Development And Characterization Of Composite Ni-Cr-C-Caf2 Laser Cladding On Gamma-Tial Intermetallic Alloy

A process of laser cladding Ni-CF-C-CaF2 mixed powders to form a multifunctional composite coatingd on gamma-TiAl substrate was carried out. The microstructure of the coating was examined using XRD, SEM and EDS. The coating has a unique microstructure consisting of primary dendrite or short-stick TiC and block Al4C3 carbides reinforcement as well as fine isolated spherical CaF2 solid lubrication particles uniformly dispersed in the NiCrAlTi (gamma) matrix. The average microhardness of the composite coatings is approximately HV 650 and it is 2-factor greater than that of the TiAl substrate. (C) 2008 Elsevier B.V. All rights reserved.

Effect of cerium on microstructure and electrochemical performance of Ti-V-Cr-Ni electrode alloy

Effect of cerium on the microstructure and electrochemical performance of the Ti0.25V0.35-xCexCr0.1Ni0.3 (x = 0, 0.005) electrode alloy was investigated by X-ray diffraction (XRD), field emission scanning electron microscopy/energy dispersive X-ray spectrometry (FESEM-EDS), and electrochemical impedance spectroscopy (EIS) measurements. On the basis of XRD and FESEM-EDS analysis, the alloy was mainly composed of V-based solid solution with body-centered-cubic structure and TiNi-based secondary phase. Ce did not exist in two phases, instead, it existed as Ce-rich small white particles, with irregular edges, distributed near the grain boundaries of the V-based solid solution phase. Discharge capacity, cycle stability, and high-rate discharge ability of the alloy electrode were effectively improved with the addition of Ce at 293 K. It was very surprising that the charge retention was abnormal with larger discharge capacity after standing at the open circuit for 24 h. EIS indicated that addition of Ce improved the dynamic performance, which caused the charge transfer resistance (R-T) to decrease and exchange current density (I-0) to increase markedly. The exchange current density of the electrochemical reaction on the alloy surface with Ce addition was about 2.07 and 3.10 times larger than that of the alloy without Ce at 303 and 343 K, respectively.

A Numerical Model of Rapid Solidification Processing of Ni-Al Alloy in Planar Flow Casting

A numerical model has been developed for simulating the rapid solidification processing (RSP) of Ni-Al alloy in order to predict the resultant phase composition semi-quantitatively during RSP. The present model couples the initial nucleation temperature evaluating method based on the time dependent nucleation theory, and solidified volume fraction calculation model based on the kinetics model of dendrite growth in undercooled melt. This model has been applied to predict the cooling curve and the volume fraction of solidified phases of Ni-Al alloy in planar flow casting. The numerical results agree with the experimental results semi-quantitatively.

Ni-Cr系光谱选择性吸收薄膜制备与表征

太阳能选择性吸收薄膜是中高温太阳能集热器的最关键部分，目前世界很多国家都在积极研究工艺简单、成本低廉、性能优良稳定的中高温光谱选择性吸收薄膜。本论文根据金属陶瓷型太阳能光谱选择性吸收表面和磁控溅射技术的原理，在国内外研究发展的基础上，针对目前国内平板型太阳能集热器的现有状况，结合太阳能热水器建筑一体化的发展趋势，开展了磁控溅射制备光谱选择性吸收薄膜的研究。本工作以直流反应磁控溅射方法作为制备手段，选择Ni-Cr合金作为靶材，以N2, 02两种气体为反应气体，反应溅射制备折射率变化的NiCr-NiCrO,N

The effect of tungsten additive on the surface characteristics of amorphous Ni-P alloy

The variation of surface compositions on amorphous Ni80.4W1.5P18.1 alloy by O-2 oxidation and H-2 reduction treatments have been studied by XPS, UPS and ISS. It shows that addition of tungsten in the amorphous Ni-P alloy leads to dramatic changes of the relating component distributions in the surface layers before and after these treatments. Oxidation of a Ni80.4W1.5P18.1 amorphous alloy in 1 bar of oxygen at 513 K caused a significant segregation of nickel in different oxide states at the surface. The subsequent reduction of the oxidized surface with I bar hydrogen at 553 K resulted in only a small portion of Ni and P being reduced into elemental states, while most of them was found to combine to form a kind of nickel phosphate compound. On the other hand, under the same conditions, the oxidation and reduction of a Ni80P20 alloy gave rise to metallic Ni and elemental P as the predominate species on the alloy surface. The addition of W in the amorphous alloy might act as nuclei for a favorable formation of the phosphate structure which was proposed to be an active species for hydrogen-relating catalytic reactions. (C) 1999 Elsevier Science B.V. All rights reserved.

Microstructure and high-temperature wear and oxidation resistance of laser clad gamma/W2C/TiC composite coatings on gamma-TiAl intermetallic alloy

There are very strong interests in improving the high-temperature wear resistance of the y-TiAl intermetallic alloy, especially when applied as tribological moving components. In this paper, microstructure, high-temperature dry sliding wear at 600 degrees C and isothermal oxidation at 1000 degrees C on ambient air of laser clad gamma/W2C/TiC composite coatings with different constitution of Ni-Cr-W-C precursor mixed powders on TiAl alloy substrates have been investigated. The results show that microstructure of the laser fabricated composite coatings possess non-equilibrium microstructure consisting of the matrix of nickel-base solid solution gamma-NiCrAl and reinforcements of TiC, W2C and M23C6 carbides. Higher wear resistance than the original TiAl alloy is achieved in the composite coatings under high-temperature wear test conditions. However, the oxidation resistance of the laser clad gamma/W2C/TiC composite coatings is deceased. The corresponding mechanisms resulting in the above behaviors of the laser clad composite coatings are discussed. (c) 2006 Elsevier B.V. All rights reserved.

Characterization and thermodynamic study of ultra-fine particle of Ni-B amorphous alloy

Ultra-fine particle of Ni-B amorphous alloy was prepared by chemical reduction of Ni2+ with NaBH4 and characterized with TEM and XRD. The heat capacity and thermal stability were measured with a high-precision automatic adiabatic calorimeter and DTA. The upper limit of applied temperature of the substance was found to be 684 K for use as catalyst. (C) 1999 Elsevier Science B.V. All rights reserved.

Shear Localization In Dynamic Deformation: Microstructural Evolution

Investigations made by the authors and collaborators into the microstructural aspects of adiabatic shear localization are critically reviewed. The materials analyzed are low-carbon steels, 304 stainless steel, monocrystalline Fe-Ni-Cr, Ti and its alloys, Al-Li alloys, Zircaloy, copper, and Al/SiCp composites. The principal findings are the following: (a) there is a strain-rate-dependent critical strain for the development of shear bands; (b) deformed bands and white-etching bands correspond to different stages of deformation; (c) different slip activities occur in different stages of band development; (d) grain refinement and amorphization occur in shear bands; (e) loss of stress-carrying capability is more closely associated with microdefects rather than with localization of strain; (f) both crystalline rotation and slip play important roles; and (g) band development and band structures are material dependent. Additionally, avenues for new research directions are suggested.

激光热处理对化学沉积Ni-P合金薄膜性能的影响

用扫描电镜(SEM)观察了化学沉积Ni-P合金薄膜/单晶硅基体的结构与颗粒度,利用X射线衍射(XRD)技术测试了其化学沉积后的残余应力,测量了激光热处理后残余应力的变化规律,分析了残余应力对磨损性能及界面结合强度的影响。实验结果表明,化学沉积Ni-P合金薄膜/硅基体的残余应力均表现为拉应力,经过激光热处理后残余应力发生了变化,由高值的拉应力变为低值的拉应力或压应力；薄膜残余应力对其磨损性能有明显的影响,其磨损量随着残余应力的减小而减小；薄膜与基体结合强度随着残余应力的增大而减小,合理地选择激光热处理参数可

Ti-V-Cr固溶体储氢合金的结构及电化学性能研究

本论文首先研究了Ni、Zr分别对Ti-V－Cr固溶体储氢合金中Cr和Ti部分取代的影响，得到了性能良好的Ti0．17Zr0．08V0．35Cr0．10Ni030基质合金。在此基础上进一步研究了入甄、B、Fe、Co、Al元素的添加或取代对基质合金的结构及电化学性能的影响。采用XRD、ICP、SEM一EDX、XPS、EIS、线性极化和阳极极化等表征手段对Ti一V－Cr固溶体储氢合金的结构及电化学性能进行分析和表征，主要结果如下：①Ti一V－Cr合金自身在碱性电解液中几乎无电化学活性。当用Ni部分取代Cr后，合金中出现具有电化学活性的第二相，其电化学性能得到有效地改善和提高。②Ti0.25-xZr_xV0.35Cr0.1Ni0.3（x＝0．05-0．15）合金主要是由bcc相和c14Laves相组成。随Zr含量从0．05增加到0．08，合金电极的放电容量和倍率放电能力增加；当x继续从0．08增加到0．15时，其变化较小。合金电极的电荷转移电阻随x增加而降低，当x在0．08到0．15之间变化时，电荷转移电阻变化也比较小。表明电荷转移电阻的大小与合金的电化学性能密切相关。③经过50次充、放电循环后，Tio．17zr"sV时scrol0Ni03。合金电极在303K和313K的放电容量能保持在90％以上；在70℃时的放电容量仍能达到275mA扮g。根据不同温度时的交换电流密度，计算了Ti。，17Zr008V时SCr川0Ni030合金电极表面电化学反应的表观活化能，其值约为50kJ／mol。④通过Nln、B、Fe、C。、AI对Tio．17zroosvo35Crol0Nio3。合金基质的添加与取代的研究，得到了具有高容量的储氢合金。其中Tio．17Zr008Vo35Cro．10Ni020Mnol。合金室温最高放电容量达到390n1A扮g；在253一343K的温度范围内，Tiol7Zr08V035Cr0JONioz5Mnoos合金具有高的放电容量，其容量在167一298mA树g之间变化，但是这些合金的稳定性有待进一步的提高。⑤合金充、放电过程中，晶格的扭曲和膨胀、Zr和V的溶解使得合金结构发生变化；合金的严重粉化及表面致密氧化膜的形成，是导致Ti一V－Cr合金电化学性能的衰减的主要原因。

Microstructure and wear resistance of in situ TiCp composite coating by laser cladding

A new in situ method was realized by one step laser cladding to produce Ni-base alloy composite coating reinforced by in situ reacted and gradiently distributed TiCp particles. The submicron TiCp particles were formed and uniformly distributed because of the in situ reaction and trapping effect under the rapid solidification condition. And, TiCp particles were of gradient distribution on a macro scale and their volume fraction increased from 1.86% at the layer/substrate interface to a maximum 38.4% at the surface of the layer. Furthermore, the in situ generated TiCp/gamma-Ni interfaces were free from deleterious surface reactions. Additionally, the clad coating also revealed a high microhardness of gradient variation with the layer depth and the superior abrasive wear resistance.

Ni25Al75合金快速凝固过程中的包晶反应与凝固进程

用平面流铸技术制备了Ni25Al75合金条带，利用XRD，TEM和EDS对快速凝固后的显微组织和微区成分进行了分析。研究表明，Ni—A1合金快速凝固过程中的包晶反应受到了很大程度的抑制，从而影响到快速凝固进程，造成最终相组成中出现了平衡条件下不可能出现的α(A1)，并使NiAl3相有效合金浓度和生长速度增加，导致最终相组成中NiAl_3相质量分数增加。

等离子熔覆gamma/Cr7C3复合材料涂层组织与耐磨性研究

为探索提高工程机械易损零部件服役寿命的新技术,采用等离子熔覆工艺,以Ni-Cr-C混合合金粉末为添加材料,在易损零部件用钢Q235表面形成了以初生块状金属陶瓷Cr7C3为硬质耐磨相,以强韧性良好的γ/Cr7C3共晶为基体的复合材料冶金涂层,分析了涂层的显微组织和硬度,在室温干滑动磨损条件下测试了其耐磨性.研究结果表明:涂层组织致密,硬度较高,与基体之间为完全的冶金结合,在干滑动磨损条件下具有良好的耐磨性.

横截面压入时典型涂层界面的剥离行为

为发展涂层/基体界面结合性能表征方法,本文用横截面压入法对铝基喷涂Ni层(弱结合界面)和钢基电镀Cr层(强结合界面)进行对比性实验研究。结果发现,横截面压入时两种涂层都能与基体剥离,但界面裂纹形状存在明显差异。

Fabrication of Silicon-Based Template-Assisted Nanoelectrode Arrays and Ohmic Contact Properties Investigation

A convenient fabrication technology for large-area, highly-ordered nanoelectrode arrays on silicon substrate has been described here, using porous anodic alumina (PAA) as a template. The ultrathin PAA membranes were anodic oxidized utilizing a two-step anodization method, from Al film evaporated on substrate. The purposes for the use of two-step anodization were, first, improving the regularity of the porous structures, and second reducing the thickness of the membranes to 100 similar to 200 nm we desired. Then the nanoelectrode arrays were obtained by electroless depositing Ni-W alloy into the through pores of PAA membranes, making the alloy isolated by the insulating pore walls and contacting with the silicon substrates at the bottoms of pores. The Ni-W alloy was also electroless deposited at the back surface of silicon to form back electrode. Then ohmic contact properties between silicon and Ni-W alloy were investigated after rapid thermal annealing. Scanning electron microscopy (SEM) observations showed the structure characteristics, and the influence factors of fabrication effect were discussed. The current voltage (I-V) curves revealed the contact properties. After annealing in N-2 at 700 degrees C, good linear property was shown with contact resistance of 33 Omega, which confirmed ohmic contacts between silicon and electrodes. These results presented significant application potential of this technology in nanosize current-injection devices in optoelectronics, microelectronics and bio-medical fields.