Effects of Ultrasonic Vibration on Material Flow and Thermal Cycles in Friction Stir Welding of Dissimilar Al/Mg Alloys

Comparative experiments are performed in friction stir welding (FSW) of dissimilar Al/Mg alloys with and without assistance of ultrasonic vibration. Metallographic characterization of the welds at transverse cross sections reveals that ultrasonic vibration induces differences in plastic material flow in two conditions. In FSW, the plastic material in the peripheral area of shoulder-affected zone (SAZ) tends to flow downward because of the weakening of the driving force of the shoulder, and a plastic material insulation layer is formed at the SAZ edge. When ultrasonic vibration is exerted, the stirred zone is divided into the inner and outer shear layers, the downward material flow trend of the inner shear layer disappears and tends to flow upward, and the onion-ring structure caused by the swirl motion is avoided in the pin-affected zone. By improving the flow behavior of plastic materials in the stirred zone, ultrasonic vibration reduces the heat generation, accelerates the heat dissipation in nugget zone and changes the thermal cycles, thus inhibiting the formation of intermetallic compound layers.

     

Preparation of ceramic coatings on inner surface of steel tubes using a combined technique of hot-dipping and plasma electrolytic oxidation

A new method for inner surface modification of steel tubes, named a combined technique of hot-dipping and plasma electrolytic oxidation (PEO) was proposed and demonstrated in this paper. In this work, metallurgically bonded ceramic coatings on inner surface of steel tubes were obtained using this method. In the combined process, aluminum coatings on steel were firstly prepared by the hot-dip process and then metallurgically bonded ceramic coatings were obtained on the aluminum coatings by PEO. The element distribution, phase composition and morphology of the aluminide layer and the ceramic coatings were characterized by SEM/EDX and XRD. The corrosion resistance of the ceramic coatings were also studied. The results show that, after hot-dip treatment, the coating layers consist of two layers, where Al, Fe_xAl _(1−x) were detected from external topcoat to the aluminide/steel substrate. Then after PEO process, uniform Al₂O₃ ceramic coatings have been deposited on inner surface of steel tubes. The ceramic coatings are mainly composed of -Al₂O₃ and γ-Al₂O₃ phase. The compound coatings show favorable corrosion resistance property. The investigations indicate that the combination of hot-dipping and plasma electrolytic oxidation proves a promising technique for inner surface modification of steel tubes for protective purposes.     

SBTV铁电材料的制备和微观组织结构

采用固相反应法合成了SrBi2Ta2O9(简称SBT)和V掺杂SrBi2Ta2O9(简称SBTV)陶瓷,通过TG-DTA、XRD、SEM、TEM等技术手段研究了材料的烧结工艺、相组成和微观组织结构.研究表明V2O5是一种很好的助烧剂,掺杂后材料的烧结温度可降低200℃烧结后纯SBT均为单一的钙钛矿相SBT;掺杂后2种成型工艺所制备的SBTV除了生成少量Bi4(V2O11)外,仍主要由钙钛矿相组成;同时所有的材料都发生了一定程度的择优取向.掺杂后材料的晶粒形态发生变化棒状转化为片状.同时V掺杂后引起了晶格畸变,产生应变,SBTV材料在透射中观察到具有α-边界特征的90°畴.     

Effect of temperature on anodic behavior of 13Cr martensitic steel in CO2 environment

The corrosion behavior of 13Cr martensitic stainless steel in a CO₂ environment in a stimulated oilfield was studied with potentiodynamic polarization and the impedance spectra technique. The results showed that the microstructure of the surface scale clearly changed with temperature. This decreased the sensitivity of pitting corrosion and increased the tendency toward general (or uniform) corrosion. The capacitance, the charge transfer resistance, and the polarization resistance of the corrosion product scale decrease with increasing temperature from 90 to 120 °C, and thus the corrosion is a thermal activation controlled process. Charge transfer through the scale is difficult and the corrosion is controlled by a diffusion process at a temperature of 150 °C. Resistance charge transfer through the corrosion product layer is higher than that in the passive film.     

Study on Tribological Properties of Polytetrafluoroethylene Drawn Uniaxially at Different Temperature

Summary: Wear behavior correlations with morphology have been established from polytetrafluoroethylene (PTFE) drawn at 200, 327, and 375 °C with draw ratio about 4. The friction coefficient and wear rate for PTFE drawn at 327 °C are lower and the wear rate is lower than that of undrawn PTFE by about 30%. The structures of samples were characterized by scanning electron microscope (SEM), DSC, and wide angle X‐ray diffraction (WAXD). Results indicate that the debris morphologies of samples are different. The differences in the tribological behavior of undrawn and drawn samples were attributed to the improvement of the degree of the crystalline, fibrillation, and orderliness by drawing, especially, for PTFE drawn at 327 °C. The orderliness of molecular arrangement along the drawn direction is also higher for PTFE drawn at 327 °C than those of PTFE drawn at 200 and 375 °C, respectively. Therefore, the intensity of covalent bond along drawn direction is higher. The shear resistance and the deformability of the material are greatly improved and the size of the wear breakage unit decreases, which results in a good tribological property for PTFE drawn at 327 °C.

SEM morphology of fractured surface perpendicular to the draw direction for PTFE drawn at 327 °C.     

单组分阴离子水性聚氨酯胶膜的热质研究

应用热质分析（TG）研究了单组分阴离子水性聚氨酯胶膜的耐热性能，结果表明：n（--NCO）：n（--OH）增大，胶膜的耐热性能增强；聚酯相对分子质量增加，耐高温性能降低；用DEG扩链时的耐高温性能比用DEG／TMP时的好；TDI型水性聚氨酯成膜物的耐高温性能优于IPDI型水性聚氨酯。     

生态型高吸水性树脂的研究

从高吸水性树脂的化学结构出发，论述了树脂的降解机理和降解方法，归纳和评述了近期我国在可降解天然聚合物、丙烯酸接枝共混和丙烯酸（盐）合成聚合物方向的研究，并对未来作出展望。     

免水型生态卫生设施用降解菌的分离筛选

本文对免水型生态卫生设施中的生物填料及施有机肥农田的土壤进行了人类粪便降解菌的分离。筛选得到的各菌种在实验条件下，降解粪便效果较好，除臭除味，COD下降率在30％左右。其中在土壤中分离出来的9号菌，COD下降率达41％，全部菌种复合培养处理的下降率高达59％。结果表明，实验采用的分离筛选方法是比较有效的，筛选得到了具有较好降解效果的菌种，为降解菌的进一步试验打下了基础。     

改性低毒脲醛树脂的合成及性能研究

采用六亚甲基四胺做催化剂，加入聚乙烯醇（PVA）、三聚氰胺和硫脲作为改性剂，通过降低甲醛与尿素物质的量比、采用尿素分批加入的合成方法，制备出改性低毒的脲醛树脂（UF），使游离甲醛质量分数低于0．30％；采用捏合和模压成型方法，将改性和普通UF树脂分别与剑麻纤维（SF）制备UF／SF共混复合材料，研究了复合材料的力学性能和吸水性能。结果表明，甲醛和尿素物质的量比为1．1时，游离甲醛质量分数降低到0．16％；甲醛和尿素物质的量比为1．2时，三聚氰胺、PVA及硫脲加入量分别为尿素总量的2．0％，1．5％，1．0％（质量分数）时，游离甲醛质量分数降低到了0．10％，粘度达到0．41Pa·S，贮存期大于80d；改性UF／SF复合材料的性能比普通UF／SF复合材料的冲击性能和耐磨性能分别提高了114％和261％。