材料期刊网

On the Crack Initiation and Growth in a Strongly Dynamic Strain Aging Aluminum Alloy Sheet

W.Tong , N.Zhang

材料科学技术（英文）

Serrated plastic flows in an Al sheet (AA5182-H19) were first characterized temporally and spatially under quasistatic uniaxial tension. Discrete types B and C serrations or Portevin Le-Chatelier (PLC) bands started to appear at a plastic strain of 2.54% with an average stress drop of 2.5 MPa and an average time interval of 7.75 s between serrations. The width of the individual PLC bands was about twice of the thickness of the sheet (0.235 mm) and the plastic strain inside the bands was as high as 2%. V-notched tear test coupons made of the same Al alloy were then stretched under both continuous monotonic and periodic interrupted loading conditions and their crack initiation and growth processes were monitored by direct digital imaging. The crack tip opening angle (CTOA) and the crack tip opening displacement (CTOD) were measured to be about 2.5～3℃ and 0.07～0.1 mm, respectively. While no major load serrations were observed before crack initiation at the notch tip, discontinuous or intermittent crack advances or crack jumps were unambiguously detected in the crack growth stage. The unstable crack propagation in the AA5182-H19 sheet seems to be related closely with its strong dynamic strain aging behavior exhibited under quasistatic loading conditions at the ambient temperature.

关键词: Crack growth , null , null , null

METASTABLE CHARACTERISTICS OF β-W

HUANG Huimin CHEN Xinmin Central South University of Technology , Changsha , China HUANG Huimin Associate Professor , Department of Chemistry , Central South University of Technology , Changsha , China

金属学报(英文版)

The nature of the oxygen contained in β-W was investigated with DSC,X-ray analysis on quenched samples and Auger spectroscope.It was shown that the oxygen contained in nonpyrophoric β-W consists of the reversibly chemisorbed oxygen and the interstitial oxygen which could form an interstitial solid solution with β-W.It seems better to consider β-W to be a metastable phase of tungsten with the interstitial oxygen as stabilizer.

关键词: tungsten , null , null , null

Effect of W on structural stability of TiAl intermetallics and the site preference of W

Physical Review B

The effect of W on the structural stability of TiAl intermetallic systems and the site preference of W in B2 and L1(0) TiAl were studied based on first-principles calculations. It was found find that about 15 at. % W addition, in good agreement with experiment, is required to stabilize the B2 structure in a TiAl base alloy. W was predicted to occupy Al sites in the B2 phase, but Ti sites in the L1(0) phase. The B2-stabilizing effect of W and its site preference can be explained perfectly on the basis of the pseudogap effect and the strong covalent W-Ti bonding. The strong W-Ti bonding pairs are maximized when W occupies Al sites in B2 TiAl. But when W occupies Al sites in L1(0) TiAl, the W-Ti bonding is weakened by the existence of Al in the alternating (002) plane, which can, however, strengthen the in-plane W-Ti bonding when W occupies Ti sites.

关键词: gamma-titanium aluminides;electronic-structure;microstructure;deformation;systems;alloys

降低IF钢w(O)的工艺研究

王雄

钢铁研究 doi:10.3969/j.issn.1001-1447.2006.05.016

IF钢中w(O)的大小直接影响到成品板的表面质量.分析了武钢近年来IF钢w(O)偏大的生产现状,找到钢中w(O)、精炼处理前温度及钢包内炉渣等转炉冶炼、精炼及连铸工序对IF钢w(O)的影响,通过采用低氧钢生产工艺,使IF钢w(O)得到很好的控制.

关键词: IF钢 , w(O) , 转炉复吹

Valence bond structure of Ta-W alloys

Xiaobo LI , Youqing XIE

金属学报(英文版) doi:10.1016/S1006-7191(08)60099-X

The valence bond structure of substitutional BCC based Ta-W alloys is studied using characteristic crystal (CC) theory. This theory is based on cluster statistics of random alloys. By studying the correlativity between energy and volume of the CC in Ta-W alloys, the valence bond structure of CC is determined by the energy and shape method. Then, following additive law of CC, the valence bond structure of Ta-W alloys is calculated. It is found that the outer shell valence electronic distribution of Ta-W alloys shows a continuous change in the whole composition range. The covalent electrons e_c(d_c, s_c, and p_c) increase, whereas near free electrons e_f decrease with increasing W concentration. The bond length and single-bond radius decrease, whereas bond energy and bond valence increase with increasing W concentration. The mechanism of solid solution strengthening of Ta-W alloys is analyzed based on their valence bond structure.

关键词: Valence bond structure , null

Phase stability of Ta-W alloys

Xiaobo LI

金属学报(英文版)

The characteristic crystal model is applied to the study of phase stability and thermodynamics in substitutional bcc-based Ta-W alloys. The basic principle and method of alloy thermodynamics which is described by the characteristic crystal model is introduced in detail. The Gibbs energy of various phases including both disordered and ordered phases of the Ta-W system are evaluated. The phase diagram of Ta-W alloys is assessed and predicted. The results are in good agreement with experiments and better than that of first principle.

关键词: Ta-W alloys , phase diagram , characteristic crystal model , thermodynamics , phase stability

Microstructure characterization of long W core SiC fiber

材料科学技术（英文）

Microstructure of SiC fiber manufactured by chemical vapor deposition (CVD) onto tungsten (W) wire core was investigated by analytical electron microscopy (AEM). The results reveal that the fiber consists of W core, SiC sheath and C-coating. SiC sheath could be subdivided into two parts according to whether containing C rich stripe, or not. An emphasis was put on W/SiC interfacial reaction products and the transition zone between sub-layers in SiC sheath. The W/SiC interface consists of three layers of reaction production, namely, W2C, W5Si3 and WC. And there are amounts of facet faults existing in (100) face of WC crystalline and two classes of stack faults in WC have been revealed. The formation essence of different sublayers in SiC sheath was also discussed.

关键词: siC fiber;chemical vapor deposition (CVD);analytical electron;microscopy (AEM);C-rich zone;reaction products;chemical vapor-deposition;silicon-carbide;model;dichlorodimethylsilane;interface;pyrolysis;hydrogen;strength

Abnormal saturation magnetization dependency on W  content for Co-W thin films

Bo YANG

金属学报(英文版)

A series of hexagonal close-packed (HCP) Co-W thin films were deposited by sputtering on surface oxidized silicon substrates at 300℃. A linear dependency of saturation magnetization (M_s) on W content was found up to about 9~at.~pct W, and then it underwent an increased M_s vs. W content curve as compared to the initial linear dependency. The thermal magnetization technique was used to confirm that the increased M_s behaviour is correlated to the phase separation of the Co-W thin films. The phase separation behaviour was also found to be dependent on W content and the reason was discussed in detail. Finally an interesting composition range was suggested to be about 13at.pct-17 at. pct W for the Co-W thin films, in which they exhibit much higher magnetic anisotropy energy than Co-Cr thin films and improved phase separation.

关键词: Magnetic recording media

代铬镀层--Ni-W、Ni-W-B非晶态合金镀层性能研究

朱立群 , 李卫平

电镀与涂饰 doi:10.3969/j.issn.1004-227X.2004.05.003

通过在浓硝酸、w=5% NaCl溶液、c＝1 mol/L H2SO4溶液中的浸渍试验,研究了不同基体上的Ni-W非晶态合金镀层的耐蚀性;通过测定在w=5% NaCl溶液及c=1 mol/L的HNO3溶液、H2SO4溶液、HCl溶液中的阳极极化曲线,研究了Ni-W非晶态合金镀层薄膜本身的耐蚀性;采用线性极化方法对Ni-W-B非晶态合金镀层在w=5% NaCl溶液、c＝1 mol/L H2SO4溶液及HNO3溶液中的腐蚀速度进行了测定,并测定了以上2种非晶态合金镀层的硬度与耐磨性.结果表明,非晶态的Ni-W、Ni-W-B镀层比晶态镀层的耐腐蚀性能要好,而Ni-W-B 非晶态合金镀层比Ni-W非晶态合金镀层的耐蚀性能又明显提高;经热处理后,Ni-W-B非晶态镀层的硬度值明显高于Ni-W非晶态镀层,耐磨性能都提高了1倍以上.Ni-W、Ni-W-B非晶态镀层极有望成为一种比较好的代铬镀层.

关键词: 代铬镀层 , 非晶态镀层 , Ni-W , Ni-W-B , 耐蚀性能

ELECTRONIC STRUCTURE OF γ'-PHASE IN SUPERALLOY CONTAINING Mg AND W

ZHU Kai University of Science and Technology of China , Hefei , China WANG Chongyu Central Iron and Steel Research Institute , Ministry of Metallurgical Industry , Beijing , China Central Iron and Steel Research Institute , No.13 , Taipingzhuang , Beijing , China

金属学报(英文版)

The calculation of electronic structure of γ'-Ni_3Al phase with or without Mg and W by the Recursion and LCAO methods clarified that Mg and W atoms lose their outer electrons par- tially after they entered γ'-Ni_3Al.It causes the reduction of the radii of the atoms.So it is preferable for Mg atom to enter γ'-phase by the substitution.The interaction between Mg and γ'-phase matrix may be strengthened and a more stable structure of γ'-phase may be formed while Mg and W entered γ'-Ni_3Al simultaneously.

关键词: superalloy , null , null , null