TiN和TiC涂层对碳氢燃料裂解结焦的影响

采用化学气相沉积(CVD)法,在304型不锈钢管道内壁分别沉积了TiN和TiC涂层,并采用SEM、EDS、金相显微镜和热冲击等方法对其进行了性能表征和测试。结果表明,两种涂层均匀致密,TiN涂层厚度为7.24μm,TiC涂层为11.52μm,且均具有良好的结合强度。为评价涂层抑制结焦效果,选用某碳氢燃料A,采取程序升温法进行超临界裂解实验,当反应管前后压差超过1 MPa时停止实验,结果表明,304空白管由于严重结焦,在650℃只运行了180 s;而TiC和TiN涂层管分别在780℃运行了275和1560 s。通过压差、产气组成和积炭微观形貌的综合分析表明,TiN、TiC涂层均呈现出优良的抑焦效果,且TiN涂层抑焦效果更优。     

稀土对AlTiC细化剂组织及细化效果的影响

应用自蔓延高温合成法制备出含稀土及不含稀土两种AlTiC细化剂. 应用扫描电镜及X射线衍射等手段分析了中间合金及细化剂的成分、组织和形貌. 结果表明: 稀土对反应合成TiC微细颗粒具有重要的促进作用, 添加稀土明显加快反应速度; 在AlTiCRE细化剂中, 由于稀土的作用, 改变了TiAl3和TiC的形态和分布, 减小了TiC的聚集倾向, 细化了TiC颗粒尺寸, 从而增加了形核基底数. AlTiCRE细化晶粒的效果优于AlTiC, 而且稀土还具有明显细化枝晶组织的作用.     

Dry sliding wear characteristics of in situ synthesized Al-TiC composites

Abstract

Aluminum-based composites containing 0.06, 0.09, 0.12 fractions of in situ-synthesized TiC (Titanium carbide) particles have been prepared through in-melt reaction from Ai–SiC–Ti system following a simple and cost-effective stir-casting route. The TiC forms by the reaction of Ti with carbon which is released by SiC at temperatures greater than 1073 K. However, some amount of titanium aluminide (Al₃Ti) is also formed. The formation of TiC has been confirmed through X-ray diffraction studies of the composite. The hardness and tensile strength have been found to increase with increasing amount of TiC. The friction and wear characteristics of the composites have been determined by carrying out dry sliding tests on pin-on-disc machine at different loads of 9.8 N, 19.6 N, 29.4 N, 39.2 N at a constant sliding speed of the 1 m/s speed. The wear rate i.e. volume loss per unit sliding distance has been found to increase linearly with increasing load following Archard’s law. However, both the wear rate and friction coefficient have been observed to decrease with increasing amount of TiC in the composite. This has been attributed to (i) a relatively higher hardness of composites containing relatively higher amount of TiC resulting in a relatively lower real area of contact and (ii) the formation of a well-compacted mechanically mixed layer of compacted wear debris on the worn surface which might have inhibited metal–metal contact and resulted in a lower wear rate as well as friction coefficient.     

Dual functions of TiC nanoparticles on tribological performance of Al/graphite composites

In this study, the effect of TiC nanoparticles as a reinforcement on the mechanical and tribological properties of Aluminum-based self lubricating composite was investigated. The microstructure, relative density, hardness, and tribological properties of Al/graphite and Al/TiC/graphite composites were examined as a function of graphite content. The tribo-surfaces of the samples were analyzed using SEM and EDS elemental mapping. The results indicated that the addition of TiC nanoparticles not only decreased the wear rate and coefficient of friction of the composites, but also facilitated the formation of a stable graphite layer at longer sliding distances and high sliding velocities by forming a durable graphite/TiC composite on the tribo-surface. Therefore, the stability of graphite layer can be considered as a possible cause for decrease in wear rate of the Al/TiC/graphite composite.     

Study of the interfacial structure and chemistry of CVD κ-Al2O3/TiC multilayer coatings

This article describes the interfacial regions in CVD grown TiC/κ-Al₂O₃ multilayers. A number of microanalytical techniques were used including HREM, EDX and EELS. Occasionally, the first 50 nm of the alumina layers deposited on the intermediate TiC layers grew as a cubic alumina, heavily faulted, containing small amounts of sulphur (S), maybe as a stabiliser. The presence of slightly rounded TiC (111) facets may act as preferred nucleation sites for the cubic Al₂O₃ phase, with a ‘cube on cube’ orientation relationship. In this way the nucleation of κ-Al₂O₃ is less favourable. After some tens of nanometres the cubic phase cannot be stabilised any longer and the layer continues to grow as κ-Al₂O₃. A number of observations point towards the reaction zone (RZ) being η- and/or γ-Al₂O₃. The diffraction work and the FFT analysis of the HREM images show that the RZ is an fcc phase with a=7.9 Å, which matches with η- and γ-Al₂O₃. The EELS Al fine structure indicate more tetrahedral Al ions than in κ-Al₂O₃, as in η- and γ-Al₂O₃. The RZ contains small amounts of S, as has been reported for γ-Al₂O₃. Due to the structural similarities between η- and γ-Al₂O₃ it was not possible to determine which of these cubic phases is present in the RZ.     

稀土对TiC基金属陶瓷耐磨堆焊材料组织性能的影响

应用扫描电镜、透射电镜等测试手段和冲击试验,磨损试验,研究了TiC基金属陶瓷堆焊材料中加入稀土氧化物,对堆焊材料的组织,界面相结合,显微硬度,冲击韧性和磨损性能的影响,初步探讨了稀土氧化物改善界面显微结构,提高的胎体金属韧性的作用机制,研究结果表明,稀土氧化物能细化堆焊层胎体金属组织,消除胎体金属的缺陷,细化胎体金属断口韧窝并使撕裂棱数量增加,提高堆焊层冲击韧性和塑性,促使金属基陶瓷与胎体金属界面成多晶过渡区和局部非晶态物相,提高界面的结合强度,稀土氧化物的加入对胎体金属显微硬度的影响不大,但能显著提高堆焊层干摩擦磨损状态下的耐磨性,具有一定的减摩作用。     

Surface and interface of Ti(film)/SiC(substrate) system: a soft X-ray emission and photoemission electron microscopy study

We have conducted a soft X-ray emission spectroscopy (SXES) and a photoemission electron microscopy (PEEM) study on the heat-treated Ti/4H–SiC system. This spectro-microscopy approach is an ideal surface and interface characterization techniques due to the non-destructive nature of SXES and the real-time surface imaging of PEEM.

The Si L_2,3 and C K soft X-ray emission spectra, which reflect Si (s+d) states and C p states, respectively, revealed formations of Ti₅Si₃ and TiC in the reacted interfacial region of Ti (50 nm)/4H–SiC(0 0 0 1) sample.

The surface of the Ti films on 4H–SiC samples during heat-treatment up to 850 °C was investigated by PEEM. The variation in brightness in the image of the sample was attributed to the surface deoxidation in the early stage of the treatment and to the formation of reacted region at the later stage. The darkening of the surface could be attributed to the formation of TiC and/or excess C atoms that could have migrated to the surface.     

Silver macro‐texture substrates fabricated by plasma selective etching for surface‐enhanced Raman scattering

We have demonstrated a novel method to generate the nanostructured substrate that shows a large enhancement with a spatially uniform enhancement factor of approximately 10⁶ in surface enhanced Raman scattering (SERS). The substrates are fabricated using plasma selective etching. First, the Al₂O₃–TiC template which contains mixed Al₂O₃ and TiC grains with the diameters of ~400 nm is selected as a base plate. The Al₂O₃ and TiC grains have different physical properties, such as hardness, which corresponds to different etching rate in a plasma gas. Then, the Al₂O₃–TiC substrate is selectively etched to generate a random macro‐texture (MT) with different depths using the plasma of mixed gas of Ar and C₂H₄. Third, the MT substrate is deposited with a silver film (Ag). We further demonstrate that by varying the thickness of Ag layer, the EF is different which is confirmed by the plasmonic localized electric fields calculations using finite difference time domain. Finally, we combine this novel Ag MT substrate with ultrathin dielectric film, and the prepared substrates are coated with a 10 Å ta‐C film. The 10 Å ta‐C film can protect the oxygen‐free Ag in air and prevent Ag ionizing in aqueous solutions. More importantly, the ultrathin ta‐C can release the strongest plasmonic electric field to the outside of ta‐C layer and get a higher electric field than the uncoated Ag substrate. We expect that this method has more potential applications in analytic assays using SERS technology. Copyright © 2012 John Wiley & Sons, Ltd.     

Comparative study of microstructure and tribological behavior of TiC/a‐C:H and a‐C:H coatings in a sand‐dust environment

TiC/a‐C:H and a‐C:H nanocomposite coatings were prepared on AISI 440C steel substrates using magnetron sputtering process. A comparative study was made on their composition and microstructure by Raman spectroscopy and high‐resolution transmission electron microscopy (HRTEM). The tribological properties of two types of carbon‐based coatings were investigated by pin‐on‐disc tribometer under the sand‐dust conditions concerning the influence of applied load, amount of sand and sand particle sizes. The results show that these carbon‐based coatings exhibited high tribological performance with low friction coefficient and wear rate under the sand‐dust environments. However, the TiC/a‐C:H coatings exhibit relatively higher fluctuant friction coefficient as well as higher wear rate in comparison with the a‐C:H coatings under sand‐dust environments. The formation of nanocrystalline hard TiC phase distributed in amorphous carbon matrix decreased the residual stress but significantly increased the hardness and Young's modulus of TiC/a‐C:H coatings, and consequently caused a relatively higher abrasive and fatigue wear loss under the sand‐dust conditions. Copyright © 2010 John Wiley & Sons, Ltd.     

反应烧结Ti_3SiC_2/TiC复合材料摩擦磨损性能研究

采用无压反应烧结技术制备Ti3SiC2/TiC复合材料,利用XRD-7000型衍射仪、INSTRON-1195型电子万能试验机、JSM-6700F型扫描电子显微镜、HST-100型摩擦磨损试验机对Ti3SiC2/TiC复合材料烧结试样的相组成、抗弯强度、断口显微形貌和载流摩擦磨损性能进行了研究.结果表明:在1550℃下可制备得到均匀致密的Ti3SiC2/TiC复合材料;随着试样中TiC含量的增加,复合材料抗弯强度逐渐增大;当TiC质量分数达到18%左右时,抗弯强度明显增加,摩擦系数趋于稳定,磨损率快速下降;电流强度是Ti3SiC2/TiC复合材料摩擦磨损性能的主要影响因素,随着试验电流强度的增强,摩擦系数和磨损率明显增大;同时在摩擦表面生成一层熔融状氧化膜(非载流:SiO2、TiO2和FeTiO3载流:FeTiO3和Fe2.35Ti0.65O4),主要磨损形式为电弧烧蚀和氧化磨损.