激光熔覆TiC陶瓷涂层的组织和摩擦磨损性能研究

采用激光熔覆技术在TC4合金表面上制备了TiC陶瓷涂层,分析了熔覆层的微观组织,测试了熔覆层的硬度和摩擦磨损性能。结果表明:TiC激光熔覆层分为熔覆区和稀释区两个区域,熔覆区未受到基底的稀释,由TiC颗粒和TiC树枝晶组成;稀释区受到了基底的稀释,由TiC树枝晶和钛合金组成;TiC激光熔覆层的显微硬度在HV700~1500之间,明显地改善了TC4合金表面的摩擦和磨损性能。     

CVD TiC/alumina multilayer coatings grown on sapphire single crystals

Multilayers of TiC/α-Al₂O₃ consisting of three (1 μm thick) alumina layers separated by thin (∼10 nm) oxidized TiC layers have been deposited onto c-, a- and r-surfaces of single crystals of α-Al₂O₃ by chemical vapour deposition (CVD). The aim of this paper is to describe and compare the detailed microstructure of the different multilayer coatings by using transmission electron microscopy (TEM).The general microstructure of the alumina layers is very different when deposited onto different surfaces of α-Al₂O₃ single crystal substrates. On the c- and a-surfaces the alumina layers grow evenly resulting in growth of single crystal layers of TiC and alumina throughout the coating. However, when deposited on the r-surface the alumina layers generally grow unevenly. No pores are observed within the alumina layers, while a small number of pores are found at the interfaces below the TiC layers. The TiC and alumina layers grow epitaxially on the c- and a-surface substrates. On the r-surface, epitaxy is present only at some rare locations. The TiC layers were oxidized in situ for 2 min in CO₂/H₂ prior to the alumina layer deposition. For all three samples chemical analyses show that the whole TiC layer is oxidized. On the c- and a-surfaces the TiC layer was oxidized to an fcc TiCO phase. On the r-surface the oxidation stage resulted in a transformation of the initially deposited fcc TiC to a monoclinic TiCO phase, which appears to be a modified TiO structure with a high carbon content.     

Laser embedding of TiC particles into the surface of phosphor bronze‐bearing material

A carbon film containing 5% TiC particles is formed on a pre‐prepared bronze surface prior to laser treatment. The carbon film provides increased absorption of the incident laser beam and hosts TiC particles with a uniform distribution at the workpiece surface. Optical and scanning electron microscopy are used to examine the metallurgical and morphological changes in the laser treated layer. Micro‐hardness of the laser‐treated surface is measured, and the residual stress formed in the surface vicinity is measured using the X‐ray diffraction technique. It was found that a dense layer with fine grains was formed in the laser‐treated layer. The micro‐hardness of the laser‐treated surface increases almost three times compared with the base material hardness. The presence of a dense layer and the formation of Cu₃N in the surface region contribute to the hardness enhancement at the surface. Copyright © 2012 John Wiley & Sons, Ltd.     

Nanocomposite TiC/a-C：H film prepared on titanium aluminium alloy substrates by PSII assistant MW-ECRCVD

Thin films of titanium carbide and amorphous hydrogenated carbon have been synthesized on titanium aluminium alloy substrates by PSII assisted MW-ECRCVD with a mirror field. The microstructure, chemical composition and mechanical property were investigated. Using XPS and TEM, the films were identified to be a-C：H film containing TiC nanometre grains （namely, the so-called nanocomposite structure）. The size of TiC grains of nanocomposite TiC/DLC film is about 5 nm. The nanocomposite structure has obvious improvement in the mechanical properties of DLC film. The hardness of a-C：H film with Ti is enhanced to 34 G Pa~ while that of a-C：H film without Ti is about 12 G Pa, and the coherent strength is also obviously enhanced at the critical load of about 35N.     

稀土和钛对奥氏体中锰钢的变质作用

通过热力学计算、光学显微镜、扫描电子显微和透射电子显微镜观测及微观成分分析证明：ＲＥ（Ｃｅ）可加剧奥氏体中锰钢凝固时的成分过冷现象，促进树枝晶的发展、熔断、游离和增殖、提高结晶形核率、有效地细化奥氏体晶粒；Ｔｉ和Ｃ可以直接在液相中反应形成ＴｉＣ，并可作为渗碳休珠结晶核心，使一次渗碳体和共晶渗碳体发生粒化和细化，从而避免连续网状碳化物的形成。     

Structural and Microstructural Evolution During Pyrolysis of Hybrid Polydimethylsiloxane-Titania Nanocomposites

The evolution during pyrolysis of hybrid polydimethylsiloxane-titania nanocomposites has been studied as a function of the ratio between polysiloxane and titania phases. The xerogels, prepared by the sol–gel process starting from diethoxydimethylsilane and titanium isopropoxide, have been heated under argon atmosphere and the evolution with temperature has been followed by infrared and ²⁹Si solid state nuclear magnetic resonance spectroscopies, thermal analyses, X-ray diffraction, N₂ sorption measurements and scanning electron microscopy. Below 800C, the polymer-to-ceramic conversion takes place at different temperatures with changing the titania content. The stability of Si–C bonds in polydimethylsiloxane networks depends on the metal oxide amount. The high reactivity of titanium atoms towards the Si–C bonds produces Si–C bond cleavage with mild thermal treatments and in the case of 30 mol% TiO₂, leads to the ceramization of the hybrid nanocomposite at 500C. Decreasing the titania load, a shift towards higher temperatures to complete the polymer-to-ceramic conversion is observed. The structural rearrangement of the siloxane moiety produces mesoporous and microporous materials, depending on the composition; in the case of 10 and 20 mol% TiO₂ content, the samples present high specific surface area up to 1200C.The crystallization process begins at 1000C and the phase evolution depends on the composition. The phase analysis obtained from XRD spectra shows that different crystalline oxide and oxycarbide phases develop during the thermal process, as a function of the amount of available carbon, ultimately leading to the preferential crystallization of titanium carbide. Between 1000 and 1600C the amorphous silicon oxycarbide phase undergoes a continuous structural evolution caused by the decrease of carbon content in the phase, leading to almost pure silica at 1600C.     

Microstructural analysis of TiC reinforced ferrous surface composites processed by accelerated electron beam irradiation

The present study aims to analyze microstructures of TiC reinforced ferrous surface composites processed by accelerated electron beam irradiation. Two kinds of powder/flux mixtures, i.e., TiC and (Ti + C) powders with 40 wt% of CaF₂ flux, were deposited evenly on an AISI 304 stainless steel substrate, which was then irradiated with electron beam. TiC agglomerates and pores were found in the surface composite specimen processed by irradiation of TiC powders because of insufficient melting of TiC powders. In the specimen processed by irradiation of Ti and C powders having lower melting points than TiC powders, a lot of large TiC carbides were precipitated in the melted region, together with a few TiC agglomerates or pores. This indicated the more effective TiC precipitation obtained from the melting of Ti and C powders, instead of TiC powders. The hardness of the surface composite layer was about two times higher than that of the AISI 304 substrate mainly due to the precipitation of TiC carbides.     

Surface characterisation of TiCxN1 − x coatings processed by cathodic arc physical vapour deposition: XPS and XRD analysis

The properties of titanium carbonitride (TiCN) can be controlled by maintaining the C―N ratio within the coating to a certain level. An experimental study was carried out to vary the composition and properties of TiCN using cathodic arc physical vapour deposition (CAPVD). The substrate used was tungsten carbide (WC-6Co), which was prepared in-house through a powder metallurgy process. In order to form the TiC_xN_1 − x coatings, titanium (Ti) was used as the cathode, while methane (CH₄) and nitrogen (N₂) gases were used as sources for C and N, respectively. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) were used to investigate the composition, chemical state, and bonding structure of the deposited coatings. The results show that the composition, intensity of elements, lattice parameter, and d-value of TiC_xN_1 − x coatings were successfully varied by controlling the CH₄ fraction (CH₄/N₂ ratio). With the increase in CH₄ fraction, the intensity of C and N within the TiC_xN_1 − x coatings increased and decreased, respectively. Consequently, the C―Ti and C―N bonds were increased and N―Ti bonds were decreased.     

TiC颗粒含量及尺寸对原位TiCp／Fe复合材料耐磨性的影响

研究了ＴｉＣ颗粒的含量不寸对原位ＣｔＣｐ／Ｆｅ复合材料耐磨料磨损性能的影响。结果表明：当ＴｉＣ颗粒的尺寸为５．０μｍ时,复合材料的耐磨性随ＴｉＣ颗粒含量的增加而提高;在ＴｉＣ颗粒的含量为１０．１％,尺寸小于５．０μｍ时,复合村料的耐磨性随尺寸的增大而提高;而当颗粒尺寸大于５．０－μｍ后,耐磨性因ＴｉＣ颗粒的剥落反而下降,分析认为,复合材料的耐磨性与其组织中ＴｉＣ颗粒的间距密切相关,间距赵小,复合材     

应变对析氢反应催化剂TiC2性能影响的研究

应变工程是一种有效地用来调整原子薄膜材料的电子、磁性和光学性能的策略.利用第一性原理计算,我们表明应变也可以有效地调节Ti C₂的析氢反应(HER)的催化活性,这是电解水电化学制氢所必需的.我们主要考虑0-8%范围的拉伸应变,研究发现,在25%的氢覆盖率下双轴拉伸比单轴拉伸能更有效的提高HER活性,但b方向拉伸后的Ti C₂结构具有更高的氢最大覆盖率,且b方向的拉伸应变对不同氢覆盖率的Ti C₂单层片的催化性能都有很大的提高.电子结构计算表明,拉伸应变可以激活相对惰性的内部价电子,从而引起体系的失稳和催化活性的提高.在本工作中获得的见解可能有助于利用应变作为一种有效手段来提高二维材料的催化活性,并探索更有效地调整其电子结构和催化活性的新方法.