Z.M. Zhang
,
C.J. Xu
,
X.F. Guo
,
S.Z. Jia
金属学报(英文版)
Mg 2 Si reinforced Mg-Al based composite with
high amount of silicon was prepared by permanent mould casting, and
then extruded by reciprocating extrusion (RE) after the composite
was processed by homogenization heat treatment. The effect of RE
processing on the morphology and size of Mg 2 Si and the
mechanical properties of the composite were investigated, to develop
new ways to refine the Mg 2 Si phase and improve its shape. The
result showed that RE was very useful in refining the Mg 2Si
phase. The more the RE processing passes, the better the refining
effect would be. Moreover, the uniform distribution of Mg 2 Si
phases would be more in the composite. After the composite was
processed by RE for 12 passes, most Mg 2 Si phases were equiaxed,
with granular diameter below 20 um, and distributed uniformly in
the matrix of the composite. The mechanical properties of the
composite could be increased prominently by RE processing, and were
much higher than that in the as-cast state. As the temperature
rises, the tensile strength is reduced. For the composite RE
processed for 12 passes, the tensile strength, yield strength, and
elongation are 325.9 MPa, 211.4 MPa, and 3.3 % at room temperature,
whereas, 288.2 MPa, 207.7~MPa, and 7.8 %, respectively, at
150 C. In comparison with the properties at room
temperature, the tensile strength and yield strength are high and
only decrease by 11.6 and 1.8 at 150 C. The Mg 2 Si
reinforced Mg-Al based composite possesses good heat resistance at
150 C. The excellent resistance to effect of heat is
attributed to the high melting temperature and good thermal
stability of fine Mg 2 Si phases, which are distributed uniformly
in the composite, and effectively hinder the grain boundary gliding
and dislocation movement.
关键词:
Reciprocating extrusion
,
null
,
null
,
null
Z.M. Zhang
,
T. Lu
,
C.J. Xu
,
X.F. Guo
金属学报(英文版)
Directionally solidified binary Mg-Al eutectic
alloy wires of approximately 5mm in diameter were produced by the
Ohno continuous casting (OCC) process and the microstructure was
examined. It was found that the wires possess obvious unidirectional
growth characteristic along its axial direction. The microstructure
consists of parallel columnar grains that resulted from the
competitive growth of equiaxed grains solidified on the head of
dummy bar. Each columnar grain comprises regular eutectic
α-Mg and β-Mg17Al2 phases, which grew along the axial direction of the wires. The morphology of the eutectic ismainly lamellar, meanwhile rod eutectic exists. The formation of rod eutectic was attributed to the ``bridging effect" caused by
incidental elements in the alloy.
关键词:
Mg-Al alloy
,
null
,
null
,
null
H.X. Zheng
,
H. Xie
,
X.F. Guo
金属学报(英文版)
The structural evolution of undereooled single-phase Ni-2wt%Pb monotectic alloy wassystematically investigated by using the method of molten glass denucleating combinedwith superheating cycle. Within the achieved undercooling range of 22 to 280K, thesolidification structure undergoes three changes at 22K, 88K and 187K, respectively.With the increase of undereooling, common dendrites, the first class granular grains,undercooled dendrites and the second class granular grains come out one after theother. Analytical results show that the granulation mechanism of the first class gran-ular grains is owing to dendrite remelting and recrystallization, and the second isowing to dendrite break-up and recrystallization.
关键词:
undereooling
,
null
,
null
,
null
Z.M. Zhang
,
C.J. Xu
,
X.F. Guo
金属学报(英文版)
As an icosahedral Mg3YZn6 quasicrystalline phase can be produced in Mg-Zn-Y system alloys when a proper amount of Zn and Y is contained, it is feasible to prepare the quasicrystal phase-reinforced low-density magnesium alloy. The purpose of this paper is to analyze phase constituents and the effect of reciprocating extrusion on microstructures and properties of the as-cast Mg-6.4Zn-1.1Y alloy. The microstructure of as-cast Mg-6.4Zn-1.1Y alloy consists of the α-Mg solid solution, icosahedral Mg3YZn6 quasicrystal, and Mg3Y2Zn3 and MgZn2 compounds. After the alloy is reciprocatingly extruded for 4 passes, grains were refined, Mg3Y2Zn3 and MgZn2 phase dissolved into the matrix, whereas Mg3YZn6 precipitated and distributed uniformly. The alloy possesses the best performance at this state, the tensile strength, yield strength, and elongation is 323.4MPa, 258.2MPa, and 19.7%, respectively. In comparison with that of the as-cast alloy, the tensile strength, yield strength, and elongation of the reciprocatingly extruded alloy increase by 258.3％, 397.5％, and 18 times, respectively. It is concluded that reciprocating extrusion can substantially improve the properties of as-cast Mg-6.4Zn-1.1Y alloy, particularly for elongation. The high performance of the Mg-6.4Zn-1.1Y alloy after reciprocating extrusion can be attributed to dispersion strengthening and grain-refined microstructures.
关键词:
Reciprocating extrusion
,
null
,
null
Z.M. Zhang
,
C.J. Xu
,
X.F. Guo
金属学报(英文版)
In order to explore the methods to prepare high-strength quasicrystal-reinforced magnesium alloys, the flakes of rapidly solidified Mg-6.4Zn-1.1Y magnesium alloy with thickness of 50-60冚m were obtained by a melt spinning single-roller device, and then the flakes were processed into rods by reciprocating extrusion and direct extrusion. The microstructure of the alloy was analyzed by optical microscope and SEM, and the constituent phases were identified by XRD. Phase transformation and its onset temperature were determined by differential thermal analyzer (DTA). The analysis result shows that rapid solidification for Mg-6.4Zn-1.1Y alloy can inhibit the eutectic reactions, broaden the solid solubility of Zn in 冄-Mg solute solution, and impede the formation of Mg3Y2Zn3 and MgZn2 compounds, and thus help the icosahedral Mg3YZn6 quasicrystal formed directly from the melt. The microstructure of the flakes consists of the -Mg solid solution and icosahedral Mg3YZn6 quasicrystal. Dense rods can be made from the flakes by 2-pass reciprocating extrusion and direct extrusion. The interfaces between flakes in the rods can be welded and jointed perfectly. During the reciprocating extrusion and direct extrusion process, more Mg3YZn6 compounds are precipitated and distributed uniformly, whereas the rods possesses fine microstructures inherited from rapidly solidified flakes. The rods contain only two phases: 冄-magnesium solid solution as matrix and fine icosahedral Mg3YZn6 quasicrystal which disperses uniformly in the matrix.
关键词:
Magnesium alloy
,
null
,
null
,
null
Superconductor Science & Technology
It is shown that the superconductivity in Ce(1-x)Gd(x)FeAsO(0.84)F(0.16) compounds can be modulated by internal (chemical) pressure. The internal pressure is induced by Gd substitution for Ce in CeFeAsO(0.84)F(0.16), which compresses the crystal lattice. The temperature dependences of resistivity and magnetization show that the superconducting-transition temperature T(c) is enhanced from 40 K for CeFeAsO(0.84)F(0.16) to 47.5 K for Ce(0.6)Gd(0.4)FeAsO(0.84)F(0.16). The increase and subsequent decrease of Tc upon application of external pressure, as observed previously in LaFeAsO(0.89)F(0.11), is entirely confirmed by the modulation of Tc of the Ce(1-x)Gd(x)FeAsO(0.84)F(0.16) superconductors by internal pressure.
关键词:
layered quaternary compound;43 k;iron
Journal of Applied Physics
Structural parameters have a critical impact on superconductivity in iron-based oxypnictide superconductors. Structural evolution study was performed on Ce(1-x)Gd(x)FeAsO(0.84)F(0.16) superconductors by the analysis of the x-ray diffraction patterns with Rietveld refinement. Substitution of Gd for Ce generates internal pressure that compresses the crystal lattice. The contraction of the c axis is also indicated by the reduction of Ce/Gd-As and Ce/Gd-O/F distances, while there is a slight increase in the As-Fe-As block size, which is compensated by a large reduction in the Ce/Gd-O/F-Ce/Gd block with Gd substitution. The diagonal Fe-As-Fe angle for Ce(0.6)Gd(0.4)FeAsO(0.84)F(0.16), with the highest T(c) among Ce(1-x)Gd(x)FeAsO(0.84)F(0.16) compounds, is 111.13 degrees. It is close to the ideal value of 109.47 degrees for the perfect FeAs tetrahedron, which is situated in the region of Fe-As-Fe bond angles where RFeAsO compounds tend to have the highest T(c). (C) 2011 American Institute of Physics. [doi:10.1063/1.3565408]
关键词:
layered quaternary compound;high-temperature superconductivity
崔雅静
,
陈永亮
,
杨烨
,
王雅真
,
张勇
,
赵勇
低温物理学报
通过先制备一种纳米尺寸的GdF_3作为GdFeAsO_(1-x)F_x样品中F的反应原料,在相对较低的温度(1120℃)下成功制备出一系列GdFeAsO_(1-x)F_x(x=0,0.05,0.1,0.15,0.2,0.25)多晶样品.X射线衍射结果表明,超导样品属四方ZrCuSiAs-type结构,晶格参数随着掺F量的增加而减小.扫描电子显微镜测试结果表明,样品具有片层状晶体形貌特征.当掺F量x=0.1时,样品表现出超导电性,超导转变温度为22K,随着掺F量的增多,超导转变温度升高.和其他制备方法相比,这种制备方法更有利于F的掺入,而且可有效减少样品中杂质相的含量.
关键词:
铁基超导体
,
ZrCuSiAs结构
魏惠元
稀有金属材料与工程
介绍了可适用钛金属0.4 m～1.2 m不同焦距、微粒胶片X射线照相用的KUPTF新型曝光曲线的制作原理及方法.试验结果表明,新型曝光曲线具有制作简便、经济实用、可兼顾底片象质和拍片效率的优点,是钛制压力容器现场变焦距透照选取准确管电压值的理想工具.
关键词:
钛
,
X射线照相
,
KUPTF
,
曝光曲线
