Laser melting of Ti-15Al-20Nb alloy

Titanium aluminides have become promising materials for high-temperature applications, but the relatively poor oxidation resistance and elevated- temperature strength of these alloys limit their application to temperatures lower than 1000 °C. Niobium addition improves the properties of titanium aluminide. However, the mechanical, metallurgical, and corrosion properties of Ti- Al- Nb may be improved by treatment with a laser beam. Consequently, the present study examines the properties of Ti- 15Al- 20Nb alloy subjected to the Nd:YAG laser melting process. Hardness in the surface region increases to twice the base material hardness, and corrosion resistance improves considerably after laser treatment.     

表面处理对球墨铸铁接触疲劳性能的影响

本文研究了激光微熔处理和高频感应加热淬火对球墨铸铁表面组织、接触疲劳强度和接触疲劳破坏过程的影响。结果表明,激光处理和高频淬火均可提高球铁的接触疲劳强度,但其接触疲劳破坏过程和形式却不同,前者是由于硬化层与基体间裂纹扩展造成大块深层剥落,后者则是表层裂纹在油楔作用下造成小块浅层脱落。     

表面修饰TiO2光催化薄膜的表征

利用射频磁控溅射技术，以Ar和O2气混合气体为溅射气体在载玻片上制备了锐钛相TiO2薄膜。为了提高Ti02薄膜的光催化活性，在TiO2薄膜表面进行了钽修饰。利用X射线衍射(XRD)，原子力显微镜(AFM)和UV-VIS-NIR分光光度计等技术对薄膜进行了表征。结果表明：对TiO2薄膜的表面进行适量的Ta元素修饰可以提高其光催化活性。     

Surface nanocrystallization of commercial pure titanium by shot peening

The surface nanostructures of commercial pure titanium was realized by the modified shot peening equipment commonly used in industry through the special treatment process. The results show that high-energy-shot-peening(HESP) commonly used to prepare nanostructured surface layers can be achieved by the increase of pill size, pill speed, and treatment time in the commercial shot peening equipment. XRD, SEM and TEM were used to characterize the surface layer microstructure of treated specimens. The analytic results show that the main deformation mode of commercial pure Ti is twinning. At the beginning of deformation, the dislocations are formed and twins occur within or on plane, then twins in intersection plane appear, and at last the twin characteristics disappear in the surface layer after longer treatment time. The deformation layer depth increases with treatment time in a certain period when the pill size and speed are unchanged. And in the severe plastic deformation (SPD) layer in which the twins are not identified easily by using SEM, the nanocrystalline microstructures are found under TEM. The finest grain size in the surface layer is about 40 nm, and the depth of nanostructured layers is over 60 μm. The microhardness of the nanostructured surface layers is enhanced significantly after shot peening compared with that of the initial simple.     

黄铁矿微生物浸出体系中的表面热力学和扩展DLVO理论

根据Young s方程的推导公式结合接触角的测定结果计算黄铁矿和氧化亚铁硫杆菌的表面能参数。结果表明,氧化亚铁硫杆菌的表面能明显高于黄铁矿的表面能。应用热力学计算氧化亚铁硫杆菌在黄铁矿表面吸附的自由能,发现其吸附自由能为正值,无法解释氧化亚铁硫杆菌在黄铁矿表面的吸附现象,而通过扩展DLVO理论建立的Lifshitz-van der Waals(LW)、Lewis acid-base(AB)和静电(EL)作用自由能与作用距离(d)之间的势能曲线,能够准确的预言氧化亚铁硫杆菌在黄铁矿表面的吸附现象。     

核电工程材料的应力腐蚀破裂研究

采用慢应变速率试验(SSRT)和U型弯曲试验技术研究了水中杂质离子、溶解氧(DO)、外加电位以及温度等对核电工程材料304不锈钢(SS)、316SS以及A533B压力容器用钢在高温水中应力腐蚀破裂(SCC)的影响,并结合电化学测试和表面膜分析结果进行了讨论,还根据304SS的U型弯曲和SSRT结果的差异提出了SCC加速试验的选择原则建议。     

Initial stages of the high-temperature corrosion of commercial Fe-Cr-Ni alloys in a carburizing atmosphere of low oxygen partial pressure

The early stages of corrosion of AISI 314, HK 40, and Alloy 800H have been studied in a strongly carburizing (a_C=0.8), weakly oxidizing atmosphere at 1098 K. Samples with electropolished and cold-worked surfaces were exposed for up to 400 min. at temperature, in a conventional corrosion rig or in a reaction vessel which was installed within an X-ray photoelectron spectrometer. The latter facility allowed the effects of the specimen heating rate and the rat of gas flow to be investigated. Examination of the corrosion products was accomplished with the aid of XPS, SEM, TEM, and conventional metallography. Initially, surface layers comprised of -Cr₂O₃, (Mn, Cr)₃O₄, and SiO₂ formed, with layer structure, microstructure, and composition being functions of alloy composition and surface condition. Only on the cold-worked surfaces did a well-developed duplex oxide, consisting of an outer, Cr-rich oxide layer and an inner, SiO₂ layer, form. In good agreement with the predicted value of 1.9 wt.%, between 1.4 and 2 wt.% Si in the alloy was required to form a complete SiO₂ layer. After an incubation period, -Cr₂O₃ became unstable and transformed to M₇C₃; the carbides then grew by diffusion of metal from the alloy substrate. The presence of manganese, as (Mn, Cr)₃O₄, in the surface oxide influenced the mode of carbide growth, whereas the rate of carbide growth was severely suppressed by a continuous SiO₂ layer which acted as a diffusion barrier both to metal and to carbon. It is argued that the SiO₂ layer is most effective in reducing carburization when it is free from or contains very few structural defects.     

高频窄脉冲电化学光整加工工艺特性研究

阐述了高频窄脉冲电化学光整加工原理;比较了其与脉冲电化学加工的区别与联系;通过实验,研究及分析了电流密度、加工间隙、工件材料、加工时间及脉冲参数等因素对加工后表面质量的影响.实验结果表明:在合适的工艺参数情况下,高频窄脉冲电化学光整工艺可大幅度提高加工效率,获得镜面级的表面质量,并能降低加工成本.     

离子注入工模具材料表面改性及其展望

介绍了我国及先进工业国家离子注入工模具改性的研究和应用方面取得的成果。展示了我国在离子注入改善工模具材料的抗磨损特性及使改性层韧化方面所做的有益探索和应用实例。作出我国离子注入表面改性的产业化进程已经获得进展的判断 ,并从经济因素和产业政策等方面 ,对推广离子束改性技术 ,加快产业化进程提出了建议     

消失模铸钢件表面局部合金化研究

在泡沫模表面涂覆富钒涂层 ,利用液态铸钢浇铸时的高温和液态钢水的作用 ,使涂层被烧结成合金层 ,同时 ,涂层中的钒渗入铸钢基体组织中 ,形成渗钒层。结果表明 ,该工艺可以使钒渗入到铸钢基体中达 15 0 0～2 0 0 0 μm ,烧结层和渗钒层均为α (Fe ,V)单相组织 ,基体为铁素体和珠光体 ,渗钒层显微硬度与基体硬度相当 ,当涂层粉体粒度 <4 7μm时可得到理想的合金化渗层。涂层粉体粒度越小 ,钒原子在涂层中的扩散越容易 ,渗钒层中钒含量越高 ,渗钒层越厚。