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1.
Yeong Hwan Song Masakazu Tane Takuya Ide Yoshihiro Seimiya Bo Young Hur Hideo Nakajima 《Metallurgical and Materials Transactions A》2010,41(8):2104-2111
Al-3.7 pct Si-0.18 pct Mg foams strengthened by AlN particle dispersion were prepared by a melt foaming method, and the effect
of foaming temperature on the foaming behavior was investigated. Al-3.7 pct Si-0.18 pct Mg alloy containing AlN particles
was prepared by noncompressive infiltration of Al powder compacts with molten Al alloy in nitrogen atmosphere, and it was
foamed at different foaming temperatures ranging from 1023 to 1173 K. The porosity of prepared foam decreases and the pore
structure becomes homogeneous with increasing foaming temperature. When the foaming temperature is higher than 1123 K, homogeneous
pores are formed in the prepared ingot without using oxide particles and metallic calcium granules, which are usually used
for stabilizing a foaming process. This stabilization of the foaming at high temperatures is possibly caused by Al3Ti intermetallic compounds formed at high temperature and AlN particles. Compression tests for the prepared foams revealed
that the absorbed energy per unit mass of prepared Al-3.7 pct Si-0.18 pct Mg foam is higher than those of aluminum foams strengthened
by alloying or dispersion of reinforcements. It is remarkable that the oscillation in stress, which usually appears in strengthened
aluminum foams, does not appear in the plateau stress region of the present Al-3.7 pct Si-0.18 pct Mg foam. The homogeneity
in cell walls and pore morphology due to the stabilization of pore formation and growth by AlN and Al3Ti particles is a possible cause of this smooth plateau stress region. 相似文献
2.
I. G. Davies J. M. Dennis A. Hellawell 《Metallurgical and Materials Transactions B》1970,1(1):275-280
The microstructure of a ternary alloy, Al-5 wt pct Ti, 1 wt pct B, has been examined by optical and electron transmission microscopy, by selected area diffraction, and electron probe microscopy, by selected area diffraction, and electron probe microanalysis. Particles of Al3Ti are found at the center of grains and there exist preferred epitaxial orientations between this compound and the surrounding aluminum. Particles containing titanium and boron occur at aluminum grain boundaries and have no preferred configurations with respect to the aluminum or to one another. It is concluded that the active heterogeneous nuclei are therefore Al3Ti and that particles of TiB2, AlB2, or a ternary compound are not active in this alloy. Grain size measurements in binary Al-Ti alloys suggest that particles of a nucleating phase must be present at concentrations as low as 0.01 wt pct Ti, and it is suggested that these could be Al3Ti if the existing binary phase diagram Al-Ti is in error. 相似文献
3.
A. Munitz V. Y. Zenou C. Cotler M. Talyanker 《Metallurgical and Materials Transactions A》1997,28(4):1035-1046
The impact of cooling rates on the microstructure of Al-U alloys was studied by optical, scanning electron, and transmission
electron microscopy. A variety of solidification techniques were employed to obtain cooling rates ranging between 3 × 10−2 and 106 K/s. High-purity uranium (99.9 pct) and high-purity aluminum (99.99 pct), or “commercially pure” type Al-1050 aluminum alloys
were used to prepare Al-U alloys with U concentration ranging between 3 and 22 wt pct. The U concentration at which a coupled
eutectic growth was observed depends on the cooling rates imposed during solidification and ranged from 13.8 wt pct for the
slower cooling rates to more than 22 wt pct for the fastest cooling rates. The eutectic morphology and its distribution depends
on the type of aluminum used in preparing the alloys and on the cooling rates during solidification. The eutectic in alloys
prepared from pure aluminum was evenly distributed, while for those prepared from Al-1050, the eutectic was unevenly distributed,
with eutectic colonies of up to 3 mm in diameter. Two lamellar eutectic structures were observed in alloys prepared from pure
aluminum containing more than 18 wt pct U, which solidified by cooling rates of about 10 K/s. One structure consisted of the
stable eutectic between UAl4 and Al lamella. The other structure consisted of a metastable eutectic between UAl3 and Al lamella. At least three different eutectic morphologies were observed in alloys prepared from Al-1050. 相似文献
4.
5.
The coarsening of γ′ and the elevated-temperature hardness have been studied as a function of molybdenum content, time, and
temperature in experimental wrought nickel-base superalloys. The alloys were selected from a systematic series containing
3, 4 1/2, and 6 wt pct Al and 1 wt pct Al plus 3 1/2 wt pct Ti. Each of the aluminum (plus titanium) series consisted of four
alloys containing 0, 2, 5, and 8 wt pct Mo. The alloys were solution-treated plus aged up to 112 h at 1700°F (925°C) and up
to 1000 h at 1400°F (760°C). Molybdenum retards the coarsening of γ′ on aging; this retarding effect is most pronounced in
alloys containing 6 wt pct Al. The coarsening of γ′ particles follows Ostwald ripening kinetics. Hardness testingin vacuo at temperatures up to 1750°F (955°C) shows that molybdenum also increases the elevated-temperature hardness significantly.
The relation of elevated-temperature hardness to the volume fraction of γ′ is considered, and the influence of aluminum and
titanium contents is discussed. 相似文献
6.
Silicide precipitation in the Ti−Zr−Al−Si system 总被引:1,自引:0,他引:1
H. M. Flower P. R. Swann D. R. F. West 《Metallurgical and Materials Transactions B》1971,2(12):3289-3297
Silicide precipitation has been studied in a number of martensitic Ti−Si alloys and ternary and more complex alloys containing
zirconium and aluminum. The precipitation has been shown to be strongly influenced by composition. Heterogeneous nucleation
of Ti5Si3 occurs at, and above, 500°C in binary Ti−Si alloys containing up to 2.4 pct Si and little conventional precipitation hardening
can be achieved. Zirconium additions are incorporated into the silicide and produces finer, more stable particle dispersions
accompanied by an improved aging response. If critical concentrations of zirconium (approximately 5 pct) and silicon (approximately
1 pct) are present, matrix nucleation of G.P. zones occurs at, and below 550°C. This is accompanied by a significant aging
response. Additions of aluminum reduce the rate of precipitate growth while having little effect on the nature of the precipitates
produced. It has been shown that typical commercial heat treatments of “near α” silicon-bearing alloys (0.5 pct Si max) do
not produce silicide dispersions.
This paper is based upon a thesis submitted by H. M. FLOWER in partial fulfillment of the requirements of the degree of Doctor
of Philosophy at the University of London. 相似文献
7.
M. A. Doheim A. M. Omran A. Abdel-Gwad G. A. Sayed 《Metallurgical and Materials Transactions A》2011,42(9):2862-2867
Al-Ti-C master alloys have a great potential as efficient grain refiners for aluminum and its alloys. In the present work,
the Al-Ti-C master alloys are synthesized via a relatively novel technique through the reaction of a compacted mixture of K2TiF6 and graphite with molten aluminum. The obtained alloys are examined using scanning electron microscopy (SEM), energy-dispersive
spectroscopy, and X-ray diffraction (XRD) methods. The results indicate that the produced Al-Ti-C master alloys contain TiC
and TiAl3 particles within the aluminum matrix. Also, these alloys were evaluated using the KBI test mold. The results indicate that
the produced Al-Ti-C master alloy is an efficient grain refiner for pure aluminum and its alloys compared with the Al-Ti-B
one. The factors affecting the grain refinement of aluminum and its alloys are studied. The proper conditions for evaluating
the efficiency of the produced Al-Ti-C master alloy to obtain a minimum grain size are as follows: temperature, 993 K (720 °C);
holding time, 2 minutes; and (Ti/Al) weight ratio, 0.01 pct. 相似文献
8.
G. S. Vinod kumar M. Chakraborty F. Garcia-Moreno J. Banhart 《Metallurgical and Materials Transactions A》2011,42(9):2898-2908
A novel foamable aluminum alloy has been developed. It contains sub-micron-sized MgAl2O4 (spinel) particles that are generated in situ by a reaction of SiO2 with a molten Al-Mg alloy. The study involves an optimization of parameters such as Mg concentration, SiO2 particles size, and reaction time and shows that a composite containing MgAl2O4 particles as chief reinforcement in the matrix leads to effective foaming. Composites containing large sized transition phases
and particle agglomerates in the matrix yield poor foam structure. The best foamable composite obtained contained 3.4 vol.
pct of ultrafine (80 nm to 1 μm) MgAl2O4 particles uniformly distributed in an Al-Si alloy matrix. The corresponding metal foam contained 75 pct porosity and exhibited
a uniform distribution of cells. 相似文献
9.
The phase diagram of the isopleth section of the Ti-7 at. pct Mo-Al system has been improved and expanded to include alloys
up to 25 at. pct aluminum. The mechanical and thermal stability of alloys aged in the two-phase region, β +Ti3Al, was correlated to the microstructure. X-ray rocking-curve studies of the polycrystalline specimens showed that after 2
pct deformation of a Ti-7 Mo-16 Al alloy theβ matrix became preferentially plastically deformed, while the Ti3Al particles functioned as hard particles undergoing little lattice distortions.
Formerly a Graduate Student.
This paper is based on a thesis submitted by T. Hamajima in partial fulfillment of the requirements for a Ph.D. degree from
Rutgers University. 相似文献
10.
L. Christodoulou J. R. Gordon J. R. Pickens 《Metallurgical and Materials Transactions A》1985,16(5):945-951
An investigation of the stress-corrosion cracking (SCC) behavior of three aluminum powder alloys, containing 0.0, 0.4, and
0.8 wt pct Co, using double cantilever beam specimens has shown a significant increase in SCC resistance with increasing Co
content. This resistance to cracking takes the form of both a decrease in plateau crack velocity and an increase in the threshold
stress intensity factor for cracking (K
ISCC
) as the Co content increases. The SCC fracture is intergranular and the crack path is tortuous because of the oxides and
Co2Al9 intermetallic particles contained within the powder metallurgy alloys. We propose that the improvements in SCC resistance
result from the Co2Al9 particles, which catalyze the recombination and evolution of hydrogen, thereby reducing hydrogen absorption and embrittlement.
Formerly with Martin Marietta Laboratories 相似文献
11.
T. H. Okabe Ph.D. Candidate K. Fujiwara T. Oishi K. Ono 《Metallurgical and Materials Transactions B》1992,23(4):415-421
Fine niobium aluminide powders such as NbAl3 were produced directly from mixtures of Nb2O5 and aluminum powder by calciothermic reduction. Prior to the reduction experiment, phase equilibria between Nb-Al and Ca-Al
alloys were studied. Isothermal annealing of the specimens in the Nb-Al-Ca system at 1273 K showed that NbAl3 is in equilibrium with CaAl2 and Al-rich Ca-Al liquid alloys and that Nb3Al and Nb2Al equilibrate with Ca-Al alloys containing around 9 to 18 and 18 to 36 mol pct Al, respectively. Based on these experimental
phase equilibria and on reported thermodynamic data of the Al-Ca system, the activities of Al in Nb-Al alloys were evaluated.
This information is necessary in determining suitable compositions and conditions for the coreduction and ultimate production
of single-phase niobium aluminide. The procedure for preparation of niobium aluminide powders by calciothermic reduction of
Nb2O5 consists of three steps: (1) blending of starting materials (Nb2O5 + Al); (2) high-temperature reaction with calcium; and (3) acid leaching. After the reduction of Nb2O5 with calcium and aluminum to produce niobium aluminide powders, by-products of Ca-Al alloy, CaAl2, and CaO were formed. These were removed by leaching in aqueous acid solution. The NbAl3 particles obtained were a few micrometers in size and contained about 0.15 wt pct oxygen. 相似文献
12.
Development of Al-Ti-C grain refiners containing TiC 总被引:32,自引:0,他引:32
Cast Al-Ti-C grain refiners were synthesized by reacting up to 2 pct graphite particles of 20 micron average size with stirred
Al-(5 to 10) pct Ti alloy melts, which generated submicron-sized TiC particles within the melts, and their solidified structures
showed preferential segregation of the carbide phase in the grain or cell boundary regions and occasional presence of free
carbon whose amount exceeded equilibrium values. At the usual melt temperatures of below 1273 K, though, TiC formed first,
but was subsequently found to react with the melt forming a sheathing of A14C3 and Ti3AlC which resulted into poisoning of the TiC particles. However, it was possible to reverse these reactions in order to regain
the virgin TiC particles by superheating the melts in the temperature region where TiC particles are thermodynamically stable.
Grain refining tests using the TiC master alloys produced fine equiaxed grains of cast aluminum whose sizes were comparable
to that obtainable with the standard TiB2 commercial grain refiner. TiC particles introducedvia the master alloys were found to occur in the grain centers, thereby confirming that they nucleated aluminum crystals.
On leave from Regional Research Laboratory (CSIR), Bhopal, is Research Associate. 相似文献
13.
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
14.
F. S. Lin S. B. Chakrabortty E. A. Starke 《Metallurgical and Materials Transactions A》1982,13(3):401-410
The microstructure and tensile properties of two A1-3 wt pct Li-2 wt pct Cu-0.2 wt pct Zr alloys, one Cd-free and one containing
0.2 wt pct Cd, have been investigated. The Cd-free alloy remained unrecrystallized for all solutionizing treatments studied,
whereas a special treatment had to be developed to prevent recrystallization during solutionizing of the 0.2 wt pct Cd alloy.
In combination with cadmium, zirconium either enters into, or nucleates on, the course Al7Cu2Fe and T2 phases during high temperature annealing. This reduces the volume fraction of small coherent Al3Zr particles in the matrix which normally inhibits recrystallization. Consequently, a low temperature anneal to precipitate
Al3Zr is necessary prior to high temperature solutionizing in order to prevent recrystallization in the Cd-containing alloy.
Unlike its effect in lower lithium, higher copper content aluminum alloys, cadmium does not significantly affect the nucleation
of the strengthening precipitates. If anything, cadmium has a detrimental effect on the age hardening response of this alloy,
since it increases the formation of coarse Al-Cu-Li equilibrium phases at grain and subgrain boundaries and thus removes some
of the copper and lithium from participating in the formation of the strengthening precipitates T1 and δ′. Subgrain boundary fracture occurred during tensile tests of both alloys in the unrecrystallized condition; however,
transgranular fracture occurred in tests of the partially recrystallized 0.2 wt pct Cd alloy. Both types of fractures are
believed due to a form of strain localization associated with precipitate free zones and shearable precipitates.
Formerly with the Fracture and Fatigue Research Laboratory, Georgia Institute of Technology, Atlanta, GA 相似文献
15.
Yen-Hung Tan Sheng-Long Lee Yu-Lom Lin 《Metallurgical and Materials Transactions A》1995,26(11):2937-2945
The effect of Be and Fe content on the plane strain fracture toughnessK
IC of aluminum-based A357 alloys is investigated. The fracture behavior of A357 alloys has been evaluated as a function of both
the magnitude and morphology of iron-bearing compounds and silicon particles. Addition of Be is beneficial for tensile properties
and fracture toughness in the case of alloys containing intermediate (0.07 pct) and higher (0.15 pct) Fe levels. On the other
hand, Be added to alloys containing the lower Fe (0.01 pct) level appears detrimental to tensile strength, but the quality
index, notch-yield ratio (NYR), and plane strain fracture toughness were improved. Fractographic analysis reveals that crack
extension of A357 alloys occurs mainly in an intergranular fracture mode. The fracture processes are initiated by void nucleation
at iron-bearing compounds or irregularly shaped eutectic silicon particles as a result of their cracking and decohesion from
the matrix. Then, void growth and coalescence result in growth of the main crack by shear-linkage-induced breakdown of submicronstrengthening
particles. The effect of Be on increasingK
IC is more apparent in the higher Fe alloys than in the lower Fe alloys. Superior toughness obtained by microstructural control
has also been achieved in the intermediate and higher Fe levels of Be-containing alloys, with values equal to those obtained
in alloys of lower Fe content. 相似文献
16.
A. K. Jena A. K. Gupta M. C. Chaturvedi 《Metallurgical and Materials Transactions A》1993,24(10):2181-2187
The influence of silicon on the precipitation kinetics of Al-Cu-Mg alloys is not yet understood, although its effect on the
improvement of mechanical properties is well established. In this study, the kinetics of the first stage of precipitation
in Al-1.52 pct Cu-0.75 pct Mg alloy con-taining 0.49, 0.76, and 1.03 pct Si were investigated by differential scanning calorimetry.
From the calorimetric data, the extent of reactionY and the reaction rate(dY/dt) were evaluated as functions of the reaction temperature. The rates are expressible by the relation(dY/dt) = (1 —Y)k0 exp(— Q*/RT), whereK
0
is the frequency factor andQ* is the activation energy. For the alloys containing 0.49, 0.76, and 1.03 pct Si, the activation energies are 76.7, 70.1,
and 64.6 kJ/mole, respectively, andk
0
changes systematically with silicon content. Critical analysis of these results and those available in the literature on
the silicon-free and 0.23 pct Si containing alloys shows that GP zones precipitate in the 0.49, 0.76, and 1.03 pct Si alloys,
while only GPB zones precipitate in the silicon-free and 0.23 pct Si containing alloys. The sudden change in the precipitation
behavior occurs due to the preferential removal of magnesium from the matrix by the insoluble particles which are present
in 0.49, 0.76, and 1.03 pct Si alloys. The alteration of the matrix composition is also responsible for systematic decrease
in the activation energy. 相似文献
17.
While superferritic stainless steels containing 29 pct chromium possess excellent resistance to corrosion, they may, under
certain conditions, be embrittled by the precipitation of intermetallic phases. The extent to which the precipitation reactions
can be retarded by alloying additions of aluminum and copper has been evaluated. It was found that additions of aluminum to
an Fe-29 pct Cr-4 pct Mo-1.5 pct Ni base alloy suppress the precipitation of the undesirable sigma and chi intermetallic phases,
but additions of up to 3 pct aluminum promote 475 ‡C embrittlement. Additions of copper slightly reduce the precipitation
of sigma and chi phases under most conditions but enhance 475 ‡C embrittlement. The resistance to corrosion in 10 pct H2SO4 and 10 pct FeCl3 was assessed. All the aluminum-containing alloys performed significantly better in H2SO4 than the base alloy; however, large additions of aluminum had a deleterious effect on the pitting resistance in FeCl3. Additions of copper improved the resistance to FeCl3 and lowered the rate of corrosion in the H2SO4 solution used. 相似文献
18.
Q. G. Wang C. H. Caceres J. R. Griffiths 《Metallurgical and Materials Transactions A》2003,34(12):2901-2912
The strain dependence of particle cracking in aluminum alloys A356/357 in the T6 temper has been studied in a range of microstructures
produced by varying solidification rate and Mg content, and by chemical (Sr) modification of the eutectic silicon. The damage
accumulates linearly with the applied strain for all microstructures, but the rate depends on the secondary dendrite arm spacing
and modification state. Large and elongated eutectic silicon particles in the unmodified alloys and large π-phase (Al9FeMg3Si5) particles in alloy A357 show the greatest tendency to cracking. In alloy A356, cracking of eutectic silicon particles dominates
the accumulation of damage while cracking of Fe-rich particles is relatively unimportant. However, in alloy A357, especially
with Sr modification, cracking of the large π-phase intermetallics accounts for the majority of damage at low and intermediate strains but becomes comparable with silicon
particle cracking at large strains. Fracture occurs when the volume fraction of cracked particles (eutectic silicon and Fe-rich
intermetallics combined) approximates 45 pct of the total particle volume fraction or when the number fraction of cracked
particles is about 20 pct. The results are discussed in terms of Weibull statistics and existing models for dispersion hardening. 相似文献
19.
The effects of supercooling on the microstructure of Cu-Co alloys containing 10 to 65 wt pct Co were investigated. Supercooling
of the alloys below a characteristic temperature,t
SEP, resulted in a metastable phase separation into two liquids: one Co rich (L1) and the other Cu rich (L2). The microstructure
of the phase-separated alloys consisted of spherulites of one phase embedded in a matrix of the other. The spherulites in
alloys containing less than 40 wt pct Co were solidified from the L1 melt and from L2 in alloys containing more than 55 wt
pct Co. Supercooling of copper alloys containing around 50 wt pct Co resulted in a duplex structure of fine and coarse dendrites.
Microstructural evidence was presented for the formation of aε-Cu metastable phase in alloys containing less than 30 wt pct Co. 相似文献
20.
Abdul Khaliq Muhammad Akbar Rhamdhani Geoffrey A. Brooks John Grandfield 《Metallurgical and Materials Transactions B》2014,45(2):784-794
Transition metal impurities (V, Ti, Zr, and Cr) reduce the electrical conductivity of smelter grade aluminum. These impurities are removed in the form of their borides by reacting with added Al-B master alloys i.e., boron treatment. Although, boron treatment is widely used for the production of high purity aluminum alloys in casthouse the fundamental understanding is lacking and published industrial data are limited. In the current study, industrial trials on the removal of impurities were conducted at one of the high purity aluminum alloys producers in Australasia. Kinetics analysis revealed that the rate of reaction is controlled by the mass transfer of impurities in the bulk melt. The measured mass transfer coefficient (k m) of V and Ti were 1.1 × 10?4 and 2.6 × 10?4 m/s respectively, in the naturally stirred molten aluminum. The rate of V and Ti removal was faster compared to Zr and Cr during the boron treatment of smelter grade aluminum. Mass balance analysis revealed that 70 wt pct of V and Ti combined as borides in the first hour of the total 12 hours of boron treatment process. The calculated amount of un-reacted B was approximately 25.5 wt pct of initial amount added that remained in the final alloy. There was no evidence of boride rings formation, although partially dissolved AlB12 particles were observed under scanning electron microscope. Finally, implications for industrial practice are discussed for the improvement of current boron treatment process that include changing the source of boron, multiple stage addition of boron and better stirring of the molten aluminum. 相似文献