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1.
The transverse creep behavior of a unidirectional 30 vol pct boron/1145-0 aluminum composite material was investigated over
the temperature range 573 to 773 K. The creep curve of the composite exhibited primary, steady state, and tertiary stages
of creep, as did the unreinforced laminated matrix; however, the primary stage of creep was consid-erably less pronounced
in the composite than in the matrix. The minimum (or steady state) creep rate of the composite was less than that of the laminated
matrix alone below a transition stress Σ = 1.74 × 10−4
E whereE is Young's Modulus of aluminum. Above this transition stress, the minimum creep rate of the composite exceeds that of the
unreinforced matrix; further, the strain to failure of the composite generally decreased when the applied stress was above
the transition stress. The temperature dependence of the minimum creep rate was the same for both the composite and the laminated
matrix. Failure in the composite was initiated by debonding of the filament-matrix interface and it is suggested that debonding
of the interface contributes in an additive way to the creep of the composite and to a greater extent at high stresses, leading
to the transition stress observed. 相似文献
2.
The transverse creep behavior of a unidirectional 30 vol pct boron/1145-0 aluminum composite material was investigated over
the temperature range 573 to 773 K. The creep curve of the composite exhibited primary, steady state, and tertiary stages
of creep, as did the unreinforced laminated matrix; however, the primary stage of creep was consid-erably less pronounced
in the composite than in the matrix. The minimum (or steady state) creep rate of the composite was less than that of the laminated
matrix alone below a transition stress Σ = 1.74 × 10−4
E whereE is Young's Modulus of aluminum. Above this transition stress, the minimum creep rate of the composite exceeds that of the
unreinforced matrix; further, the strain to failure of the composite generally decreased when the applied stress was above
the transition stress. The temperature dependence of the minimum creep rate was the same for both the composite and the laminated
matrix. Failure in the composite was initiated by debonding of the filament-matrix interface and it is suggested that debonding
of the interface contributes in an additive way to the creep of the composite and to a greater extent at high stresses, leading
to the transition stress observed.
Formerly graduate student 相似文献
3.
Minoru Furukawa Jingtao Wang Zenji Horita Minoru Nemoto Yan Ma Terence G. Langdon 《Metallurgical and Materials Transactions A》1995,26(3):633-639
Experiments were conducted to compare the influence of temperature on the flow and strain-hardening characteristics of an
Al-6061 metal matrix composite, reinforced with ∼20 vol pct of Al2O3-based microspheres, with the unreinforced monolithic alloy. At room temperature, the yield stresses and the strain-hardening
rates are higher in the composite material in the asquenched condition and after aging at 448 K for periods of time up to
300 hours. The 0.2 pct proof stress and the strain-hardening rate decrease with increasing temperature in both materials,
but the rate of decrease is faster in the composite so that the unreinforced monolithic alloy exhibits higher yield stresses
and strain-hardening rates at temperatures in the vicinity of 600 K. Under conditions of constant stress at high temperatures,
the composite exhibits both a higher creep strength than the monolithic alloy and higher values for the stress exponents for
creep.
Formerly Visiting Scholar, Kyushu University, is Associate Professor, Department of Metallurgy, Xian Institute of Metallurgy
and Construction Engineering, Xian 710055, People’s Republic of China. 相似文献
4.
Axial, low cycle fatigue properties of 25 and 44 fiber vol pct SiC/Ti(6Al-4V) composites, measured at 650 °C, were compared
with the fatigue properties of unreinforced Ti(6Al-4V) at the same temperature. A prior study of the fatigue behavior of this
composite system at room temperature indicated that the SiC fiber reinforcement did not provide the anticipated improvement
of fatigue resistance of this alloy. At 650 °C, the composite fatigue properties degraded somewhat from those at room temperature.
However, these properties degraded more for the unreinforced matrix at 650 °C with the result that the composite fatigue strength
was two to three times the fatigue strength of the matrix alloy. The reasons for this reversal are discussed in terms of crack
initiation at broken fibers and residual matrix stresses. 相似文献
5.
Creep tests were conducted on an Al-6092 alloy reinforced with 25 vol pct SiC particulates and on an unreinforced Al-6092
matrix alloy. Both materials exhibit creep behavior indicating the presence of a threshold stress and both have a true stress
exponent of 3, but with meaured activation energies for creep of ∼135 and ∼230 kJ mol−1 in the unreinforced and reinforced materials, respectively. By incorporating a temperature-dependent load transfer into the
analysis, it is shown that the activation energy for the composite is reduced to ∼130 kJ mol−1. Both materials therefore exhibit creep behavior consistent with viscous glide and the dragging of Mg solute atmospheres,
and in addition the results for the composite are consistent with the proposal that the creep of metal matrix composites divides
into two classes depending upon the rate-controlling process in the matrix alloys. 相似文献
6.
The creep rupture life of an Al/Al2O3 composite and its creep behavior were studied. The metal matrix composite was produced by using a squeeze casting technique.
High-temperature tensile tests and creep experiments were conducted on a 15 vol pct alumina fiber-reinforced AC2B Al alloy
metal matrix composite (MMC). The high-temperature tensile strength of Al/Al2O3 composite is 14 pct higher than that of an AC2B Al alloy. The steady-state creep rate and the creep life were measured. The
stress exponent in Norton’s equation and the activation energy were computed. The stress exponents of the AC2B and Al/Al2O3 composites were found to be 4 and 12.3, respectively. The activation energy of the AC2B and Al/Al2O3 composites was found to be 242.74 and 465.35 kJ/mol, respectively. A new equation for predicting creep life was established,
which was based on the conservation of the creep strain energy. The theoretical predictions were compared with those of the
experiment results, and a good agreement was obtained. It was found that the creep life is inversely proportional to the (n + 1)th power of the applied stress and strain failure energy of creep is conserved. The creep fracture surface, examined
by scanning electron microscopy (SEM), showed that the MMC specimen failed in a brittle manner. 相似文献
7.
Creep processes in magnesium alloys and their composites 总被引:1,自引:0,他引:1
Sklenička V. Pahutová M. Kuchařová K. Svoboda M. Langdon T. G. 《Metallurgical and Materials Transactions A》2002,33(13):883-889
A comparison is made between the creep characteristics of two squeeze-cast magnesium alloys (AZ 91 and QE 22) reinforced with
20 vol pct Al2O3 short fibers and the unreinforced AZ 91 and QE 22 matrix alloys. The results show the creep resistance of the reinforced
materials is considerably improved by comparison with the unreinforced matrix alloys. It is suggested that creep strengthening
in these short-fiber composites arises primarily from the existence of a threshold stress and the effect of load transfer.
By testing samples to failure, it is demonstrated that the unreinforced and reinforced materials exhibit similar times to
failure at the higher stress levels. A detailed microstructural investigation by transmission electron microscopy (TEM) reveals
no substantial changes in matrix microstructure due to the presence of the reinforcement. This suggests that direct composite
strengthening dominates over indirect effects.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
8.
Creep processes in magnesium alloys and their composites 总被引:1,自引:0,他引:1
V. Sklenička M. Pahutová K. Kuchařová M. Svoboda T. G. Langdon 《Metallurgical and Materials Transactions A》2002,33(3):883-889
A comparison is made between the creep characteristics of two squeeze-cast magnesium alloys (AZ 91 and QE 22) reinforced with
20 vol pct Al2O3 short fibers and the unreinforced AZ 91 and QE 22 matrix alloys. The results show the creep resistance of the reinforced
materials is considerably improved by comparison with the unreinforced matrix alloys. It is suggested that creep strengthening
in these short-fiber composites arises primarily from the existence of a threshold stress and the effect of load transfer.
By testing samples to failure, it is demonstrated that the unreinforced and reinforced materials exhibit similar times to
failure at the higher stress levels. A detailed microstructural investigation by transmission electron microscopy (TEM) reveals
no substantial changes in matrix microstructure due to the presence of the reinforcement. This suggests that direct composite
strengthening dominates over indirect effects.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
9.
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
10.
G. Wang P. Shi M. Qi F. X. Chen D. Z. Yang J. J. Xu 《Metallurgical and Materials Transactions A》1998,29(6):1741-1747
The objective of this article is to characterize the sliding wear behavior of a 30 vol pct Ti50Ni25Cu25 particulate-reinforced aluminum matrix composite under dry conditions. The transformation temperatures of Ti50Ni25Cu25 particles were measured before and after the compounding procedure by the differential scanning calorimeter (DSC) method.
The wear tests were carried out on a pin-on-disc machine. A 10 vol pct SiC particulate-reinforced composite and pure aluminum
were chosen as the comparison specimens. The results indicate that Al-30 vol pct Ti50Ni25Cu25 composites exhibit higher wear resistance than their unreinforced matrices and are comparable with Al-10 vol pct SiC composites
in this experiment. A self-adaptive mechanism that contributes to the wear resistance of an Al-30 vol pct Ti50Ni25Cu25 composite is proposed. Scanning electron microscopy (SEM) and energy diffraction spectrum (EDS) examinations were carried
out to investigate the wear mechanism and interface reactions. The results indicate that the interfacial reaction is a predominant
factor in determining the wear behavior of the Ti50Ni25Cu25/Al composite. 相似文献
11.
The microstructure and tensile properties of an 8090 Al-Li alloy reinforced with 15 vol pct SiC particles were investigated,
together with those of the unreinforced alloy processed following the same route. Two different heat treatments (naturally
aged at ambient temperature and artificially aged at elevated temperature to the peak strength) were chosen because they lead
to very different behaviors. Special emphasis was given to the analysis of the differences and similarities in the microstructure
and in the deformation and failure mechanisms between the composite and the unreinforced alloy. It was found that the dispersion
of the SiC particles restrained the formation of elongated grains during extrusion and inhibited the precipitation of Al3Li at ambient temperature. The deformation processes in the peak-aged materials were controlled by the S′ precipitates, which acted as barriers for dislocation motion and homogenized the slip. Homogeneous slip was also observed
in the naturally aged composite, but not in the unreinforced alloy, where plastic deformation was concentrated in slip bands.
The most notorious differences between the alloy and the composite were found in the fracture mechanisms. The naturally aged
unreinforced alloy failed by transgranular shear, while the failure of the peak-aged alloy was induced by grain-boundary fracture.
The fracture of the composite in both tempers was, however, precipitated by the progressive fracture of the SiC reinforcements
during deformation, which led to the early failure at the onset of plastic instability. 相似文献
12.
Creep strengthening in a discontinuous SiC-Al composite 总被引:2,自引:0,他引:2
Kyung-Tae Park Farghalli A. Mohamed 《Metallurgical and Materials Transactions A》1995,26(12):3119-3129
High-temperature strengthening mechanisms in discontinuous metal matrix composites were examined by performing a close comparison
between the creep behavior of 30 vol pct SiC-6061 Al and that of its matrix alloy, 6061 Al. Both materials were prepared by
powder metallurgy techniques. The experimental data show that the creep behavior of the composite is similar to that of the
alloy in regard to the high apparent stress exponent and its variation with the applied stress and the strong temperature
dependence of creep rate. By contrast, the data reveal that there are two main differences in creep behavior between the composite
and the alloy: the creep rates of the composite are more than one order of magnitude slower than those of the alloy, and the
activation energy for creep in the composite is higher than that in the alloy. Analysis of the experimental data indicates
that these similarities and differences in creep behavior can be explained in terms of two independent strengthening processes
that are related to (a) the existence of a temperature-dependent threshold stress for creep, τ0, in both materials and (b) the occurrence of temperature dependent load transfer from the creeping matrix (6061 Al) to the
reinforcement (SiC). This finding is illustrated by two results. First, the high apparent activation energies for creep in
the composite are corrected to a value near the true activation energy for creep in the unreinforced alloy (160 kJ/mole) by
considering the temperature dependence of the shear modulus, the threshold stress, and the load transfer. Second, the normalized
creep data of the composite fall very close to those of the alloy when the contribution of load transfer to composite strengthening
is incorporated in a creep power law in which the applied stress is replaced by the effective stress, the stress exponent,n, equals 5, and the true activation energy for creep in the composite,Q
c
, is equal to that in the alloy.
formerly Research Associate, Materials Section, Department of Mechanical and Aerospace Engineering, University of California
This article is based on a presentation made in the symposium entitled “Creep and Fatigue in Metal Matrix Composites” at the
1994 TMS/ASM Spring meeting, held February 28–March 3, 1994, in San Francisco, California, under the auspices of the Joint
TMS-SMD/ASM-MSD Composite Materials Committee. 相似文献
13.
Induction melting and electron beam melting techniques were employed in the production of unidirectionally solidified eutectic composites of Ti-1.7 wt pct B and Ti-8.5 wt pct Si. The grown eutectics were reinforced by 7.7 volume pct of TiB fibers and 31 volume pct of Ti5Si3 fibers respectively. Controlled dendritic solidification of a hypereutectic composition of Ti-12 wt pct Si was also accomplished. Tensile, compressive, creep, and stress rupture specimens were cut from the eutectic composites and tested with reinforcing fibers parallel to the load axis. Ti?TiB eutectic was found to have less than the critical volume fraction of fibers necessary for reinforcement, while Ti?Ti5Si3 composite attained a compressive yield strength of 275,000 psi and a compressive Young's modulus of 30×108 psi after heat treatment. The 500 and 4000 hr stress rupture properties of Ti?Si eutectic were superior to commercial titanium alloys at 1000° and 1200°F. The minimum creep rate of Ti?Ti5Si3 eutectic composite was lower than all other titanium alloys at 1000°F. Tensile, compressive, and creep properties of the Ti-8.5 wt pct Si eutectic are discussed in terms of the current theories of composite behavior. 相似文献
14.
P. E. Krajewski J. W. Jones J. E. Allison 《Metallurgical and Materials Transactions A》1995,26(12):3107-3118
The effect of TiC particle reinforcement on the creep behavior of Al (99.8) and Al-1.5Mg is investigated in the temperature
range of 150 °C to 250 °C. The dislocation structure developed during creep is characterized in these materials. The addition
of TiC increases creep resistance in both alloys. In pure aluminum, the presence of 15 vol pct TiC leads to a factor of 400
to 40,000 increase in creep resistance. The creep strengthening observed in Al/TiC/15p is substantially greater than the direct strengthening predicted by continuum models. Traditional methods for explaining
creep strengthening in particle-reinforced materials(e.g., threshold stress, constant structure, and dislocation density) are unable to account for the increase in creep resistance.
The creep hardening rate(h) is found to be 100 times higher in Al/TiC/15p, than in unreinforced Al. When incorporated into a recovery creep model, this increase inh can explain the reduction in creep rate in Al/TiC/15p. Particle reinforcement affects creep hardening, and thus creep rate, by altering the equilibrium dislocation substructure
that forms during steady-state creep. The nonequilibrium structure generates internal stresses which lower the rate of dislocation
glide. The strengthening observed by adding TiC to Al-1.5Mg is much smaller than that found in the pure aluminum materials
and is consistent with the amount of strengthening predicted by continuum models. These results show that while both direct
(continuum) and indirect strengthening occur in particle-reinforced aluminum alloys, the ratio of indirect to direct strengthening
is strongly influenced by the operative matrix strengthening mechanisms.
This article is based on a presentation made in the symposium entitled “Creep and Fatigue in Metal Matrix Composites” at the
1994 TMS/ASM Spring meeting, held February 28–March 3, 1994, in San Francisco, California, under the auspices of the Joint
TMS-SMD/ASM-MSD Composite Materials Committee. 相似文献
15.
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
16.
A. B. Pandey R. S. Mishra Y. R. Mahajan 《Metallurgical and Materials Transactions A》1996,27(2):305-316
The effect of an alloying element, 4 wt pct Mg, on the steady-state creep behavior of an Al-10 vol pct SiCp composite has been studied. The Al-4 wt pct Mg-10 vol pct SiCp composite has been tested under compression creep in the temperature range 573 to 673 K. The steady-state creep data of the
composite show a transition in the creep behavior (regions I and II) depending on the applied stress at 623 and 673 K. The
low stress range data (region I) exhibit a stress exponent of about 7 and an activation energy of 76.5 kJ mol-1. These values conform to the dislocation-climb-controlled creep model with pipe diffusion as a rate-controlling mechanism.
The intermediate stress range data (region II) exhibit high and variable apparent stress exponents, 18 to 48, and activation
energy, 266 kJ mol-1, at a constant stress, σ = 50 MPa, for creep of this composite. This behavior can be rationalized using a substructure-invariant
model with a stress exponent of 8 and an activation energy close to the lattice self-diffusion of aluminum together with a
threshold stress. The creep data of the Al-Mg-A12O3f composite reported by Dragone and Nix also conform to the substructure-invariant model. The threshold stress and the creep
strength of the Al-Mg-SiCp, composite are compared with those of the Al-Mg-Al2O3f and 6061 Al-SiCp.w, composites and discussed in terms of the load-transfer mechanism. Magnesium has been found to be very effective in improving
the creep resistance of the Al-SiCp composite. 相似文献
17.
P. E. Krajewski J. E. Allison J. W. Jones 《Metallurgical and Materials Transactions A》1993,24(1):2731-2741
The influence of matrix microstructure and reinforcement with 15 vol pct of TiC particles on the creep behavior of 2219 aluminum
has been examined in the temperature range of 150 °C to 250 °C. At 150 °C, reinforcement led to an improvement in creep resistance,
while at 250 °C, both materials exhibited essentially identical creep behavior. Precipitate spacing in the matrix exerted
the predominant influence on minimum creep rate in both the unreinforced and the reinforced materials over the temperature
range studied. This behavior and the high-stress dependence of minimum creep rate are explained using existing constant structure
models where, in the present study, precipitate spacing is identified as the pertinent substructure dimension. A modest microstructure-independent
strengthening from particle reinforcement was observed at 150 °C and was accurately modeled by existing continuum mechanical
models. The absence of reinforcement creep strengthening at 250 °C can be attributed to diffusional relaxation processes at
the higher temperature. 相似文献
18.
P. E. Krajewski J. E. Allison J. W. Jones 《Metallurgical and Materials Transactions A》1993,24(12):2731-2741
The influence of matrix microstructure and reinforcement with 15 vol pct of TiC particles on the creep behavior of 2219 aluminum
has been examined in the temperature range of 150 ‡C to 250 ‡C. At 150 ‡C, reinforcement led to an improvement in creep resistance,
while at 250 ‡C, both materials exhibited essentially identical creep behavior. Precipitate spacing in the matrix exerted
the predominant influence on minimum creep rate in both the unreinforced and the reinforced materials over the temperature
range studied. This behavior and the high-stress dependence of minimum creep rate are explained using existing constant structure
models where, in the present study, precipitate spacing is identified as the pertinent substructure dimension. A modest microstructure-independent
strengthening from particle reinforcement was observed at 150 ‡C and was accurately modeled by existing continuum mechanical
models. The absence of reinforcement creep strengthening at 250 ‡C can be attributed to diffusional relaxation processes at
the higher temperature. 相似文献
19.
The deformation and failure mechanisms under cyclic deformation in an 8090 Al-Li alloy reinforced with 15 vol pct SiC particles
were studied and compared to those of the unreinforced alloy. The materials were tested under fully reversed cyclic deformation
in the peak-aged and naturally aged conditions to obtain the cyclic response and the cyclic stress-strain curve. The peak-aged
materials remained stable or showed slight cyclic softening, and the deformation mechanisms were not modified by the presence
of the ceramic reinforcements: dislocations were trapped by the S′ precipitates and the stable response was produced by the mobile dislocations shuttling between the precipitates to accommodate
the plastic strain without further hardening. The naturally aged materials exhibited cyclic hardening until failure, which
was attributed to the interactions among dislocations. Strain localization and slip-band formation were observed in the naturally
aged alloy at high cyclic strain amplitudes, whereas the corresponding composite presented homogeneous deformation. Fracture
was initiated by grain-boundary delamination in the unreinforced materials, while progressive reinforcement fracture under
cyclic deformation was the main damage mechanism in the composites. The influence of these deformation and damage processes
in low-cycle fatigue life is discussed. 相似文献
20.
J. S. Marte T. F. Zahrah S. L. Kampe 《Metallurgical and Materials Transactions A》2004,35(5):1603-1611
A series of in-situ, deformation-processed metal matrix composites were produced by direct powder extrusion of blended constituents. The resulting
composites are comprised of a metallic Ti-6Al-4V matrix containing dispersed and co-deformed discontinuously reinforced-intermetallic
matrix composite (DR-IMC) reinforcements. The DR-IMCs are comprised of discontinuous TiB2 particulate within a titanium trialuminide or near-γ Ti-47Al matrix. Thus, an example of a resulting composite would be Ti-6Al-4V+40 vol pct (Al3Ti+30 vol pct TiB2) or Ti-6Al-4V+40 vol pct (Ti-47Al+40 vol pct TiB2), with the DR-IMCs having an aligned, high aspect ratio morphology as a consequence of deformation processing. The degree
to which both constituents deform during extrusion has been examined using systematic variations in the percentage of TiB2 within the DR-IMC, and by varying the percentage of DR-IMC within the metal matrix. In the former instance, variation of
the TiB2 percentage effects variations in relative flow behavior; while in the latter, varying the percentage of DR-IMC within the
metallic matrix effects changes in strain distribution among components. The results indicate that successful co-deformation
processing can occur within certain ranges of relative flow stress; however, the extent of commensurate flow will be limited
by the constituents’ inherent capacity to plastically deform. 相似文献