Numerical simulation of solidification and liquation behavior during welding of low-expansion superalloys

Low-expansion superalloys are susceptible to weld solidification cracks and heat-affected zone (HAZ) microfissures. To predict solidification cracking, QBasic procedures were developed and solidification reaction sequence, type, and amount of eutectic product were calculated. As manifested, primary solidification is followed by L → (γ+NbC) and L → (γ+Laves) eutectic reaction sequentially for GH903 and GH907; hence, the terminal eutectic constituents are made up of γ/NbC and γ/Laves. While for GH909, only reaction L → (γ+Laves) occurs and more γ/Laves eutectic forms. Therefore, GH909 is more sensitive to solidification cracking. To predict HAZ liquation, cracking Visual FORTRAN procedures were developed, and constitutional liquation of NbC was simulated. As shown, solid dissolution of NbC prior to liquation decreases, and initial liquid film increases with the rate of thermal cycle. Higher rate of thermal cycle promotes the melting of the matrix adjacent to the liquid film and postpones the solidification of the liquid by the liquid-to-γ mode. Thus, more residual liquid film remains at the eutectic point, which will promote HAZ microfissuring. The increase in original grain size and peak temperature also promotes liquation. Finally, these conclusions were verified indirectly by hot ductility tests.     

论建立我国宪法监督解释制度:完善我国宪法监督制度的思考

本文针对我国宪法监督现状,尝试提供建立宪法监督解释制度来完善我国宪法监督实施,即在全国人大之下设立宪法监督解释委员会,作为全国大专门委员会,专司宪法监督解释,并对该委员会的产生,组成,职权,解释原则作了探讨。     

梯度合金中脱碳区η相的研究

采用衍射与金相分析方法对梯度合金中的脱碳区进行了研究,分析了影响η相成分与渗碳过程中η相长大的原因。研究显示:随着基体C含量的降低,η相中的η1(Co3W3C)比例逐渐减少,而η2(Co6W6C)含量比例逐渐增加;凡能够缩小两相区与脱碳区界面处成分过冷区域的因素都能减缓或避免脱碳区界面处η相的长大。     

Growth restriction effects during solidification of aluminium alloys

The effects of solute elements during solidification on the grain size are very important and can be quantified by the growth-restriction parameter Q, and Q possesses the better correlation with the grain size. Based on the constitutional undercooling generated by the growth of an adjacent grain during the initial solidification, the growth-restriction parameter Q is deduced and a comprehensive physical basis of Q is obtained by using an initial solute distributing equation. For the alloys with more potent nucleants, Q is a suitable predictor of the grain size. For less potent nucleants, the relative grain size(RGS) is a more accurate prediction of the grain size. This prediction coincides with the experimental behaviors for Al-Ti and Al-Cu alloys with lower solute content.     

关于司法体制改革的深层次思考

改革开放以来,我国的法制建设逐步恢复并迅速发展,特别是党的十五大提出依法治国的基本方略之后,法制建设进入了一个新的阶段.但是,我国现行的司法体制却不能适应新形势的需要,暴露出许多问题,最高人民法院院长肖扬将其归结为三大主要问题,司法权地方化,司法权力行政化,法官职业大众化,可谓切中要害.为保障司法独立,实现司法公正,司法体制改革势在必行,而学术界、司法界提出的建议和设想,原则性强,可操作性弱,同时,也存在着急于求成的思想倾向,司法体制改革必须在党的领导下,统揽全局,协调各方,积极稳妥,循序渐进地进行.在现阶段,关键在于落实法院的宪法地位,而切入点是在把握共产党执政规律的基础上加强党对法院的领导.     

"中国史境"下的宪政道路与政治现代化的特点

＂中国史境＂是研究中国问题的理论和方法,宪政是一个国家走向政治现代化所必须经历的过程,研究中国的宪政道路,就应将其置于＂中国史境＂下来进行.从中国宪政道路与中国政治现代化的关系中可以得出中国政治现代化的特点,由这些特点决定了＂中国史境＂下中国的宪政道路和政治现代化的实现方式.     

Beyond Chemical Synthesis: Self-Organization?!

The present text presents briefly some general considerations on the steps from molecular synthesis to the development of chemistry beyond the molecule, towards mastering progressively the processes underlying the generation of complex matter by self-organization.     

高温后钢筋混凝土粘结性能试验研究

为了提高建筑物火灾后加固设计的可靠性,探究高温后钢筋混凝土的粘结性能成为过火后钢筋混凝土性能研究的关键。通过中心拔出试验,研究了经历不同温度后钢筋和混凝土粘结性能的变化情况,得到不同温度下的τ-s曲线,并给出温度因素影响下的粘结应力-滑移本构方程。     

Irradiation behaviour of α2 and γ phases in He ion implanted titanium aluminide alloy

A Ti–45Al–2Nb–2Mn + 0.8 vol.% TiB₂ (at.%) alloy with fully lamellar microstructure consisting of hexagonal-close-packed (hcp) α₂ and face-centred-tetragonal (fct) γ phases was irradiated by implanting helium ions to different fluences. Microstructural examination showed that helium cavities are formed in both the α₂ and γ phases after He-ion irradiation. However, the helium cavities and their size change with fluence are much larger in the α₂ phase than those in the γ phase, indicating that the γ phase exhibits better tolerance to the He-ion irradiation than the α₂ phase. Since α₂ and γ phases have different crystal structures, they possess differences in helium solubility and interstitial migration. These differences are responsible for the variation in radiation damage behaviour between the two phases.     

MECHANICAL PROPERTIES OF STRONGLY ORDERED B2 COMPOUNDS

１　ＩＮＴＲＯＤＵＣＴＩＯＮＢ２ｏｒｏｒｄｅｒｅｄｂｏｄｙｃｅｎｔｅｒｅｄｃｕｂｉｃｃｒｙｓｔａｌｃｏｍｐｏｕｎｄｓｏｆｔｅｎｅｘｉｓｔｏｖｅｒａｒａｎｇｅｏｆｃｏｍｐｏｓｉｔｉｏｎｓｏｎｅｉｔｈｅｒｓｉｄｅｏｆｔｈｅｓｔｏｉｃｈｉｏｍｅｔｒｉｃｃｏｍｐｏｓｉｔｉｏｎ［１］．Ｄｅｖｉａｔｉｏｎｓｆｒｏｍｔｈｅｓｔｏｉｃｈｉｏｍｅｔｒｉｃｃｏｍｐｏｓｉｔｉｏｎａｒｅａｃｃｏｍｍｏｄａｔｅｄｂｙｃｏｎｓｔｉｔｕｔｉｏｎａｌｄｅｆｅｃｔｓ，ｔｈａｔｉｓ，ｅｉｔｈｅｒｂｙｖａｃａｎｃｉｅｓｏｎｔｈ…