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1.
Fatigue experiments were conducted on polycrystalline and monocrystalline samples of a high purity Al, 5.5 wt pct Zn, 2.5
wt pct Mg, 1.5 wt pct Cu alloy in the peak-hardened heat treatment condition. These experiments were conducted in dry laboratory
air and in 0.5N NaCl solutions at the corrosion potential and at applied potentials cathodic to the corrosion potential. It has been shown
that saline solutions severely reduce the fatigue resistance of the alloy, resulting in considerable amounts of intergranular
crack initiation and propagation under freely corroding conditions for polycrystalline samples. Applied cathodic potentials
resulted in still larger decreases in fatigue resistance and, for poly crystals, increases in the degree of transgranular
crack initiation and propagation. Increasing amounts of intergranular cracking were observed when applied cyclic stresses
were reduced (longer test times). The characteristics of cracking, combined with results obtained on tensile tests of deformed
and hydrogen charged samples, suggest that environmental cracking of these alloys is associated with a form of hydrogen embrittlement
of the process zones of growing cracks. Further, it is suggested that stress corrosion cracking and corrosion fatigue of these
alloys occurs by essentially the same mechanism, but that the often observed transgranular cracking under cyclic loading conditions
occurs due to enhanced hydrogen transport and/or concentrations associated with mobile dislocations at growing crack tips. 相似文献
2.
J. S. Santner 《Metallurgical and Materials Transactions A》1981,12(10):1823-1826
The purpose of the present investigation is to determine the relative importance of minor variations in alloy chemistry and
thermomechanical treatment on the low cycle fatigue behavior of 7000 series aluminum alloys. Two types of alloying variations
are considered: changing the alloy purity level by controlling the iron and silicon content, and changing the grain refiner
from chromium to zirconium. The effects of these alloying variations, with regard to mechanical properties other than low
cycle fatigue, have been discussed elsewhere.1-4The purpose of thermomechanical processing is to provide increased strength over 7075-T7351 with equivalent fracture toughness
and corrosion properties.5-7 The effect of the dislocation substructure introduced by thermomechanical processing (TMP) on the high cycle fatigue behavior
of 7075 was documented by Reimann and Brisbane.8 The present work was undertaken to determine the relative importance of purity level, dispersoid type, and dislocation substructure
(TMP) on the low cycle fatigue behavior of 7000 series aluminum alloys.
formerly with the Air Force Materials Laboratory, Wright-Patterson AFB, OH 相似文献
3.
Solidification time and heat treatment are known to have a large effect on the microstructure of cast aluminum alloys. This
study was conducted to quantify how the fatigue properties of a 319-type aluminum alloy are affected by solidification time
and heat treatment. Both porosity-containing (non-hot isostatically pressed (HIP)) and porosity-free (HIP) samples in the
T6 (“peak aged”) or T7 (“overaged”) heattreated conditions were tested. As the solidification time increased, the average
initiating pore diameter increased and stress-controlled fatigue life decreased. Heat treatment was observed to have a large
effect on fatigue properties of the HIP samples. However, in the non-HIP fatigue samples, heat treatment did not significantly
change the fatigue life or fatigue strength of the cast 319-type alloy. The absence of an influence of heat treatment on fatigue
response is attributed to the predominance of the microporosity in fatigue crack initiation in cast aluminum. 相似文献
4.
Y. V. V. R. S. Murty T. Z. Kattamis O. F. Devereux 《Metallurgical and Materials Transactions B》1973,4(11):2575-2580
The morphological and kinetic nature of corrosion of directionally solidified aluminum-4.5 wt pct copper alloy in the as-cast,
solutionized and solutionized-and-aged conditions in air-saturated aqueous 3.5 wt pct NaCl solution were evaluated. In the
solutionized and solutionized-and-aged conditions the intergranular attack and pitting are similar to those occurring in solutionized
wrought alloys; the extent of attack at long times increases with increasing severity of solidification rate. The as-cast
alloy exhibits a cored dendritic structure with significant formation of interdendritic nonequilibrium eutectic. Extensive
inter dendritic corrosion of the α-phase containing more than 3.2 wt pct copper is seen; α containing less than 3.2 wt pct
copper and the θ-Al2Cu phase are cathodic. Corrosion of the as-cast alloy is parabolic with time and increases with increasing severity of solidification
rate in proportion to the amount of nonequilibrium second phase. 相似文献
5.
J. Lindigkeit A. Gysler G. Lütjering 《Metallurgical and Materials Transactions A》1981,12(9):1613-1619
The effect of slip distribution on the fatigue crack propagation behavior in vacuum of a high purity Al-5.9Zn-2.6Mg-l.7Cu
alloy in various age-hardened conditions has been investigated. The crack propagation resistance was observed to be significantly
higher for underaged microstructures containing shearable precipitates in comparison to overaged conditions with nonshearable
precipitates. The improved crack propagation resistance is attributed in part to an increased amount of reversed slip in the
plastic zone at the crack tip due to a higher degree of planar slip for conditions with shearable precipitates. The observed
increase in fatigue crack propagation resistance with decreasing precipitate size for microstructures containing a constant
volume fraction of shearable precipitates cannot be explained on the basis of such slip reversibility alone. The variation
in ductility for the different microstructures has also to be taken into account. It was found that the enhanced crack propagation
resistance can be correlated to the increased ductility with decreasing precipitate size. This explanation was supported by
the experimental observation that microstructures containing different volume fractions and sizes of shearable precipitates
but exhibiting the same ductility showed approximately the same resistance against fatigue crack propagation.
formerly with German Aerospace Research Establishment (DFVLR), Cologne, Germany.
formerly with Ruhr-University, Bochum, Germany. 相似文献
6.
7.
Axial fatigue tests were performed on a 7075-T6 aluminum alloy in tension-compression and under superimposed positive mean
stresses in dry air and in aqueous 0.5N NaCl solution. Both corrosive environments and positive mean stresses resulted in
lower fatigue lives but no interaction between these variables was observed. Crack initiation in air occurred at electropolish
pits at inclusion/alloy interfaces and propagated primarily in a Stage I (crystallographic) mode. Crack initiation in NaCl
solutions occurred at heavily corroded regions surrounding non-metallic inclusions and propagated in a cleavage mode normal
to the direction of applied stress. The relative number of cycles to crack initiation is shown to be a function of the magnitude
of cyclic stress but not of mean stress. Similarly, the percentage of reduction in fatigue life due to corrosive environments
is approximately constant at all mean stress levels. These data indicate that fatigue crack initiation is primarily related
to mobile dislocations associated with cyclic deformation. Crack propagation on the other hand appears to be controlled by
the maximum applied stress. A model for environment assisted cracking is presented which suggests that hydrogen induced cleavage
is responsible for the degradation in fatigue properties of this alloy.
Formerly Research Assistant, Materials Division, Rensselaer Polytechnic Institute, Troy, N. Y. 12181. 相似文献
8.
A new surface treatment process is presented that improves the properties of Ti-6 Al-4 V alloy.This process is based on thermal oxidation, in which the surface properties of the titanium alloy are improved via simultaneous nitriding and oxidation.The test results indicate that the resulting surface layer consists of TiO_2 and TiN.The sample with the best mechanical properties and corrosion resistance was sintered at a temperature of 800 ℃. 相似文献
9.
A. Mohamed Y. El-Madhoun M. N. Bassim 《Metallurgical and Materials Transactions A》2004,35(9):2725-2728
Two different sets of fatigue specimens were heat treated at different times or temperatures to investigate the effect of
grain size on the low-cycle fatigue behavior of Al-2024 polycrystalline alloy. Strain-controlled low-cycle fatigue testing
with a strain rate of 1×10−4 s−1 was conducted at room temperature. The fatigue response of the alloy was evaluated macroscopically in terms of cyclic stress
strain response and microscopically in terms of appearance of cyclic slip bands. The cyclic stress strain response of Al-2024
polycrystalline alloy exhibited a definite plateau region where saturation stress remained constant with plastic strain. It
was found that the smaller the grain size, the lower the saturation stress and the longer the plateau, whereas the larger
the grain size, the higher the saturation stress and shorter the plateau (i.e., reverse grain size effect). Microscopic observations using scanning electron microscope revealed that persistent slip bands
(PSBs) were observed at 45 deg orientations from the grain boundary. The volume fraction of PSBs was higher in small-grained
Al-2024 polycrystalline alloy as compared to large-grained Al-2024 polycrystalline alloy.
This article is based on a presentation given in the symposium “Dynamic Deformation: Constitutive Modeling, Grain Size, and
Other Effects: In Honor of Prof. Ronald W. Armstrong.” March 2–6, 2003, at the 2003 TMS/ASM Annual Meeting, San Diego, California,
under the auspices of the TMS/ASM Joint Mechanical Behavior of Materials Committee. 相似文献
10.
J. J. Kai C. H. Tsai T. A. Huang M. N. Liu 《Metallurgical and Materials Transactions A》1989,20(6):1077-1088
A series of heat treatments were performed to study the sensitization effect on the stress corrosion cracking (SCC) behavior
of INCONEL 600 alloy. The microstructural evolution and the chromium depletion near the grain boundary were carefully studied
using analytical electron microscopy (AEM). Comparable constant load tests in the solution containing various concentrations
of sodium thiosulfate (Na2S2O3) were, also performed in order to characterize the critical chromium concentration under the test conditions. It is observed
that thermal treatment has a great effect on the microstructure and the chromium depletion profile of this alloy. Most specimens
contained precipitates which were formed along grain boundaries in the semicontinuous form and were identified as M7C3 with a hexagonal crystal structure (a
0=1.398 nm,C
0=0.45 nm). Some intragranular precipitates which were identified as M23C6 with an fec crystal structure (a
0=1.06 nm) were observed in the specimens aged for a longer period of time. The results of the constant load test showed that
the susceptibility to SCC is sensitive to the chromium concentration at the grain boundary, and the minimum value to prevent
SCC failure, under the test conditions, is approximately 8 wt pct. 相似文献
11.
Kazuaki Shiozawa Shuming Sun R. L. Eadie 《Metallurgical and Materials Transactions A》2000,31(4):1137-1145
The corrosion fatigue crack propagation behavior of a squeeze-cast Al-Si-Mg-Cu aluminum alloy (AC8A-T6), which had been precracked
in air, was investigated at testing frequencies of 0.1, 1, 5, and 10 Hz under a stress ratio (R) of 0.1. Compact-toughness specimens were precracked about 6 mm in air prior to the corrosion fatigue test in a 3 pct saline
solution. At some near-threshold conditions, these cracks propagated faster than would be predicted by the mechanical driving
force. This anomalous corrosion fatigue crack growth was affected by the initial stress-intensity-factor range (ΔK
i), the precracking conditions, and the testing frequency. The initial crack propagation rate was as much as one order of magnitude
higher than the rate for the same conditions in air. This rapid rate was associated with preferential propagation along the
interphase interface in the eutectic structure. It is believed that a chemical reaction at the crack tip and/or hydrogen-assisted
cracking produced the phenomenon. Eventual retardation and complete arrest of crack growth after this initial rapid growth
occurred within a short period at low ΔK values, when the testing frequency was low (0.1 and 1 Hz). This retardation was accompanied by corrosion product-induced
crack closure and could be better explained by the contributory stress-intensity-factor range (ΔK
cont) than by the effective stress-intensity-factor range (ΔK
eff). 相似文献
12.
The stress corrosion cracking resistance of 24 heats of INCONEL* alloy X-750 was measured in high purity pH 10 water at 360
°C. An overaging heat treatment of 96 hours at 760 °C produced an improved combination of strength and cracking resistance
because of the homogenization of slip in the matrix. Examination of residual elements showed that Zr additions further improved
the cracking resistance by stabilizing theγ′ precipitate in the grain boundary region. Combining the new heat treatment with
the Zr addition produced approximately a 50 pct improvement in stress corrosion cracking resistance at a 10 pct lower yield
strength. 相似文献
13.
《中国稀土学报(英文版)》2016,(3)
The influences of the hot extrusion process on the microstructure, corrosion behavior and corrosion mechanism for Mg-Y magnesium alloy were studied by means of the microstructure observation, weight loss test, electrochemical test and corrosion morphology test. The results showed that with increasing of the extrusion ratio, the shear flow line on the vertical section of the extruded alloy increased, the shear bands parallel lines became more clearly visible, and a large number of fine equiaxed grains distributed in parallel with the flow lines. The open circuit potential had a certain degree of improvement after extrusion, the open circuit potential increased with increment of extrusion ratio, and the corrosion potential of the vertical section was higher than that of the same alloy in the same compression ratio. The shift rate of the corrosion potential relatively became larger with increasing of the extrusion ratio, and the cathode corrosion current corresponding to the branch migration shifted to the positive direction. The high frequency capacitive arc increased with increment of the extrusion ratio, and the radius of capacitive arc of the vertical section was slightly larger than that of the transverse section. The corrosion morphologies of Mg-0.25 Y alloy were uniform corrosion, and the corrosion morphologies of Mg-(2.5, 5, 8 and 15) were the pitting corrosion and the small range, deep depth localized corrosion. 相似文献
14.
A. J. Sedriks J. A. S. Green D. L. Novak 《Metallurgical and Materials Transactions B》1970,1(7):1815-1819
A comparison has been made of the corrosion and stress-corrosion behavior of an aged Al-5.3 wt pet Zn-2.5 wt pct Mg alloy
in aqueous chloride solutions of varying pH (i.e., 1 to 6.2). It is found that lowering the pH to values 〈4 accelerates corrosion
in the absence of stress, due to enhancement of the overall cathodic process, and accelerates the propagation of stress-corrosion
cracks. However, the pH dependence of cracking is not as marked as the pH dependence of corrosion rate, and this difference
has been explained in terms of local variations in pH within the crack. It is concluded that the present observations are
consistent with the view that the propagation of stress-corrosion cracks in this metal-environment system involves localized
anodic dissolution of the plastically deforming solid solution within the precipitate-free zone. 相似文献
15.
The corrosion fatigue behavior of an Al-2.5 pct Li-0.12 pct Zr alloy has been studied as a function of heat treatment by performing
smooth specimen fatigue life experiments on differently aged alloys in dry air and humid nitrogen. Results indicated that
aging decreased the fatigue life of the Al-Li-Zr alloy in dry air. However, exposure to water vapor reduced the fatigue resistance
of the underaged (UA) alloys but increased the fatigue life of the overaged alloys (OA) alloys. Hydrogen precharging experiments
(either exposure to moist air or cathodic charging in HC1 solutions) followed by fatigue testing in dry air confirmed that
the UA alloys were susceptible to hydrogen embrittlement and that the OA alloys were insensitive to a hydrogen effect. The
experimental results suggest that the susceptibility of the Al-Li-Zr alloy to hydrogen-assisted fracture is essentially related
to the effectiveness of hydrogen transport to the region ahead of the crack tip, which is controlled by the microstructure
of the alloy. Environmental and aging effects which influence the fatigue characteristics of the studied alloy are discussed. 相似文献
16.
17.
18.
综述了Cu-Ni合金腐蚀行为的宏观电化学的国内外研究进展.介绍了合金成分、外界环境、腐蚀产物膜及初始表面膜等因素对Cu-Ni合金耐蚀性能的影响,详细介绍了合金元素通过影响腐蚀产物膜的组织结构从而影响腐蚀过程的各种理论,针对目前Cu-Ni合金腐蚀行为的研究不足作出了适当的分析并指出了今后的研究方向. 相似文献
19.
The effect of heat treatment on the gouging abrasion resistance of alloy white cast irons 总被引:2,自引:0,他引:2
A series of heat treatments was employed to vary the microstructure of four commercially important alloy white cast irons,
the wear resistance of which was then assessed by the ASTM jaw-crusher gouging abrasion test. Compared with the as-cast condition,
standard austenitizing treatments produced a substantial increase in hardness, a marked decrease in the retained aus-tenite
content in the matrix, and, in general, a significant improvement in gouging abrasion resistance. The gouging abrasion resistance
tended to decline with increasing austenitizing tem-perature, although the changes in hardness and retained austenite content
varied, depending on alloy composition. Subcritical heat treatment at 500 ° following hardening reduced the retained austenite
content to values less than 10 pct, and in three of the alloys it caused a significant fall in both hardness and gouging abrasion
resistance. The net result of the heat treatments was the development of optimal gouging abrasion resistance at intermediate
levels of retained aus-tenite. The differing responses of the alloys to both high-temperature austenitizing treatments and
to subcritical heat treatments at 500 ° were related to the effects of the differing carbon and alloying-element concentrations
on changes in theM
s
temperature and secondary carbide precipitation. 相似文献
20.
The effects of heat treatment on the chromium depletion,precipitate evolution,and corrosion resistance of INCONEL alloy 690 总被引:1,自引:0,他引:1
J. J. Kai G. P. Yu C. H. Tsai M. N. Liu S. C. Yao 《Metallurgical and Materials Transactions A》1989,20(10):2057-2067
A series of heat treatments were performed to study the sensitization and the stress corrosion cracking (SCC) behavior of
INCONEL Alloy 690. The microstructural evaluation and the chromium depletion near grain boundaries were carefully studied
using analytical electron microscopy (AEM). The measured chromium depletion profiles were matched well to the calculated results
from a thermodynamic/kinetic model. The constant extension rate test (CERT) was performed in the solution containing 0.001
M sodium thiosulfate (Na2S2O3) to study the SCC resistance of this alloy. The Huey test was also performed in a boiling 65 pct HNO3 solution for 48 hours to study the intergranular attack (IGA) resistance of this alloy. Both tests showed that INCONEL 690
has very good corrosion resistance. It is believed that the superior IGA and SCC resistances of this alloy are due to the
high chromium concentration (≈30 wt pct). It is concluded in this study that INCONEL 690 may be a better alloy than INCONEL
600 for use as the steam generator (S/G) tubing material for pressurized water reactors (PWR's) 相似文献