Z. Li
,
S.F. Tian
,
X.G. Zhao
,
Z.K. Liang
,
L.P. Ren
,
G.F.Mi and M.G. Yan(Bejing Institute of Aeronautical Materials
,
Beijing 100095
,
China Manuscript received 26 August 1996)
金属学报(英文版)
In this paper,part of the research and development work in the field of spray formed superalloys at BIAM of China is briefly summarized. With an experimental spray forming facility,whose melting capacity is suitable for making disk and columnar shaped integral-dense and clean Ni-base superalloy preforms with low oxygen content,fine grain, uniform chemistry and improved forgeability, a series of Ni-base superalloys have been spray atomized and deposited, among which three alloys have been chosen for microstructural and mechanical properties evaluation.
关键词:
:spray forming
,
null
,
null
Philosophical Magazine
The EPR g factors, g// and g perpendicular to, of tetragonally elongated and compressed CuIIN6 octahedral clusters (with the ground states |dx2 - y2 > and |dz2 >, respectively) in [image omitted] (MI = K, Rb, Cs; MII = Ca, Sr, Ba, Pb) crystals were calculated using a two-mechanism model. In the model, the contributions to the g-shifts, gi (= gi - gs, where i = // or perpendicular to; gs approximate to 2.0023 is the free-ion g value), from both the crystal-field (CF) mechanism related to CF excited states and the charge-transfer (CT) mechanism related to CT excited states, which is neglected in the widely-used CF theory, were considered. For the CF mechanism, two theoretical methods, the perturbation theory method (PTM) and the complete diagonalization (of energy matrix) method (CDM), were applied. The CF parameters used were calculated from the superposition model, in which the structural data for CuIIN6 clusters in [image omitted] crystals were measured exactly by X-ray diffraction. The calculated g factors for both the tetragonally elongated and compressed CuIIN6 octahedra are in reasonable agreement with the experimental values. For the strongly covalent CuIIN6 clusters in crystals with different ground states, both the PTM and CDM can be applied to calculate the g-shifts, [image omitted], arising from the CF mechanism, but exact and reasonable calculations of g factors should take both CF and CT mechanisms into account.
关键词:
crystal field;electron paramagnetic resonance;octahedral cluster;charge transfer;spin-hamiltonian parameters;atomic screening constants;jahn-teller;distortion;temperature-dependence;lead hexanitrocuprate(ii);2-mechanism model;scf functions;br crystals;complexes;bands
林水东
,
丁马太
功能材料
用示差扫描量热法(DSC)考察了聚丙烯(PP)、聚丙烯/云母(PP/M)和聚丙烯/聚(丙烯-g-甲基丙烯酸甲酯)/云母复合材料(PP/PP-g-MMA/M)的非等温结晶过程.用Avrami方程和Ozawa方程对上述过程进行分析,n、t1/2、F(T)、Tp等参数表明,M和PP-g-MMA,特别是PP-g-MMA的掺入改变了PP的结晶成核和生长机理.用Dobreva方法分析填料的成核活性,ε数值表明,M有较强的成核活性,PP-g-MMA的掺入又进一步增强其成核活性,从而使结晶温度明显提高.Kissinger方法的计算结果表明,添加M可使PP的结晶活化能减小,再添加PP-g-MMA又使PP/M复合体系的结晶活化能进一步减小.
关键词:
聚丙烯
,
聚(丙烯-g-甲基丙烯酸甲酯)
,
云母
,
复合材料
,
非等温结晶动力学
沈基显
,
黄剑锋
,
曹丽云
,
曾燮榕
,
熊信柏
稀有金属材料与工程
以羟基磷灰石-壳聚糖(HA-CS)为基体,玻璃纤维G(f)为增强相,采用原位杂化法制备短玻璃纤维增强HA-CS基生物复合材料.研究交联剂、羟基磷灰石含量和玻璃纤维含量对复合材料性能的影响.采用红外吸收光谱、扫描电子显微镜和万能材料试验机对材料的结构和性能进行表征.结果表明:原位杂化法能制备性能较好的复合材料;用戊二醛交联改性复合材料可以明显增加其韧性和弯曲强度,使复合材料抗弯曲强度提高16%;当CS/HA=10/1(质量比)和玻璃纤维含量为1.5%时复合材料抗折强度达到极大值84.47 MPa;随玻璃纤维含量的增加,复合材料的断裂面由平整向多层断裂变化,材料的韧性有所提高.
关键词:
G(f)/HA-CS复合材料
,
玻璃纤维
,
交联剂
,
弯曲强度
Journal of Magnetism and Magnetic Materials
The electron paramagnetic resonance g factors g(parallel to) and g(perpendicular to) for the trigonal Er3+-V-K centers (where V-K denotes K+ vacancy) in KMF3 (M = Mg and Zn) are theoretically investigated from the perturbation formulas of the g factors for a 4f(11) ion in trigonal symmetry. In these formulas, the contributions to the g factors from the second-order perturbation terms and the admixture of various energy levels are taken into account. In the above trigonal centers, the impurity Er3+ resides in the octahedral M2+ site of both crystals, associated with one V-K in the C-3-axis due to charge compensation. By analyzing their g factors, we find that the impurity Er3+ in both centers would move towards the V-K by an amount DeltaZ along the C-3-axis due to electrostatic attraction. The calculated g factors for the Er3+ centers based on the above displacements DeltaZ show good agreement with the observed values. The validity of the results is discussed. (C) 2004 Elsevier B.V. All rights reserved.
关键词:
electron paramagnetic resonance (EPR);defects and impurities;crystal-field and spin hamiltonians;Er3+;KMF3;(M = Mg and Zn);crystal-field;superposition-model;perovskite kmgf3;conversion;parameters;fluorides;kznf3
马敬翙
,
刘光明
,
曾潮流
,
杜楠
,
赵晴
表面技术
doi:10.3969/j.issn.1001-3660.2006.04.005
采用电化学方法、扫描电镜、能谱分析等技术,研究了常温下镍基高温合金M17和M38G在NaCl溶液和含S2O2-3的NaCl溶液中的腐蚀行为.结果表明,在含质量分数为3.5% NaCl的溶液中,M17和M38G均会遭受严重的点腐蚀;向NaCl溶液(NaCl质量分数为3.5%)添加Na2S2O3(Na2S2O3质量分数为1.5%)后,由于溶液中的S2O2-3在试样表面活性点与Cl-竞争吸附并与H+结合,使两种合金的点蚀均受到抑制;M38G中存在微量的Nb、Ta、Mo等元素使得M38G合金在NaCl溶液中的耐腐蚀性能明显优于M17合金.
关键词:
镍基
,
高温合金
,
点蚀
,
电化学方法
,
腐蚀行为
Intermetallics
The phase transformation of alumina formed during oxidation of beta-NiAl coating prepared on M38G alloy by pack cementation was investigated. Oxidation experiments were conducted at 950 degrees C for various times from 2 to 180 min. The phase composition and microstructure of the oxide scales were investigated by using glancing angle XRD, AFM and SEM. The results showed that at the initial oxidation stage needle-like theta-Al2O3 was formed and then it covered the sample surface rapidly. The formation of alpha-Al2O3 grains beneath the theta-Al2O3 layer was favored by depletion of Al in the beta-NiAl coating during oxidation. alpha-Al2O3 preferred growing on the top (ridge) of beta-NiAl grains, which resulted in the formation of net-like alpha-Al2O3 inner layer. With increasing time, theta-Al2O3 transformed to alpha-Al2O3 gradually. After 180 min oxidation, most of alpha-Al2O3 grains transformed into alpha-Al2O3. A mechanism of excessive voids' formation at the oxide/coating interface was also proposed in this paper. (c) 2007 Elsevier Ltd. All rights reserved.
关键词:
nickel aluminides, based on NiAl;oxidation;phase transformations;coatings, intermetallic and otherwise;high-temperature oxidation;theta-alpha-al2o3 transformation;behavior;coatings;superalloy;transition;layers
