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1.
Jeff Rodelas Greg Hilmas Rajiv S. Mishra 《International Journal of Refractory Metals and Hard Materials》2009,27(5):835-841
Cobalt-cemented tungsten carbide (WC–Co) powder was sinterbonded to nickel–iron tungsten heavy alloy (WHA) for use in high-temperature tooling applications. Sinterbonding was performed under various conditions, including changes to the sintering conditions and initial WHA material forms, to determine various processing conditions that yield a consolidated interface indicative of a high degree of bonding. Sinterbonding WC–Co to fully dense WHA bar stock yielded a consolidated interface comprised primarily of complex η-carbides. Defects at the interface, including voids, microcracking, and porosity were the result of other sinterbonding processing conditions explored in this work. Co-rich η-carbides were found to form at the interface in every condition examined. A thermodynamic evaluation of η-carbides as a function of carbon activity determined that Co-rich η-carbides formed preferentially in regions of low carbon activity. The predicted thermodynamic trends are in agreement with interfacial microstructural observations. 相似文献
2.
The microstructure and properties of liquid-phase sintered tungsten heavy alloys were studied. The structure and segregation
of the impurity elements at the interfacial boundaries were examined using scanning electron microscopy (SEM) and fine-probe
energy dispersive spectroscopy (EDS) microanalysis. Test results of mechanical properties are presented and correlated with
fracture behavior of the liquid-phase sintered tungsten alloys. It was found that the Fe-Ni-W alloy exhibits superior properties
as compared with the Cu-Ni-W alloy. The detection of copper was found across tungsten grains and matrix that could be associated
with inferior properties of the Cu-Ni-W alloy as compared to the Fe-Ni-W alloy. Although the fracture was predominantly brittle
in both alloys, complex fracture modes seem to be operative due to the composite microstructure of the alloys. Evidence of
microsegregation was observed that also contributed primarily to the brittle failure in the alloys. The impurity elements,
such as sulfur and phosphorus, were detected at the tungsten matrix and tungsten-tungsten particle boundaries. 相似文献
3.
I. Wesemann W. SpielmannP. Heel A. Hoffmann 《International Journal of Refractory Metals and Hard Materials》2010
In many high temperature applications tungsten is superior to molybdenum alloys. For structural components very often joining technology is the limiting factor. If brazing or welding is used ductility at room temperature has to be considered. Particularly when handling or transporting they run the risk of brittle fracture. 相似文献
4.
The effects of the size and shape of tungsten particles on dynamic torsional properties in tungsten heavy alloys were investigated.
Dynamic torsional tests were conducted on seven tungsten alloy specimens, four of which were fabricated by repeated sintering,
using a torsional Kolsky bar, and then the test results were comparedvia microstructure, mechanical properties, adiabatic shear banding, and deformation and fracture mode. The size of tungsten particles
and their hardness were increased with the increasing of the sintering temperature and time, thereby deteriorating the fracture
toughness. The dynamic torsional test results indicated that a cleavage fracture occurred predominantly with little shear
deformation in the specimens whose tungsten particles were coarse and irregularly shaped whereas shear deformation was concentrated
into the center of the gage section in the conventionally fabricated specimens. The deformation and fracture behavior of the
specimens having coarse tungsten particles correlated well with the observation of thein situ fracture test results,i.e., cleavage crack initiation and propagation. These findings suggested that there would be an appropriate tungsten particle
size condition in the penetration performance since the cleavage fracture mode would be beneficial for the self-sharpening
of tungsten heavy alloys. 相似文献
5.
The microstructure and properties of liquid-phase sintered 93W-4.9Ni-2.1Fe tungsten heavy alloys using ultra-fine tungsten powders (medium particle size of 700 nm) and original tungsten powders (medium particle size of 3um) were investigated respectively. Commercial tungsten powders (original tungsten powders) were mechanically milled in a high-energy attritor mill for 35 h. Ultra-fine tungsten powders and commercial Ni, Fe powders were consolidated into green compacts by using CIP method and liquid-phase sintering at 1465℃ for 30 rain in the dissociated ammonia atmosphere. Liquid-phase sintered tungsten heavy alloys using ultra-fine tungsten powders exhibit full densification (above 99% in relative density) and higher strength and elongation compared with conventional liquidphase sintered alloys using original tungsten powders due to lower sintering temperature at 1465℃ and short sintering time. The mechanical properties of sintered tungsten heavy alloy are found to be mainly dependent on the particles size of raw tungsten powders and liquid-phase sintering temperature. 相似文献
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The paper consists of analytical and applied parts. The mathematical means of mechanics of hexagonal polycrystals are used in the former. Here the correspondence of the published data on single crystal elastic constants of tungsten monocarbide to elasticity moduli of polycrystalline WC has been analyzed. The relationship between ultimate tensile stress and ultimate compressive stress of polycrystalline tungsten monocarbide has been established too. The dependence of ultimate tensile stress and ultimate compressive stress of polycrystalline tungsten monocarbide on mean grain diameter is considered in the applied part. Here the available experimental data are used. 相似文献
9.
超高强铝合金的显微组织 总被引:6,自引:0,他引:6
全面地介绍和评述国内外关于Al-Zn-Mg-Cu系铝合金显微组织的研究状况。Al-Zn-Mg-Cu合金的显微组织主要由基体析出相(MPt)、晶间析出相(GBP)、晶界无析出带(PFZ)和抑制再结晶化合物(过渡族元素化合物)组成,它们几乎影响着合金的所有宏观性能。因此,控制了显微组织中的基体析出相、晶间析出相、晶界无析出带和抑制再结晶化合物的大小、分布及均匀性就控制了性能,而实现控制的主要途径是热处理。 相似文献
10.
The chromium (5.8 to 30.7 wt. %) effect on the superfine magnetic structure and surrounding electrons of the 57Fe nuclei in quenched and annealed Fe-Cr alloys is studied with the use of nuclear -resonant (Mö ssbauer) spectroscopy. The following parameters of the Mössbauer spectra are calculated by using PC with a Normos software: the effective magnetic intensity H
ef (in kOe), the isomeric (chemical) shift ° (in mm/s), the quadrupole electric splitting eq (in mm/s), and the area fraction S (%) of the superfine-structure subspectrum. Significant changes in the superfine magnetic structure and the electron surrounding of the 57Fe nuclei are revealed as functions of the chromium content in the alloys. The conclusion on a correlation between the electronic structure of the alloys and their passivability is drawn.Translated from Zashchita Metallov, Vol. 41, No. 2, 2005, pp. 127–132.Original Russian Text Copyright © 2005 by Kasparova, Baldokhin, Solomatin. 相似文献
11.
93W-5.6Ni-l.4Fe tungsten heavy alloys with controlled microstructures were fabricated by mechanically alloying of elemental
powders of tungsten, nickel and iron by two different process routes. One was the full mechanical alloying of blended powders
with a composition of 93W-5.6Ni-l.4Fe, and the other was the partial mechanical alloying of blended powders with a composition
of 30W-56Ni-14Fe followed by blending with tungsten powders to form a final composition of 93W-5.6Ni-l.4Fe. The raw powders
were consolidated by die compaction followed by solid state sintering at 1300°C for 1 hour in a hydrogen atmosphere. The solid
state sintered tungsten heavy alloys were subsequently liquid phase sintered at 1445∼1485°C for 4-90 min. The two-step sintered
tungsten heavy alloy using mechanically alloyed 93W-5.6Ni-l.4Fe powders showed tungsten particles of about 6-15 μm much finer
than those of 40 um in a conventional liquid phase sintered tungsten heavy alloy. An inhomogeneous distribution of the solid
solution matrix phase was obtained in the two-step sintered tungsten heavy alloy using partially mechanically alloyed powders.
The two-step sintered tungsten heavy alloy using mechanically alloyed 93W-5.6Ni-l.4Fe powders showed larger elongation of
16% than that of 1% in the solid state sintered tungsten heavy alloy due to the increase in matrix volume fraction and decrease
in W/W contiguity. Dynamic torsional tests of the two-step sintered tungsten heavy alloys showed reduced shear strain at maximum
shear stress than did the sintered tungsten heavy alloys using the conventional liquid phase sintering. 相似文献
12.
Seung -Woo Lee 《Metals and Materials International》2000,6(3):241-247
A cell model is presented and numerical analyses are implemented to find the distribution of thermally induced stress, thermally
induced deformation and the effect of the tungsten volume fraction during a single step of the quenching process for a 2-dimensional
cell model and to find the strengthening mechanisms through the cyclic heat treatment of tungsten alloys. The thermal stresses
induced from a single step of quenching mostly concentrated on the W/matrix interface and WAV grain boundary region and the
stresses were distributed locally in tensile and locally in the compressible state both in matrix and particle. The mechanism
of matrix phase formation at tungsten-tungsten boundaries during cyclic heat-treatment was found to be due to the combination
effect of the super saturated matrix phase precipitation into WAV grain boundaries and the thermal stresses state. These results
enhance the impact energy enhancement in tungsten heavy alloys. 相似文献
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Dynamic torsional tests were conducted using a torsional Kolsky bar for five alloys, one of which was fabricated by double-cycled sintering process, and then the test data were compared via microstructures, mechanical properties, adiabatic shear banding, and fracture mode. The double-sintered tungsten alloy specimen whose tungsten particles were very coarse and irregularly shaped showed cleavage fracture in the central area of the gage section with little shear deformation, whereas shear deformation was concentrated in the central area of the gage section in the other alloys. The deformation and fracture behavior of the double-sintered alloy correlated well with the observation of the impacted penetrator specimen and thein situ fracture test results,i.e., microcrack initiation at coarse tungsten particles and cleavage crack propagation through tungsten particles. These findings suggested that the cleavage fracture mode would be beneficial for the serf-sharpening effect and, thus, the improvement of the penetration performance of the double-sintered tungsten heavy alloy would be expected. 相似文献
15.
Ralf Eck Erwin Pink 《International Journal of Refractory Metals and Hard Materials》1992,11(6):337-341
The variations in strength and ductility characteristics during industrial working of dispersion-strengthened molybdenum and tungsten alloys are described. With progressive working the ductile-brittle transition is decreased. Both strength and fracture elongation increase, in contrast to the usually observed inverse relation between these two properties. This is explained by the beneficial effects of dynamic strain aging which operates while the ingot is deformed at certain critical temperatures. However, such a twofold improvement is not observed in all alloys. It is not possible when the dispersates cannot dissociate; then, the alloying elements are not dissolved in the matrix and are not available for initiating dynamic strain aging, nor may the fracture elongation improve when extensive static age hardening is superimposed. 相似文献
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《Acta Materialia》2000,48(15):3879-3893
The experimental data on the concentration of free electrons in fcc iron-based alloys, results of theoretical calculations on the electronic structure and experimental data of atomic distribution are analysed. The electron structure of iron-based substitutional solid solutions and CrNi austenitic steels alloyed by Mn, Mo, Cu, Si, Al and C, N was studied by means of the measurement of conduction electron spin resonance. The electron exchange in binary fcc Fe–N and Fe–C alloys was also calculated using an ab initio norm-conserving pseudopotential method. It is shown that Ni, Cu, Si and Al increase the concentration of free electrons, whereas Cr, Mn and Mo decrease it. Theoretical calculations as well as experimental data show that nitrogen in fcc iron and iron-based solid solutions increases the state density at the Fermi surface, whereas carbon contributes its electrons to the states below the Fermi surface. Mössbauer spectroscopy was used to study the distribution of carbon and nitrogen in binary fcc Fe–C and Fe–N alloys, while the data on the distribution of d-solutes in multicomponent solid solutions were obtained from the analysis of the contributions of different electronic subsystems, namely free electrons, isolated localized d-electrons (single solute d-atoms) and superparamagnetic clusters (clusters of d-atoms), to the temperature dependence of the magnetic susceptibility. The results of studies concerning the atomic distribution are consistent with the available data on the short range order in iron-based alloys. The following correlation is found: an increase in the concentration of free electrons assists the short range atomic ordering in iron-based alloys, whereas the localization of electrons promotes clustering of solute atoms. The state of atomic order influences properties like austenite stability, corrosion resistance and strength. 相似文献
18.
A. Saxena S. K. Shukla S. K. Chaudhuri 《Journal of Materials Engineering and Performance》2003,12(3):317-323
A comprehensive understanding was developed on the evolution of microstructure and texture during annealing of Nb bearing
microalloyed drawing quality high strength cold rolled (HSCR) sheet with specific reference to cold rolling and annealing
practices. Further, this study aimed at establishing the best combination of these processing parameters to achieve an YET
value of 1.4 min. For a hot rolled microstructure of moderately coarse ferrite grain of size 16 μm, it was observed that 70%
cold reduction guaranteed high intensity of (222) component accompanied with minimum intensity of (200) component. Further,
investigation was carried out to understand the influence of annealing time on recrystallization behavior and texture development
during intermediate annealing of 60% and 70% cold reduced specimens at 550 °C. It was found that recrystallization ceased
after 12 h of intermediate annealing at 550 °C. The textures and microstructures produced during final annealing of 70% cold
rolled specimens at various temperatures like 670, 690, 710, and 730 °C with varied duration of soaking (12–18 h) were critically
examined. An YET value of ∼1.5 was achieved in HSCR microalloyed steel when 70% cold rolled specimens were intermediately
annealed at 550 °C for 12 h followed by final annealing at 710 °C for 12 h. 相似文献
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