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1.
Kwangjun Euh Jung-Moo Lee Duk-Hyun Nam Sunghak Lee 《Metallurgical and Materials Transactions A》2011,42(13):3961-3968
The fracture property improvement of Ni-Mn-Ga-Fe ferromagnetic shape memory alloys containing ductile γ particles was explained by direct observation of microfracture processes using an in-situ loading stage installed inside a scanning electron microscope (SEM) chamber. The Ni-Mn-Ga-Fe alloys contained a considerable
amount of γ particles in β grains after the homogenization treatment at 1073 K to 1373 K (800 °C to 1100 °C). With increasing homogenization temperature,
γ particles were coarsened and distributed homogeneously along β grain boundaries as well as inside β grains. According to the in-situ microfracture observation, γ particles effectively acted as blocking sites of crack propagation and provided the stable crack growth, which could be confirmed
by the R-curve analysis. The increase in fracture resistance with increasing crack length improved overall fracture properties of
the Ni-Mn-Ga-Fe alloys. This improvement could be explained by mechanisms of blocking of crack propagation and crack blunting
and bridging. 相似文献
2.
Z. W. Liu M. Rakita Q. Han J. G. Li 《Metallurgical and Materials Transactions A》2012,43(6):2116-2124
Quick preheating treatment of the Al-Ti-C pellets and high-intensity ultrasonic vibration are introduced in the fabrication
of in-situ TiC
p
/Mg composites. Al-Ti-C pellets are preheated for about 130 seconds in the furnace at 1023 K (750 °C), in which magnesium
is melted as well. In this process, plenty of heat can be accumulated due to the reactive diffusion between liquid aluminum
and solid titanium in Al-Ti-C, and a small amount of Al3Ti phase is formed as well. After adding the preheated Al-Ti-C into the molten magnesium, thermal explosion takes place in
a few seconds. In the meantime, high-intensity ultrasonic vibration is applied into the melt to disperse in-situ formed TiC particles into the matrix and degas the melt as well. Microstructural characterization indicates that in-situ formed TiC particles are spherical in morphology and smaller than 2 μm in size. Furthermore, a homogeneous microstructure with low porosity of the magnesium composite is obtained due to the effect
of ultrasonic vibration. A novel approach using the quick preheating treatment technique and high-intensity ultrasonic vibration
to synthesize in-situ TiC
p
/Mg composites is proposed in our research. 相似文献
3.
Abdulhaqq A. Hamid S. C. Jain P. K. Ghosh Subrata Ray 《Metallurgical and Materials Transactions B》2006,37(4):519-529
Aluminum alloy—based cast in-situ composite has been synthesized by dispersion of externally added molybdenum trioxide particles (MoO3) in molten aluminum at the processing temperature of 850 °C. During processing, the displacement reaction between molten
aluminum and MoO3 particles results in formation of alumina particles in situ and also releases molybdenum into molten aluminum. A part of this molybdenum forms solid solution with aluminum and the remaining
part reacts with aluminum to form intermetallic phase Mo(Al1−x
Fe
x
)12 of different morphologies. Magnesium (Mg) is added to the melt in order to help wetting of alumina particles generated in situ, by oxidation of molten aluminum by molybdenum trioxide, and helps to retain these particles inside the melt. The mechanical
properties of the cast in-situ composite, as indicated by ultimate tensile stress, yield stress, percentage elongation, and hardness, are relatively higher
than those observed either in cast commercial aluminum or in cast Al-Mo alloy. The wear and friction of the resulting cast
in-situ Al(Mg,Mo)-Al2O3(MoO3) composites have been investigated using a pin-on-disc wear testing machine under dry sliding conditions at different normal
loads of 9.8N, 14.7N, 19.6N, 24.5N, 29.4N, 34.3N, and 39.2 N and a constant sliding speed of 1.05 m/s. The results of the
current investigation indicate that the cumulative volume loss and wear rate of cast in-situ composites are significantly lower than those observed either in cast commercial aluminum or in cast Al-Mo alloy, under similar
load and sliding conditions. Beyond about 30 to 35 N loads, there appears to be a higher rate of increase in the wear rate
in the cast in-situ composite as well as in cast commercial aluminum and cast Al-Mo alloy. For a given normal load, the coefficient of friction
of cast in-situ composite is significantly lower than those observed either in cast commercial aluminum or in cast Al-Mo alloy. The coefficient
of friction of cast in-situ composite increases gradually with increasing normal load while those observed in cast commercial aluminum or in cast Al-Mo
alloy remain more or less the same. Beyond a critical normal load of about 30 to 35 N, the coefficient of friction decreases
with increasing normal load in all the three materials. 相似文献
4.
The fracture toughness of Nb-based in-situ composites typically decreases with increasing volume fractions of hard intermetallic phases, despite the presence of a ductile
niobium solid-solution phase in the microstructure. For composites with a continuous intermetallic matrix, the fracture toughness
can be more than double that of the monolithic intermetallics, but is still low in absolute terms, indicating that the solid-solution
phase is not very effective in inducing ductile-phase toughening. The lack of enhancement of the fracture resistance appears
to arise from an embrittlement effect instigated by the brittle phases in the microstructure, whose nondeformability results
in a high plastic constraint acting on the ductile phase. In this article, an analytical model is developed for treating both
brittle-phase embrittlement and ductile-phase toughening in terms of constituent properties and microstructural variables.
The model is then used to (1) delineate brittle-phase embrittlement and ductile-phase toughening in Nb-based in-situ composites, and (2) design fracture-resistant in-situ composites based on Nb-Ti-Cr, Nb-Ti-Al, and Nb-Ti-Si systems. 相似文献
5.
Effect of shield gas composition on surface tension of steel droplets in a gas-metal-arc welding arc 总被引:1,自引:0,他引:1
A technique for in-situ measurement of the surface tension of molten steel droplets in a gas-metal-arc welding plasma is described. Surface tension
measurements obtained using this method are reported for ER 70S-6 wire, with varying shielding gas compositions, and compared
with previously reported results. The in-situ technique is found to produce results consisten with values found in the literature, while incorporating the effects of alloy
composition and arc atmosphere. 相似文献
6.
The principle of electromagnetic separation of phases (primary phase) in alloy melt is that the electromagnetic force scarcely
acts on the primary phases due to its low electric conductivity as compared to the melt. As a result, a repulsive force acts
on the primary iron-rich phases to push them to move in the direction opposite to that of the electromagnetic force. The in-situ surface composite and the functionally gradient composite reinforced by primary Si are produced when the hypereutectic Al-Si
alloy solidifies under electromagnetic force induced by static magnetic field and DC current. Similarly, the Al-Si-1.20 pct
Fe-1.60 pct Mn alloy in-situ surface composite reinforced by primary iron-rich phase is produced. Based on this, a new method for production of in-situ multigradient composite with several layers, by electromagnetic separation of phases and directional solidification technique,
is proposed. 相似文献
7.
A fully-dense Cu-75 vol pct ZrW2O8 metal matrix composite was fabricated by hot isostatic pressing of Cu-coated ZrW2O8 particles. A small amount of the high-pressure γ-ZrW2O8 phase was created during the cooldown and depressurization following densification; near complete transformation to γ-ZrW2O8 was achieved by subsequent cold isostatic pressing. The thermal expansion behavior of the composite between 25 °C and 325
°C was altered by the cold isostatic pressing treatment, and also depended on the length of time that had passed between thermal
cycles. The measured thermal expansion coefficients within specific temperature ranges varied from −6 · 10−6 K−1 to far above the thermal expansion coefficient of the copper matrix. The complex temperature-dependent expansion/contraction
behavior could be justified by considering the evolution of phase transformations taking place in the ZrW2O8 phase, which were observed by in-situ synchrotron X-ray diffraction measurements. 相似文献
8.
Abdulhaqq A. Hamid S. C. Jain P. K. Ghosh Subrata Ray 《Metallurgical and Materials Transactions A》2006,37(2):469-480
In-situ particle-reinforced aluminum alloy-based cast composites have been synthesized by solidification of the slurry obtained by
dispersion of externally added titanium dioxide (TiO2) particles in molten aluminum at different processing temperatures. Alumina particles (Al2O3) form in situ through chemical reaction of TiO2 particles with molten aluminum. Simultaneously, the chemical reaction also releases titanium, which dissolves into molten
aluminum and results in the formation of intermetallic phase Ti(Al1−x
,Fe
x
)3 during solidification. Increasing the processing temperature increases (1) the amount of elongated as well as blocky intermetallic
phase Ti(Al1−x
,Fe
x
)3, (2) the proportion of alumina particles in the reinforcing oxides, and (3) the porosity content in the resulting cast in-situ composite. The difference in particle content and porosity between the top and the bottom of the cast ingot increases with
increasing processing temperature. The hardness of the cast in-situ composite is significantly more than that of the matrix alloy due to the presence of reinforcing particles, but the hardness
is greatly impaired by the presence of porosity at the top of the cast ingot. The percent elongation of the cast in-situ composite decreases with increasing processing temperature possibly due to increasing porosity as well as an increasing amount
of elongated intermetallic phase, which affects the percent elongation of the matrix alloy. The tensile and yield stresses
of the cast in-situ composite decreases with increasing processing temperature again due to increasing porosity, which affects the ultimate tensile
stress more than the yield stress. In the cast in-situ composite containing 3.31 ± 0.77 vol pct of porosity, the Brinell hardness is about 6 times its yield stress. The estimated
yield stress of the cast in-situ composite at zero porosity as given by the linear least-squares fit appears to increase with particle content at a significantly
higher rate than that predicted by the shear-lag model. 相似文献
9.
H. Krawiec V. Vignal O. Heintz R. Oltra E. Finot J. M. Olive 《Metallurgical and Materials Transactions A》2004,35(11):3515-3521
The morphology, the chemical composition, and the pitting corrosion resistance of a resulfurized stainless steel heated at
1000 °C for 2 hours were investigated at the microscale using ex-situ (field-emission-scanning electron microscope/electron dispersion spectrometer (FE-SEM/EDS) and secondary ion mass spectroscopy
(SIMS)) and in-situ (electrochemical microcell technique and in-situ atomic force microscope (AFM) techniques. Although microcracks, which may have a deleterious effect, exist, the formation
of a compound (Cr,Mn)2(O,S)3 instead of MnS is responsible for the better pitting corrosion resistance of sites containing an inclusion. Local electrochemical
measurements indicate that no pitting was detected on these sites below 800 mV/SCE (saturated calomel electrode), whereas
stable pitting was observed at around 350 mV/SCE before heating. Micropores were detected on the highly oxidized grains in
which the ionic activity was found to be more marked than on the remaining surface (determined using in-situ AFM). Local electrochemical measurements revealed that the presence of such defects reduces significantly the corrosion resistance
of the metallic alloy in NaCl-based media. 相似文献
10.
Transition-metal trialuminide intermetallics such as Al3Zr and Al3Ti, having low densities and high elastic moduli, are good candidates for the in-situ reinforcement of light-metal matrices based on Al and Mg alloys. In this work, in-situ composites based on Al and Al-Mg matrices reinforced with an Al3Zr intermetallic were successfully processed by conventional ingot metallurgy. The microstructural studies showed that “needle”
or “feathery”-like particles of Al3Zr phase, whose volume fraction increased with increasing concentration of Zr, were formed in the Al matrix in the investigated
range of Zr contents from 0.9 to 11.6 at. pct. Properties of Al-Zr alloys were investigated as a function of volume fraction
of Al3Zr. It is shown that the density, hardness, and yield strength of the in-situ Al/Al3Zr composites can be quite adequately described by the composite rule-of-mixtures (ROM) behavior. Alloying of a binary Al-2.4
at. pct Zr alloy with Mg up to ∼25 at. pct reduces profoundly its density and, additionally, strengthens the matrix by a Mg
solid-solution strengthening mechanism. 相似文献
11.
Jiangbo Sha Hisatoshi Hirai Hidetoshi Ueno Tatsuo Tabaru Akira Kitahara Shuji Hanada 《Metallurgical and Materials Transactions A》2003,34(1):85-94
To improve the high-temperature strength of Nb-Mo-Ti-Si in-situ composites, alloying with W and a directional solidification technique were employed. The alloy composition of Nb-xMo-10Ti-18Si (x=10 or 20) was used as the base, and Nb was further replaced by 0, 5, 10 and 15 mol pct W. For samples without W, the as-cast
microstructure was a eutectic mixture of fine Nb solid solution (Nb
SS
) and (Nb, Me)5 Si3 silicide (Me = Mo, W, or Ti), while large primary Nb
SS
particles appeared besides the eutectic mixture as a result of replacing Nb by W. The directionally solidified samples consisted
of coarse Nb
SS
and (Nb,Me)5 Si3 silicides, and the microstructure showed a slight orientation in the direction of growth. The maximum compressive ductility
(ɛ
max) at room temperature decreased with increasing W content and was in the range of 0.8 to 2.3 pct, in contrast to the Vickers
hardness (HV), which increased with W content. The 0.2 pct yield compressive strength (σ
0.2) and the specific 0.2 pct yield compressive strength (σ
0.2S
) (σ
0.2 divided by the density of sample) at elevated temperatures were markedly improved by the W addition. The directionally solidified
samples always showed higher σ
0.2 and σ
0.2S
values than the as-cast samples. At elevated temperatures, the directionally solidified sample with 10 mol pct Mo and 15
mol pct W had the highest σ
0.2 and σ
0.2S
values; even at 1770 K, σ
0.2 was as high as 650 MPa. The directionally solidified materials alloyed with W exhibited excellent compressive creep performance.
The sample with 10 mol pct Mo and 15 mol pct W had a minimum creep rate
of 1.4×10−7s−1 and retained steady creep deformation at 1670 K and an initial stress of 200 MPa. Under compression, the damage and failure
of these in-situ composites were dominated by decohesion of interfaces between the Nb
SS
and silicide matrix. 相似文献
12.
J. T. Bell J. D. Redman H. P. Bittner 《Metallurgical and Materials Transactions A》1980,11(5):775-782
The tritium permeabilities,DK, of Incoloy 800 and Sanicro 31 have been determined for tube samples that were protected from surface oxidation by electroplated
nickel. The permeabilities of these analogous alloys over the 400 to 750°C range were essentially equal;DK = 0.566 exp (-16120/RT) and 0.367 exp (-15610/RT cm3
(T2 · STP) · mm/(cmsu2 · min · torr1/2), respectively. The effects ofin-situ steam oxidation of Incoloy 800 were observed to reduce tritium permeabilities by factors up to 400 at 150 days. Permeation
rates through oxide-coated Incoloy 800 were observed to be 0.5 rather than 1.0 power dependent on the tritium pressure. Permeabilities
of the oxides formed at 520, 660 and 725°C were determined to be 5.4 E-11, 4.9 E-10 and 2.4 E-9 cc (T2,STP) · mm/(cm2 · min · torr1/2), respectively. Severe thermal shock was observed to essentially destroy the permeation barrier characteristics of the oxide
coatings while mild temperature cycling had no observable effects on permeation rates through the oxide coated material.
H. F. BITTNER formerly on the Research Staff, Oak Ridge National Laboratory. 相似文献
13.
Uniaxial compression tests were conducted on aluminum composites containing 34 and 37 vol pct submicron alumina particles,
to study the effect of temperature and strain rate on their flow stress. For temperatures between 25 °C and 600 °C and strain
rates between 10−3 and 1 s−1, the flow stress of the composites is significantly higher than that of unreinforced aluminum tested under similar conditions.
This can be attributed to direct strengthening of the composites due to load sharing between the particles and the matrix,
and an enhanced in-situ matrix flow stress resulting from a particle-induced increase in dislocation density. The composites, however, exhibit the
same stress dependence on temperature and strain rate as unreinforced aluminum, indicating a common hardening mechanism, i.e., forest dislocation interactions. The forest hardening present under the explored testing conditions masks the effects of
direct dispersion strengthening operative at lower deformation rates in these materials. 相似文献
14.
Role of Mg in the stress corrosion cracking of an Al-Mg alloy 总被引:4,自引:0,他引:4
R. H. Jones D. R. Baer M. J. Danielson J. S. Vetrano 《Metallurgical and Materials Transactions A》2001,32(7):1699-1711
The corrosion and stress corrosion cracking (SCC) susceptibility of an Al-Mg alloy, AA5083, has been shown to depend on the
precipitation of the Mg-rich β phase, (Al3Mg2), but not the enrichment of elemental Mg at grain boundaries to an enrichment ratio of 1.4. These results were determined
by measuring the progress of Mg enrichment at grain boundaries, for increasing thermal-treatment times, using auger electron
spectroscopy (AES) of grain boundaries exposed by fracture within the spectrometer and by analytical electron microscopy (AEM)
of thin foils. The progress of the β phase precipitation was followed by AEM and scanning electron microscopy (SEM), for the same thermal-treatment times. The
lack of a Mg-segregation effect on SCC was demonstrated by results obtained with X-ray photoelectron spectroscopy (XPS) analysis
of Mg-implanted Al following in-situ electrochemical tests and SCC tests, while the dominance of β phase precipitation was demonstrated by electrochemical analysis and SCC testing. Crack-growth tests of alloy AA5083 demonstrated
faster cracking at potentials anodic to the open circuit potential (OCP) with no increase at potentials cathodic to the OCP. 相似文献
15.
A fully-dense Cu-75 vol pct ZrW2O8 metal matrix composite was fabricated by hot isostatic pressing of Cu-coated ZrW2O8 particles. A small amount of the high-pressure γ-ZrW2O8 phase was created during the cooldown and depressurization following densification; near complete transformation to γ-ZrW2O8 was achieved by subsequent cold isostatic pressing. The thermal expansion behavior of the composite between 25°C and 325°C
was altered by the cold isostatic pressing treatment, and also depended on the length of time that had passed between thermal
cycles. The measured thermal expansion coefficients within specific temperature ranges varied from −6·10−6 K−1 to far above the thermal expansion coefficient of the copper matrix. The complex temperature-dependent expansion/contraction
behavior could be justified by considering the evolution of phase transformations taking place in the ZrW2O8 phase, which were observed by in-situ synchrotron X-ray diffraction measurements. 相似文献
16.
The foaming behaviour equations were given for the foam originating from carbonate decomposition in the Na2B4O7 melt. The foam height was measured during the foaming phenomenon under different conditions in the laboratory. The formation and rupture coefficients (K and k) in the foam behaviour equation were determined by means of regression of the experimental data. The parameters such as temperature, size, crystal types of carbonate, the composition of melt and so on have an influence on the foaming phenomenon. With K and k the formation and rupture processes could be described quantitatively. The relationship between the foam height and the foaming phenomenon duration could be expressed quantitatively. This method can be used to describe quantitatively the foaming phenomenon originating from reaction in the melt. 相似文献
17.
探讨了2-(5-碘-2-吡啶偶氮)-5-二甲氨基苯胺(5-I-PADMA)与钯(Ⅱ)的显色反应。实验表明,在0.6 mol/L高氯酸介质中,5-I-PADMA与钯(Ⅱ) 反应形成摩尔比为1∶1的蓝色稳定络合物,该络合物最大吸收峰位于613 nm处。钯(Ⅱ)含量在0~0.6 μg/mL范围内符合比尔定律,线性回归方程为△A=0.828 4 ρ(μg/mL)- 0.001 6,相关系数r=0.999 9,表观摩尔吸光系数为8.82 × 104 L·mol-1·cm-1。方法应用于钯分子筛和矿样中钯的测定,结果与原子吸收光谱法一致,相对标准偏差(n=6)为1.2%~1.4%。 相似文献
18.
O. Muránsky P. Šittner J. Zrnik E.C. Oliver 《Metallurgical and Materials Transactions A》2008,39(13):3097-3104
Tensile deformation behavior of two transformation-induced plasticity (TRIP)–assisted multiphase steels with slightly different
microstructures due to different thermomechanical treatment conditions applied was investigated by in-situ neutron diffraction. The steel with lower austenite volume fraction (f
γ
= 0.04) and higher volume fraction of needlelike bainite in the α-matrix exhibits higher yield stress (sample B, 600 MPa) but considerably lower elongation in comparison to the steel with
higher austenite volume fraction (f
γ
= 0.08), granular bainite, and polygonal ferrite matrix (sample A, 500 MPa). The neutron diffraction results have shown that
the applied tensile load is redistributed at the yielding point in such a way that the retained austenite bears a significantly
larger load than the α matrix during the TRIP-assisted steel deformation.
This article is based on a presentation given in the symposium entitled “Neutron and X-Ray Studies for Probing Materials Behavior,”
which occurred during the TMS Spring Meeting in New Orleans, LA, March 9–13, 2008, under the auspices of the National Science
Foundation, TMS, the TMS Structural Materials Division, and the TMS Advanced Characterization, Testing, and Simulation Committee. 相似文献
19.
It is well known that alumina inclusions on the surface of molten Al-killed steel quickly attract each other to form clusters.
On the other hand, alumina-magnesia complex inclusions on the surface of molten low-carbon steel with a high oxygen content
have a much weaker tendency to form clusters. In the present work, the reason for the different behaviors of the two types
of inclusions was analyzed in detail. A confocal scanning laser microscope was used to carry out the experiment of in-situ observation of the two types of inclusion on the molten pool. The first type of inclusion was 93 mass pct alumina-7 mass
pct magnesian, obtained in a Mg-added Al-killed steel. The second type of inclusion was nearly pure magnesia, obtained in
a Mg-killed steel. The attractive force between a pair of inclusions, for both cases, was found to be approximately 1O−17 to 10−16 N and one-tenth of that between a pair of alumina inclusions. The various effects of contact angle, surface tension, and
oxygen content of the steel melt on the attractive force are discussed in detail from the viewpoint of the capillary force. 相似文献
20.
Nickel aluminide intermetallics (e.g., Ni3Al and NiAl) are considered to be attractive materials for high-temperature structural applications. Laser-engineered net
shaping (LENS) is a rapid prototyping process, which involves laser processing fine metal powders into three-dimensional shapes
directly from a computer-aided design (CAD) model. In this work, an attempt has been made to fabricate aluminide intermetallic
compounds via reactive in-situ alloying from elemental powders using the LENS process. In-situ reactive alloying was achieved by delivering elemental Ni and Al powders from two different powder feeders, eliminating segregation
observed in the samples deposited by using the premixed elemental powders. Nickel aluminides of various compositions were
obtained easily by regulating the ratio of their feed rates. The aluminide deposits exhibited a high solidification and subsolidus
cracking susceptibility and porosity formation. The observed porosity resulted from a water-atomized Ni powder and can be
minimized or eliminated by the use of a N2-gas-atomized Ni powder of improved quality. Cracking was due to the combined effect of the high thermal stresses generated
from the LENS processing and the brittleness of the intermetallics. Crack-free deposits were fabricated by preheating the
substrate to a temperature of 450 °C to 500 °C during LENS processing. Compositionally graded Ni-Al deposits with a gradient
microstructure were also produced by the in-situ reactive processing. 相似文献