朱胜江
,
J.H. Hamilton
,
A.V. Ramayya
,
王建国
,
丁怀博
,
顾龙
,
J.K. Hwang
,
K. Li
,
S.H. Liu
,
N.T. Brewer
,
Y.X. Luo
,
J.O. Rasmussen
,
I.Y. Lee
,
徐强
,
杨韵颐
,
肖志刚
,
李红洁
,
马文超
原子核物理评论
doi:10.11804/NuclPhysRev.30.02.099
对于近年来清华大学与美国合作研究组在原子核结构实验研究中有关奇A核的多声子γ振动带方面的进展进行了评述。研究人员通过有效的国际合作，识别了质量数A=100丰中子核区的奇A核103Nb，105Mo，107Tc和109Tc中的两声子γ振动带，这是迄今为止国际上在奇A核的结构研究中发现的仅有的4例这样的结构。对于实验方法、研究结果以及这些多声子γ振动带的特性进行了评述，并对目前在多声子带其他方面的研究及今后进一步的工作进行了概述。
关键词:
原子核结构
,
高自旋态
,
多声子γ振动带
,
奇A核
Acta Materialia
The fatigue behavior of as-cast Mg-12%Zn-1.2%Y-0.4%Zr alloy has been investigated. The S-N curve showed that the fatigue strength at 107 cycles was 45 MPa. Scanning electron microscopy observations on the surfaces of the failed and unfailed specimens (after up to 1 X 10(7) cycles) suggested that the slip bands could act as preferential sites for non-propagating fatigue crack initiation, and the I-phase could effectively retard fatigue crack propagation (FCP). The macro fracture morphology clearly indicated that the overall fracture surface was composed of three regions, i.e. a fatigue crack initiation region (Region 1), a steady crack propagation region (Region 2) and a tearing region (Region 3). High-magnification fractographs showed that only porosities can act as the crack initiation sites for all specimens. Moreover, for specimens with fatigue lifetimes lower than 2 x 10(5) cycles, the cracks mostly initiated at the subsurface or surface of the specimen. However, when the fatigue lifetime was equal to or higher than 2 x 10(5) cycles, the fatigue crack initiation sites transferred to the interior of the specimen. The maximum stress intensity factors corresponding to the transition sites between Regions 1, 2 and 3 were 2 and 4.2 MPa m(1/2), respectively. When the maximum stress intensity factor K(max) was lower than 4.2 MPa m(1/2), in the steady crack propagation region, due to the retarding effect of I-phase/alpha-Mg matrix interfaces, the fatigue cracks tended to pass the I-phase/alpha-Mg matrix eutectic pockets directly and propagated through the grain cells, resulting in the formation of many flat facets on the fracture surface. However, when the maximum stress intensity factor was higher than 4.2 MPa m(1/2), in the sudden failure region, the rigid bonding of I-phase/alpha-Mg matrix interfaces was destroyed and the cracks preferentially propagated along the interfaces, which resulted in the fracture surface being almost completely composed of cracked I-phase/alpha-Mg matrix eutectic pockets. Based on microstructural observation and the fracture characteristics of the two regions, it is suggested that with an increase in crack tip driving force, the FCP mode changes from transgranular propagation to intergranular propagation. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
关键词:
mg alloy;I-phase;fatigue crack initiation;casting porosity;fatigue;behavior;magnesium alloy;re alloys;deformation;mechanism;growth
Physica Status Solidi B-Basic Research
The perturbation formulas of EPR g factors g(\\) g(perpendicular to) and hyperfine structure constants A(\\) A(perpendicular to) for the trigonal octahedral 3d(7) cluster are derived considering not only the configuration interaction effect due to the admixture among ground and excited states, but also the covalency effect due to the admixture between the d electrons of the 3d(7) ion and the p electrons of ligands. In these formulas, the parameters related to both effects and the trigonal field parameters are estimated from the optical spectra and the structural parameters of the studied system. According to these formulas, the EPR parameters g(\\), g(perpendicular to), A(\\) and A(perpendicular to) for Co2+ in the octahedral sites of Y3Al5O12 and Y3Ga5O12 garnets are satisfactorily explained from the optical spectra and the structure data. The role of the covalency effect is discussed.
关键词:
superposition model;phase-transition;absorption;linbo3;ions
骆良顺
,
刘桐
,
张延宁
,
苏彦庆
,
郭景杰
,
傅恒志
金属学报
doi:10.11900/0412.1961.2015.00619
对Al-15%Y (质量分数)过共晶合金在1~100 μm/s的抽拉速率下进行定向凝固实验, 研究抽拉速率对组织演化及Al3Y相生长规律的影响. 结果表明, 铸态Al-15%Y合金主要由Al3Y先析出相和Al3Y/Al共晶体组成. 在定向凝固过程中, 当抽拉速率为1 μm/s时, Al3Y相为不规则形状且边界清晰, 为小平面的生长特性. 随着抽拉速率的增加, Al3Y相的形貌逐渐转变为拉长的六棱柱形态, 其中少量的Al3Y相具有中空形貌. 当抽拉速率为10和20 μm/s时, Al3Y相按粗大的六棱柱形态生长. 进一步增加抽拉速率至100 μm/s时, 组织中出现“十”字形貌的Al3Y相, 为2个六棱柱垂直交叉结构, 类似枝晶的生长形式. 在抽拉速率增加的过程中, 固/液界面前沿逐渐出现领先相, 且凝固速率越大, 领先距离越长.
关键词:
Al-Y过共晶合金
,
定向凝固
,
金属间化合物Al3Y
,
组织演化
史菲
,
郭学峰
,
张忠明
材料科学与工艺
采用两种不同冷却方式的普通铸造技术在Mg68Zn28Y4合金中制备了镁合金稳定态二十面体准晶相,分析了冷却速率对准晶相形成、分布、数量和晶粒尺寸的影响.通过扫描电镜、能谱分析仪和透射电子显微分析技术,确定了合金的组织、相成分及准晶相结构.结果表明:Mg68Zn28Y4三元合金在室温冷却过程中,准晶相直接从液相形核、长大;在铸铁模型腔内冷却时,铸件断面的温度梯度小,温度场较为平坦,沿铸型纵横截面准晶相分布均匀、晶粒尺寸约为10～15 μm;在铸铁板表面冷却时,铸件断面的温度梯度较大,导致冷却速率显著影响准晶相的分布、数量及形貌.准晶相的晶粒尺寸为10～60 μm不等,分布由均匀弥散到不均匀散布再到均匀.
关键词:
稀土
,
铸造镁合金
,
冷却速率
,
二十面体准晶
彭晓
,
王福会
,
D.R.
,
Clarke
金属学报
磁控溅射Co-Cr-Al(Y)纳米涂层在1000, 1100和1200℃氧化一定时间后, 用光激发荧光谱技术表征热生长的Al2O3相. 发现氧化层局部区域存在由非稳态相向稳态相的转变, 即: γ→θ→α; 其转变过程随温度升高显著加快, 并在1200℃下变昨不明显. 在相同温度下, Y明显减缓Al2O3相转变过程.
关键词:
光激发荧光谱术
,
null
,
null
彭晓
,
王福会
,
D.R.Clarke
金属学报
用光激发荧光谱术分析测量磁控溅射Co-Cr-Al(Y)纳米涂层经1000, 1100和1200℃氧化后Al2O3膜中的残余应力, 获得如下结果: (1) 残余应力随氧化温度升高而增大; (2) 暂态氧化出现的区域应力值明显低于无暂态氧化的区域; (3) 两种涂层1000℃下形成的氧化膜中的残余应力相差不大, 但在1100℃和1200℃下, 含Y涂层形成的氧化膜中的残余应力比不含Y中的高. 对实验结果进行了分析.
关键词:
光激发荧光谱术
,
null
,
null
薛钢
材料开发与应用
基于对材料断裂的物理本质分析,提出断裂决定于应力第一不变量I1的理论假设,并给出相应的断裂准则,即材料局部区域的应力第一不变量I1达到一临界值Ib时,断裂开始发生,定义该临界值Ib为断裂强度,用单轴拉伸试验可以确定材料的断裂强度Ib.利用该断裂准则与Mises屈服准则,四种基本力学行为判据是:(1)弹性变形σmises＜σy,I1＜Ib;(2)塑性变形σmises ≥σy,I1＜Ib;(3)脆性断裂σmises＜σy,I1≥Ib;(4)塑性断裂σmises≥σy,I1≥Ib.
关键词:
应力第一不变量
,
断裂准则
,
断裂强度
D.Q. Wan
,
G.C. Yang
金属学报(英文版)
The microstructure formation and mechanical property involving icosahedral quasicrystal (I-phase) in the Y-rich Mg-Zn-Y alloy have been studied. The equilibrium formation of I-phase from the Y-rich Mg-Zn-Y melt is through a peritectic reaction between the Y-rich melt and the primary W-phase, which is discussed in detail. The independent nucleation and coupling growth mechanism between the W-phase and the I-phase, from the melt, are revealed, which is significant for understanding the peritectic reaction process involving icosahedral quasicrystal in the Mg-Zn-Y alloy. The mechanism of the quasicrystal phase strengthened magnesium alloys is also discussed here.
关键词:
Mg-Zn-Y
,
null
,
null
