 670 °C to obtain maximum ductility with the
lowest forming pressure. 相似文献
9.
G. Frommeyer W. Kowalski R. Rablbauer 《Metallurgical and Materials Transactions A》2006,37(12):3511-3517
A rapidly solidified and thermomechanically processed fine-grained eutectic NiAl−Cr alloy of the composition Ni33Al33Cr34 (at, pct) exhibits structural superplasticity in the temperature regime from 900°C to 1000°C at strain rates ranging from
10−5 to 10−3 s−1. The material consists of a B2-ordered intermetallic NiAl(Cr) solid solution matrix containing a fine dispersion of bcc chromium.
A high strain-rate-sensitivity exponent of m=0.55 was achieved in strain-rate-change tests at strain rates of about 10−4 s−1. Maximum uniform elongations up to 350 pct engineering strain were recorded in superplastic strain to failure tests. Activation
energy analysis of superplastic flow was performed in order to establish the diffusion-controlled dislocation accommodation
process of grain boundary sliding. An activation energy of Q
c=288±15 kJ/mole was determined. This value is comparable with the activation energy of 290 kJ/mole for lattice diffusion of
nickel and for 63Ni tracer selfdiffusion in B2-ordered NiAl. The principal deformation mechanism of superplastic flow in this material is grain-boundary
sliding accommodated by dislocation climb controlled by lattice diffusion, which is typical for class II solid-solution alloys.
Failure in superplastically strained tensile samples of the fine-grained eutectic alloy occurred by cavitation formations
along NiAl‖‖Cr interfaces. 相似文献
10.
11.
W. M. Zhong G. L’Espérance M. Suéry 《Metallurgical and Materials Transactions A》1995,26(10):2637-2649
The interfaces of aluminum alloy composites (5083) reinforced by SiC particles (as-received, oxidized 3.04 wt pct and 14.06
wt pct) were studied. The composites were fabricated by compocasting and certain samples were also remelted at 800 °C for
30 minutes. The reaction mechanisms between SiC
p
and liquid Al and between the SiO2 layer and Al(Mg) are discussed. The crystal boundaries of the MgO (or MgAl2O4) reaction products are believed to be the diffusion paths (or channels) during the interfacial reactions. A SiO2 layer, formed by oxidation of the SiC particles prior to their incorporation into the melt, plays an important role in preventing
the SiC
p
from being attacked by the matrix. The interfacial reaction products are affected by both the alloy composition and the thickness
of the initial SiO2 layer. 相似文献
12.
Superplastic behavior and microstructure evolution in a commercial Al-Mg-Sc alloy subjected to intense plastic straining 总被引:1,自引:0,他引:1
F. Musin R. Kaibyshev Y. Motohashi G. Itoh 《Metallurgical and Materials Transactions A》2004,35(8):2383-2392
A commercial Al-6 pct Mg-0.3 pct Sc-0.3 pct Mn alloy subjected to equal-channel angular extrusion (ECAE) at 325 °C to a total
strain of about 16 resulted in an average grain size of about 1 μm. Superplastic properties and microstructural evolution
of the alloy were studied in tension at strain rates ranging from 1.4 × 10−5 to 1.4 s−1 in the temperature interval 250 °C to 500 °C. It was shown that this alloy exhibited superior superplastic properties in
the wide temperature range 250 °C to 500 °C at strain rates higher than 10−2 s−1. The highest elongation to failure of 2000 pct was attained at a temperature of 450 °C and an initial strain rate of 5.6
× 10−2 s−1 with the corresponding strain rate sensitivity coefficient of 0.46. An increase in temperature from 250 °C to 500 °C resulted
in a shift of the optimal strain rate for superplasticity, at which highest ductility appeared, to higher strain rates. Superior
superplastic properties of the commercial Al-Mg-Sc alloy are attributed to high stability of ultrafine grain structure under
static annealing and superplastic deformation at T ≤ 450 °C. Two different fracture mechanisms were revealed. At temperatures higher than 300 °C or strain rates less than 10−1 s−1, failure took place in a brittle manner almost without necking, and cavitation played a major role in the failure. In contrast,
at low temperatures or high strain rates, fracture occurred in a ductile manner by localized necking. The results suggest
that the development of ultrafine-grained structure in the commercial Al-Mg-Sc alloy enables superplastic deformation at high
strain rates and low temperatures, making the process of superplastic forming commercially attractive for the fabrication
of high-volume components. 相似文献
13.
H. N. Azari G. S. Murty G. S. Upadhyaya 《Metallurgical and Materials Transactions A》1994,25(10):2153-2160
The superplastic behavior of thermomechanically treated P/M 7091 aluminum alloy was assessed in the temperature range of 573
to 773 K. The thermomechanical treatment (TMT) comprised of three steps of solution treatment, overaging, and warm rolling.
There are large η-phase (MgZn2) precipitate particles of average size of 1.30 μm in the overaged condition. The warm-rolled alloy undergoes continuous recrystallization
at the test temperatures of 573 and 623 K, exhibiting a maximum tensile elongation of 450 pct at 573 K and a strain rate of
8 × 10−5 s−1. The precipitate particles play a major role in the process of continuous recrystallization. For a given volume fraction
of precipitate particles and constant amount of warm rolling (in the course of TMT), an optimum precipitate particle size
is expected to maximize the rate of continuous recrystallization and render the finest recrystallized grain size. The warm-rolled
alloy undergoes static recrystallization at temperatures above 673 K. The grain growth accompanying the deformation at these
test temperatures limits the tensile ductility to a lower value. Irrespective of the test temperature and strain rate, the
specimens undergo extensive cavitation when deformed at elevated temperatures. 相似文献
14.
The microstructure and mechanical properties of the ultra-fine grained (UFG) Al6063 alloy reinforced with nanometric aluminum
oxide nanoparticles (25 nm) were investigated and compared with the coarse-grained (CG) Al6063 alloy (~2 μm). The UFG materials were prepared by mechanical alloying (MA) under high-purity Ar and Ar-5 vol pct O2 atmospheres followed by hot powder extrusion (HPE). The CG alloy was produced by HPE of the gas-atomized Al6063 powder without
applying MA. Electron backscatter diffraction under scanning electron microscopy together with transmission electron microscopy
studies revealed that the microstructure of the milled powders after HPE consisted of ultra-fine grains (>100 nm) surrounded
by nanostructured grains (<100 nm), revealing the formation of a bimodal grain structure. The grain size distribution was
in the range of 20 to 850 nm with an average of 360 and 300 nm for Ar and Ar-5 pct O2 atmospheres, respectively. The amount of oxide particles formed by reactive mechanical alloying under the Ar/O2 atmosphere was ~0.8 vol pct, whereas the particles were almost uniformly distributed throughout the aluminum matrix. The
UFG materials exhibited significant improvement in the hardness and yield strength with an absence of strain hardening behavior
compared with CG material. The fracture surfaces showed a ductile fracture mode for both CG and UFG Al6063, in which the dimple
size was related to the grain structure. A mixture of ductile–brittle fracture mode was observed for the UFG alloy containing
0.8 vol pct Al2O3 particles. The tensile behavior was described based on the formation of nonequilibrium grain boundaries with high internal
stress and dislocation-based models. 相似文献
15.
Ahmadali Yousefiani Farghalli A. Mohamed 《Metallurgical and Materials Transactions A》1998,29(6):1653-1663
The sigmoidal relationship between stress and steady-state strain rate that has been reported for micrograin superplastic
alloys is characterized by the presence of three regions: region I at low stresses, region II (the superplastic region) at
intermediate stresses, and region III at high stresses. Recent results on the superplastic Zn-22 pct Al eutectoid have shown
that the characteristics of region I are influenced by the impurity level of the alloy, and that neither region I nor significant
cavitation is observed when such a level is reduced to about 6 ppm. These observations are in agreement with the suggestion
that the origin of region I is related to strong impurity segregation at boundaries. The present investigation was conducted
to study the effect of Cu, as a selected impurity, on superplastic deformation and cavitation in Zn-22 pct Al. The results
show that Zn-22 pct Al-0.13 pct Cu exhibits two primary characteristics: region I is absent and cavitation is not extensive.
These characteristics, which are essentially similar to those reported previously for high-purity Zn-22 pct Al but are different
from those documented for a grade of the alloy containing a comparable atomic concentration of Fe, suggest that Cu has little
or no tendency to segregate at boundaries. Indirect evidence in support of this suggestion is inferred from studying the effect
of impurities on former α boundaries that form in the microstructure of Zn-22 pct Al as a result of solution treatment above the eutectoid temperature.
Although further studies are needed to provide direct evidence for the absence of Cu segregation at boundaries, the present
results clearly indicate that superplastic flow and cavitation at low stresses are controlled not only by the impurity level,
but also by its type. 相似文献
16.
G. M. Ludtka R. E. Oakes R. L. Bridges J. L. Griffith 《Metallurgical and Materials Transactions A》1993,24(2):369-377
A uranium-2 molybdenum (U-2Mo) alloy was shown to exhibit superplastic behavior over the β + γ two-phase field temperature
regime and over a limited temperature span in the α + γ field. At Oak Ridge, two distinct processes were developed that evolved
microstructures conducive to superplasticity. These microstructures were shown to exhibit superplasticity (elongations >500
pct) over a broad range of strain rates, from 2.5 × 10-4 to 1 × 10-2 s-1. A maximum value of 700 pct elongation was reached at 695 °C and a true constant strain rate of 2.5 × 10-3 s-1. This study details the processing sequences, microstructures, strain-rate sensitivity, and maximum elongation data generated
to characterize the superplastic U-2Mo alloy. In addition, the fracture and cavitation analyses conducted on constant strain-rate
tensile test specimens are discussed. 相似文献
17.
Hajime Iwasaki Takasuke Mori Mamoru Mabuchi Kenji Higashi 《Metallurgical and Materials Transactions A》1998,29(2):677-683
High-strain-rate superplastic behavior has been investigated for Si3N4p
/Al-Mg-Si (6061) composites with a V
f
=20 and 30 pct, respectively, where V
f
is the volume fraction of reinforcements. A maximum elongation was attained at a temperature close to the onset temperature
for melting for both composites. The maximum elongation for the 30 vol pct composite was larger than that for the 20 vol pct
composite. Development of cavities transverse to the tensile direction is responsible for the lower maximum elongation of
the 20 vol pct composite. However, development of the transverse cavities was limited to the optimum superplastic temperature
for the 30 vol pct composite. The differential scanning calorimetry (DSC) investigation showed that a sharp endothermic peak
appeared for the 30 vol pct composite, indicating that sufficient partial melting occurs. It is, therefore, likely that the
stress concentrations are sufficiently relaxed by a liquid phase and that the development of transverse cavities is limited
for the 30 vol pct composite. 相似文献
18.
Characterization of superplastic deformation behavior of a fine grain 5083 Al alloy sheet 总被引:3,自引:0,他引:3
R. Verma P. A. Friedman A. K. Ghosh S. Kim C. Kim 《Metallurgical and Materials Transactions A》1996,27(7):1889-1898
Superplastic deformation behavior of a fine grain 5083 Al sheet (Al-4.2 pct Mg-0.7 pct Mn, trade name FORMALL 545) has been
investigated under uniaxial tension over the temperature range of 500 °C to 565 °C. Strain rate sensitivity values >0.3 were
observed over a strain rate range of 3 × 10−5 s−1 to 1 × 10−2 s−1, with a maximum value of 0.65 at 5 × 10−4 s−1 and 565 °C. Tensile elongations at constant strain rate exceeded 400 pct; elongations in the range of 500 to 600 pct were
obtained under constant crosshead speed and variable strain rates. A short but rapid prestraining step, prior to a slower
superplastic strain rate, provided enhanced tensile elongation at all temperatures. Under the two-step schedule, a maximum
tensile elongation of 600 pct was obtained at 550 °C, which was regarded as the optimum superplastic temperature under this
condition. Dynamic and static grain growth were examined as functions of time and strain rate. It was observed that the dynamic
grain growth rate was appreciably higher than the static growth rate and that the dynamic growth rate based on time was more
rapid at the higher strain rate. Cavitation occurred during superplastic flow in this alloy and was a strong function of strain
rate and temperature. The degree of cavitation was minimized by superimposition of a 5.5 MPa hydrostatic pressure during deformation,
which produced a tensile elongation of 671 pct at 525 °C.
R. VERMA, formerly Visiting Scientist, Department of Materials Science and Engineering, University of Michigan 相似文献
19.
《粉末冶金学》2013,56(5):349-353
The new type of Mg–8Al–1Sn (AT81) magnesium matrix composites reinforced with different volume fractions (5, 10, 15, 20, 25 and 30 vol.-%) of SiC particles (average size of 10 μm) was fabricated by powder metallurgy. With the increasing volume fraction of SiC particles (SiCp), the particles gradually show more homogeneous distribution. Compared with the AT81 alloy, the yield strength (YS) and ultimate compressive strength of the SiCp/AT81 composites are improved simultaneously. With the increasing SiCp from 0 to 30 vol.-%, the YS and ultimate compressive strength increase from 69 to 239 MPa and 286 to 385 MPa respectively, while the corresponding fracture strain (ε) decreases from 19·3 to 4·8%. The improvement of the YS and ultimate compressive strength of the SiCp/AT81 composites benefits from the more homogeneous microstructure due to the increase in the SiC particles. 相似文献
20.
Roberto B. Figueiredo Terence G. Langdon 《Metallurgical and Materials Transactions A》2014,45(8):3197-3204
Experiments show that the magnesium AZ31 (Mg-3 pct Al-1 pct Zn) alloy exhibits excellent superplastic properties at 623 K (350 °C) after processing by equal-channel angular pressing using a die with a channel angle of 135 deg and a range of decreasing processing temperatures from 473 K to 413 K (200 °C to 140 °C). A maximum elongation to failure of ~1200 pct was achieved in this alloy at a tensile strain rate of 1.0 × 10?4 s?1. Microstructural inspection showed evidence for cavity formation and grain growth during tensile testing with the grain growth leading to significant strain hardening. An examination of the experimental data shows that grain boundary sliding is dominant during superplastic flow. Furthermore, a comprehensive review of the present results and extensive published data for the AZ31 alloy shows the exponent of the inverse grain size is given by p ≈ 2 which is consistent with grain boundary sliding as the rate-controlling flow mechanism. 相似文献