非贵金属活化预处理化学镀Ni包覆TiC陶瓷粉体的研究

采用非贵金属活化预处理对TiC陶瓷粉体进行化学镀前处理,预处理后通过常温超声波辅助化学镀方法成功制备了Ni包覆TiC陶瓷粉体,通过场发射扫描电子显微镜(FE-SEM)和能谱(EDS)研究分析了原始TiC粉体、非贵金属活化预处理后TiC粉体和Ni包覆TiC粉体表面形貌,探讨了化学镀Ni包覆TiC陶瓷粉体的生长机理.结果表明:非贵金属活化预处理后TiC陶瓷粉体表面出现了大量的缺陷(台阶),化学镀Ni包覆TiC陶瓷粉体表面Ni层覆盖完整、致密均匀;Ni颗粒的形核、长大和聚集的过程为:化学镀溶液中的反应物在TiC表面缺陷上吸附,发生氧化-还原反应沉积出Ni颗粒;Ni颗粒依附“线条状”突起以“线型”方式长大、弯曲、分叉和聚集,而后缠绕成“胞状”结构,犹如“缠毛线团”.“胞状”结构Ni颗粒不断长大聚集,最后成膜.     

简化预处理辅助化学镀制备Cu包覆TiC复合粉末

研究了一种简化预处理辅助化学镀工艺制备Cu包覆TiC复合粉末.利用场发射扫描电子显微镜和能谱仪分析了原始TiC粉末,预处理之后的TiC粉末,Cu包覆TiC复合粉末的表面形貌和成分,同时也阐述了Cu镀层的生长机理.结果表明,经过简化预处理之后的TiC出现了很多表面缺陷,Cu能够均匀的包覆在TiC颗粒表面.其生长机理如下:经过预处理之后的TiC出现很多表面缺陷,成为化学镀过程中的活性点;化学镀过程中,Cu在TiC表面的各个缺陷处形核长大;Cu与Cu之间相互接触相互作用形成密集的网状结构最终形成致密的Cu镀层.     

碳化钛粉末制备方法的研究进展

碳化钛粉末具有耐高温、耐磨、耐腐蚀、导热导电等优异性能,近年来被广泛应用于制作陶瓷、切削刀具、耐磨材料等领域。当今探索一种高效节能的方法,制备出粒度分布均匀、颗粒团聚小、纯度高、近化学计量的碳化钛粉已成为国内外研究关注的热点。本文介绍了碳化钛的结构和性能;综述了碳化钛粉末的各种制备方法;探讨了近年来国内外对碳化钛粉制备的最新进展。同时,提出了制备碳化钛粉方法中存在的一些问题,并展望了研究和发展的方向。     

Laser cladding of Ti-6Al-4V alloy with TiC and TiC+NiCrBSi powders

Laser cladding of Ti-6Al-4V alloy with TiC and TiC+NiCrBSi powders was carried out, and microstructure, as well as microhardness profile, in the clad layers was examined. The results showed that, in the TiC clad layer, TiC was melted and solidified to form dendrites in the clad zone, and dissolved into the melted Ti-alloy substrate and precipitated to form well-developed dendrites in the dilution zone. With increasing specific laser energy, the dilution effect of the Ti-alloy substrate was enhanced, and the microhardness decreased in both the clad and the dilution zones. In the TiC+NiCrBSi laser clad layers, TiC particles dissolved into the melted Ni-based alloy (binder material) in the clad zone. With increasing specific laser energy, the degree of solution of TiC particles was increased. During cooling, fine spherical particles and dendrites of TiC precipitated from the Ni-based alloy. When the TiC volume fraction increased to more than 50%, clustering of TiC particles was observed in the clad zone. The clustering of TiC particles resulted in a decrease in the homogeneity of the microstructure and microhardness distribution in the clad zone. The dilution zone of the TiC+NiCrBSi clad layers is a mutually melted region of the Ni-based alloy and titanium-alloy substrate and presents a microstructure of dendrites.     

溶胶-凝胶法制备SiO_2包覆型水性铝粉

以正硅酸乙酯(TEOS)为前驱体,采用溶胶-凝胶法制备SiO2包覆型水性铝粉,研究TEOS、水和乙二胺的用量、反应温度和反应时间对包覆效果的影响。结果表明:当TEOS、水、乙二胺和片状铝粉的质量比为1.4:36:0.75:1,反应温度为40℃,反应时间为6h时,所得水性铝粉的缓蚀效率达95.4%,而涂膜光泽度为86.1Gs,仅比溶剂型铝粉的低5.1%。采用扫描电镜、激光粒度分布和红外光谱等手段对SiO2包覆型水性铝粉进行表征,证实SiO2包覆层的存在。     

Oxidation behavior of nano-scaled and micron-scaled TiC powders under air

The oxidation behavior of several batches of TiC nanopowders and micropowders under air has been studied. Using TGA, the oxidation of nanopowders is completed faster and at a lower temperature compared to micropowders. This is related to the higher specific surface area of the nanopowders. Using an amount of powder of about 41.6 mg through DTA, three different exothermic peaks were observed for both kinds of powders. Correlated to the in-situ temperature XRD diffractograms, these peaks were attributed to the following oxidation reactions: i) TiC → TiC_xO_1 − x up to TiO, ii) → Ti₃O₅, and iii) → TiO₂. The same successive oxide phases for nanopowders and micropowders were observed, meaning that the oxidation mechanism is similar in both cases but with a shift of temperature. In this article, the role of the oxygen trapped in the powder and the effect of powder quantity on the oxidation kinetics and on the occurrence of one or three oxidation peaks are discussed.     

真空碳热还原法制备碳化钛粉末

采用XRD、SEM、XRF以及激光粒度分析仪等分析手段,研究真空条件下碳热还原TiO2制备的碳化钛粉末。热力学计算和实验结果表明：真空条件下容易获得碳化钛,且随温度逐渐升高得到的产物顺序为：Magneli相（Ti4O7）、Ti3O5、Ti2O3、TiCxO1-x和TiC。当物料配比为1：3.2-1：6时,在1550℃保温4h的条件下可获得单相TiC粉末;物料配比为1：4和1：5时,产物粉末为标准化学计量的TiC1.0粉末;物料配比为1：4时,得到的产物为单相低杂质超细碳化钛粉末（D50为3.04μm）、SEM观察表明在产物块体表面存在分布均匀、团聚小、结构疏松的结构。     

TiC含量对微波烧结钢结硬质合金组织及性能影响

以铁粉为基体,TiC颗粒为增强相,通过球磨、压制成型,微波烧结制备出TiC钢结硬质合金。结果表明,在1400℃微波烧结时,TiC颗粒与Fe具有良好的润湿性和流动性。随TiC含量升高,合金的晶粒逐渐变得均匀细小,合金的相对密度、显微硬度和抗弯强度均先升高后下降,相对密度和抗弯强度在TiC含量5%时达到最高值,分别为94.61%和1327.20 MPa,显微硬度在TiC含量10%时达到最高值,为760 HV。随TiC含量增加,钢结硬质合金的断裂方式由韧性断裂向脆性断裂过渡。     

Nanocrystalline FeAl matrix composites reinforced with TiC obtained by hot-pressing consolidation of mechanically alloyed powders

Bulk FeAl matrix nanocomposites reinforced with 50%, 30% and 10% of TiC were produced by hot-pressing consolidation of mechanically alloyed nanocrystalline Fe(Al)–TiC composite powders containing different amounts of reinforcement. The powders were compacted at 1000 °C under a pressure of 7.7 GPa. Structural investigations of the consolidated materials revealed that transformation of the Fe(Al) solid solution into FeAl intermetallic had occurred during sintering and that both the matrix and the reinforcement remained nanocrystalline, with the mean crystallite size of about 20 nm. We infer that applying of a high pressure hinders grain growth at elevated temperature. The microhardness of the produced materials is relatively high, ranging between 1363 and 1608 HV0.2, depending on the amount of TiC. The density of the obtained bulk materials is very close to 100% of the “ideal” value and the open porosity is zero. These results as well as structural investigations show that the quality of compaction with preserving of the nanometric grain size of the composite constituents is satisfactory.     

Surface modification of TC4 Ti alloy by laser cladding with TiC+Ti powders

Laser surface cladding was applied on a TC4 Ti alloy to improve its surface properties.Mixed TiC and Ti powders with a TiC-to-Ti mass ratio of 1:3 were put onto the TC4 Ti alloy and subsequently treated by laser beam.The microstructure and composition modifications in the surface layer were carefully investigated by using SEM,EDX and XRD.Due to melting,liquid state mixing followed by rapid solidification and cooling,a layer with graded microstructures and compositions formed.The TiC powders were completely dissolved into the melted layer during melting and segregated as fine dendrites when solidified.The inter-dendritic areas were filled with fine α' phase lamellae enrich in Al.Mainly due to the reduced TiC volume fraction with increasing depth,the hardness decreases with increasing depth in the laser clad layer with a maximum value of HV1400,about 4.5 times of the initial one.     

Effect of starting powders size on the Al2O3–TiC composites

Al₂O₃–TiC composites with a content of 30 wt% TiC with various size of starting powders were manufactured by hot pressing. The Vickers hardness, bending strength and fracture toughness were studied. The experiment results show that the starting powder size has a significant effect on the properties of the Al₂O₃–TiC composites. The maximum bending strength of the submicron Al₂O₃ with the fine TiC powders addition is 712 MPa, while the maximum fracture toughness of the same Al₂O₃ matrix with the large TiC powders addition is 6.5 MPa m^1/2.     

Effect of femtosecond laser pretreatment on wear resistance of Al2O3/TiC ceramic tools in dry cutting

A femtosecond pulsed laser (pulse width: 120 fs, wavelength: 800 nm and repetition rate: 500 Hz) was used for the pretreatment on the rake face of Al₂O₃/TiC ceramic cutting tools. The evolution of surface morphology of pretreated cutting tools irradiated with different pulse energies was measured by scanning electron microscope (SEM) and atomic force microscope (AFM). Dry cutting tests were carried out with these pretreated tools and conventional tools on hardened steel. The effect of pulse energy on the wear resistance of these pretreated tools was investigated. Results show that the cutting forces have no significant difference between laser pretreated tools and the conventional tool; the cutting temperatures of laser pretreated tools were slightly reduced compared with the conventional tool. Meanwhile, we found that the laser pretreated tools increased the adhesions of chips on the rake face, but they can significantly improve the wear resistance of the rake face; and laser pulse energy was found to have a profound effect on the wear resistance of the laser pretreated tools.     

Preparation of cemented carbide diamond films by gaseous boronizing pretreatment combines with self-assembly seeding process

In order to enhance the adhesion of cemented carbide diamond film and improve the cutting performance of cemented carbide diamond coating tools. This paper was the first to combine gaseous boronizing pretreatment with self-assembly seeding process to prepare diamond films on cemented carbide substrate. It not only eliminated the negative influence of cobalt (Co), but also improved the nucleation density of diamond. The gaseous boronizing pretreatment completed the boronation of the cemented carbide in a short time and obtained the CoWB phase which effectively prevented the diffusion of Co. By application of a self-assembly seeding process with the help of [2-(Methacryloyloxy) ethyl] trimethylammonium chloride (TMAEMC) highly improved the colloidal stability of nanodiamond (ND) particles. When the concentration of TMAEMC was 5 × 10⁻⁶ mol/l, the nucleation density of diamond was the highest. Rockwell indentation shows that the combination of gaseous boronizing pretreatment and TMAEMC self-assembly seeding process significantly improved the film-substrate adhesion. The reciprocating friction test shows that the diamond films prepared by this method had low friction coefficient and excellent wear resistance. Therefore, gaseous boronizing pretreatment combines with self-assembly seeding process is an effective way to achieve strong adhesion and high cutting performance of industrial diamond coating tools.     

Effect of high energy ball milling on displacement reaction and sintering of Al−Mg/SiO2 composite powders

High-energy ball milling and low temperature sintering were successfully employed to fabricate a metal matrix composite of Al reinforced with Al₂O₃ particulate. Nano- and/or submicro-sized SiO₂ particles embedded in an Al−Mg matrix particle can be obtained by high-energy ball milling. No new phases were found in the high-energy ball milled Al-0.4 wt.% Mg-14 wt.%SiO₂ powder. Milling of the Al−Mg−SiO₂ powder increased the sintering rate and decreased the sintering temperature. The hardness ofthe sintered Al−Mg−SiO₂ composite using the ball-milled powder was about twice that of a sintered composite using a mixed powder due to the fine and homogeneous distribution of Al₂O₃ particles formed by the displacement reaction between Al and SiO₂ during sintering.     

Study on activated W powders by chemical activation pretreatment and its sintering behavior

In this study, tungsten (W) powders were subjected to chemical activation pretreatment by immersion into an aqueous solution of hydrofluoric acid and ammonium fluoride, and then were reinforced with an ultrasonic wave at room temperature. A field emission electron microscope was utilized to observe the surface topography of the original W and simply pretreated W. The results showed the surface of the as-pretreated was more rough and had more surface defects than original W. Both as-received and pretreated W powders were sintered under identical conditions. Their sinterability was compared and analyzed in terms of their densification, hardness and microstructure. It was concluded that increased surface area and defects which facilitate atomic mobility during the sintering process were responsible for the improved densification.     

TiC含量对TiC/Cu-Al_2O_3复合材料热变形行为的影响

采用真空热压-内氧化烧结法制备TiC体积分数分别为0、10 vol%、20 vol%的TiC/Cu-Al2O3复合材料,观察和分析了其显微组织、测试和分析了其性能;利用Gleeble-1500D热力模拟试验机,研究了3种复合材料在变形温度为450~850℃,应变速率为0.001~1 s-1条件下的热变形行为。结果表明,复合材料的相对密度在97.1%以上,随着TiC含量的增加,其导电率下降、硬度升高。TiC/Cu-Al2O3复合材料的真应力-真应变曲线主要以动态再结晶机制为特征,峰值应力随变形温度的降低或应变速率的升高而增加;高温变形条件下TiC/Cu-Al2O3复合材料流变应力本构方程可以用双曲线正弦方程和Z参数描述;其热变形激活能分别为163.939 k J/mol(0 vol%TiC)、164.142 k J/mol(10 vol%TiC)和210.762 k J/mol(20 vol%TiC)。     

五甲基槲皮素预处理对大鼠心肌细胞缺氧复氧损伤保护作用的机制研究

目的: 探讨五甲基槲皮素(PMQ)预处理对大鼠心肌细胞缺氧/复氧(A/R)损伤的保护作用及其线粒体功能的影响。方法: 原代培养SD大鼠乳鼠心肌细胞,经终浓度分别为10、30、100 μmol/L PMQ预处理 24 h 后,制作A/R损伤,检测培养液中乳酸脱氢酶(LDH)活性、MTT法检测细胞存活率、流式细胞法检测线粒体膜电位和细胞凋亡情况、线粒体肿胀法检测各组心肌细胞线粒体通透性转换孔(mPTP)开放情况。结果: 不同剂量PMQ (10、30、100 μmol/L)预处理 24 h 后可剂量依赖性地降低LDH活性、增加细胞存活率、减少细胞凋亡(P<0.05 或P<0.01);30、100 μmol/L PMQ预处理 24 h 后,线粒体膜电位更为稳定、mPTP开放减少(P<0.05 或P<0.01)。结论: PMQ预处理 24 h 后,可产生药理性延迟保护作用,机制与其稳定线粒体膜电位、抑制mPTP开放,进而减少细胞凋亡有关。     

Al-Ti-C体系中Al对合成TiC的影响

通过压块在不同温度下的烧结反应,借助DTA、XRD分析手段,研究了Al-Ti-C体系中Al对合成TiC的影响。结果表明,烧结后的压块显示出典型的自蔓延高温合成特点。无Al的条件下,Ti很难与C直接反应生成TiC,液态铝可作为很好的扩散介质,并且Al是通过生成Al3Ti而参加自蔓延高温反应。当Ti/C原子比为1,烧结温度为1000℃,压块中的Al量在10wt%左右时,Al-Ti-C体系能较为完全地生成TiC。     

The effects of gaseous pretreatment and oxide sintering on oxidation of Ti-4.32 wt.%Nb alloy

Oxidation kinetics in either air or oxygen of prenitrided Ti-4.32 wt.% Nb alloy are investigated in the temperature range of 900–1200°C. Based on X-ray and electron microprobe analyses, thermogravimetric measurements, microhardness data, and sintering experiments, a quantitative oxidation model is developed to explain the gas-metal reactions. Temperature cycling experiments, in the temperature range of 900–1200°C and for a 12-hr duration, are performed in an attempt to reduce the oxidation rates of the alloy in air or oxygen. The oxidation resistance of nitrogen pretreated alloy is comparable to that in air and it is considerably higher than in oxygen alone.Presently on academic leave at Max-Planck-Institut für Metallforschung, Institut für Werkstoffwissenschaften, Stuttgart, Bundesrepublik Deutschland.