TiAl合金层片组织的瑞利分解现象及应用

ＴｉＡｌ合金层片组织具有相当好的室温断裂韧性和抗高温蠕变性能，但层片团中强烈的塑性各异性导致其室温塑性很低。研究了Ｔｉ－４６．５Ａｌ－２．５Ｖ－１Ｃｒ（ａｔ．％）合金层片组织发生瑞利分解（Ｒａｙｌｅｉｇｈ‘ｓＢｒｅａｋｄｏｗｎ）现象的热处理条件及σ２片间断对塑性的作用，实验发现，在一定温度区间进行循环热处理过程中，α２相的溶解析出相变能有效地强化瑞利分解现象，α２层片发生瑞利分解后，从４点弯曲实验     

Phase behavior and structural properties for the triton X-100/<Emphasis Type="Italic">n</Emphasis>-C<Subscript>n</Subscript>H<Subscript>2n+1</Subscript>COOH/H<Subscript>2</Subscript>O system

In the Triton X-100/n-C_nH_2n+1COOH/H₂O system, n-C_nH_2n+1COOH can be used as a cosurfactant. As its chain length increases, the regions of the microemulsions showing oil-in-water (O/W), water-in-oil (W/O), and bicontinuous structures decrease and at the same time, the region of the lamellar liquid crystal increases. In the O/W region, the distribution coefficient K of n-C_nH_2n+1COOH between Triton X-100 micellar phase and water phase increases with the chain length of saturated unbranched monocarboxylic acid. The relationship between the standard solubilization Gibbs free energy of saturated unbranched monocarboxylic acid and the number of methylene groups in the saturated unbranched monocarboxylic acid is given by the equation: ΔG _m ⁰=−2.364−2.818 n(CH₂) kJ·mol⁻¹ in the Triton X-100 micellar system. In the lamellar liquid crystal region, small-angle X-ray diffraction shows that the thickness of the bilayer d ₀ is independent of the weight ratio of n-C_nH_2n+1COOH to Triton X-100, but the volume of the solvent penetrating from the solvent layer to the amphiphilic bilayer increases with the weight ratio of n-C_nH_2n+1COOH to Triton X-100. Furthermore, the d ₀ value increases with the chain length of saturated unbranched monocarboxylic acid, which will contribute to the formation and stabilization of the lamellar liquid crystal.     

Variations in polymeric structure of ferroelectric poly(vinylidene fluoride) films during annealing at various temperatures

To clarify the thermal degradation mechanisms of uniaxially drawn poly(vinylidene fluoride) (PVDF) films, variations due to annealing in the polymeric structures of the films were investigated using the small‐angle X‐ray scattering (SAXS) and Fourier transform infrared (FTIR) spectroscopy. The films were composed of lamellar crystals that were stacked perpendicular to the stretch direction. Although the crystallinity of the films decreased during annealing in the temperature range above the preannealing temperature, the lamellar structure was maintained even after the annealing process. There are two kinds of irreversible relaxation mechanisms during the annealing process of the films, including both a decrease in crystallinity within the lamellae and also thickening of the lamellae. A significant lamella thickening effect was observed when the films were annealed above ～ 100°C. FTIR spectra suggested some disordered structures are developed during thickening of the lamellae. Furthermore, a long‐range periodic structure was formed in the films that were annealed above the melting temperature of PVDF. The polymeric structures formed during the fabrication process (including high‐order structures and disorders in molecular conformation) were clarified as having a significant influence on the annealing behavior of ferroelectric PVDF films. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

超高强珠光体钢丝冷拔过程中片层组织的定量表征

定量表征珠光体钢丝在大应变量拉拔过程中珠光体片层间距的变化规律,对掌握超高强珠光体钢丝的组织与性能关系以及强韧化机理具有重要意义。本文工作根据珠光体钢丝组织变化特点,研究了72A珠光体钢丝在累计应变量3.58范围内的片层组织表征方法,在低应变量(ε1.75)时,采用SEM图像观察,用圆周测量法统计测量了珠光体片层间距的变化;在高应变量(ε≥1.75)时,采用FIB制备TEM样观察,用线性截距法统计测量了珠光体片层间距的变化。结果表明,72A珠光体钢丝的珠光体片层间距由最初的81 nm左右减小到最终的17 nm左右。分析了72A珠光体钢丝的组织与性能关系,为研究珠光体钢丝拉拔过程中的变形及强化机理奠定了基础。     

Lamellar orientation control in directionally solidified TiAl intermetallics

TiAl-based alloys are potentially used as high-temperature structural materials with a high specific strength in the range of~900°C.However,the mechanical properties of TiAl-based alloys are extremely anisotropic with respect to the lamellar orientation of the microstructures.A balance combination of room-temperature ductility and strength can be achieved when the lamellar orientation are aligned parallel to the tensile stress direction.Lamellar orientation control of TiAl-based alloys by directional solidification technique has been widely studied in recent years.Two different directional solidification processes can be used to modify the lamellar orientation.One is a seeding technique and the other is adjusting the solidification path.This paper reviews the principles of the two methods and their progress.The influence of alloy composition and solidification parameters on lamellar orientation control is also discussed.     

The 9th China International Diecasting Congress& The 1st International Symposium on Nonferrous Alloys and Special Casting Technologies held in Shanghai

The 9th China International Diecasting Congress and the 1st International Symposium on Nonferrous Alloys and Special Casting Technologies （ISNASCT） were successfully held in Shanghai on July 19-22, 2014. Both events were jointly sponsored by Chinese Mechanical Engineering Society, Die Casting Commission of World Foundry Organization and Non-Ferrous Materials Commission of World Foundry Organization, and organized by the Foundry Institution of Chinese Mechanical Engineering Society （FICMES） and China Productivity Promotion Center of Foundry Industry.     

热处理TiAl(W,Si)合金的拉伸性能及裂纹扩展

对铸态Ti-46Al-0.5W-0.5Si合金进行淬火回火热处理,获得了近层片组织和双态组织。对两种不同组织的合金进行室温拉伸试验,并对试样断口和断口附近的组织进行分析,研究了拉伸断裂机制。结果表明:双态组织比近层片组织具有更好的室温塑性和抗拉强度。双态组织中的裂纹可以绕过较小的γ相颗粒,沿γ相和α2/γ片层团的界面扩展,也会以穿越层片的方式扩展。而近层片组织中的裂纹则是以沿片层和穿越片层的混合方式扩展。     

14MnNbq钢焊接性试验

对芜湖长江大桥钢梁用14MnNbq钢焊接性进行了试验研究，并与国内外常用桥梁用钢16Mnq、SM490C进行了相关对比分析，通过试验为14MnNbq钢梁焊接工艺的制定提供依据。     

弹簧钢55SiCrA过冷奥氏体动态连续冷却转变

采用热膨胀法结合金相-显微硬度法,在Gleeble-1500热模拟试验机上测定了弹簧钢55SiCrA的相变临界点Ac1、Ac3、Ar1、Ar3和Ms;同时测定了奥氏体在不同冷却速度下连续转变时的膨胀曲线,并绘制了动态连续冷却转变曲线（CCT图）;通过FE-SEM研究了不同的冷却速度对显微组织形貌和珠光体片层间距的影响。结果表明：随着冷速的增加,珠光体片层间距减小,显微硬度值增大;弹簧钢55SiCrA线材控制冷却理想的冷速范围为0.5～1℃/s。     

Effect of clay on the morphology of blends of poly(propylene) and polyamide 6/clay nanocomposites

PP/NPA6 blends composed of poly(propylene) (PP) and polyamide 6/clay nanocomposites (NPA6) were prepared by twin‐screw extrusion and melt‐drawn into ribbons by a ribbon extrusion process. The influence of clay on the morphology of PP/NPA6 ribbons was investigated by means of field‐emission scanning electron microscopy and optical microscopy. The results show that at low clay content (3, 5 wt%), NPA6 exhibited continuous lamellar structure in PP as pristine PA6 did in a PP/PA6 blend, but at a higher clay content (10 wt%) only ellipsoids or elongated ellipsoids were observed. In order to explain the morphological difference, two factors, ie the compatibilization effect and melt rheology, have been taken into consideration. It has been found that both factors, and probably mainly the variation in melt rheology, were responsible for the morphological difference in the PP/NPA6 blends with different clay contents under the extensional flow field. Copyright © 2004 Society of Chemical Industry