纳米Y2O3/钴基合金激光熔覆层的组织

利用5 kW CO2激光器,在Ni基高温合金表面,熔覆纳米稀土氧化物(Y2O3)/钴基合金复合材料,制备了涂层.利用光学显微镜、扫描电镜及透射电镜分析了熔覆层的组织结构.结果表明: 熔覆层的主要相组成为γ-Co,ε-Co,Cr23C6和Y2O3;加入纳米Y2O3,凝固组织由细长的柱状树枝晶转变为较短的树枝晶;纳米Y2O3含量增大至1%时整个断面获得等轴晶组织;纳米Y2O3作为异质形核的核心,细化了组织;纳米Y2O3在熔覆层中分布不均匀,促进了γ-Co向ε-Co的转变;熔覆层的亚结构为堆跺层错.对熔覆层等轴组织形成机制进行了分析.     

含镧Fe-B激光熔覆层的摩擦学性能研究

为研究稀土对Fe—B激光熔覆层摩擦学性能的影响，采用自配Fe，B4C，硅铁稀土混合粉末在45^#钢基体上进行激光熔覆实验，并在HQ-1摩擦磨损实验机上对不同稀土含量的熔覆层进行摩擦磨损实验。结果表明：含适量稀土熔覆层的耐磨性得到很大提高，在本实验条件下，硅铁稀土加入量最佳值为4％～5％，此时熔覆层耐磨性提高25．8％，当硅铁稀土加入量过多时，熔覆层耐磨性反而降低，甚至低于不加稀土时的耐磨性。通过对磨斑表面硼元素(1s电子轨道)的XPS图谱分析表明，熔覆层中铁与硼主要以Fe2B相存在。磨损表面部分镧元素被氧化，生成La2O3。     

La2O3对铁基合金激光熔覆层耐蚀性能的影响

通过扫描电镜(SEM)观察和X射线衍射(XRD)分析, 研究了不同稀土加入量对铁基合金激光熔覆层组织形貌、相组成的影响; 通过极化曲线和交流阻抗谱(EIS)的测量, 研究了熔覆层的电化学性能. 结果表明, 加入稀土细化了熔覆层的晶粒, 使组织趋向均匀; 同时降低了材料的极化电位, 减小了极化电流密度, 降低了熔覆层在腐蚀性介质中的溶解速度, 随着稀土加入量的增加, EIS曲线低频区感抗弧逐渐减小, 容抗弧逐渐增大, 增强了熔覆层表面在交变电流下形成钝化膜的能力. 腐蚀失重实验结果表明, 加入稀土改善了熔覆层表面钝化膜的抗剥落能力, 不同程度上减轻了材料的腐蚀失重, 提高了熔覆层的耐腐蚀能力.     

纳米Y_2O_3对14CrSiMnV硬质合金涂层耐磨耐热氧化性影响

利用激光熔覆表面复合纳米Y_2O_3颗粒的14CrSiMnV铁基合金粉体,制备了14CrSiMnV硬质合金钢涂层。研究了纳米Y_2O_3对涂层微观结构、微观硬度、耐热以及耐滑动摩擦的影响。结果表明:在合金涂层成型过程中,添加小于1%(质量分数)纳米Y_2O_3可以促进涂层组织中的树状晶向等轴晶转变,且减少涂层在600℃高温条件的氧化腐蚀现象,改善表面滑动摩擦的塑性剥离,从而使涂层拥有更好的耐热性能和耐滑动摩擦性能。     

稀土对真空熔结Ni基自熔性合金涂层组织结构的影响

采用真空熔结的方法在45^#钢母材上获得了稀土NiCrBSi自熔性合金涂层，借助X射线衍射、SEM及EDX研究了涂层截面的微观组织、相结构及涂层与母材界面附近的组织特征，讨论了稀土的加入对涂层组织的影响。结果表明：真空熔结NiCrBSi合金涂层为Ni基固溶体和分布在固溶体上块状、球状和针状的CrB、Fe3C、Cr7C3等硬化相组成，涂层与母材为良好的冶金结合。添加稀土元素的NiCrBSiRE合金涂层消除了针状组织，析出了新的硼化物Ni3B和碳化物Cr23C6，硬化相得到了进一步的球化；RE还阻碍了Ni、Cr、Si等原子向母材的扩散和Fe原子向涂层的扩散，减轻了Fe原子对涂层的“稀释”作用，保证了涂层的化学组成。     

纳米CeO2对Ni基合金激光熔覆层的组织与耐蚀性的影响

利用5 kWCO2激光器,在Q235低碳钢表面熔覆微米或纳米CeO2/Ni基合金复合材料,制备了涂层。利用光学显微镜、扫描电镜和X射线衍射仪分析了熔覆层的组织和相结构,利用CHI604b型电化学分析仪测定了熔覆层的阳极极化曲线。结果表明：加入微米CeO2的熔覆层组织明显细化,并出现大量的等轴晶,加入纳米CeO2的熔覆层等轴晶更加细小,并且组织致密;加入微米CeO2后Ni基合金熔覆层主要相结构的为γ-Ni,Cr23C6,CeNi3,γ-CeO2,Ni3Si和Ni3B等相,加入纳米CeO2的熔覆层中出现γ-Ni,Cr23C6,CeNi3,CeNi5,Ni3Si和Ni3B等相;当纳米CeO2的添加量为1.5%时,熔覆层的耐蚀性能大幅度提高,并且形成相对稳定的钝化膜。     

耐液锌腐蚀的铬碳化物覆层形成过程中稀土还原剂的作用

研究了热反应沉积扩散法形成耐液态锌腐蚀的铬碳化物覆层过程中稀土还原剂对覆层厚度,熔盐性质的影响。在９５０℃、含１５％Ｃｒ２Ｏ３硼砂体系中加入８％稀土铁镁合金,具有罗好的铬碳化物覆层形成能力,流动性好,老化周期长,工艺性能良好。     

含稀土复合变质剂对铸态锰钢性能的影响

研究了含稀土复合变质剂对铸态锰钢的组织及性能的影响. 铸态锰钢经变质处理后, 得到了在奥氏体基体上弥散分布有孤立碳化物的组织, 该铸态锰钢具有初始硬度高, 加工硬化能力强, 足够的冲击韧性和良好的抗磨性能.     

20Cr2Ni4A钢经稀土渗碳和传统工艺渗碳后表层组织的观察与分析

采用ＴＥＭ微观组织观察，发现２０Ｃｒ２Ｎｉ４Ａ钢经稀土渗碳直接淬火后，渗碳层的过共析区组织是在板条马氏体为主的基体上弥散分布着细小颗粒状碳化物；而传统工艺渗碳处理后则是基体为孪晶马氏体和更细小的残留碳化物。两种工艺所形成的不同类型的基体与碳化物形成过程有关。     

中空Ta_2O_5/TiO_2复合光催化剂的可控氧化制备及性能

以钛粉、钽粉为原料,炭黑作为反应性模板,通过熔盐法在炭黑表面原位生长了TaTiC_2纳米碳化物涂层,并以所得TaTiC_2/C复合物为碳化物前驱体,再经可控氧化制备出中空Ta_2O_5/TiO_2复合光催化剂。采用X射线粉末衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、紫外-可见(UV-Vis)漫反射(DRS)及N2物理吸附等手段对所制备的光催化剂进行形貌、显微结构及孔结构表征。以高压汞灯为紫外光源,以亚甲基蓝为目标降解物,通过光催化降解实验评价中空Ta_2O_5/TiO_2复合光催化剂的光催化活性。结果表明,熔盐法生长碳化物涂层厚度均匀(20~30 nm),碳化物主要以TaTiC_2晶相存在且具有纳米级的颗粒尺寸。中空Ta_2O_5/TiO_2复合光催化剂同时具有200 nm左右的中空大孔结构及壳层10 nm左右的介孔结构。中空大孔和介孔的存在提高了所制备催化剂对亚甲基蓝的吸附能力。此外,TiO_2与Ta2O5通过电子能带结构的耦合,有效提高了光生电子和空穴的分离效率,从而显著提高了光催化活性。nTi∶nTa=2.5∶1.5时,相应的中空Ta_2O_5/TiO_2复合光催化剂表现出最佳的光催化活性,对亚甲基蓝的紫外光催化降解率高达97%。     

Electrodeposition and characterization of chromium–tungsten carbide composite coatings from a trivalent chromium bath

The electrodeposition of chromium from a trivalent chromium bath has been described in this work. The electrocomposite coatings of chromium with hard abrasive particles were investigated. The chromium–tungsten carbide (Cr? WC) composite coatings were obtained by suspending different concentrations of WC particles in a trivalent chromium plating solution to improve the various properties of the chromium deposit layers. The effect of operating conditions on the deposit layers has been studied. On the other hand, the effect of non‐ionic polymeric surfactant [nonyl phenol ethoxylate with 12 units of ethylene oxide (NPE)] as an additive in enhancing the incorporation of the WC ceramic particles in the chromium metal matrix was investigated. It was found that the co‐deposition of the WC ceramic particles depends on the concentration of the additive and its efficiency in reducing the surface tension of the electroplating solution. The mechanism of incorporation of WC particles into a growing deposit was suggested and discussed in view of the zeta potential and degree of wetability of WC particles in the plating solution. Furthermore, the adsorption behaviour of the additive on WC particles was analysed according to the Frumkin isotherm. The surface morphology and the distribution of WC in the chromium metal matrix were investigated. The properties of the deposit layers, hardness, corrosion resistance and wear resistance were determined and compared with free chromium deposits. The test results reveal that the Cr? WC deposit layer shows better performance compared with the chromium‐free deposit. Copyright © 2005 John Wiley & Sons, Ltd.     

核壳结构碳化钨/碳化钨铁复合材料的制备与电催化活性

以铁黄为载体,偏钨酸铵为钨源,将直接包覆与原位还原碳化技术相结合制备了碳化钨/碳化钨铁复合材料.经X射线衍射(XRD)分析和透射电子显微镜(TEM)观察,复合材料的主要物相为碳化钨铁(Fe3W3C)、碳化钨(WC)和碳化二钨(W2C),且构成了以Fe3W3C为核、WC和W2C为壳的核壳结构.采用三电极体系循环伏安法测试了复合材料在酸性、中性和碱性体系中对甲醇的电催化氧化活性.结果表明,与颗粒状碳化钨和介孔空心球状碳化钨相比,复合材料的电催化活性有了明显的提高;进一步研究发现,复合材料的电催化活性不仅受到体系性质的影响,还与其物相组成和微结构相关.上述结果说明,通过控制复合材料的物相组成及微结构,以及反应体系的性质可实现对其电催化活性的调控;同时表明,核壳结构是提高碳化钨催化材料活性的有效途径之一.     

合成聚苯胺/碳化钨复合材料及聚合机理探讨

采用在原位聚合苯胺的反应介质中分散碳化钨(WC)的方法制备了掺杂聚苯胺/碳化钨(PANI/WC)复合物,并研究了苯胺在WC表面的聚合机理.通过扫描电镜(SEM)、透射电镜(TEM)、傅立叶红外光谱(FTIR)、拉曼光谱(Raman)和X射线衍射(XRD)对复合物进行了表征.结果表明,苯胺的聚合倾向于在WC颗粒表面进行,形成了PANI包覆WC的复合材料;WC粒子与PANI大分子之间存在强的相互作用,并且复合前后WC的晶型并未发生变化,WC的存在导致红外光谱有明显的蓝移现象,复合后在3446 cm-1处的红外吸收峰变得很弱;在拉曼光谱中,代表醌环C N键的伸缩振动峰红移了9 cm-1,并且强度也有很大程度提高.说明PANI与WC之间有化学键的作用,它们之间的化学键作用发生在C N键的N原子上.聚合反应优先在WC粒子表面进行,生成PANI包覆结构,并提出了PANI/WC复合物的形成机制.     

碳化钨/碳化二钨核壳结构纳米复合材料的制备及电化学性能

以偏钨酸铵为钨源, 铁黄(FeOOH)为载体, 将表面包覆法与原位还原碳化技术相结合, 制备出了具有核壳结构的碳化钨(WC)/碳化二钨(W₂C)纳米复合材料; 应用X射线衍射(XRD)分析、透射电子显微镜(TEM)和X射线能量散射谱(EDS)等手段对不同阶段样品的晶相、形貌、微结构和化学组成等特征进行了表征. 结果表明, 负载体经煅烧后, 载体及包裹层的物相均发生了变化, 形貌也相应地发生了改变; 经盐酸处理及还原碳化后, 样品由WC和W₂C纳米颗粒构成, 并构成了以W₂C为壳, 以WC为核的典型核壳结构; 结合表征结果对核壳结构的形成机理进行了探讨. 采用三电极体系循环伏安法测试了样品在酸性、中性和碱性溶液中对甲醇的电催化氧化活性. 结果表明, 与颗粒状碳化钨和介孔空心球状碳化钨相比, 样品的电催化活性有了明显的提高. 这说明W₂C与WC构成核壳结构纳米复合材料后, 其电化学性能有了明显的提升, 核壳结构纳米复合材料是提高碳化钨催化材料活性的有效途径之一.     

Ti阳极上电沉积制备Pb-聚丙烯腈-碳化钨复合镀层及其电化学性能

通过在酒石酸钾钠体系中加入聚丙烯腈（PAN）、碳化钨（WC）和PbO固体颗粒,在Ti阳极上电沉积制得Pb-PAN-WC复合镀层。 主要研究了电沉积工艺条件(电流密度、温度等)对Pb-PAN-WC复合镀层沉积速度及析氧动力学参数的影响。 在ZnSO4-H2SO4体系中测定的阳极极化曲线表明,最佳工艺条件及固体颗粒加入量为：电流密度1.5 A/dm2,温度35 ℃,15 g/L的PAN,40 g/L的WC。 通过和纯铅镀层的阳极极化曲线和析氧动力学参数对比可知,Pb-PAN-WC复合镀层的电化学性能优于纯铅镀层。     

碳化钨与蒙脱石纳米复合材料的制备与电催化活性

具有类铂催化性能的碳化钨(WC)催化材料是当前研究的热点与难点. 本文以六氯化钨为钨源, 用剥离后的蒙脱石片层为载体, 将化学浸渍法与原位还原碳化法技术相结合制备了碳化钨与蒙脱石纳米复合材料; 复合材料由碳化钨、碳化二钨(W₂C)和蒙脱石(MMT)组成, 碳化钨呈颗粒状分散或呈层状负载于MMT外表面; 样品的晶相组成与其还原碳化时间有关; 样品的微结构特征与前驱体中钨与蒙脱石的比例有关. 采用三电极体系和循环伏安法测试了样品在酸性溶液中对甲醇的电催化氧化性能, 结果表明, 碳化钨与蒙脱石复合之后对甲醇的电催化性能明显提升, 并具有类铂电催化活性; 当钨与蒙脱石质量比为4 的前驱体经5 h 还原碳化后, 样品中WC占绝对主导, WC和W₂C的质量分数分别为82%和18%, 两者的比值为4.556, 且在MMT外表面形成均匀的负载层. 此时样品的电催化活性最高. 这为制备具有类铂催化活性的高性能碳化钨催化材料奠定了坚实基础.     

Effect of ZrO2 incorporation on the mechanical behavior of an AlSi alloy

AlSi–ZrO₂ composite was prepared by stir casting method using a vortex technique. Micrograph observations exhibit a microstructure containing primary Si particles, eutectic silicon cells and intermetallic particles embedded in a dendritic primary α-phase in both Al–Si and AlSi–ZrO₂ homogenized alloys. Difference in thermal conductivity between the α matrix and the ZrO₂ particles generates a high temperature gradient resulting in an increase in the cooling rate which affects the microstructure and, consequently, the mechanical properties. On the other hand, the difference of the structures and the thermal expansion coefficient between ZrO₂ particles and the matrix generates stress and increases the dislocation density. Presence of the ZrO₂ particles enhances the ductility of the composite materials and reduces its Young's modulus. Addition of the ZrO₂ particles increases the hardness of the composite materials at low aging temperature and reduces it at higher aging temperature.     

Crystal Orientation Mapping Applied to the Y-TZP/WC Composite

 Crystal orientation measurements made by electron backscattered diffraction (EBSD) in the scanning electron microscope (SEM) and microscopic observations provided the basis for a quantitative investigation of microstructure in an yttria stabilised, tetragonal zirconia-based (Y-TZP) composite. Automatic crystal orientation mapping (ACOM) in a SEM can be preferable to transmission electron microscopy (TEM) for microstructural characterisation, since no sample thinning is required, extensive crystal data is already available, and the analysis area is greatly increased. A composite with a 20 vol.% tungsten carbide (WC) content was chosen since it revealed crystal relationships between the matrix and carbide phase already established by TEM analysis. However, this composite was difficult to investigate in the EBSD/ SEM since it is non-conductive, the Y-TZP grain size is of the order of the system resolution, and the sample surface, though carefully prepared, reveals a distinctive microtopography. In this paper, some useful solutions to these problems are discussed and the resulting data, which confirm crystal correlations previously established by TEM analysis, are presented.     

Synthesis of palladium nanoparticles supported on reduced graphene oxide-tungsten carbide composite and the investigation of its performance for electrooxidation of formic acid

Palladium (Pd) nanoparticles are uniformly distributed on tungsten carbide (WC)-reduced graphene (RGO) oxide composite to synthesize a new electrocatalyst Pd-WC/RGO. The catalysts prepared with various amounts of tungsten carbide are characterized by transmission electron microscopy, energy dispersive spectrometry, and X-ray diffraction. The electrocatalytic performance of the prepared materials toward formic acid oxidation reaction is tested to evaluate the effect of adding WC. The results show that Pd-WC/RGO electrocatalyst with a 25 wt% WC (Pd-WC(25)/RGO) presented a narrow Pd particle size distribution both on the surface of RGO and WC nanocrystallites. Its current density of the positive main anodic peak of formic acid electrooxidation is up to 42.35 mA cm^?2. Compared with the other catalysts, especially the Pd/RGO, the Pd-WC(25)/RGO demonstrate better electrocatalytic activity and higher stability toward the formic acid oxidation reaction. It is attributed to the small size and uniform dispersion of Pd NPs on both RGO sheets and WC nanocrystallines, and to the stronger synergistic effect between Pd NPs and WC nanocrystallines, which result from the proper mass percentage of 25 % WC in the Pd-WC(25)/RGO composite. The present work reveals that WC could be a good additive component, and the composite WC/RGO could be a better support in preparing Pd-based catalysts.     

碱处理对PtRu/WC电极材料结构及甲醇电催化氧化性能的影响

本文采用不同pH值的KOH溶液对WC材料进行了不同时间的碱处理,并以该WC为载体通过微波加热还原法制备PtRu/WC 复合材料. 采用XRD对材料进行结构表征,通过循环伏安法和计时电流法测试电极对甲醇的电催化氧化性能. 结果表明,经不同碱性条件处理的WC材料表面更易于铂钌的负载,其中经强碱（pH = 14）的KOH溶液处理后可在WC表面得到结晶度最好的铂钌合金,且所得电催化剂PtRu/WC电极的性能最佳,而经碱处理5 h的WC负载的PtRu/WC电极对甲醇氧化的效果最优.