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1.
The present study was undertaken to investigate the effect of solution treatment (in the temperature range 520 °C to 550 °C)
and artificial aging (in the temperature range 140 °C to 180 °C) on the variation in the microstructure, tensile properties,
and fracture mechanisms of Al-10 wt pct Si-0.6 wt pct Mg/SiC/10p composite castings. In the as-cast condition, the SiC particles are observed to act as nucleation sites for the eutectic
Si particles. Increasing the solution temperature results in faster homogenization of the microstructure. Effect of solution
temperature on tensile properties is evident only during the first 4 hours, after which hardly any difference is observed
on increasing the solution temperature from 520 °C to 550 °C. The tensile properties vary significantly with aging time and
temperature, with typical yield strength (YS), ultimate tensile strength (UTS), and percent elongation (EL) values of ∼300
MPa, ∼330 MPa, and ∼1.4 pct in the underaged condition, ∼330 MPa, ∼360 MPa, and ∼0.65 pct in the peakaged condition, and ∼323
MPa, ∼330 MPa, and ∼0.8 pct in the overaged condition. Prolonged solution treatment at 550 °C for 24 hours results in a slight
improvement in the ductility of the aged test bars. The fracture surfaces exhibit a dimple morphology and cleavage of the
SiC particles, the extent of SiC cracking increasing with increasing tensile strength and reaching a maximum in the overaged
condition. Microvoids act as nucleation sites for the formation of secondary cracks that promote severe cracking of the SiC
particles. A detailed discussion of the fracture mechanism is given. 相似文献
2.
K. H. Eckelmeyer A. D. Romig L. J. Weirick 《Metallurgical and Materials Transactions A》1984,15(7):1319-1330
The effect of cooling rate on the microstructure, mechanical behavior, corrosion resistance, and subsequent age hardenability
of U-6 wt pct Nb is described and discussed. Cooling rates in excess of 20 Ks-1 cause the parent γ-phase to transform martensitically to a niobium supersaturated variant of the α-phase. This martensitic
phase exhibits low hardness and strength, high ductility, good corrosion resistance, and substantial age hardenability. As
cooling rate decreases from 10 Ks-1 to 0.2 Ks-1, fine scale microstructural changes (consistent with spinodal decomposition) occur to an increasing extent. These changes
produce large increases in hardness and strength and large decreases in ductility, slight decreases in corrosion resistance,
and slight changes in age hardenability. At cooling rates less than 0.2 Ks-1 the parent phase undergoes cellular decomposition to a coarse two-phase lamellar microstructure. This lamellar microstructure
exhibits intermediate strength and ductility, substantially reduced corrosion resistance, and no age hardenability. An analysis
of the cooling rates at the centers of water quenched plates indicates that fully martensitic microstructures can be obtained
in plates as thick as 50 mm. 相似文献
3.
S. M. Skolianos T. Z. Kattamis O. F. Devereux 《Metallurgical and Materials Transactions A》1989,20(11):2499-2516
The microstructure and corrosion behavior of as-cast and heat-treated Al-4.5 pct Cu-2.0 pct Mn alloy specimens solidified
at various cooling rates were investigated. The equilibrium phases Al6Mn and θ-Al2Cu, which are observed in the conventionally solidified alloy in the as-cast condition, were not detected in rapidly solidified
(melt-spun) material. Instead, the ternary compound Al20Cu2Mn3 was present in addition to the α phase, which was present in all cases. The morphological and kinetic nature of corrosion
was investigated metallographically and through potentiostatic techniques in 3.5 wt pct NaCl aqueous solution. Corrosion of
the as-cast material was described by two anodic reactions: corrosion of the intermetallic phases and pitting of the α-Al
solid solution. The corrosion rate increased with cooling rate from that for the furnace-cooled alloy to that for the copper
mold-cast alloy and, subsequently, decreased in the rapidly solidified alloy. In the heat-treated material, corrosion could
be described by two anodic reactions: corrosion of Al20Cu2Mn3 precipitate particles and pitting of the α-Al matrix.
S.M. Skolianos, formerly Graduate Student, Department of Metallurgy, University of Connecticut 相似文献
4.
Corbett C. Battalle R. N. Grugel A. B. Hmelo T. G. Wang 《Metallurgical and Materials Transactions A》1994,25(4):865-870
The Pb-50 wt pct Sn alloys were directionally solidified at 21.1 μm s−1 through a temperature gradient of ∼3.5 K mm−1. With the aid of a centrifuge, the solidifying dendritic interfaces were subjected to constant gravity levels, opposite to
the growth direction, up to 15.3 times that of Earth’s. Microstructural examination revealed no significant change in the
secondary dendrite arm spacing, the interdendritic eutectic spacing, or the primary dendrite trunk diameter as a function
of increasing gravity level; the primary dendrite arm spacing, however, decreased significantly. The primary spacing decrease
is argued to result from suppressing convection in the bulk liquid or by modification of the rejected solute layer as a result
of enhanced buoyancy. 相似文献
5.
The effect of powder particle size on the microstructure, mechanical properties, and fracture behavior of Al-20 wt pct Si
alloy powders was studied in both the gas-atomized and extruded conditions. The microstructure of the as-atomized powders
consisted of fine Si particles and that of the extruded bars showed a homogeneous distribution of fine eutectic Si and primary
Si particles embedded in the Al matrix. The grain size of fcc-Al varied from 150 to 600 nm and the size of the eutectic Si
and primary Si was about 100 to 200 nm in the extruded bars. The room-temperature tensile strength of the alloy with a powder
size <26 μm was 322 MPa, while for the coarser powder (45 to 106 μm), it was 230 MPa. The tensile strength of the extruded
bar from the fine powder (<26 μm) was also higher than that of the Al-20 wt pct Si-3 wt pet Fe (powder size: 60 to 120 μm)
alloys. With decreasing powder size from 45 to 106 μm to <26 μm, the specific wear of all the alloys decreased significantly
at all sliding speeds due to the higher strength achieved by ultrafine-grained constituent phases. The thickness of the deformed
layer of the alloy from the coarse powder (10 μm at 3.5 m/s) was larger on the worm surface in comparison to the bars from
the fine powders (5 μm at 3.5 m/s), attributed to the lower strength of the bars with coarse powders. 相似文献
6.
The effect of powder particle size on the microstructure, mechanical properties, and fracture behavior of Al-20 wt pct Si
alloy powders was studied in both the gas-atomized and extruded conditions. The microstructure of the as-atomized powders
consisted of fine Si particles and that of the extruded bars showed a homogeneous distribution of fine eutectic Si and primary
Si particles embedded in the Al matrix. The grain size of fcc-Al varied from 150 to 600 nm and the size of the eutectic Si
and primary Si was about 100 to 200 nm in the extruded bars. The room-temperature tensile strength of the alloy with a powder
size <26 μm was 322 MPa, while for the coarser powder (45 to 106 μm), it was 230 MPa. The tensile strength of the extruded bar from the fine powder (<26 μm) was also higher than that of the Al-20 wt pct Si-3 wt pct Fe (powder size: 60 to 120 μm) alloys. With decreasing powder size from 45 to 106 μm to <26 μm, the specific wear of all the alloys decreased significantly at all sliding speeds due to the higher strength achieved by
ultrafine-grained constituent phases. The thickness of the deformed layer of the alloy from the coarse powder (10 μm at 3.5 m/s) was larger on the worn surface in comparison to the bars from the fine powders (5 μm at 3.5 m/s), attributed to the lower strength of the bars with coarse powders. 相似文献
7.
Nb-1 wt pct Zr/218W long-fiber composite monotapes, nominally containing 0 to 70 vol pct of 218 tungsten fibers, were fabricated
by arc spraying the Nb-1 pct Zr matrix onto the tungsten fibers. The monotapes were consolidated by hot pressing and hot isostatic
pressing techniques. Tensile tests conducted between 1400 and 1600 K, under engineering strain rates varying between 1.5×10−5 and 1.5×10−3 s−1, demonstrated that composites containing 70 vol pct of fibers had the highest strength-to-density ratio. Microstructural
observations of specimens tested at 1400 K revealed that composites containing less than 50 vol pct of fibers showed extensive
matrix cavitation, fiber-matrix debonding, and necking of the fibers. Above 50 vol pct, the composite matrix was less prone
to cavitation, with an increasing tendency toward shear deformation of the fibers as the fiber volume fraction increased.
No fiber damage was observed at 1400 K away from the fractured end, but significant fiber damage was observed at higher temperatures.
A phenomenological model is presented to rationalize these observations.
L.J. GHOSN, formerly Researcher with Case Western Reserve University, Cleveland, OH 44115
This article is based on a presentation made in the Symposium “Mechanisms and Mechanics of Composites Fracture” held October
11–15, 1998, at the TMS Fall Meeting in Rosemont, Illinois, under the auspices of the TMS-SMD/ASM-MSCTS Composite Materials
Committee. 相似文献
8.
Atif Mossad Ali Abdel-Fattah Gaber Kenji Matsuda Susumu Ikeno 《Metallurgical and Materials Transactions A》2013,44(11):5234-5240
The influence of addition of 0.4 wt pct Mg on the precipitation sequence in the balanced Al-1.0 wt pct Mg2Si bearing 0.5 wt pct Ag has been investigated during the continuous heating of the quenched alloy from the solid solution state. Differential scanning calorimetry (DSC) and high-resolution transmission electron microscopy techniques have been used. The DSC experiments showed that all processes occurred are thermally activated. The activation energies of the precipitation processes have been determined and hence the kinetics of these precipitates have been determined. The obtained results have shown that the existence of excess Mg inhibits the formation of the early stage clusters of solute-vacancy clusters. These clusters can be assisted by the binding energies between solute Si, Mg, and Ag atoms and the excess vacancies. On the other hand, excess Mg accelerates the precipitation of random, β′-phase and β-phase precipitates. 相似文献
9.
The effect of dispersed oxides on the oxidation behavior of Al-and Ti-Containing Ni-20 pct Cr alloys
Harold T. Michels 《Metallurgical and Materials Transactions A》1977,8(2):273-278
The effect of dispersed Y2O3 and La2O3 on the isothermal and cyclic oxidation behavior of Al- and Ti-containing Ni-20Cr alloys has been investigated. It has been
found that the dispersolids improve the oxidation resistance of these alloys, but this improvement is less than that observed
in aluminum- and titanium-free Ni-20Cr alloys. The oxidation resistance imparted by the presence of the dispersoids was found
to increase as the aluminum and titanium contents were decreased. It is proposed that these changes in oxidation resistance
arise from differences in the extent of subscale attack, oxidation induced alloy porosity and internal oxidation. 相似文献
10.
The effect of Mg on the microstructure and mechanical behavior of Al-Si-Mg casting alloys 总被引:3,自引:0,他引:3
C. H. Caceres C. J. Davidson J. R. Griffiths Q. G. Wang 《Metallurgical and Materials Transactions A》1999,30(10):2611-2618
The microstructure and tensile behavior of two Al-7 pct Si-Mg casting alloys, with magnesium contents of 0.4 and 0.7 pct,
have been studied. Different microstructures were produced by varying the solidification rate and by modification with strontium.
An extraction technique was used to determine the maximum size of the eutectic silicon flakes and particles. The eutectic
Si particles in the unmodified alloys and, to a lesser extent, in the Sr-modified alloys are larger in the alloys with higher
Mg content. Large Fe-rich π-phase (Al9FeMg3Si5) particles are formed in the 0.7 pct Mg alloys together with some smaller β-phase (Al5FeSi) plates; in contrast, only β-phase plates are observed in the 0.4 pct Mg alloys. The yield stress increases with the Mg content, although, at 0.7 pct
Mg, it is less than expected, possibly because some of the Mg is lost to π-phase intermetallics. The tensile ductility is less in the higher Mg alloys, especially in the Sr-modified alloys, compared
with the lower Mg alloys. The loss of ductility of the unmodified alloy seems to be caused by the larger Si particles, while
the presence of large π-phase intermetallic particles accounts for the loss in ductility of the Sr-modified alloy. 相似文献
11.
The strain rate sensitivity of the tensile properties of polycrystalline Fe-Si alloys with 2.5, 3.5, or 4.5 wt pct Si and
a C+N content of 0.005 to 0.010 wt pct has been determined at room temperature. From these and previous results the influence
of silicon on the athermal and thermal components of the yield (proof) stress of ferrite has been deduced. Both components
increase with silicon content, but at the highest strain rates (and lowest temperatures) the thermal component varies little
with silicon content and is smaller than that reported for pure iron. Transmission electron microscopy of ductile alloys has
shown that the density and arrangements of dislocations are not greatly influenced by silicon content or strain-rate within
the range investigated. At room temperature the dislocation velocity exponent,m*, increases with silicon content, being 4.5, 7.4, and 10.6 (±1.0) in the three alloys. For the grain size studied (5 to 7
ASTM) it appears that the stress for yielding by glide must not exceed about 700 MN/m2 (100 ksi) if brittle behavior is to be avoided. The combinations of temperature and strain rate at which the ductile-brittle
transition occurs are indicated for different silicon contents and different grain sizes.
Formerly with the same Institute 相似文献
12.
The beneficial effect of aging on the intergranular embrittlement of the shape memory Cu-AI-Ni β phase alloys is described.
The fracture progressively changes from completely intergranular to transgranular when quenched samples are aged. The change
in fracture behavior appears to be associated with the precipitation of a ductile phase (a) in the grain boundary region.
This hypothesis is supported by the results of electron microprobe analysis and Auger electron spectroscopy. Aging does not
have any significant effect on the microhardness of samples. Some transmission electron microscopic observations of the changes
occurring on aging are also presented.
Formerly with The University of Connecticut, Storrs, CT 06268. 相似文献
13.
M. G. Mendiratta S. K. Ehlers D. K. Chatterjee H. A. Lipsitt 《Metallurgical and Materials Transactions A》1987,18(2):283-291
The tensile properties, fracture modes, and deformation mechanisms of two DO3 alloys, Fe-25 and Fe-31 at. pct Al, have been investigated as a function of temperature up to 600°C. The first alloy was
produced by powder metallurgy and hot-extrusion, the second by casting and hot-extrusion. At room temperature extensive plastic
deformation occurs in these intermetallics, exhibiting an elongation to fracture of 8 pct and 5.6 pct, respectively. In the
Fe-25Al alloy the deformation process consisted of motion and extensive cross-slip of ordinary dislocations and associated
formation of antiphase-boundary (APB) bands, while in the Fe-31 Al alloy, plasticity occurred by the motion of superlattice
dislocations which eventually dissociated to form APB bands. At room temperature both alloys exhibited transgranular cleavage
fracture modes. The variation of tensile properties and fracture modes with temperature is presented.
H. A. LIPSITT, formerly with the Materials Laboratory of the Air Force Wright Aeronautical Laboratories, Wright-Patterson
Air Force Base, OH 45433-6533 相似文献
14.
V. Kain P. Sengupta P. K. De S. Banerjee 《Metallurgical and Materials Transactions A》2005,36(5):1075-1084
This article describes the corrosion behavior of special austenitic alloys for waste management applications. The special
stainless steels have controlled levels of alloying and impurity elements and inclusion levels. It is shown that “active”
inclusions and segregation of chromium along flow lines accelerated IGC of nonsensitized stainless steels. Concentration of
Cr+6 ions in the grooves of dissolved inclusions increased the potential to the transpassive region of the material, leading to
accelerated attack. It is shown that a combination of cold working and controlled solution annealing resulted in a microstructure
that resisted corrosion even after a sensitization heat treatment. This imparted extra resistance to corrosion by increasing
the fraction of “random” grain boundaries above a threshold value. Randomization of grain boundaries made the stainless steels
resistant to sensitization, IGC, and intergranular stress corrosion cracking (IGSCC) in even hot chloride environments. The
increased corrosion resistance has been attributed to connectivity of random grain boundaries. The reaction mechanism between
the molten glass and the material for process pot, alloy 690, during the vitrification process has been shown to result in
depletion of chromium from the reacting surfaces. A comparison is drawn between the electrochemical behavior of alloys 33
and 22 in 1 M HCl at 65 °C. It is shown that a secondary phase formed during welding of alloy 33 impaired corrosion properties
in the HCl environment.
This article is based on a presentation made in the symposium “Effect of Processing on Materials Properties for Nuclear Waste
Disposition,” November 10–11, 2003, at the TMS Fall meeting in Chicago, Illinois, under the joint auspices of the TMS Corrosion
and Environmental Effects and Nuclear Materials Committees. 相似文献
15.
16.
M. H. Mulazimoglu R. A. L. Drew J. E. Gruzleski 《Metallurgical and Materials Transactions A》1989,20(3):383-389
The changes in electrical conductivity of cast Al−Si alloys, in the range of 2 to 12.6 wt pct silicon due to strontium additions
(0.03 wt pct) have been investigated and explained in terms of variations in microstructure. The strontium-containing alloys
exhibited a higher conductivity than alloys with no strontium, and this conductivity difference increased as the silicon and
magnesium contents were increased and the solidification rate was decreased. It has been demonstrated that this difference
is due to changes in microstructural features of the eutectic silicon upon modification. 相似文献
17.
18.
19.
K. H. Ellison T. R. McNelley A. G. Fox 《Metallurgical and Materials Transactions A》1993,24(9):2001-2007
The elevated temperature deformation behavior of an Al-2. 0 wt pct Li alloy in the temperature range 300 °C to 500 °C was
studied using constant extension-rate tension testing and constant true-stress creep testing under both isothermal and temperature
cycling conditions. Optical microscopy and transmission electron microscopy (TEM) were employed to assess the effect of deformation
on microstructure. The data showed that the stress exponent,n, has a value of about 5. 0 at temperatures above theα +δAlLi solvus (approximately 380 °C) and that subgrains form during plastic deformation. Models for dislocation-climb and dislocation-glide
control of creep were analyzed for alloys deformed in the temperature range of stability of the terminal AlLi solid solution.
A climb model was shown to describe closely the behavior of this material. Anomalous temperature dependence of the activation
energy was observed in this same temperature range. This anomalous behavior was ascribed to unusual temperature dependence
of either the Young’s modulus or the stacking fault energy, which may be associated, in turn, with a disorder-order transformation
on cooling of the alloy.
Formerly with the Materials Engineering Section. Department of Mechanical Engineering, Naval Postgraduate School. 相似文献
20.
Constant strain rate tests at 10-6 s-1 have been carried out at 823 K and 923 K on a vacuum melted 1 1/2 pct Cr 1/2 pct V ferritic steel containing 3 different
carbon contents. After straining to various elongation values specimens were unloaded, cooled and fractured at 77 K. This
gave fracture surfaces consisting almost entirely of intergranular facets, enabling a quantitative study to be made of the
different stages of cavity nucleation and growth. It was found that cavity growth rates were independent of carbon content
but were higher at 923 K than at 823 K. Subsequent grain boundary sliding measurements, using a surface offset technique showed
that sliding increased with increasing carbon content and that cavity nucleation occurred selectively at large grain boundary
carbides.
Formerly of the Department of Metallurgy, University of Manchester. 相似文献