S.H. Ai
,
Y.Q. Wu
,
Z.G. Wang and Y.Zhang(State Key Laboratory for Fatigue and Fracture of Materials
,
Institute of Metal Research
,
The Chinese Academy of Sciences
,
Shenyang 110015
,
China)
金属学报(英文版)
Low cycle fatigue (LCF)tests under different total strain amplitudes have been conducted in order to ascertain the effect of precipitate sizes on LCF behavior of 8090 Al-Li alloy. A constant strain rate of 3×10-3s-1 and symmetrical triangular waveform were employed for all tests. It is found that the cyclic stress response of the alloy varied with the precipitate sizes and strain amplitudes. The materials in all conditions cyclically handen at first and the higher the strain amplitude, the greater the amount of hardening. The low cyclic flow stress is the highest in the peakaged condition. TEM and SEM observations demonstrated that cyclic stress-strain behavior and fracture mode of Al-Li alloy are closely related to an increase in the dislocation density and interaction between the precipitates and dislocations, sizes of δ particles and pricipitate free zone (PFZ) at grain boundaries.
关键词:
Al-Li alloy
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null
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null
Transactions of Nonferrous Metals Society of China
Low cycle fatigue(LCF) tests under different total strain amplitudes have been conducted in four aging conditions of 8090 Al-Li alloy. It was found that the cyclic stress response and the LCF lifetime of the alloy varied with the aging conditions and strain amplitudes. The cyclic stress-strain behaviour and fracture mode of Al-Li alloy are closely related to an increasing in the dislocation density, dislocation-dislocation interactions and interactions between the precipitates with dislocations.
关键词:
low cycle fatigue;cyclic hardening;precipitate phase;mechanical-properties
SONG Shihong LI Xuzhi ZHANG Weibin Central-South University of Technology
,
Changsha
,
China SONG Shihong
,
Department of materials Science
,
Central-South University of Technology
,
Changsha
,
China
金属学报(英文版)
The correlation between the diverse fracture modes and the microstructural variation with recrystallization in the Al-Li alloys under heat treatment was observed by means of triplanar optical and scanning electron microscopy.The growth,propagation and feature of their frac- tures were described from the viewpoint of microstructure,energy and geometry.
关键词:
Al-Li alloy
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null
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null
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null
CHEN Zheng Northwestern Polytechnical University
,
Xi′an
,
China Lab.No.401
,
Northwestern Polytechnical University
,
Xi′an 710072
金属学报(英文版)
Threshold of fatigue for short through cracks for Al-Li alloy 8090 was evaluated to be lower than that of long cracks,and to decrease with the shortening of the crack length.The correla- tion among the threshold,crack wake,and crack tip shielding of the short fatigue cracks was discussed.The super demarcation length and lowest theoretical threshold of short through fa- tigue cracks were presented.
关键词:
Al-Li alloy
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null
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null
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null
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WANG Zhongguang ZHANG Yun HU Zhuangqi State Key Laboratory for Fatigue and Fracture of Materials
,
Institute of Metal Research
,
Academia Sinica
,
Shenyang
,
ChinaHE Shiyu LI Qingjian Harbin Institute of Technology
,
Harbin
,
China
金属学报(英文版)
Fatigue crack growth rates of Al-Li alloy 8090 in air were found to be strongly dependent up- on the aging conditions.The naturally aged and underaged specimens showed the highest re- sistance to the fatigue crack propagation.The fatigue crack growth resistance of the overaged specimen is the lowest and that of the peakaged specimen in between.As compared to air, 3.5% NaCl solution does not change the effect of aging conditions on the fatigue crack growth,but causes a decrease of the resistance to the fatigue crack growth under the same ag- ing condition.Both short cracks from notch and physically short cracks showed much higher rates of fatigue crack propagation in comparison with long cracks under the same aging condi- tion and stress intensity level.The growth behavior of the short crack depends on its type.The growth rate of short crack from notch decreases first to a minimum and then increases with in- creasing △K.However,the physically short crack grows at a progressively increasing rate. The effects of aging conditions are explained in terms of the slip planarity of dislocations and the cyclic slip reversibility.The observed short crack behavior is considered to be dependent on the crack closure and the local plasticity near the crack tip.
关键词:
Al-Li alloy
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null
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null
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SUN Dongli YANG Dezhuang LEI Tingquan CUI Yuexian Harbin Institute of Technology
,
Harbin
,
China Lecturer
,
Department of Metallic Materials and Technology
,
Harbin Institute of Technology
,
Harbin 150006
,
China
金属学报(英文版)
The fracture mechanism of deformation-aged Al-Li alloy was approached by investigating the influence of prior cold deformation on the precipitation kinetics as well as the behaviours of work hardening and fracture for Al-2.73Li alloy.The experimental results show that the work hardening rate and the strength are increased and the ductility is decreased by prior cold deformation.The decrease in ductility is mainly due to the cell dislocaton substructure distrib- uted inhomogeneously and the hardening of precipitate free zones at grain boundaries caused by prior cold deformation.The failure mode in the alloy is a mixed integranular and transgranular one.The tendency of intergranular fracture is intensified through the deformation-aging.The mechanisms of intergranular failure in the alloy are different under various deformation-aging treatments.
关键词:
Al-Li alloy
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null
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null
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null
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null
Suhua AI
,
Zhongguang WANG
,
Yun ZHANG and Zhuangqi HU(State Key Laboratory for Fatigue and Fracture of Materials
,
Institute of Metal Research
,
Chinese Academy of Sciences
,
Shenyang 110015
,
China)
材料科学技术（英文）
Fatigue lives for the smooth and notched specimens of 8090 Al-Li alloy jn the different ageing conditions have been studied. For the smooth samples of 8090 alloy the artificial ageing results in an increase in fatigue life in comparison with natural ageing. On the contrary, the notched specimens of 8090 alloy in the naturally aged condition show higher fatigue life than in the peak-aged. The exposure to either the peak-aged or naturally aged leads to superior fatigue properties of Al-Li alloy to the traditional high strength aluminum alloys of 7075 and 2024, especially in the latter aged condition. In all ageing conditions, i,e. naturally, under-, peak- and over-aged, the peak-aged 8090 alloy displays the highest fatigue life and the over-aged material has a minimum value at the same stress amplitude. The difference in fatigue life is mainly attributable to the size and distribution of strengthening precipitates as well as the wide of precipitate free zones (PFZ's) along grain boundaries.
关键词:
ZHANG Hongxue XU Zhichao CHEN Guoliang University of Science and Technology Beijing
,
Beijing
,
China Professor
,
Faculty of Superalloy
,
University of Science and Technology Beijing
,
Beijing
,
China
金属学报(英文版)
The relative ratio of fatigue resistance to creep resistance of materials varies with test temper- ature.As the temperature decreases,the creep resistance,since it is a thermal activation pro- cess,becomes relatively larger than fatigue resistance.Therefore the fatigue damage becomes predominant,and results in expansion of fatigue fracture region(region F),and shrinkage even complete elimination of creep fracture region(region C).A materials parameter Ω can be defined to estimate the temperature at which the creep fracture region is completely de- pressed.This phenomenon could be understood on the basis of the integrated model of compet- itive and cumulative models of fatigue creep interaction.
关键词:
creep fracture
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null
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