Synthesis mechanism of titanium carbide nano-fiber during self-propagating high temperature synthesis

Titanium carbide nano-fiber was synthesized by self-propagating high temperature synthesis (SHS) method. The final products after the SHS reaction were titanium carbide containing excess carbon and metallic titanium, which were removed by additional leaching process. TEM observation revealed that the average diameter is about 20 nm. Neutron diffraction analysis was carried out to study non-stoichiometric number of the titanium carbide. The non-stoichiometric numbers of the titanium carbide were 0.89–0.94. The Rietveld refinement of each patterns converged to good agreement (÷2=0.49–1.34). The formation mechanism of the carbide is related to a liquid-solid reaction including the preferential diffusion process of carbon atom into liquid titanium. This article is based on a presentation made in the 2002 Korea-US symposium on the “Phase Transformations of Nano-Materials,” organized as a special program of the 2002 Annual Meeting of the Korean Institute of Metals and Materials, held at Yonsei University, Seoul, Korea on October 25–26, 2002.     

Comparison between Ni-Cr-40vol%TiC wear-resistant plasma sprayed coatings produced from self-propagating high-temperature synthesis and plasma densified powders

Plasma sprayed Ni-Cr-40vol%TiC coatings produced from powders obtained by self-propagating hightemperature synthesis (SHS) and plasma densification (PD) processes are characterized. Chemical composition, microstructure, and mechanical properties, such as microhardness and wear resistance, are evaluated and compared. SHS coatings exhibit good sliding wear performance. The exact stoichiometry of titanium carbide inclusions in the metallic matrix affects the dimension of the crystal lattice parameter and was investigated by examining the shift of x-ray diffraction (XRD) peaks of the TiC. A value of the combined carbon/titanium ratio of about 0.6 was calculated for both powders, thus excluding the influence of the stoichiometry of the carbide inclusions on the wear properties of the coatings.     

Effects of γ/γ interfacial structures on continuous coarsening of lamellar microstructure in TiAl alloy during aging

The effects of γ/γ interfacial structures on continuous coarsening of the fully lamellar microstructure in Ti-48Al alloy aged at 1 150 ℃ were investigated by using transmission electron microscopy(TEM). Continuous lamellar coarsening can be achieved not only by migration of interface faults(such as ledges, edges and curved interfaces) but also by migration and decomposition of perfect γ/γ lamellar interfaces. Thermal grooves, initiative positions of interfacial dissociation, can frequently form at the triple point junctions between the 120°-rotational ordered γ domain boundaries within γ lamellae and the lamellar interfaces. During the early stage of aging at 1 150 ℃, the interface migration and dissociation took place preferentially at the 120°-rotational ordered lamellar interfaces. Comparing the relative thermal stability of the true-twin, pseudo-twin and 120°-rotational ordered γ/γ lamellar interfaces shows that the 120°-rotational ordered lamellar interface is the most unstable. The reason of this phenomenon was analyzed through the comparisons of the interfacial energies and atomic arrangements of the three types of γ/γ lamellar interfaces.     

Selective Al-Ti reactivity in laser-processed Al/Ti multilayers

Multilayers consisting of five (Al/Ti) bilayers were deposited on (100) silicon wafers. On top was deposited the Ti layer, aimed at preventing Al from diffusing to the surface upon laser treatment. The total thickness of the thin-film structure was 200?nm. Laser irradiations with Nd:YAG picoseconds laser pulses in the defocused regime were performed in air. Laser beam energy was 4?mJ and laser spot diameter on the sample surface was 3?mm (fluence 0.057?J?cm^?2). The samples were treated with different numbers of laser pulses. Structural characterizations were performed by different analytical methods and nano-hardness was also measured. Laser processing induced layer intermixing, formation of titanium aluminides, oxidation of the surface titanium layer and enhanced surface roughness. Aluminum appears at the sample surface only for the highest density of laser irradiation. Laser processing induces increment of nano-hardness by approximately 20% and decrease of residual Young’s modulus for a few percentages from the starting value of the untreated samples. These results can be interesting toward achieving structures with a selective extent of Al-Ti reactivity in this multilayered system, within the development of biocompatible materials.     

钛合金交替供气GMAW焊接研究

研究了钛合金GMAW保护气交替供气方式对TA2平面堆焊焊缝的影响。利用高速摄像、电流传感器对焊接过程电弧形态、熔滴过渡、电流信号等信息进行采集,并记录焊缝的形貌特征,试验结果表明,交替保护下熔滴过渡方式为细滴状轴向过渡和粗滴状非轴向排斥过渡的混合过渡模式;平均焊接电流随时间延长以类似正弦波上下交替变化,变化频率与交替频率保持一致;相比Ar气、预先混合气,交替保护能够获得熔深更深、熔宽更宽的焊缝。     

钛基亚氧化钛电极电化学降解性能研究

采用SEM、EDS对钛基亚氧化钛电极进行形貌和成分表征,用线性极化曲线法和循环伏安法测试电化学性能,通过降解模拟污水测试降解性能以及用荧光光谱法检测自由基。结果表明,钛基亚氧化钛电极上不能发生直接氧化反应,但是电极析氧电位可达2.18 V(vs.SCE),并且检测到生成大量·OH,是一种类似于Ti/SnO_2的惰性电极,在Na Cl和Na2SO4电解质溶液中电流效率分别达40.95%和22.52%,降解效果优于Ti/SnO_2和Ti/Ru Ir电极。     

生物医用多孔钛及钛合金激光快速成形研究进展

多孔钛及钛合金具有良好的生物相容性和与人骨更匹配的力学性能,是人体理想的替代材料,因此其制备技术及相关性能研究引起了广泛关注。激光快速成形是一项先进的制造技术,在制备生物多孔金属材料时具有独特的优势。介绍了激光快速成形的工作原理和技术特征,根据成形工艺特点简要回顾了4种代表性激光快速成形技术(选择性激光烧结、选择性激光熔化、激光近净成形和激光立体成形)的国内外发展现状,并重点论述了这几种技术在制备生物医用多孔钛及钛合金方面的最新研究进展,最后指出了今后在该领域的主要研究工作。     

水热反应温度对PMMA/TiO_2复合纳米纤维膜的形貌和性能的影响

利用静电纺丝技术成功制备了聚甲基丙烯酸甲酯/钛酸四正丁酯(PMMA/TBT)复合纳米纤维膜,通过水热法处理得到了PMMA/TiO_2柔性复合纳米纤维膜。通过傅立叶红外光谱(FTIR)、热失重分析法(TGA)、X射线衍射法(XRD)等手段对PMMA/TiO_2复合纳米纤维膜进行了表征,借助扫描电子显微镜(SEM)、全自动比表面积及孔隙分析仪(BET)对该材料的形貌结构、孔隙结构进行分析,最后探讨了所制备的纳米纤维膜的光催化降解能力,综合分析了反应温度对水热法制备PMMA/TiO_2复合纳米纤维膜的形貌、结构及性能的影响。结果表明:水热反应温度为200℃时,得到的PMMA/TiO_2复合纳米纤维膜中TiO_2晶型为纯锐钛矿型,且晶体生长速率较快,比表面积较大,对污染物亚甲基蓝的脱色效率最高,可达98.93%。     

低成本钛合金研究现状与发展趋势

钛合金较高的成本限制了其应用范围,低成本钛合金已成为当前钛合金研究的热点。概述了低成本钛合金国内外的研究现状,着重介绍了宝钛集团研发的低成本钛合金及钛合金的低成本化制备情况,新近研制的BTi31、Ti-3111、BTi-341、BTi-421111、BTi-61111S等低成本钛合金已在汽车、体育休闲等领域获得应用;在钛合金的低成本化制造方面,利用电子束冷床炉熔炼,大量添加返回料,熔炼的扁锭直接轧制板材,显著降低原料成本和加工成本。同时对低成本钛合金的发展方向进行展望,指出今后的研究重点是进一步优化熔炼和加工工艺,提升合金性能水平,提高成材率,拓展应用范围。