Jun Luo
,
Hong Yan
,
Nan Zheng
,
Rong-Shi Chen
金属学报(英文版)
doi:10.1007/s40195-016-0378-1
Four kinds of Mg alloys with different Zn and Ca concentration were selected to analyze the effect of Zn and Ca concentration on the microstructure and the mechanical properties of Mg-Zn-Ca alloys. It was found that Zn and Ca concentration has a great influence on the volume fraction, the morphology and the size of second phase. The Mg-1.95Zn-0.75Ca (wt%) alloy with the highest volume fraction, continuous network and largest size of Ca2Mg6Zn3 phase showed the lowest elongation to failure of about 7%, while the Mg-0.73Zn-0.12Ca (wt%) alloy with the lowest volume fraction and smallest size of Ca2Mg6Zn3 phase showed the highest elongation to failure of about 37%. It was suggested that uniform elongations of the Mg-Zn-Ca alloys were sensitive to the volume fraction of the Ca2Mg6Zn3 phases, especially the network Ca2Mg6Zn3 phases; post-uniform elongations were dependent on the size of the Ca2Mg6Zn3 phase, especially the size of network Ca2Mg6Zn3 phase. Reduction in Zn and Ca concentration was an effective way to improve the room-temperature ductility of weak textured Mg-Zn-Ca alloys.
关键词:
Mg-Zn-Ca
,
alloys
,
Ductility
,
Hot
,
rolling
,
Texture
,
Second
,
phase
Zhijun LIN
,
Meishuan LI
,
Yanchun ZHOU
,
null
,
null
材料科学技术（英文）
Layered ternary ceramics represent a new class of solids that combine the merits of both metals and ceramics. These unique properties are strongly related to their layered crystal structures and microstructures. The combination of atomic-resolution Z-contrast scanning transmission electron microscopy (STEM) and transmission electron microscopy (TEM), selected area electron diffraction (SAED), convergent beam electron diffraction (CBED) represents a powerful method to link microstructures of materials to macroscopic properties, allowing layered ternary ceramics to be investigated in an unprecedented detail. Microstructural information obtained using TEM is useful in understanding the formation mechanism, layered stacking characteristics, and defect structures for layered ternary ceramics down to atomic-scale level; and thus provides insight into understanding the ``Processing-Structure-Property" relationship of layered ternary ceramics. Transmission electron microscopic characterizations of layered ternary ceramics in Ti-Si-C, Ti-Al-C, Cr-Al-C, Zr-Al-C, Ta-Al-C and Ti-Al-N systems are reviewed.
关键词:
Layered ternary ceramics
,
ternary
,
ceramics
,
MAX
,
phase
,
TEM
,
S
马文有
,
韩雅芳
,
李树索
,
郑运荣
,
宫声凯
金属学报
摘 要：采用螺旋选晶法制备镍基单晶高温合金，研究了2%，3%，4%(质量分数)三种成分Mo含量对合金显微组织和高温持久性能的影响。结果表明： 3种成分合金铸态组织均由γ，γ′相组成。热处理后，4%Mo合金开始有μ相析出。1100℃,500h热暴露后，4%Mo合金中的μ相大量析出并长大，3%Mo合金中只有少量μ相析出，2%Mo合金中不析出μ相。析出的μ相主要由Mo、Re、W、Cr、Co和Nb等元素组成，其中Mo形成μ相倾向最强，Re、W和Cr次之，Nb和Co最小。大量棒状μ相的析出严重损害了合金的高温持久性能，少量μ相不降低合金的高温持久性能，反而因Mo的固溶强化作用使合金高温持久性能升高。对于Ni-5Cr-10Co-
4W-3Re-5.6Al-8Ta-1Ti-0.5Nb基础成分合金，最佳的Mo含量为3wt.%。
关键词:
单晶高温合金
,
molybdenum
,
µ
,
phase
,
microstructure
,
stress rupture properties
Xinhua LI
,
Kai QIU
,
Fei ZHONG
,
Zhijun YIN
,
Changjian JI
,
Yuqi WANG
,
null
,
null
,
null
,
null
,
null
,
null
材料科学技术（英文）
The preparation of porous structure on the molecular beam epitaxy (MBE)-grown mixed-polarity GaN epilayers was reported by using the wet chemical etching method. The effect of this porous structure on the residual stress of subsequent-growth GaN epilayers was studied by Raman and photoluminescence (PL) spectrum. Substantial decrease in the biaxial stresse can be achieved by employing the porous buffers in the hydride vapour phase epitaxy (HVPE) epilayer growth.
关键词:
GaN
,
vapour
,
phase
,
epitaxy
Jun ZHANG
材料科学技术（英文）
An ideal method has been established for calculating the precipitation ofα2 ordered phase in near-α titanium alloys based on the theory on the critical electron concentration for the precipitation of α2 ordered phase in near-α titanium alloys. With complete precipitation of α2 phase in near-α titanium alloys, the alloys can be considered to be composed of two parts: (1) the ®2 ordered phase with the stoichiometric atomic ratio of Ti3X; (2) the disorder solid solution with the critical composition in which the α2 ordered phase is just unable to precipitate. By using this method, the volume fractions of α2 ordered phase precipitated in Ti-Al, Ti-Sn, Ti-Al-Sn-Zr alloys with various Al, Sn and/or Zr contents have been calculated. The influences of Al and Sn on the precipitation of α2 ordered phase are discussed. The calculating results show substantial agreement with the experimental ones.
关键词:
Ordered α2 phase
,
2
,
phase
,
precipitation
,
electron
Applied Physics Letters
Martensitic transformation in Ni(2+x)Mn(1-x)Ga alloys is known to be controlled by the soft tetragonal elastic constant C' of the high-temperature austenitic phase. The temperature (T) and composition (x) dependence of C'(T, x) are calculated using the first-principles exact muffin-tin orbitals method. We show that the temperature factor of C' is dominated by the phonon-smearing term. The competition between the negative alloying effect (partial derivative C'/partial derivative x < 0) and the positive temperature effect (partial derivative C'/partial derivative T > 0) is found to lead to nearly constant C'(T(M)(x), x) at the critical temperature TM(x). We demonstrate that a proper account of the temperature and composition dependence of C'(T, x) is indispensable for reasonable theoretical TM(x) values. VC 2011 American Institute of Physics. [doi: 10.1063/1.3603935]
关键词:
phase
WANG Jian WU Xingfang CHEN Xunping CAI Jun University of Science and Technology Beijing
,
Beijing
,
China LIU Baixin Tsinghua University
,
Beijing
,
China FANG Zhengzhi Beijing Institute of Space Physics
,
Academia Sinica
,
Beijing
,
China
金属学报(英文版)
Co thin films were subjected to 50 keV carbon ion implantation.At the dose of 2.5× 10~(17)/cm~2,a hexagonal Co-carbide phase was observed for the first time.The lattice con- stants from electron diffraction are a=0.2685 nm and c=0.4335 nm.The phase does not dis- appear until the dose of 9×10~(17)/cm~2.Auger spectra showed that the stoichiometry was Co_(2-3)C.The behavior of the ferromagnetic carbides along the descending sequence of Ni-Fe-Co by Fermi energy of solids was interpreted.Furthermore,based on the kinetic con- dition of phase transformation and the band theory of solids,a possible explanation about the difference of the results of ion-metallurgy and thermal metallurgy was proposed.
关键词:
ion implantation
,
null
,
null
,
null
,
null
Y.H.Zhu
材料科学技术（英文）
Furnace cooling is a slow cooling process. It is of importance to study structural evolution and its effects on the properties of alloys during the furnace cooling. Decomposition of aluminium rich α phase in a furnace cooled eutectoid Zn-Al based alloy was studied by transmission electron microscopy. Two kinds of precipitates in the α phase were detected in the FCZA22 alloy during ageing at 170℃. One was the hcp transitional α′m phase which appears as directional rods and the round precipitates. The other was the fcc α′′m phase. It was found that the transitional phaseα′m grew in three preferential directions of <110>, <011> and <101>. The orientation relationship between the α phase and transitional phase α′m was determined as , . The non-equilibrium phase decomposition of the α phase is discussed in correlation with the equilibrium phase relationships. (02-2) 'm (fcc)// (02-2) (fcc) , [-111] 'm (fcc)// [-233] (fcc).
The non-equilibrium phase decomposition of the phase is discussed in correlation with the equilibrium phase relationships.
关键词:
Phase decomposition
,
decomposition
,
microstructural
,
evo
李克俭
,
蔡志鹏
,
李轶非
,
潘际銮
金属学报
doi:10.11900/0412.1961.2015.00590
采用热模拟的方法研究了FB2钢(一种新型9%Cr马氏体耐热钢)中Laves相在焊接热循环中的演化行为. 首先借助SEM观察到存在于原始供货状态下的FB2钢中尺寸在微米级别的Laves相颗粒; 进一步的分析表明, 这些Laves相的出现是由铸造过程中的枝晶偏析导致的. 焊接热模拟实验结果表明, 在加热过程中, Laves相与基体γ-Fe发生共晶反应导致的组分液化会给FB2钢热影响区带来热裂倾向; 在冷却后的样品中发现了一些网状的共晶组织, 利用SEM/EDS和TEM分别得到了该共晶组织的成分信息和结构信息, 确定该共晶组织的2个组分为χ相和γ-Fe. 在此基础之上, 较为详细地分析了不同峰值温度热模拟后样品中共晶组织的形成过程, 解释了共晶组织不同形貌的产生原因.
关键词:
FB2钢
,
Laves相
,
组分液化
,
χ
,
相
,
热裂倾向
,
焊接
