材料期刊网

INFLUENCE OF LOADING RATE AND SPECIMEN HEIGHT ONFLEXURAL STRENGTH OF Al2O3 AT HIGH TEMPERATURES

Author S.H. Bai , S.R. Qiao , S.R. Zhou and M.K. Kang Faculty 401 , Northwestern Polytechnical University , Xian 710072 , China Manuscript received 18 October 1998

金属学报(英文版)

In this paper, the influence of loading rate and specimen height on flexural strength of Al2O3 at high temperatures has been studied by three-point bending method. The experimental results show that the flexural strength of Al2O3 decreases with increasing specimen height at room temperature, and it tends to stability when height increases to a certain degree (h=5mm in this paper), while the flexural strength of Al2O3 variates unapparently at high temperature with increasing height. There is a critical loading rate R . c. When loading rate R . is less than R . c, the flexural strength of Al2O3 increases with increasing loading rate and it drops sharply when loading rate is higher than R . c. The sensitivity of flexural strength to the loading rate decreases with elevating temperatures.

关键词: loading rate , null , null , null

Secondary M6C precipitation in K40S cobalt-base alloy

Materials Letters

Secondary M,C precipitation was investigated in K40S cobalt-base alloy after 100 h aging at 950 degreesC. The results showed that it was closely related to the tungsten-rich zones inherited from the as-cast condition and the degeneration of the primary M7C3 carbide. A direct element reaction, 6M + C --> M6C, in which C comes from the decomposition of the M7C3 carbides, is suggested as the mechanism of secondary M6C precipitation in K40S alloy. (C) 2001 Elsevier Science B.V. All rights reserved.

关键词: M6C precipitation;aging;M7C3 carbide;superalloy

Magnetic properties of R2Fe14M3 compounds with M=Ga and Si; R=Y, Nd, Sm, Gd, Tb, Dy, Ho, Er and Tm

Solid State Communications

Samples with composition R2Fe14M3 (M = Ga and Si; R = Y, Nd, Sm, Gd, Tb, Dy, Ho, Er and Tm) have been prepared by are-melting. Crystal-structure studies have shown that the prepared samples are single phase with the rhombohedral Th2Zn17 and/or the hexagonal Th2Ni17 structure. Substitution of Ga for Fe in R2Fe17 leads to an increase of the unit-cell volume, whereas Si substitution reduces the unit-cell volume. The Curie temperatures of the R2Fe14Ga3 and R2Fe14Si3 compounds are much larger than those of the corresponding R2Fe17 compounds. The Fe moment decreases upon Ga or Si substitution. The compounds R2Fe14Ga3 and R2Fe14Si3 With R = Er and Tm exhibit a spin-reorientation transition at low temperature. (C) 1997 Elsevier Science Ltd.

关键词: neutron-diffraction;solid-solutions;substitution;anisotropy;nd2fe17

Creep rupture Behavior of K40S alloy at elevated temperatures

材料科学技术（英文）

Creep testing was conducted on K40S alloy. The detailed creep deformation and fracture mechanisms under constant load were studied. The results show that the stress exponent ranges between 7 and 14.4 at elevated temperature 973similar to1173 K, and that the activation energy is approximately 449.1 kJ/mol. During creep, the grain boundary sliding cut off primary carbides at the boundary, generating the "O" model cracks. The creep failure mode of K40S alloy is transgranular ductile and cracks originate at the primary carbides. A long carbide and matrix interface is often a preferential path for crack propagation. The creep mechanism is discussed in light of the creep microstructure, the stress exponent and the activation energy.

关键词: K40S alloy;creep;fracture;crack propagation;activation-energies;superalloy;term

Exact solutions of nonlinear dispersive K(m, n) model with variable coefficients

Applied Mathematics and Computation

The variable-coefficient Korteweg-de Vries (KdV) equation with additional terms contributed from the inhomogeneity in the axial direction and the strong transverse confinement of the condense was presented to describe the dynamics of nonlinear excitations in trapped quasi-one-dimensional Bose-Einstein condensates with repulsive atom-atom interactions. To understand the role of nonlinear dispersion in this variable-coefficient model, we introduce and study a new variable-coefficient KdV with nonlinear dispersion (called vc-K(m, n) equation). With the aid of symbolic computation, we obtain its compacton-like solutions and solitary pattern-like solutions. Moreover, we also present some conservation laws for both vc-K(+)(n, n) equation and vc-K (n, n) equation. (C) 2011 Elsevier Inc. All rights reserved.

关键词: Vc-K(m, n) equation;Nnonlinear dispersion;Symbolic analysis;Compacton-like solutions;Solitary pattern-like solutions;Conservation;laws;compacton solutions;solitary patterns;equations;solitons

Zn-5%Al合金超塑性的m-C-δ(或m-k-δ)关系

刘勤 , 夏锄 , 刘晓东

金属学报

在170,190,210,230,250℃的温度下,采用3.7×10~2,7.4×10~2和1.1×10~(-1)min(-1)的应变速率(平均)对Zn-5%Al共晶合金的m-C-δ(或m-k-δ)关系曲线(简称m-δ关系曲线)进行了测定.所有的曲线均随应变的δ增加而快速上升.俟达到某一定的应变量(极限应变量δ1)后。开始缓慢下降并保持平稳直至断裂.Zn-5%A1共晶合金的m-δ关系曲线不存在k_(?)=k_I(k_(I 1),k_(I 2),k_(I 3),……)=k_F(或C_0=C_I(C_(I 1),C_(I 2),C_(I 3),……)=C_F=1)的简单情况.可应用m-δ方程式[4,5]对曲线上各点C值(包括所有的C_I和C_F值)进行计算.C值随δ值的增加成近似的直线上升.直线的斜率在极限应变(δ1)处突然减小.

关键词:

Bain对应和K-S模型的数学描述

王宝奇 , 谷南驹 , 郭素珍 , 马晓莉

金属学报

利用Bain点阵对应对K-S模型的晶格改建过程进行了严密的数学描述.对于不同的马氏体正方度,提出了计算第一切变、第二切变及晶格调整的计算依据,并给出了普遍的计算公式.以Fe-1.4C和纯铁为例,计算了马氏体相变的点阵畸变.进一步分析表明,K-S模型实质是Bain模型的旋转.计算的结果与实测的取向关系相符合.

关键词: K-S模型 , null , null

Bain对应和K-S模型的数学描述

王宝奇 , 谷南驹 , 郭素珍 , 马晓莉

金属学报 doi:10.3321/j.issn:0412-1961.2002.05.006

利用Bain点阵对应对K-S模型的晶格改建过程进行了严密的数学描述.对于不同的马氏体正方度,提出了计算第一切变、第二切变及晶格调整的计算依据,并给出了普遍的计算公式.以Fe-1.4C和纯铁为例,计算了马氏体相变的点阵畸变.进一步分析表明,K-S模型实质是Bain模型的旋转.计算的结果与实测的取向关系相符合.

关键词: K-S模型 , 马氏体相变 , 点阵畸变

Fatigue crack propagation behavior of K40S cobalt-base superalloy at elevated temperature

Transactions of Nonferrous Metals Society of China

Fatigue crack propagation behavior of K40S cobalt-base superalloy under ambient atmosphere at 700 degreesC and 900 degreesC was investigated. The detailed fatigue crack propagation and fracture mechanism under the alternating loads were studied. The results show that, there is a defined threshold for K40S alloy at elevated temperatures. The fatigue threshold is 23. 9 MPa . m(1/2) at 700 degreesC and 12 MPa . m(1/2) at 900 V. The significant decrease of the threshold with increasing temperature is associated with the oxidation induced embrittlement at crack tip. Observation on the fatigue fracture surfaces indicates a ductile fracture mechanism related to the fatigue crack growth.

关键词: cobalt-base superalloy;fatigue crack propagation;fatigue threshold;ductility;growth-behavior;alloy;steel

Investigations of the electron paramagnetic resonance parameters and the tetragonal local structure for (VCl(6))(4-) coordination complex in MCl:V(2+) (M=Na, K, Rb) systems

Chinese Physics B

By simulating the electron paramagnetic resonance (EPR) and optical spectra on the basis of the 120x120 complete energy matrix, this paper determines the local lattice structure parameters R(1) and R(2) for MCl:V(2+) (M=Na, K, Rb) systems at 77 K, 195 K and RT (room temperature 295 K or 302 K), respectively. The theoretical results indicate that there exists a compressed distortion in MCl:V(2+) systems. Meanwhile, it finds that the structure parameters R(1), R(2) and vertical bar Delta R vertical bar (= R(1) - R(2)) increase with the rising temperature. Subsequently, from the analysis it concludes that the relation of EPR parameter D vs. Delta R is approximately linear. Finally, the effects of orbital reduction factor k on the g factors for the three systems have been discussed.

关键词: complete energy matrix;EPR parameters;(VCl(6))(4-) coordination;complex;local structure;doped alkali-halides;lattice structure;ground-state;epr-spectra;crystals;field;ions;mn2+;temperature;fe-3+