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A. N. Solonin A. Yu. Churyumov A. V. Mikhailovskaya M. A. Ryazantseva 《Russian Journal of Non-Ferrous Metals》2011,52(1):44-49
Natural ageing in alloys of the Al-Cu and Al-Cu-Mg systems is investigated and modeled. To determine the kinetic parameters, a method for measuring the electrical resistance is applied as the basic method. With the use of the Avrami equation in the differential form, a model for the structure evolution (changes in the volume fraction of the Guinier-Preston zones (GPZs) and the depletion of the solid solution) and the change in the yield strength for the alloys during natural ageing is constructed. In the case of the Al-Cu-Mg ternary system, two types of zones are present (the GPZ and the Guinier-Preston-Bagaryatskii zone (GPBZ)). In this case, the dissociation of the oversaturated solid solution at room temperature is described by a set of differential equations. The accuracy of the constructed model of the dependence of the yield strength on the alloy composition and the natural ageing time is 6%, which is within the error of experimental determination for this parameter. 相似文献
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R. E. Stoller 《Metallurgical and Materials Transactions A》1990,21(7):1829-1837
Neutron irradiation of structural materials leads to such observable changes as creep and void swelling. These effects are
due to differential partitioning of point defects. Although most radiationproduced point defects recombine with an antidefect,
a very small fraction of the defects survives. The surviving defect fraction is directly related to the density and type of
extended defects that act as point defect sinks. Defect partitioning requires the presence of more than one type of sink and
that at least one of the sinks has a capture efficiency for either vacancies or interstitials that is different from that
of the other sink(s). For example, dislocations provide the interstitial “bias” that drives swelling, and the ratio of the
dislocation to cavity sink strength determines the swelling rate. These sink strengths change during irradiation, and an explicit
model of their evolution is required to simulate swelling or creep. Such a model has been developed; the influences of various
model assumptions and parameters are discussed. The model simulates the evolution of Frank faulted interstitial loops, providing
a dislocation source and the glide/climb of the dislocation network leading to annihilation of dislocation segments. Good
agreement is found between model predictions and experimental data. Swelling simulations are shown to be quite sensitive to
the dislocation model.
This paper is based on a presentation made in the symposium “Irradiation-Enhanced Materials Science and Engineering” presented
as part of the ASM INTERNATIONAL 75th Anniversary celebration at the 1988 World Materials Congress in Chicago, IL, September
25-29, 1988, under the auspices of the Nuclear Materials Committee of TMS-AIME and ASM-MSD. 相似文献
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This study of Al-Zn-Mg alloys was undertaken to establish the specific combination of mechanical and thermal conditions which
is necessary for stress-corrosion susceptibility to occur in these alloys. The work included a study by electron transmission
microscopy of the microstructure of this alloy system. A new mechanism is proposed to account for the observations made. It
suggests that the high corrosion potential at grain boundaries in stress-corrosion susceptibile Al-Zn-Mg alloys is due to
segregation of zinc and magnesium. By taking precautions to reduce this segregation, the stress-corrosion life can be increased. 相似文献
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Corrosion fatigue crack propagation tests were performed on commercial 7075 alloys. Testing was done in a 3.5 pct sodium chloride
solution under constant impressed potential and under reversed anodic-cathodic current conditions. Results indicated that
a cathodic potential of -1.400 V vs SCE was sufficient to reduce corrosion fatigue crack growth rates to the level observed
in dry argon. By alternately impressing anodic and cathodic currents, it was shown that anodic potentials enhance the crystallographic
dependence of the fracture mode, resulting in brittle striations, while cathodic potentials result in ductile striations formed
by shear. Modification of the alloy chemistry and lower impurity content resulted in a two-fold reduction in crack growth
rates. Thermomechanical treatment of these alloys to refine the grain size proved detrimental. Adding an inhibitor to the
sodium chloride solution was found to be the most effective means for reducing corrosion fatigue crack growth rates. A model
for the environment-surface interaction is suggested. 相似文献
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A process model for the heat-affected zone microstructure evolution in Al-Zn-Mg weldments 总被引:2,自引:0,他引:2
B. I. Bjørneklett Ø. Grong O. R. Myhr A. O. Kluken 《Metallurgical and Materials Transactions A》1999,30(10):2667-2677
In the present investigation, process modeling techniques have been applied to unravel the sequence of reactions occurring during welding and subsequent natural aging of Al-Zn-Mg extrusions. The model uses a combination of chemical thermodynamics and diffusion theory to capture the heat-affected zone (HAZ) dissolution and aging kinetics, with the particular feature of writing the constitutive evolution equation in a differential form. Separate response equations are then developed to convert the calculated values for the particle volume fraction and the matrix solute content into engineering quantities such as hardness or strength, for a direct comparison to experiments. The model indicates that particle dissolution is the main factor contributing to strength loss during welding. At the same time, growth of the remaining particles occurs during cooling, leading to solute depletion within the aluminium matrix. This, in turn, reduces the precipitation potential and contributes to the development of a permanent soft zone within the partly reverted region after prolonged room-temperature aging. It is concluded that the combination of a microstructure model with an appropriate heat-flow model creates a powerful tool for alloy design and optimization of welding conditions for Al-Zn-Mg extrusions, and an illustration of this is given toward the end of the article. 相似文献
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Y. F. Gu Y. Ro T. Kobayashi H. Harada 《Metallurgical and Materials Transactions A》2005,36(3):577-582
In an effort to enhance ductility and strength of Cr-base alloys, a series of Cr-Ru alloys with Ru contents ranging from 3
to 30 at. pct were made to study their microstructure evolution and mechanical properties. The microstructure of the alloys
with 6 to 20 at. pct Ru showed signs of a eutectic structure. However, no corresponding eutectic reaction is indicated in
the published Cr-Ru phase diagram. The yield strength of the Cr-Ru alloys increased with increasing Ru content at both room
temperature and 1200 °C. The tensile ductility of Cr-3 at. pct Ru is about 1.5 pct at room temperature, while the alloys containing
6 at. pct or more Ru showed zero tensile elongation. The deformation mechanisms of the Cr-Ru alloys are discussed in terms
of the microstructure and fracture behavior.
This article is based on a presentation made in the symposium entitled “Beyond Nickel-Base Superalloys,” which took place
March 14–18, 2004, at the TMS Spring meeting in Charlotte, NC, under the auspices of the SMD-Corrosion and Environmental Effects
Committee, the SMD-High Temperature Alloys Committee, the SMD-Mechanical Behavior of Materials Committee, and the SMD-Refractory
Metals Committee. 相似文献
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C. D. S. Tuck 《Metallurgical and Materials Transactions A》1985,16(8):1503-1514
Al4.5Zn1.5Mg and Al5Mg were reacted in water-vapor saturated air (WVSA) at 120°C and tensile tested. After an initial loss
of ductility with exposure time, probably caused by hydrogen embrittlement of the grain boundaries, between 15 hours and 25
hours exposure the mechanical properties of Al4.5Zn1.5Mg improved, this effect being due both to a reduced corrosion activity
of the grain boundaries in producing embrittling hydrogen at the external surface and to grain boundary MgZn2 precipitates acting as hydrogen traps. After 25 hours exposure water was shown to penetrate the grain boundaries, and a layered
corrosion product identified as the aluminum hydroxides boehmite and diaspore was formed. This resulted in a marked fall of
ductility. Re-solution heat treatment and reaging partially recovered the mechanical properties of Al4.5Zn1.5Mg if the exposure
time was less than 50 hours, and would not recover properties for longer exposure times. Small additions (0.1 pct) of iron
and nickel to Al4.5Zn1.5Mg lessened the grain boundaries’ sensitivity to corrosive attack whereas the addition of 0.1 pct
copper did not. Also, the former two additions did not cause the relative ductility increase during 15 to 25 hours exposure
in WVSA at 120°C shown by Al4.5Zn1.5Mg. It is proposed that these elements alter the magnesium segregation levels at the grain
boundaries which in turn affects their electrochemical attack. 相似文献
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X. J. Jiang B. Noble V. Hansen J. Tafto 《Metallurgical and Materials Transactions A》2001,32(5):1063-1073
The effects of zirconium and copper on the early stages of the precipitation processes in an Al-5.5 wt pct Zn-1.2 wt pct Mg alloy have been studied by differential scanning calorimetry (DSC) thermal analysis. Electron diffraction has been used as a complementary technique to aid in the interpretation of the thermal effects observed in the DSC thermograms. The results show that the initial stages of Guinier-Preston zone I (GP(I)) formation at room temperature are not affected by the presence of zirconium, but the rate of Guinier-Preston zone II (GP(II)) precipitation is slowed down significantly. For aging at 100 °C, the stability of GP zones is reduced by the addition of zirconium, and this leads to a reduction in the amount of η′ produced during aging. The addition of copper to an Al-5.4 wt pct Zn-1.2 wt pct Mg-0.2 wt pct Zr alloy intensifies the electron diffraction spots from GP(I), suggesting that the strong electron-scatterer copper may be incorporated into GP zones. The rate of growth of GP(I) at room temperature is unaffected by the presence of copper, but the rate of formation of GP(II) at room temperature is retarded. For artificial aging at 100 °C, the development of GP(I) and GP(II) is not affected significantly by the presence of copper, but the formation of η′ is stimulated, producing a high number density of very fine η′ precipitates. Preaging at room temperature results in accelerated η′ formation during subsequent aging at 100 °C in the zirconium-containing alloy. However, this acceleration of η′ formation is absent when copper is present in the alloy. 相似文献
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K. V. Mani Krishna R. Raghavan D. Srivastava G. K. Dey S. K. Sahoo I. Samjadar 《Transactions of the Indian Institute of Metals》2011,64(3):309-313
Evolution of dislocation structure as a function of deformation, in case of a two phase zirconium alloy, was characterized by transmission electron microscopy as well as X-ray line profile analysis. Dislocation structures up to a deformation of 10% show that deformation is mitigated by a single active slip system. Dislocation cellular structures were observed at a deformation of 27%. Two different X-ray based techniques of evaluation of dislocation density were used in the present study. The methods though differed in the absolute values of dislocation densities (ρ), agreed with each other in terms of trend in variation of ρ with the amount of plastic strain. 相似文献
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The room temperature tensile properties of age-hardened Ti-Cu alloys, 0.9 and 4 at. pct Cu, were investigated. The results
were correlated to the microstructure and to the observed interaction mechanism between moving dislocations and precipitated
particles. Two types of precipitates were observed upon aging between 400° and 500°C. One type was identified as a metastable,
ordered precipitate coherent with the matrix. The other type was the stable Ti3Cu phase which was partially coherent with the matrix. Both types of particles were precipitated from a martensitic microstructure
which resulted from the β → α transformation. Although the martensitic microstructure contributed to the high flow stress,
the elongation to fracture was principally determined by the dislocation-particle interaction mechanism. The maximum elongation
to fracture was obtained by inducing a dislocation by-pass mechanism in a structure containing homogeneously distributed,
partially coherent Ti3Cu particles. The tendency of the Ti3Cu particles to precipitate preferentially on boundaries was minimized by low temperature aging.
Formerly Assistant Professor Materials Research Laboratory, Rutgers University, New Brunswick, N.J. 相似文献
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M. Raghavan 《Metallurgical and Materials Transactions A》1980,11(6):993-999
In order to better understand the formation of Precipitate Free Zones (PFZ), microanalysis was conducted on heat treated Al-2.2
at. pct Zn-4.7 at. pct Mg and Cu-30 at. pct Ni-0.9 at. pct Nb alloys. In both the alloys, no appreciable solute depletion
at the grain boundaries was observed in the as-quenched condition. After aging, marked solute depletion was observed in the
PFZ of both the alloys. In the Al-Zn-Mg alloy, the PFZ were supersaturated with respect toη andT phases up to 4 h of aging at 473 K. In the Cu-Ni-Nb alloy, the PFZ were supersaturated only with respect to theβ phase but not the metastable γ″ phase. Based on the results, the factors affecting the formation and growth of PFZ are discussed. 相似文献
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Differential scanning calorimetry and electron diffraction investigation on low-temperature aging in Al-Zn-Mg alloys 总被引:3,自引:0,他引:3
X. J. Jiang J. Tafto B. Noble B. Holme G. Waterloo 《Metallurgical and Materials Transactions A》2000,31(2):339-348
Differential scanning calorimetry (DSC) has been combined with transmission electron microscopy (TEM) to investigate the low-temperature
decomposition processes taking place in an Al-5 wt pct Zn-1 wt pct Mg alloy. It was confirmed that two types of GP zones,
i.e., GP(I) (solute-rich clusters) and GP(II) (vacancy-rich clusters), formed independently during decomposition of the supersaturated
solid solution. The GP(I) zones form at a relatively low aging temperature and dissolve when the aging temperature is increased.
The GP(II) zones are stable over a wider range of temperatures. To investigate the nature of the zones in the Al-Zn-Mg alloy,
differential scanning calorimetry and transmission electron microscopy have also been carried out on binary Al-Zn alloys containing
5 wt pct and 10 wt pct Zn. In these Al-Zn alloys, GP zones formed rapidly during quenching, and they gave rise to characteristic
electron diffraction patterns identical to those from GP(II) in the Al-Zn-Mg alloy system, implying that GP(II) zones in Al-Zn-Mg
alloys are very similar to the zones formed in binary Al-Zn alloys. Thus, it is likely that GP(II) zones in Al-Zn-Mg alloys
are zinc-rich clusters. In the Al-5 wt pct Zn-1 wt pct Mg alloy, both GP(I) and GP(II) were found to transform to η′ and/or η particles during heating in the differential scanning calorimeter. The η′ was also observed to form after prolonged isothermal aging of the Al-Zn-Mg alloy at 75 °C or after short aging times at
125 °C. 相似文献