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1.
The tensile properties of pseudobinary Ll 3-type intermetallic compounds based on Ni 3Al and Ni 3Mn were examined on recrystallized specimens. The alloys with manganese composition lower than 15 at. pct were tested from
room temperature to 1073 K (1273 K for some alloys). The yield stress appears to be controlled by solid solution hardening
(athermal component) at room temperature and by the so-called Kear-Wilsdorf mechanism (thermal component) at elevated temperatures.
The activation constant for the latter mechanism, i.e., for the anomalous positive temperature depen-dence of the yield stress, increases with increasing the manganese composition.
The tensile elongation shows a maximum at 9 at. pct Mn and at intermediate temperatures (≈700 K). Also, at sufficient higher
temperatures (1273 K), an increase of elongation due to dynamic recrystallization was ob-served. The temperature and compositional
dependence of the ultimate tensile strength are similar to that of the elongation. The fracture mode was closely correlated
with the elongation behavior: the more the transgranular fracture, the higher the ductility.
formerly Graduate Student, Tohoku University, Sendai, Japan, 相似文献
2.
The structure and mechanical properties of nanocrystalline intermetallic phase dispersed amorphous matrix composite prepared
by hot isostatic pressing (HIP) of mechanically alloyed Al 65Cu 20Ti 15 amorphous powder in the temperature range 573 K to 873 K (300 °C to 600 °C) with 1.2 GPa pressure were studied. Phase identification
by X-ray diffraction (XRD) and microstructural investigation by transmission electron microscopy confirmed that sintering
in this temperature range led to partial crystallization of the amorphous powder. The microstructures of the consolidated
composites were found to have nanocrystalline intermetallic precipitates of Al 5CuTi 2, Al 3Ti, AlCu, Al 2Cu, and Al 4Cu 9 dispersed in amorphous matrix. An optimum combination of density (3.73 Mg/m 3), hardness (8.96 GPa), compressive strength (1650 MPa), shear strength (850 MPa), and Young’s modulus (182 GPa) were obtained
in the composite hot isostatically pressed (“hipped”) at 773 K (500 °C). Furthermore, these results were compared with those
from earlier studies based on conventional sintering (CCS), high pressure sintering (HPS), and pulse plasma sintering (PPS).
HIP appears to be the most preferred process for achieving an optimum combination of density and mechanical properties in
amorphous-nanocrystalline intermetallic composites at temperatures ≤773 K (500 °C), while HPS is most suited for bulk amorphous
alloys. Both density and volume fraction of intermetallic dispersoids were found to influence the mechanical properties of
the composites. 相似文献
3.
Diffusion bonding is a near net shape forming process that can join dissimilar materials through atomic diffusion under a high pressure at a high temperature.Titanium alloy TC4(Ti-6 Al-4 V)and 4 J29 Kovar alloy(Fe-29 Ni-17 Co)were diffusely bonded by a vacuum hot-press sintering process in the temperature range of 700-850°C and bonding time of 120 min,under a pressure of 34.66 MPa.Interfacial microstructures and intermetallic compounds of the diffusion-bonded joints were characterized by optical microscopy,scanning electron microscopy,X-ray diffraction(XRD)and energy dispersive spectroscopy(EDS).The elemental diffusion across the interface was revealed by electron probe microanalysis.Mechanical properties of joints were investigated by micro Vickers hardness and tensile strength.Results of EDS and XRD indicated that(Fe,Co,Ni)-Ti,TiNi,Ti_2Ni,TiNi_2,Fe_2 Ti,Ti_(17) Mn_3 and Al_6 Ti_(19) were formed at the interface.When the bonding temperature was raised from 700 to 850°C,the voids of interface were reduced and intermetallic layers were widened.Maximum tensile strength of joints at 53.5 MPa was recorded by the sintering process at 850°C for 120 min.Fracture surface of the joint indicated brittle nature,and failure took place through interface of intermetallic compounds.Based on the mechanical properties and microstructure of the diffusion-bonded joints,diffusion mechanisms between Ti-6 Al-4 Vtitanium and Fe-29 Ni-17 Co Kovar alloys were analyzed in terms of elemental diffusion,nucleation and growth of grains,plastic deformation and formation of intermetallic compounds near the interface. 相似文献
4.
Metastable fcc phase with highly ductile nature has been found in melt-quenched Mn-Al-C alloys instead of extremely brittle
equilibrium phases. This formation range is limited to about 9 to 22 at. pct Al and about 3.0 to 6.5 at. pct C. Further, the
fee phase wires with circular cross section have been manufactured by an in-rotating-water spinning method. The wire diameter
is in the range of 70 to 150 μm diameter and the average grain size is about 3 μm. The Vickers hardness, yield strength, and
tensile strength of the wires increase with aluminum and carbon content and reach about 285 DPN, 560 MPa, and 960 MPa, respectively,
for Mn 74.5Al 20.5C 5-Elongation increases with decrease in aluminum and carbon, and the highest value is about 28 pct for Mn-13.5 pct Al-4 pct
C alloy. The cold-drawing to about 60 pct reduction in area results in a very significant increase of tensile strength from
260 to 1460 MPa, through a remarkable work-hardening effect. Thus, the use of the in-rotating-water spinning method, being
a new type of rapid quenching technique, is very useful to endow the manganese-base alloy wires exhibiting high strength combined
with good ductility. 相似文献
5.
The electrochemical behaviour of Al, Li, and Er were investigated by electrochemical techniques, such as cyclic voltammograms, chronopotentiometric, chronoamperograms, and open circuit chronopotentiogram on molybdenum electrodes. The results showed that the underpotential deposition of erbium on pre-deposited Al electrodes formed two Al-Er intermetallic compounds. The codeposition of Al, Li, Er occurred and formed Al-Li-Er alloys in LiCl-KCl-AlCl3 -Er2O3 melts at 773K. Different phases such as Al2Er, Al2Er3 and βLi phase of Al-Li-Er alloys were prepared by galvanostatic electrolysis and characterized by X-ray diffraction (XRD). Scanning electron microscopy (SEM) indicated that Er element mainly distributed at the grain boundary. ICP analyses showed that lithium and erbium contents of Al-Li-Er alloys could be controlled by AlCl3 and Er2O3 concentration and electrochemical parameters. 相似文献
6.
High-temperature tensile testing and X-ray microscope (XRM) characterization were performed to assess the effects of the micro-addition of Gd and the three-dimensional (3-D) network structure on the improvement of Al-6Cu-3.5Ni-0.8Fe alloy under as-cast conditions. Gd addition contributed to the modification of the microstructure, where a new thermally stable micro-sized Al3CuGd phase was formed, and the refinement occurred in Al3CuNi and Al9FeNi. The tensile test results revealed that the alloy modified with 0.4 pct Gd exhibited optimal properties at 623 K (350 °C), with an ultimate tensile strength, yield strength, and elongation of 74.1 MPa, 61.2 MPa, and 15.5 pct, respectively. Fractographic analysis after the tensile tests indicated that at ambient temperature, brittle cleavage-type fracture of the precipitates and ductile fracture of the matrix were dominant, whereas the transformation from mixed fracture to fully ductile trans-crystalline fracture was detected at elevated temperatures. According to the CT characterization, there was no significant difference in the curvature or interconnectivity of the 3-D network structure formed by the aluminides between before and after the tensile test at 623 K (350 °C). It is believed that the 3-D continuous network structure of aluminides, equipped with excellent heat resistance, plays a pivotal role in the high-temperature performance of the studied alloys. This work provides a new and promising idea for solving the current heat resistance problems of cast Al alloys. 相似文献
7.
In reaction synthesis (RS) route of powder metallurgy, heat of reaction between elemental powders is utilised to obtain intermetallic
compounds. Prior to reaction synthesis of quaternary alloy Ti48Al2Cr2Nb (with 10 at. % B), reaction kinetics studies were
carried out. Powder mixture was prepared and Differential Scanning Calorimetry (DSC) experiments were carried out at 3 different
heating rates. Activation energy and Avrami Index ‘n’ are obtained by Johnson-Mehl-Avrami (JMA) equation. Formation of Al 3Ti was confirmed through X-ray diffraction (XRD). Reaction mechanisms are identified in accordance with ‘n’ values. In the
temperature range of 1060–1150K, it proceeds as instantaneous nucleation and three dimensional growth with an activation energy
of 176 kJ mole −1. 相似文献
8.
Consolidation of rapidly solidified titanium aluminide (Ti 3Al) powders employing explosive shock pressure followed by hot isostatic pressing (“hipping”) was carried out successfully.
Shock densification was achieved by using a double tube design in which the flyer tube was explosively accelerated, impacting
the powder container. Elemental mixtures of Ti (15 wt pet) and Al (15 wt pct) powders were added to intermetallic compound
powders (Ti 3Al). Hipping was used to chemically induce bonding between Ti 3Al particles. The highly exothermic reactions were activated by hipping at 1000 ‡C and enhanced the bonding between the inert
intermetallic powders. Compression tests indicated strong bonding between Ti 3Al particles. Well-bonded Ti 3Al compacts having an average ultimate compressive strength of 2 GPa and compressive fracture strain of 20 pct were produced
by this technique. The ultimate tensile strengths, due to the presence of flaws in the microstructure (microcracks and voids)
and intergranular fracture observed in the reacted regions, were much lower (~250 MPa). 相似文献
9.
The influence of small additions of C, Zr, and Hf, alone or in combination with B, on the microstructure and tensile behavior
of substoichiometric FeAl was investigated. Tensile prop-erties were determined from 300 to 1100 K on powder which was consolidated
by hot extrusion. All materials possessed some ductility at room temperature, although ternary additions generally reduced
ductility compared to the binary alloy. Adding B to the C- and Zr-containing alloys changed the fracture mode from intergranular
to transgranular and restored the ductility to ap-proximately 5 pct elongation. Additions of Zr and Hf increased strength
up to about 900 K, which was related to a combination of grain refinement and precipitation hardening. Fe 6Al 6Zr and Fe 6Al 6Hf precipitates, both with identical body-centered tetragonal structures, were iden-tified as the principal second phases
in these alloys. Strength decreased steadily as temperature increased above 700 K, as diffusion-assisted mechanisms, including
grain boundary sliding and cavitation, became operative. Although all alloys had similar strengths at 1100 K, Hf additions
significantly improved high-temperature ductility by suppressing cavitation. 相似文献
10.
Three materials containing Nb, Cr, and Ti were fabricated by consolidating powders made by mechanical alloying. The Nb/Ti
ratio was maintained at about 1.3 and Cr was increased to form the intermetallic Cr 2Nb. X-ray diffraction, metallography, and transmission electron microscopy were used to thoroughly characterize the microstructure
and substructure of the materials. Fatigue and fracture toughness properties were also evaluated at ambient temperature. The
alloyed powders contained only small amounts of intermetallic, but during the consolidation heat treatment, two of the materials
precipitated large volume fractions of Cr 2Nb. In the third material, Cr 2Nb was precipitated by heat treatment, although this was not expected from the composition based on the Nb-Cr-Ti phase diagram.
Maximum fracture toughness of the composutes was ≈ 11 MPa √m. The low fracture toughness was attributed to the high plastic
constraint of matrix deformation by the Cr 2Nb and compositional change in the matrix. 相似文献
11.
The contributions from grain boundary, solid solution, and dispersion strengthening to the yield strength of cast-to-shape specimens were calculated for seven binary alloys with compositions ranging from very dilute (0.5 mass pct Al) to concentrated (12 mass pct Al). Experimentally and theoretically determined parameters were used to explicitly account for the different microstructures at the skin and core regions of specimens’ cross sections. Microhardness maps were used to identify the specimens’ skin. The specimens’ strength was calculated as the weighted addition of the respective strengths of skin and core. The calculated strengths reproduced well the experimental values for the dilute alloys but underestimated the strength of the most concentrated alloys by as much as ~35 MPa. It is argued that the presence of the percolating network of Mg 17Al 12 eutectic intermetallic, particularly in the skin region, in conjunction with highly efficient dispersion hardening due to the convoluted shape of the intermetallics, accounts for the shortfall in the calculated strength. 相似文献
12.
A new Al-Li alloy containing 2.3 wt pct Li, 6.5 wt pct Mn, and 0.65 wt pet Zr, for high-temperature applications, has been
processed by a rapid solidification (RS) technique (as powders by inert gas atomization) and then thermomechanically treated
by hot isostatic pressing (hipping) and hot extrusion. As-received and thermomechanically treated powders (of various size
fractions) were characterized by X-ray diffraction and scanning and transmission electron microscopy (SEM and TEM, respectively).
Phase analyses in the as-processed materials revealed the presence of two Mn phases (Al 4Mn and Al 6Mn), one Zr phase (Al 3Zr), two Li phases (the stable AlLi and the metastable Al 3Li), and the αAl solid solution with high excess in Mn solubility (up to close the nominal composition in the as-atomized
powders). Extruded pieces were solutionized at 370 °C and 530 °C for various soaking times (2 to 24 hours). A variety of aging
treatments was practiced to check for the optimal (for tensile properties) aging procedure, which was found to be the following:
solutioning at 370 °C for 2 hours and water quenching + 1 pct mechanical stretching + one step aging at 120 °C for 3 hours.
The mechanical properties, at room and elevated temperatures, of the “hipped” and hot extruded powders are compared following
the optimal solutioning and aging treatments. The results indicate that Mn is indeed a favorable alloying element for rapidly
solidified Al-Li alloys to retain about 85 to 95 pct of the room-temperature tensile properties even at 250 °C, though room-temperature
strength is not satisfactory in itself. However, specific moduli are by 20 to 25 pet higher than those of the 2024 series
duralumin-type alloys. Ductilities at room temperatures are in the low 1 to 2.5 pct range and show no improvement over other
Al-Li alloys. 相似文献
13.
The present study is concerned with γ-(Ti 52Al 48) 100−x
B
x
( x=0, 0.5, 2, 5) alloys produced by mechanical milling/vacuum hot pressing (VHPing) using melt-extracted powders. Microstructure
of the as-vacuum hot pressed (VHPed) alloys exhibits a duplex equiaxed microstructure of α 2 and γ with a mean grain size of 200 nm. Besides α 2 and γ phases, binary and 0.5 pct B alloys contain Ti 2AlN and Al 2O 3 phases located along the grain boundaries and show appreciable coarsening in grain and dispersoid sizes during annealing
treatment at 1300 °C for 5 hours. On the other hand, 2 pct B and 5 pct B alloys contain fine boride particles within the γ
grains and show minimal coarsening during annealing. Room-temperature compressing tests of the as-VHPed alloys show low ductility,
but very high yield strength >2100 MPa. After annealing treatment, mechanically milled alloys show much higher yield strength
than conventional powder metallurgy and ingot metallurgy processed alloys, with equivalent ductility to ingot metallurgy processed
alloys. The 5 pct B alloy with the smallest grain size shows higher yield strength than binary alloy up to the test temperature
of 700 °C. At 850 °C, 5 pct B alloy shows much lower strength than the binary alloy, indicating that the deformation of fine
5 pct B alloy is dominated by the grain boundary sliding mechanism.
This article is based on a presentation made in the symposium “Mechanical Behavior of Bulk Nanocrystalline Solids,” presented
at the 1997 Fall TMS Meeting and Materials Week, September 14–18, 1997, in Indianapolis, Indiana, under the auspices of the
Mechanical Metallurgy (SMD), Powder Materials (MDMD), and Chemistry and Physics of Materials (EMPMD/SMD) Committees. 相似文献
14.
In the present study, microstructural and mechanical properties of diffusion bonding of AZ31–Mg with Al 5754, Al 6061, and Al 7039 alloys were compared under same conditions. The vacuum diffusion processes were performed at a temperature of 440 °C, the pressure of 29 MPa, and a vacuum of 1?×?10 ?4 torr for 60 min. The microstructural characterizations were investigated using optical microscopy and scanning electron microscopy equipped with EDS analysis and linear scanner. The XRD analysis was performed to study phase figures near the interface zone. The results revealed the formation of brittle intermetallic compounds like Al 12Mg 17, Al 3Mg 2, and their other combinations at bonding interfaces of all samples. Additionally, the hardness of Al alloys seemed to play a key role in increasing diffusion rate of magnesium atoms toward the aluminum atoms, with Al 6061 alloy having the highest diffusion rate. It consequently led to an increase in diffusion rate and thus formation of a strong diffusion bonding between magnesium and aluminum alloys. The highest strength was about 42 MPa for the diffusion bonding between Mg AZ31 and Al 6061. Further investigations on surfaces indicated that the brittle phases especially Al 3Mg 2 caused brittle fracturing. 相似文献
15.
In dissimilar-metal friction stir welding (FSW), intermetallic compounds can form in the stir zone and significantly reduce
the joint strength. The formation of intermetallic compounds in Al-to-Mg FSW was investigated in lap and butt FSW of the widely
used 6061 Al and AZ31B Mg and discussed using the binary Al-Mg phase diagram as an approximation. Temperature measurements
during lap FSW indicated a 703 K (430 °C) peak temperature, slightly below the eutectic reaction (Mg) + Al 12Mg 17 → L at 710 K (437 °C), because the thermocouples were pushed downward during welding. The intermetallic compounds in the
stir zone were revealed by color etching and identified by X-ray diffraction (XRD), electron probe microanalysis (EPMA), and
transmission electron microscopy (TEM) as Al 3Mg 2 and Al 12Mg 17. Additional FSW was conducted near the edge of the upper sheet, and the liquid droplets squeezed out during welding solidified
along the edge. Optical microscopy of the solidified droplets and EPMA revealed dendrites of Al 3Mg 2 and Al 12Mg 17 and interdendritic eutectics, thus indicating eutectic reactions (Mg) + Al 12Mg 17 → L (710 K (437 °C)) and (Al) + Al 3Mg 2 → L (723 K (450 °C)). Differential scanning calorimetry (DSC) confirmed that the solidified droplets melted at 709 K (436 °C)
and 722 K (449 °C), nearly identical to the eutectic temperatures. Formation of intermetallic compounds on the order of 1 mm
in size suggests they form upon solidification of the liquated material instead of solid-state diffusion. 相似文献
16.
A reciprocating extrusion process was developed to consolidate 6061-Al 2O 3p
composites from mixed powders. The 6061 alloy powder was first dehydrated in a vacuum chamber at 450 °C and then mixed with
12.5 μm Al 2O 3 powder in various volume fractions: 0, 5, 10, 20, and 30 pct. The mixed powders were hot pressed at 300 °C under a pressure
of 300 MPa and finally extruded reciprocatingly 14 times at 460 °C. The results show that the composites were fully densified,
with no sign of pores or oxide layers observable in the optical microscope. The Al 2O 3 particles were distributed uniformly in the matrix. As compared with 6061 alloys, the composites demonstrated a smaller precipitation
hardening and elongation, but exhibited a higher Young’s modulus and a larger work hardening capacity. The degradation of
precipitation hardening was due to the loss of Mg, which reacts with Al 2O 3 to form MgAl 2O 4. The large work-hardening capacity is attributable to the incompatibility between Al 2O 3 and the matrix, which possibly generates more dislocations to harden the matrix. The composites had much higher friction
coefficients and greater wear resistances than the 6061 alloy against steel disc surface. The friction coefficient of the
6061-30 vol pct Al 2O 3p
composite was double that of the 6061 alloy and the wear resistance was 100-fold. As compared with similar composites reported
previously, these composites possessed much higher elongation at the same strength level. A 30 vol pct Al 2O 3p
still displayed an elongation of 9.8 pct in the T6 condition. All of these improvements are attributed to the merits, including
full densification of the bulk, uniform dispersion of the Al 2O 3 particles in the matrix, and strong binding between the Al 2O 3 particles and the matrix resulting from reciprocating extrusion. 相似文献
17.
Thermomechanically processed TiAl-based intermetallic alloys with various alloy compositions and microstructures were tensile
tested in various environmental media, including air, water vapor, and a gas mixture of 5 vol pct, H 2 + Ar, as functions of temperature and strain rate. All the TiAl-based intermetallic alloys showed reduced tensile fracture
stress (or elongation) in air, in water vapor, and in a gas mixture of 5 vol pct H 2 + Ar, not only at ambient temperature (R T ∼ 600 K), but also at high temperature, from 600 to 1000 K (and sometimes at temperatures higher than 1000 K). The high-temperature
environmental embrittlement of TiAl-based intermetallic alloys depended upon the microstructure. The factors causing the high-temperature
environmental embrittlement may include hydrogen atoms decomposed from water vapor (H 2O) or hydrogen gas (H 2), similar to those causing the low-temperature environmental embrittlement. Also, it is demonstrated that the oxidized scale
is effective in reducing high-temperature environmental embrittlement. 相似文献
18.
Mg-9Li-3Al- xSr (LA93- xSr, x = 0, 1.5, 2.5, and 3.5 wt pct) alloys were cast and extruded at 533 K (260 °C) with an extrusion ratio of 28. The microstructure and mechanical response are reported and discussed paying particular attention to the influence of extrusion and Sr content on phase composition, strength, and ductility. The results of the current study show that LA93- xSr alloys contain both α-Mg (hcp) and β-Li (bcc) matrix phases. Moreover, the addition of Sr refines the grain size in the as-cast alloys and leads to the formation of the intermetallic compound (Al 4Sr). Our results show significant grain refinement during extrusion and almost no influence of Sr content on the grain size of the extruded alloys. The microstructure evolution during extrusion is governed by continuous dynamic recrystallization (CDRX) in the α-Mg phase, whereas discontinuous dynamic recrystallization (DDRX) occurs in the β-Li phase. The mechanical behavior of the extruded LA93- xSr alloy is discussed in terms of grain refinement and dislocation strengthening. The tensile strength of the extruded alloys first increases and then decreases, whereas the elongation decreases monotonically with increasing Sr; in contrast, hardness increases for all Sr compositions studied herein. Specifically, when Sr content is 2.5 wt pct, the extruded Mg-9Li-3Al-2.5Sr (LAJ932) alloy exhibits a favorable combination of strength and ductility with an ultimate tensile strength of 235 MPa, yield strength of 221 MPa, and an elongation of 19.4 pct. 相似文献
19.
The microstructures of multiphase intermetallic alloys with compositions Al 70Ti 10V 20 and Al 62Ti 10V 28 based on the trialuminide Al 3Ti have been characterized, following chill casting and postsolidification heat treatment, using a combination of scanning
electron microscopy and transmission electron microscopy (TEM). Evidence of a eutectic reaction of the form L → δ-Al 3(Ti, V)+ ζ-Al 8V 5, not previously reported in the Al-Ti-V system, has been observed in both alloys solidified at sufficient levels of undercooling.
The ζ phase is replaced by metallic β-(Ti, V) phase during subsequent heat treatment in the range 1073 to 1273 K, and differential thermal analysis (DTA) of samples
prean-nealed at 1173 K revealed an endothermic peak at ∼1560 K, consistent with equilibrium eutectic melting of the form ( δ+ β) → L. Although the chill-cast alloys retained metastable intermediate high-temperature phases, duplex metallic-intermetallic
microstructures, containing uniform fine-scale distributions of metallic β-(Ti, V) solid solution in a δ-Al 3(Ti, V) intermetallic matrix, have been produced in both alloys during isothermal heat treatments at temperatures in the range
1073 to 1273 K. For both alloys, the bulk Vickers hardness of such microstructures remained in excess of that of binary Al 3Ti, while in the Al 62Ti 10V 28 alloy, where the increased volume fraction of β phase took the form of a near-continuous network within δ matrix, there was evidence arising from indentation tests of a substantial improvement in the cracking resistance compared
to both chill-cast ternary alloy and binary Al 3Ti. 相似文献
20.
Press hardening is increasingly being used to produce ultra-high strength steel parts for passenger cars. Al-Si, Zn, and Zn-alloy coatings have been used to provide corrosion protection to press hardening steel grades. The use of coatings has drawbacks such as coating delamination or liquid metal-induced embrittlement. In the present work, the microstructural evolution of Al-Zn coating during press hardening was studied. The 55 wt pct Al-Zn coating can in principle provide both Al barrier protection and Zn cathodic protection to press hardened steel. During the heat treatment associated with the press hardening, the 55 wt pct Al-Zn alloy coating is converted to an intermetallic surface layer of Fe 2Al 5 and a FeAl intermetallic diffusion layer. The Zn is separated from both intermetallic compounds and accumulates at grain boundaries and at the surface. This Zn separation process is beneficial in terms of providing cathodic protection to Al-Zn coated press hardening steel. 相似文献
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