文玉华
,
张伟
,
李宁
,
谢文玲
,
王杉华
金属学报
为开发不需“训练”就具有高可回复形变的铁基形状记忆合金，本文研究了直接时效和形变时效对Fe-13.53Mn-4.86Si-8.16Cr-3.82Ni-0.16C合金第二相析出，马氏体相变和形状记忆效应的影响。扫描电镜和X-Ray衍射分析表明时效后有大量Cr23C6第二相析出，但直接时效后Cr23C6的析出位置是无方向性的，而形变时效后Cr23C6的析出是有方向性的。相同时效时间下，形变时效析出的Cr23C6数量要显著多于直接时效的，且尺寸只有直接时效的一半。直接时效和形变时效都能显著提高合金的形状记忆效应，且都存在一个最佳的时效时间。经过任意相同时间时效后，形变时效后的形状记忆效应显著高于直接时效的。通过控制第二相在奥氏体晶粒内的析出方式，使第二相有方向性析出，可制备出免训练高可回复形变的铁基形状记忆合金。
关键词:
形状记忆合金
,
Shape memory effect
,
Ageing
,
Carbides
,
Directional precipitation
Y.H.Zhu
,
W.B.Lee
,
S.To
材料科学技术（英文）
The nanostructural evolution and phase transformation of the films of a Zn-Al based alloy (Zn¬68Al¬10Cu¬22 in wt pct) have been studied by using X-ray diffraction and scanning electron microscopy. Nanostructural thin films of the Zn-Al based alloy were produced by using an electron beam deposition technique. It was found that a nanocrystalline phase ηn' had a strong preferred crystal orientation at (0002) crystal planes in the as-deposited films. During ageing at 220℃, the decomposition of nanophase ηn' started with clustering to form Z-zones, and transitional phase, which was accompanied by an eutectoid decomposition of the ηn' phase: ηn' →βeut'+T'. Decomposition, such as clustering and the formation of the Z-zones, and the transitional phase etc. were observed in the nanophaseβeut'. The formation and the decomposition of the transitional phase of micrometers in size were involved in the decomposition of the main nanophase ηn'. The mechanism of the Z-zones formation and the stability of nanophases were discussed.
关键词:
Ageing
,
null
,
null
,
null
Omyma Hassan Ibrahim Ibrahim Soliman Ibrahim Tarek Ahmed Fouad Khalifa
材料科学技术（英文）
In the present study, the effect of aging heat treatment at 650, 750, and 850°C on the impact toughness of 316L austenitic stainless steel, 2205 duplex stainless steel and their weldments has been investigated. Welding process was conducted using the TIG (tungsten inert gas) welding technique. Instrumented impact testing, at room temperature, was employed to determine the effect of aging treatment on the impact properties of investigated materials. Aging treatment resulted in degradation in the impact toughness as demonstrated by the reduction in the impact fracture energy and deformation parameters (strain hardening capacity, fracture deflection, and crack initiation and propagation energy). The degree of embrittlement was more noticeable in duplex stainless steel parent and weld-metal than in 316L stainless steel and became greater with the
increase of aging temperature. The degradation in impact toughness was discussed in relation to the observed precipitation of the intermetallic sigma phase in the microstructure of the stainless steel weldments and the corresponding fracture surface morphology.
关键词:
Austenitic and duplex stainless steels
,
Ageing
,
Instrumented impact toughness
Byoungho Kim
,
Jongjin Jeon
,
Yeongdo Park
,
Yongho Park
,
Ikmin Park
材料科学技术（英文）
The ageing behavior of Mg-xAl-Zn alloys with a variation of Al contents (x=3, 5, 7, 9 and 11 wt pct) were investigated. Solid solution treatment and artificial ageing were carried out at 693 and 493 K, respectively. After the solid solution treatment, β-Mg17Al12 was resolved to the α-Mg matrix in the specimens which contained Al up to 9 wt pct and partially resolved in the specimen of 11 wt pct Al. During ageing, the β-Mg17Al12 phase was precipitated at the grain boundary in the form of discontinuous precipitation and grown into the matrix. The volume fraction of β-phase was increased with the Al contents. Tensile strength increased with the volume fraction of precipitated β-phase, which was believed to strengthen the matrix.
关键词:
Ageing
,
null
,
null
Omyma Hassan Ibrahim Ibrahim Soliman Ibrahim Tarek Ahmed Fouad Khalifa
材料科学技术（英文）
In the present study, the effect of aging heat treatment at 650, 750, and 850°C on the impact toughness of 316L austenitic stainless steel, 2205 duplex stainless steel and their weldments has been investigated. Welding process was conducted using the TIG (tungsten inert gas) welding technique. Instrumented impact testing, at room temperature, was employed to determine the effect of aging treatment on the impact properties of investigated materials. Aging treatment resulted in degradation in the impact toughness as demonstrated by the reduction in the impact fracture energy and deformation parameters (strain hardening capacity, fracture deflection, and crack initiation and propagation energy). The degree of embrittlement was more noticeable in duplex stainless steel parent and weld-metal than in 316L stainless steel and became greater with the
increase of aging temperature. The degradation in impact toughness was discussed in relation to the observed precipitation of the intermetallic sigma phase in the microstructure of the stainless steel weldments and the corresponding fracture surface morphology.
关键词:
Austenitic and duplex stainless steels
,
Ageing
,
Instrumented impact toughness
A.A.Al-Aql
,
M.S.Al-Salhi
,
M.I.Ansari
材料科学技术（英文）
Precipitation study was carried out in Ni-35 at. pct Cr alloy by measuring electrical resistivity at different ageing temperatures and long ageing times. During ageing, it was observed that electrical resistivity initially rose with ageing time and then fell after very long ageing at a constant temperature. The initial increase in resistivity during ageing may be attributed to the formation of GP zones/Cr-rich precipitates at early stages by nucleation process and decrease in resistivity, and after attaining a maximum, is due to the growth of precipitate particles and subsequently by coarsening of these precipitates. The results of electrical resistivity measurements during ageing were confirmed by X-ray diffraction analysis indicating the formation of a Cr-rich phase and a Cr3Ni2 phase in the Ni matrix.
关键词:
Precipitation
,
null
,
null
,
null
,
null
P.Parameswaran
材料科学技术（英文）
Electron enregy loss spectroscopy (EELS) and energy filtering transmission electron microscopy (EFTEM) investigation on 2.25Cr-1Mo steel was carried out to understand the nature of evolution of secondary carbides. The filtered images obtained from two different ageing treatments indicate that the steel evolves to a more stable carbide namely M23C6 in comparison to M2C. Microchemical information was generated from EELS spectra. Suitable choice for estimating the microchemical state was discussed. To evaluate the behaviour of ageing an elemental ratio of Fe to Cr is employed.
关键词:
Ferritic steels
,
Steels
,
2.25Cr-1Mo
,
steels
,
EFTEM
Zhiwei DU
,
Tietao ZHOU
,
Peiying LIU
,
Huanxi LI
,
Baozhong DONG
,
Changqi CHEN
材料科学技术（英文）
The evolution of microstructure parameters (precipitate size and volume fraction) for two types of Al-Zn-Mg-Cu alloys (7075 and 7055) during aging has been studied by synchrotron-radiation small angle X-ray scattering (SAXS). The results show that the precipitates are only a few nanometers for both alloys ageing even at higher temperature of 160℃ for 72 h (4.44 and 5.82 nm, respectively). The maximum of the precipitate volume fraction increases with in creasing Zn content and is about 0.023~0.028 and 0.052~0.054, respectively. The coarsening of precipitate is consistent with LSW (Lifshitz-Slyozov-Wagner) model even at the initial stage where volume fraction is still varying. The activation energy of coarsening regime has been determined to be about 1.22±0.02 eV and 1.25±0.02 eV for alloys 7075 and 7055, respectively.
关键词:
Small angle X-ray scattering (SAXS)
,
null
,
null
,
null
,
null
Qiming DONG
,
Dongmei ZHAO
,
Ping LIU
,
Buxi KANG
,
Jinliang HUANG
材料科学技术（英文）
Age hardening in Cu-3.2Ni-0.75Si(wt pct) and Cu-1.0Ni-0.25Si (wt pct) alloys from 723 to 823 K is studied. After an incubation period strengthening appears which is due to precipitates in the Cu-1.0Ni-0.25Si (wt pct) alloy. On other hand an immediate increase of the yield strength characterizes the aging of the alloy. This is followed by the regions of constant yield strength and further by a peak. The microstructure of the alloy was studied by, means of transmission electron microscope (TEM) and X-ray diffraction (XRD). Spinodal decomposition takes place followed by nucleation of the ordering coherent (Cu,Ni)3Si particles, further precipitation annealing coherent δ-Ni2Si nucleated within the (Cu,Ni)3Si particle. Any change of the yield strength can be described by an adequate change of the structure in the sample. The nature of the aging curves with a "plateau" is discussed. The formulas of Ashby and Labusch can be used to explain the precipitation.
关键词:
Copper alloy
,
null
,
null
,
null
,
null
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null
