Keke ZHANG
,
Yunlin YANG
,
Changsheng WANG
,
Hongke LI
,
Jin XUE
材料科学技术（英）
The microstructure of 40Cr and T10A steel sample and its surface to be welded is ultra-fined through salt-bath cyclic quenching and high frequency hardening, then the surface is cleaned. Under non-vacuum and no shielded gas, the welding parameter of isothermal superplastic solid-phase welding and the effect of surface microstructure prior to pressure welding on the quality of joint are stud led. At the temperature of 730 similar to 750 ℃ and at initial strain rate of (2～4) x 10(-4) s(-1) the strength of the joint is up to or close to that of 40Cr base metal in 3 similar to5 min pressure welding.
关键词:
Jing TIAN
,
Xiang XUE
,
Yuebing ZHANG
,
Yalong GAO
,
Luzhi LIU
,
Qin SUN
,
Shiyou YUAN
材料科学技术（英）
By adopting the solid modeling software SoldEdge and the enmeshment software SRIFCast as the pre-processing platform, a Ni based alloy turbine blade was three-dimensionally modeled and automatically enmeshed. A software code for numerical simulation of fluid flow and heat transfer was developed. The Xue criterion and Niyama criterion were used to predict the position of the shrinkage defects occurring in the solidification processes of the turbine blade. The results showed that both Xue and Niyama criteria could precisely predict the shrinkage defects in the Ni based alloy turbine blade. This indicates that numerical simulation is a significant tool in improving casting quality.
关键词:
Journal of Applied Physics
Based on the developed multiple-scattering theory [C.-W. Nan and F. S. Jin, Phys. Rev. B 48, 8578 (1993)], an effective-medium theory (EMT) is proposed to treat coupled electromechanical behavior in composite media. The explicit relations for determining effective behavior of piezoelectric composites are derived. To illustrate the technique, numerical results of piezoelectric ceramic/epoxy composites for various particle shapes are presented over the whole range of concentrations. The EMT estimates are shown to be in good agreement with available experimental results. Porous piezoelectric ceramics are also discussed. The EMT predicts a similar critical behavior for heterogeneous piezoelectric materials to recent experiments.
关键词:
electromechanical properties;ceramics
Acta Materialia
In a first report [Jin ZH.. Gumbsch P, Ma E, Albe K, Lu K, Hahn H, et al. Scripta Mater 2006;54:1163], interactions between screw dislocation and coherent twin boundary (CTB) were studied via molecular dynamics simulations for three face-centered cubic (fcc) metals, Cu, Ni and Al. To complement those preliminary results, purely stress-driven interactions between 60 degrees non-screw lattice dislocation and CTB are considered in this paper. Depending on the material and the applied strain, slip has been observed to interact with the boundary in different ways. If a 60 degrees dislocation is forced by an external stress into a CTB, it dissociates into different partial dislocations gliding into the twin as well as along the twin boundary. A sessile dislocation lock may be generated at the CTB if the transited slip is incomplete. The details of the interaction are controlled by the material-dependent energy barriers for the formation of Shockley partial dislocations from the site where the lattice dislocation impinges upon the boundary. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
关键词:
dislocation;slip;twinning;twin grain boundary;molecular dynamics;molecular-dynamics simulation;grain-boundaries;nanocrystalline;materials;cross-slip;rate sensitivity;deformation;copper;strength;aluminum;fcc
曹春海
,
杨名
,
张世远
,
杨森祖
,
崔旭高
,
尤立星
,
吉争鸣
,
康琳
,
许伟伟
低温物理学报
doi:10.3969/j.issn.1000-3258.2003.03.002
采用Nd0.7Sr0.3MnO3/SrTiO3/YBa2Cu3O7-δ的异质结构,研究了自旋极化准粒子的注入效应.在56μm宽的YBCO膜条上成功地制备了与超导膜条同样宽度但不同长度的六个注入结区,长度L分别为80μm, 40μm, 20μm, 10μm, 5μm和2μm.80nm厚的YBCO薄膜在16K温度下Jc为2×105A/cm2.Iin=0.5mA的自旋电流注入下,随L从80μm逐渐顺次减小时,注入效率η=ΔJc/ΔJin逐渐增大.而当L≤20μm后,η不再增加,达到几乎相同的值(～6).初步分析认为这与自旋极化准粒子在超导膜内的有效自旋扩散长度有关.异质结构中YBCO薄膜的超导电性以及注入窗口的尺寸对获得大的自旋注入效率十分重要.
关键词:
注入效率
,
自旋准粒子
,
巨磁阻
,
异质材料
Journal of Physics and Chemistry of Solids
The layered ternary ceramics Ti3SiC2 and Ti3AlC2 are isostructural and can form Ti3Si1-xAlxC2 solid solutions combining the advanced properties of both compounds [H.B. Zhang, Y.C. Zhou, Y.W. Bao, M.S. Li, Improving the oxidation resistance of Ti3SiC2 by forming a Ti3Si0.90Al0.1C2 solid solution, Acta Mater. 52 (2004) 3631-3637; E.D. Wu, J.Y. Wang, H.B. Zhang, Y.C. Zhou, K. Sun, Y.J. Xue, Neutron diffraction studies of Ti3Si0.9Al0.1C2 compound, Mater. Lett. 59 (2005) 2715-2719; J.Y. Wang, Y.C. Zhou, First-principles study of equilibrium properties and electronic structure of Ti3Si0.75Al0.25C2 solid solution, J. Phys.: Condens. Matter 15 (2003) 5959-5968; Y.C. Zhou, J.X. Chen, J.Y. Wang, Strengthening of Ti3AlC2 by incorporation of Si to form Ti3Al1-xSixC2 solid solutions, Acta. Mater. 54 (2006) 1317-1322]. In the present work, the solid solutions of Ti3Si1-xAlxC2 (x = 0, 0.25, 0.33, 0.5, 0.67, 0.75, 1) are investigated by first-principle calculations based on pseudo-potential plan-wave method within the density functional theory framework. The results show that as Al content increases in the solid solution, all the bonds have weakened to certain extents, which lead to an unstable structure both energetically and geometrically. The calculated results are compared and discussed with the reported data for the Ti3Si1-xAlxC2 solid solutions. (c) 2007 Elsevier Ltd. All rights reserved.
关键词:
ceramics;ab initio calculations;electronic structure;electrical;conductivity;oxidation behavior;mechanical-properties;ti3sic2;temperature;ti3alc2;air;si
