X. Y. Li
,
X. T. Tian and H. C. Zhu( 1)Weldng Division
,
Beijing Polytechnic University
,
Beijing 100022
,
China 2)National ho. of Advanced Welding Technology
,
HIT
,
Harbin 150001
,
China)
金属学报(英文版)
Mismatching is one of the basic characteristics of welded joints.Overmatched welded joint with a crack in hard weld is simplified as a cracked body of CCP type SHS (a hard bar sandwiched between two soft material with a crier perallel to the interface ) in this paper.Effects of mechanical heterogeneity on fatigue crack growth and crack closure of this model are studied by experimental and elastic - plastic finite element methods. It is found that, residual plastic deformation remaining in the wake of a growing crack tip, which cases crack closure,is affected the plastic deformation in adjacent soft mate- rial near by the crack tip. Both the shape of crack tip plastic zone and stress distribution ahead of crack tip in heterogeneous cracked body are different from that of homogeneous one. Crack closure (open- ing) loads are estimated by investigating the changes of crack tip opening displacement during fatigue loading, and a new model of crack oening process is presented. Because of the difference in the effect of mechanical heterogeneity on displacement of non - fatigue crack and fatigue crack, conventional CTOD can not reflect the real deformation at crack tip of SHS specimens.
关键词:
welded joint
,
null
,
null
,
null
彭启才
,
周心明
,
蔡伯埙
材料研究学报
采用等离子体辉光放电单室系统制备的a-Si:H/a-Si_(1-x)C_x:H 多层膜结构具有低的暗电导和高的光电导特性,且不同于单层膜,有明显的S-W 效应。随着子层厚度L 减小,多层膜曝光态(B)的暗电导率σdB 较退火态(A)的σdA 减小快,即光诱导衰退程度增大,而光电导无明显变化。本文还测定了此多层膜结构的光能隙E_g,得到随子层厚度减小“蓝移”的结果。用一维单量子阱模型作了讨论,实验值与理论计算符合较好。
关键词:
a-Si:H/a-Si_(1-x)C_x:H
,
superlattice
,
amorphous semiconductors electrical properties
,
optical properties
,
null
程英
,
余忠卫
,
魏晓旭
,
杨华峰
,
郭丹
,
王军转
,
余林蔚
,
施毅
材料导报
doi:10.11896/j.issn.1005-023X.2016.04.002
氢化碳化硅薄膜作为一种宽带隙的半导体材料，具有优越的物理特性，其在光电子器件上的潜在应用引起了人们的兴趣。利用等离子增强化学气相沉积(PECVD)系统制备了一系列氢化碳化硅薄膜，通过改变反应前驱物及流量比调节薄膜的室温光致发光性质。实验发现在一定范围内随着流量比 R (CH4/SiH4)的提高，氢化碳化硅薄膜的光致发光峰位蓝移且发光强度增强；同时反应前驱物中的氢会极大影响氢化碳化硅薄膜的发光强度。通过椭偏仪(Ellipsometer)测量了薄膜的光学常数，发现薄膜沉积速率随着流量比 R 的增加而降低；傅里叶红外光谱仪(FTIR)测试表明 Si-C 有序度随着流量比的增加而增大。同时研究了三维纳米线结构对多态碳化硅薄膜发光性质的影响。光致发光测试结果表明三维纳米线结构可以有效提高薄膜的光致发光强度。
关键词:
氢化碳化硅薄膜
,
光致发光
,
纳米线
Zhiyong Liu
材料科学技术（英文）
Here we report the fabrication and superconductivity of the iron-based arsenic oxide SmO1-xFxFeAs compound. X-ray diffraction (XRD) results prove that the lattice parameters a and c decrease systematically with increasing x in between 0<x≤0.35, but when x>0.35 the a and c increase with the decrease of x in
the SmO1-xFxFeAs. The critical temperature (Tc) increases with increasing x in between 0.15≤x≤0.3, while x>0.3 the Tc decreases with the increase of x. It is found that at x=0.3 SmO0.7F0.3FeAs has the highest onset resistivity transition temperature of 55.5 K. The critical current density (Jc) value at 10 K for the obtained SmO0.7F0.3FeAs is 1.3×105 A/cm2 (0 T). Meanwhile one can estimates Hc2(0) from the slope of the Hc2(T) curve at T=Tc (HC2 is the upper critical field), and for the 90% normal-state resistivity (ρn) criterion (Tc=55 K), Hc2(0) is determined to be ~253 T.
关键词:
SmO1-xFxFeAs compound
FAN Zhanguo
,
JI Chunlin
,
WANG Kuihan
,
CUI Chuanmeng
,
LIU Sulan
,
Northeast University of Technology
,
Shenyang
,
China
金属学报(英文版)
A unidirectional reaction for synthesis of the high T_c superconductor YBa_2Cu_3O_x has been proposed, Its T_c is 90-94.5 K and △T is 1 K. The phase relationships in the system Y_2BaCuO_5-Y_2Cu_2O_5-CuO-YBa_2Cu_3O_x were studied and discussed.
关键词:
unidirectional reaction
,
null
,
null
Journal of Alloys and Compounds
As hydrogen, deuterium and tritium storage materials, a series of investigations of mechanical and thermal properties of titanium hydrides, deuterides and tritides have been performed, however, very limited theoretical studies of thermodynamic properties for them can be found. Based on density-functional theory (DFT) and density-functional perturbation theory (DFPT) we have discussed systematically the hydrogen isotope effects on the thermodynamic properties of TiX2 (X = H, D, and T) system. Our calculations indicate that for evaluating accurately their physical properties at absolute zero temperature, such as the equilibrium lattice constants, bulk modulus, and heat of formation, the zero-point energy correction must be taken into account. By performing the phonon calculation within quasiharmonic approximation (QHA), we obtain their vibrational free energies, vibrational entropies, and temperature dependence of specific heat, thermal expansion, and bulk modulus. Those results demonstrate that comparing with TiH2, TiT2 and TiD2 are more stable and the zero-point effects play an important role in their thermal expansion. The increase in the force constant between Ti and H causes the higher value of specific heat of TiH2 during the phase transition from FCC to FCT. In addition, comparing with available experimental values, we can conclude that QHA is feasible for describing the thermal properties of TiX2. (C) 2006 Elsevier B.V. All rights reserved.
关键词:
isotope effects;thermodynamic properties;density-functional;perturbation theory;quasiharmonic approximation;functional perturbation-theory;neutron spectroscopy;thermal-properties;titanium;hydrogen;dependence;expansion;constants;palladium;hydrides
Journal of Alloys and Compounds
Effects of B or C addition on phase transformation and magnetic properties of Pr17CO83-xTx (T=13 or C, x=0-10) alloys, prepared by mechanical alloying and subsequent annealing, have been studied systematically. The X-ray diffraction results show that after annealing at 650 degrees C for 2 min, the main phase of Pr17Co83 alloy is a crystalline PrCo5 phase with hexagonal CaCU5-type structure. The Pr2CO14B phase with tetragonal Nd2Fe14B-type structure appears when the B content increases. The formation of the Pr2CO14B phase is also confirmed by observing its spin reorientation transition temperature T-sr (=390 degrees C)on ac susceptibilities versus temperature curves. The amount of the Pr2Co14B phase increases with increasing B content. Further increasing the B content leads to the formation of another magnetically hard PrCo4B phase with hexagonal CeCo4B-type structure with its Curie temperature about 190 degrees C. In the Pr17CO73B10 alloys, PrCo4B phase becomes the main phase. Remanences decrease monotonously with increasing B content, whereas the coercivities increase, reaching a maximum of 17.9kOe in Pr17Co81B2 powders milled for 5 h and annealed at 650 degrees C for 2 min, and then decrease for the higher B content. In the case of C addition, however, the alloys are composed of a mixture of a major PrCO5 phase and secondary Pr2Co17 and PrCo2Cx Phases. No expected Pr2Co14C phase has been observed in all of the C-containing powders. The magnetic properties of the C-containing alloys have not been improved evidently. (c) 2006 Published by Elsevier B.V.
关键词:
alloys;phase transformation;magnetic properties;mechanical alloying;rare-earth;permanent-magnets;fe;coercivity
Journal of Physics D-Applied Physics
Pseudo-1-3 magnetostrictive composites consisting of stabilizer ( B, Co)-free, light rare earth (Pr)-containing magnetostrictive (Tb(0.3)Dy(0.7))(1-x) Pr(x) Fe(1.55) (0 <= x <= 0.4) particles with a size distribution of 10-300 mu m embedded and aligned in a passive epoxy matrix using 0.5 volume fraction are fabricated. The quasistatic magnetomechanical properties of the composites are investigated and compared with their monolithic (Tb(0.3)Dy(0.7))(1-x) Pr(x) Fe(1.55) alloys, as a function of the Pr content x. The composites show similar qualitative trends in properties with the alloys for all x. The (Tb(0.3)Dy(0.7))(0.75)Pr(0.25)Fe(1.55) composite and alloy exhibit the smallest coercivity H(c), the largest magnetostriction lambda and the highest piezomagnetic coefficient d(33) due to the successful compensation for magnetocrystalline anisotropy. The ( Tb0.3Dy0.7) 0.75Pr0.25Fe1.55 composite demonstrates a large saturation magnetostriction lambda(s) of 793 ppm at 700 kAm(-1) and a high d(33) of 3.2 nmA(-1) at 140 kAm(-1). These values approach 81% and 85% of its alloy values at the same field levels. The good properties make the (Tb(0.3)Dy(0.7))(0.75)Pr(0.25)Fe(1.55) composite and alloy a promising magnetostrictive material system.
关键词:
terfenol-d;magnetic-properties;alloys;boron
Journal of Magnetism and Magnetic Materials
The structure, magnetic and magnetostrictive properties of Sm(0.88)Nd(0.12)(Fe(1-x)Co(x))(1.93) (0 <= x <= 1.0) alloys have been investigated. The alloys have the cubic MgCu(2) structure over the whole composition range and the lattice parameter a decreases with increasing x. For 0 <= x <= 0.2, substitution of Co for Fe slightly increases the saturation magnetization M(s) and Curie temperature T(c), while further substitution causes a decrease in both M(s) and T(c). The spin reorientation is observed, and a phase diagram for the spin configurations of the Sm(0.88)Nd(0.12)(Fe(1-x)Co(x))(1.93) system is determined. The spontaneous magnetostriction lambda(111) increases as x is increased, while a monotonic decrease of the saturation magnetostriction lambda(s) with x originates from the increase of lambda(100) with opposite sign to that of lambda(111), which may be caused by the filling of the d band due to Co substitution. (C) 2010 Elsevier B.V. All rights reserved.
关键词:
Laves phase;Spin reorientation;Magnetostriction;giant magnetostriction;phase-compounds;temperature-dependence;anisotropy;substitution;alloys;fe
Journal of Magnetism and Magnetic Materials
The structure and permanent magnetic properties of isotropic powders of NdFe12-xVxNdelta compounds mere investigated by using mechanical alloying. It was found that heat treatment of as-milled powders at 700-900 degrees C resulted in the formation of Nd(Fe,V)(12) phase except for the sample with x = 1, for which the crystallization was not complete and a large amount of alpha-Fe(V) was present at temperatures lower than 750 degrees C. After nitrogenation, the volume expansion was about 5% and the Curie temperature enhancements were 140 to 160 degrees C. In NdFe12-xVxNdelta the values of T-c fall in the range 469-485 degrees C. It has been found that the intrinsic coercivities strongly increased with increasing V content. The maximum coercivity of H-i(c) = 10.96 kOe is achieved at 750 degrees C with x = 2.00. The difference between the coercivities of the mechanical alloyed Nd(Fe,V)(12)N-delta powders with different V content is attributed to their different crystallization behavior and phase stability during nitrogenation. (C) 1998 Elsevier Science B.V. All rights reserved.
关键词:
mechanical alloying;ThMn12-type structure compound;permanent magnetic;property
