铝基化学镀镍浸镍前处理的研究进展

铝基表面欲获得结合力好的镀层,关键在于前处理工艺的选择。尽管浸锌法是目前研究较多、效果较好的前处理方法,但仍存在一些不足,而浸镍法可以避免这些不足,有望取代浸锌法。较详细地阐述了浸镍法的原理及研究现状,并将文献中涉及的浸镍法分为活化浸镍、碱性预镀镍和二次浸镍。活化浸镍液中一般不含还原剂,主要通过置换反应生成一层具有催化作用的镍,进而促使化学镀过程中镍紧密均匀地沉积;碱性预镀镍则是通过含有还原剂的镍盐溶液,在铝基表面预化学镀上一薄层镍,其原理与化学镀镍相同。同时,对比分析了两种浸镍法及其组合处理法之间的区别与联系。最后,指出了浸镍法未来的发展方向:其一,简化工艺,用一次浸镍法代替二次浸镍法;其二,无毒、低污染,研发出无氟浸镍液;其三,获得高性能,即优化浸镍液配方,使得镀层与基体结合强度更好。     

pH值对镁合金化学镀Ni-P合金的影响

为进一步确定pH值对镁合金化学镀Ni-P合金的影响,利用扫描电镜(SEM),能谱仪(XPS),显微硬度仪以及极化曲线等方法分析镀层的形貌和性能.结果表明:pH值对镀层的性能影响较大,pH值很低时难于施镀 ,形貌在pH值为8时最好,镀层的含磷量随着pH值的升高而降低;在一定范围内,硬度随着pH值的升高而降低;在pH值为4时,其镀层的自腐蚀电位最高达到-0.92V,耐腐蚀性能最好.     

SiCp表面化学镀镍合金层的成分与形貌研究

SiCp因其高强度,高模量、耐热、耐磨等优良性能而被作为颗粒增强体制备金属基复合材料。采用优化后的SiCp表面化学镀镍工艺,获得了镍合金包覆SiCp,并对镀镍合金层进行了X－ray衍射成分分析以及镀覆层形貌的SEM考察。结果表明,镀覆层主要为部分非晶态的镍与镍磷合金以及Ni2P的化合物夹杂;粒子的分散很好,结团较少。     

木材化学镀镍镀层形貌及成分研究

通过化学镀镍,在木材表面可以获得连续、均匀、致密的镀层.化学镀镍后,木材表面呈光亮的银灰色,但镀层的平整度和光亮度不高.扫描电子显微镜(SEM)观察表明:经过抛光的木材看似光滑,实质上比较粗糙,存在有大量的木材纤维和导管孔洞.镀层受木材表面粗糙度影响较大.能谱分析(EDS)表明:镀层为Ni-P合金,Ni和P的质量分数分别为95.36%和4.64%,为低磷舍金镀层.     

Thermodynamic Analysis of In As Sb C H System and Design of MOVPE Process for In(As,Sb) Semiconductor

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AZ91D镁合金化学镀镍前处理工艺及腐蚀行为研究

为了改进传统的镁合金化学镀镍前处理工艺和确定以硫酸镍为主盐的镁合金化学镀镍的最佳工艺.采用碱性焦磷酸盐进行浸蚀代替铬酸浸蚀,去除合金表面的油污和氧化物;然后用氢氟酸溶液进行活化.通过正交试验确定了化学镀镍的最佳工艺.结果表明:采用碱性焦磷酸盐浸蚀的前处理工艺、在最佳施镀条件下镀2h,镀层厚度达到20μm,与基体结合良好;镀层为Ni-P微晶,表面平整、致密,磷的质量分数达11.7%.在质量分数为3.5%的NaCl溶液中的动电位极化测试结果表明,镀层可对AZ91D镁合金起到良好的防护作用.     

镁合金AZ91表面化学镀镍层的制备及性能研究

为了优化镁合金表面化学镀镍工艺,降低施镀过程中的污染,研究了AZ91镁合金表面直接化学镀镍工艺,并应用SEM对镀层表面形貌进行观察,通过EDS及XRD对镀层成分及物相进行了分析,采用划线划格法、静态浸泡法分别对镀层与镁合金基体的结合力、镀层的防腐蚀性能进行了分析.研究结果表明:AZ91镁合金表面可通过直接化学镀镍获得结合力良好、表面硬度较高的镍镀层.镀层的成分分析显示:由于NaH2PO2发生自身氧化还原反应,镀层中存在少量P.在3.5%NaCl溶液中的静态腐蚀试验结果表明:镀层的耐腐蚀性能良好,对合金基体可以起到较好的防护作用.     

In situ measurement of corrosion on the nanoscale

Measurement of the electrochemical properties phase-by-phase on the nanoscale in real (commercial) alloys is critical to understanding the microstructure-corrosion relationship and subsequently controlling it. This work presents a novel AFM based in situ corrosion probing methodology (for the first time) that is capable of resolving the electrochemical activity (impedance response) into the nanometer range; the method subsequently having major ramifications in the study of aluminium alloy corrosion, the interpretation of corrosion propagation, and the subsequent development of corrosion resistant aluminium alloys.     

棒状共晶界面成分分布及对平界面生长的影响

用定向凝固法揭示了MnSb/Sb棒状共晶 (纤维复合材料 )平界面生长条件。基于成分过冷理论 ,推导了棒状共晶组元耦合扩散边界层内浓度梯度要求的GL/V条件。并从二元共晶界面不稳定性的类型和溶质分布形式的角度 ,分析了造成界面不稳定的原因和现有判据的局限性     

In situ observations and crystallographic analysis of martensitic transformation in steel

The development of a martensitic structure in a low-carbon and low-alloy steel was characterized using in situ confocal laser microscopy, high-speed photography and crystallographic analysis, including the nature of variant selection. The initial stage of transformation involves the partitioning of the austenite grain into packets, after which the rate of transformation is gradual. The crystallographic orientation of the plates that form is not random, but involves selection determined by the relationship between the shape deformation direction and the free surface. The vicinity of austenite grain and twin boundaries, and martensite/austenite interfaces also affect variant selection.     

Recent Progress in Metallurgical Bonding Mechanisms at the Liquid/Solid Interface of Dissimilar Metals Investigated via in situ X-ray Imaging Technologies

The liquid/solid(L/S) interface of dissimilar metals is critical to the microstructure, mechanical strength, and structural integrity of interconnects in many important applications such as electronics, automotive, aeronautics, and astronautics, and therefore has drawn increasing research interests. To design preferential microstructure and optimize mechanical properties of the interconnects, it is crucial to understand the formation and growth mechanisms of diversified structures at the L/S interface during interconnecting. In situ synchrotron radiation or tube-generated X-ray radiography and tomography technologies make it possible to observe the evolution of the L/S interface directly and therefore have greatly propelled the research in this field. Here, we review the recent progress in understanding the L/S interface behaviors using advanced in situ X-ray imaging techniques with a particular focus on the following two issues:(1) interface behaviors in the solder joints for microelectronic packaging including the intermetallic compounds(IMCs) during refl ow, Sn dendrites, and IMCs during solidification and refl ow porosities and(2) growth characteristics and morphological transition of IMCs in the interconnect of dissimilar metals at high temperature. Furthermore, the main achievements and future research perspectives in terms of metallurgical bonding mechanisms under complex conditions with improved X-ray sources and detectors are remarked and discussed.     

In situ electrochemical wet cell transmission electron microscopy characterization of solid-liquid interactions between Ni and aqueous NiCl2

Electrodeposition and electropolishing of nanograined nickel has been observed using an in situ electrochemical wet cell developed for transmission electron microscopy. The cell employs two thin film nickel electrodes in a 0.1 M aqueous NiCl₂ electrolyte, which were biased at ±1 V. Anisotropic electrodeposition was observed in which growth of the nickel film across the substrate occurred much more rapidly than growth perpendicular to the substrate. The anisotropic behavior results from relatively equiaxed nanograins nucleating at the growth front with little subsequent coarsening. Grains were observed to nucleate ahead of the growth front, suggesting a new mechanism for electrochemically driven growth across a substrate which depends on ionic surface adsorption ahead of the growth front. During electropolishing the dissolution of nickel tended to occur more isotropically. The film thinned relatively uniformly until certain regions displayed Rayleigh instabilities. At this point the film broke up and some regions coarsened rapidly and/or were subject to electromigration.     

镁合金微弧氧化涂层表面原位制备MgCr-LDH层及其耐蚀防护机制研究

为了进一步提升镁合金耐蚀性,将水滑石(layered double hydroxides LDH)与微弧氧化结合(MAO)制备一种主动防护的高耐蚀复合涂层。本文采用原位法成功在AZ31镁合金MAO涂层表面制备了层间含NO3-的MgCr-LDH层,构成LDH/MAO复合涂层,研究原有MAO涂层表面LDH的微观组织结构及其与原始MAO涂层的相互作用,并利用长时间浸泡法和电化学法测试MgCr-LDH/MAO复合涂层试样在3.5wt%NaCl溶液中的耐蚀性能,揭示LDH层耐蚀保护机理,研究结果显示：LDH易于在镁合金表面MAO层的孔洞中形成,最终生成均匀致密片状结构的层。LDH的原位生长过程对原始MAO涂层没有破坏,MgCr-LDH与MAO涂层之间属于化学结合,具有强的粘附性与机械稳定性。MgCr-LDH/MAO复合涂层明显提高了AZ31镁合金的耐腐蚀性能,LDH层的其防腐保护机制主要表现为两部分,一是LDH均匀形成于原始MAO层上,有效的覆盖了MAO层的孔洞与裂纹,阻挡氯离子通过MAO涂层的固有缺陷进入合金基体产生破坏。二是LDH的硝酸根层间阴离子能够与腐蚀环境中的氯离子进行离子交换,降低溶液中的氯离子浓度,从而延长涂层的耐蚀保护性。     

In situ observation and thermodynamic calculation of MnS in 49MnVS3 non-quenched and tempered steel

Based on thermodynamics calculation, the results of the formation temperature of MnS inclusions of non-quenched and tempered steel during heating process were discussed. It is shown that while the solid fraction is 0.9, MnS inclusions began to precipitate in the final stage of solidification. The solidification process of 49MnVS3 non-quenched and tempered steel during heating has been observed in situ using a confocal scanning laser microscope (CSLM), which agrees well with the thermodynamics calculation. MnS particles were coarsening during heating process, which would reduce the pinning effect on the austenite grain boundaries and bring about the sudden growth of some austenite grains in this stage.     

Microstructure Characteristics and Mechanical Properties of Nb-17Si-23Ti Ternary Alloys Fabricated by In Situ Reaction Laser Melting Deposition

Fabrication of ternary Nb–17 Si–23 Ti alloys was attempted by in situ reaction laser melting deposition(LMD)with dual powder feeding method from Nb-28 at.% Ti powder mixture and pure Si powder. The microstructures of the asdeposited alloys were examined with scanning electronic microscope, and the phase constituents were analyzed by X-ray energy-dispersive spectrometer and X-ray diffraction. Furthermore, the effect of laser power on microstructure characteristics, microhardness and indentation fracture toughness was also investigated. The in situ reaction LMD process resulted in remarkable refinement of the microstructure. The as-deposited samples mainly consisted of NbSS,metastable(Nb Ti)3 Si and Ti-rich NbSS. With the increase in the laser power from 1000 to 2000 W, the NbSSmorphology changed from discontinuous dendritic to near equiaxed, but the Ti-rich NbSSphase tended to vanish. Furthermore, with the increase in the laser power, the microhardness of as-deposited samples increased from 822 to 951 HV, while the indentation fracture toughness was improved from 12.3 to 14.1 MPa m1/2. The corresponding mechanism is also discussed.     

In situ observation of formation and spreading of micro-droplets on magnesium and its alloy under cyclic wet-dry conditions

The formation and spreading of micro-droplets on pure magnesium and its alloy in an atmosphere of water vapor under cyclic wet-dry conditions was studied using an environmental scanning electron microscope (ESEM). The in situ observations indicated that the corrosion product stimulated the formation and spreading of micro-droplets, and the grain boundaries for pure magnesium and β phase for AZ91 magnesium alloy had no influences on this process. The oxygen concentration on the surface generally increased with the wetting time. The corrosion products decreased the corrosion rate.     

Sensing, Control, and In Situ Measurement of Coating Properties: An Integrated Approach Toward Establishing Process-Property Correlations

Over the last decade there has been an explosion in terms of available tools for sensing the particle spray stream in thermal spray processes. This has led to considerable enhancement in our understanding of process reproducibility and reliability. Despite these advances, the linkage to coating properties has continued to be an enigma. This is partially due to the complex nature of the build-up process and the associated issues with measuring properties of these complex coatings. In this paper, we identify critical issues in processing-structure-property relations particularly with respect to the linkage to particle properties. Our goal is to demonstrate an integrated strategy, one that combines particle state sensing, with process mapping and extracting coating properties in situ through the development of robust and advanced curvature-based techniques. These techniques allow estimation of coating modulus, residual stress and, non-linear response of thermal sprayed ceramic coatings all within minutes of the deposition process. Finally, the integrated strategy examines the role of process maps for control of the spray stream as well as tailoring properties of thermal spray coatings. Examples of such studies for yttria-stabilized zirconia thermal barrier coatings are discussed.