超声机械镀铜的性能研究

利用超声机械镀实验装置制备了性能良好的铜镀层,借助扫描电子显微镜及能谱仪,分析铜镀层的外观、结合强度、表面形貌及化学组成,并对镀铜层抗腐蚀性能进行测试。结果表明,超声机械铜镀层色泽均匀且致密,与基体结合强度良好,耐腐蚀性提高。     

基于超声振动的机械镀锌工艺

提出了一种湿法超声机械镀锌工艺,即利用超声振动系统为冲击介质提供动力,将金属粉冲击到工件表面形成镀锌层。阐述了新工艺的原理和设备结构,并用自行开发的设备进行镀锌。表征了镀锌层的表面形貌、断面形貌及其与基体之间的结合力。结果表明,采用湿法超声振动法机械镀,可在工件表面获得一定厚度的镀锌层。镀层是锌粒镶嵌、填充形成致密的堆积体,表面均匀、平整,与基体之间的结合力良好。     

湿法超声机械镀锌-铝层耐蚀性的研究

采用湿法超声机械镀设备制备了Zn-5%Al复合镀层。用多功能扫描电子显微镜及其配备的能谱分析仪观察并分析了复合镀层的形貌及成分,用划格法测试了复合镀层与基体间的结合强度,并用中性盐雾腐蚀试验法测试了复合镀层的耐蚀性。结果表明:湿法超声机械镀Zn-5%Al复合镀层表面平整、结合强度高、耐蚀性好,是一种综合性能优良的防护镀层。     

湿法超声机械镀锌–铝层的性能研究

以Q235钢片为基体,采用湿法超声机械镀制备Zn–Al复合镀层。用扫描电子显微镜及其配备的能谱仪分析了锌–铝复合镀层的表面形貌、断面形貌和元素组成,并用测厚仪、贴滤纸法和划格试验分别对镀层的厚度、孔隙率和结合力进行表征。结果表明,湿法超声机械镀Zn–Al复合镀层是由锌粉和铝粉颗粒相互镶嵌、填充所形成的致密堆积体,表面均匀、平整,与基体的结合强度高。镀层主要由锌、铝、锡和铁组成,铝的质量分数低于施镀前混合粉体中铝粉的质量分数。在考虑施镀过程中金属粉的损耗后,所得Zn–Al镀层的厚度满足预定的厚度(30μm)要求。     

超声振动对机械镀锌层的性能影响

分别采用机械镀和湿法超声机械镀的方法获得两种机械镀锌层。用扫描电子显微镜及其配备的能谱仪分析了镀层的表面形貌、断面形貌和镀层的组成,并分别用贴滤纸法和划格试验分别对镀层的孔隙率和结合力进行表征,采用表面硬度计测量了镀层的硬度,利用中性盐雾试验测试了镀层的耐腐蚀性能。结果表明,与机械镀锌层相比,湿法超声机械镀锌层表面质量明显改善,相同厚度的湿法超声机械镀锌层的耐腐蚀性能优于机械镀锌层,是一种综合性能优良的防护镀层。     

湿法超声机械镀锌-铝层的结构分析

提出了湿法超声机械镀Zn-Al复合镀层的工艺,采用湿法超声机械镀设备制备了Zn-Al复合镀层。采用金相显微镜、白光干涉仪、多功能扫描电子显微镜及其配备的能谱分析仪观察分析了镀层的结构形貌和镀层的化学成分。结果表明,在工件表面获得了一定厚度的锌-铝层,镀层主要由Zn、少量的Al、Sn和Fe构成,锌粉颗粒是镀层的主体,片状铝粉在镀层中分布不均匀;镀层表面细腻、均匀、平整,但镀层中铝的含量比施镀前混粉中铝的含量低。     

机械镀Zn-Cr及Zn-Al-Cr合金工艺及耐蚀性

为了获得性能良好的含铬的锌合金镀层,在机械镀锌和机械镀Zn-Al合金工艺的基础上,通过调整活化剂和促进剂的种类及用量,开发了机械镀Zn-Cr及Zn-Al-Cr合金工艺。利用该工艺在钢基表面获得了Zn-Cr及Zn-Al-Cr合金镀层。对这些镀层进行了5%NaCl溶液喷雾腐蚀试验,并与机械镀锌层进行了对比。结果表明,Zn-Cr及Zn-Al-Cr合金镀层的耐蚀性能皆好于机械镀锌层。     

施镀时间对SiCp/Al复合材料化学镀Ni-P镀层的影响

采用化学镀的方法在激光选区熔化（SLM）技术成型的SiCp/Al复合材料表面制备了Ni-P镀层，研究了施镀时间对镀层的表面形貌、截面厚度、沉积速率、相结构和显微硬度的影响。结果表明：化学镀0.5～12 h时，镀层都呈胞状形貌，且呈非晶态结构，为高磷镀层；随着施镀时间的延长，胞状组织逐渐变大，表面逐渐致密，镀层厚度逐渐增大，但增长速率越来越小，显微硬度先增大后趋于稳定。施镀时间为8 h时的镀层表面平整、致密、连续，厚度可达100μm，显微硬度为653.4 HV，镀层与基体结合强度为77.2 N。     

硬质合金镀镍层结合性能的研究

研究了在YT5硬质合金上镀镍工艺和镀层的氢等离子体处理工艺,在YT5上得到了质量较好的镍镀层.试验表明:镀前预处理对提高镀层质量起重要作用,氢等离子体处理改变了镀层的表面形态,在镀层和基体之间形成扩散层,使基体与镀层之间的结合由机械结合变成冶金结合,提高了镀层与硬质合金的结合强度.     

湿法超声波机械镀Zn、Zn-5%Al及Al层的形貌与耐蚀性研究

采用湿法超声波机械镀设备制备了Zn、Zn-5%Al及Al层。采用多功能扫描电子显微镜观察了镀层的表面形貌和断面形貌,采用测厚仪测量了镀层的厚度,并采用中性盐雾试验测试了镀层的耐蚀性。结果表明:Zn层及Zn-5%Al层表面均匀平整,Al层表面呈现微观不平整;铝粉的添加使镀层的耐蚀性增强,但厚度降低。     

玻璃纤维/环氧树脂复合材料表面金属化工艺研究

提出一种在玻璃纤维/环氧树脂复合材料表面化学镀镍的简化工艺,首先在复合材料表面引入含有镀镍短纤维的过渡层,复合材料与过渡层共固化成型。通过机械粗化、酸化、化学镀工艺成功地在玻璃纤维/环氧树脂复合材料表面沉积一层连续致密的Ni-P镀层。采用超景深显微镜观察化学镀后镀层的表面形貌,并采用SEM对镀层截面特征进行观测。系统地研究了化学镀时间、装载量对镀层表面形貌、镀层厚度与镀层沉积速度的影响规律,并测量了复合材料/镍镀层界面结合强度。试验结果表明,当化学镀时间为8 h、装载量为1.25 dm2/L时,镀层厚度能达到38.96μm,镀层结合强度达到8.45 MPa。     

双向脉冲电源在镀银中的应用

齿轮齿型面形状复杂,直流电镀银时各处电力线分布不均,造成镀层厚度不均匀,影响齿轮啮合。采用双向脉冲电源镀银,从镀层外观、厚度均匀性等方面进行比较,优选出最佳工艺参数。结果表明:镀层在外观和厚度均匀性上有较大的改善,镀层结合力、纯度及氢脆性均符合AMS 2412的要求。     

Topcoat thickness measurement of thermal barrier coating using grating laser acoustic spectrum method

The thickness of top coating is a crucial factor to characterize the performance of thermal barrier coating. Aiming at the difficulty of thickness measurement with conventional ultrasonic method, a noncontact method based on grating laser ultrasonic acoustic spectrum is proposed. Firstly, the dispersion curve of surface acoustic waves in thermal barrier coating was obtained. The numerical simulation of the established three-layer media model based on finite element method was then performed. Experiments with thermal barrier coating specimens in different thicknesses of top coating were conducted. The theoretical results and simulative results were corrected by ultrasound attenuation theory to fit experimental results. It is found that experimental results show great agreement with the theoretical curve and numerical simulation results after correction, which illustrates the usefulness and potential of the proposed method when applied to the thickness measurement of top coating in service.     

Microstructure and mechanical properties of Si3N4f/BN composites with BN interphase prepared by chemical vapor deposition of borazine

The boron nitride (BN) interphase of silicon nitride (Si₃N₄) fiber-reinforced BN matrix (Si₃N_4f/BN) composites was prepared by chemical vapor deposition (CVD) of liquid borazine, and the microstructure, growth kinetics and crystallinity of the BN coating were examined. The effects of coating thickness on the mechanical strength and fiber/matrix interfacial bonding strength of the composites were then investigated. The CVD BN coating plays a key role in weakening the interfacial bonding condition that improves the mechanical properties of the composites. The layering structure of the BN coating promotes crack propagation within the coating, which leads to a variety of toughening mechanisms including crack deflection, fiber bridging and fiber pull out. Single-fiber push-out experiments were performed to quantify the fiber/matrix bonding strength with different coating thicknesses. The physical bonding strength due to thermal mismatch was discussed.     

Preparation of nickel coating on ZTA particles by electroless plating

With the aim to effectively improve the interface between ZrO₂ toughened Al₂O₃ (ZTA) particles and metal matrix, nickel was deposited on the surface of ZTA particles by electroless plating method. Formation mechanism of nickel coating and effects of the solution pH, loading capacity of ZTA particles and temperature on the nickel deposition were investigated. Microstructures, thickness and element distributions of nickel coating were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results showed that the nickel was successfully deposited on the surface of ZTA particles by electroless plating without noticeable defects. The process of electroless nickel plating could be explained by combination of atomic hydrogen and electrochemistry theories. The interfacial nucleation of nickel is easier to form than spontaneous nucleation in the solution. Deposited Nickel has priority on the surface of ZTA particles comparing to that in solution. The optimal conditions to coat nickel on the surface of ZTA particles are: solution pH 4.7–4.8, loading capacity 15–20?g/L, and electroless plating temperature 85?°C. The ZTA particle reinforced iron matrix composites prepared by powder metallurgy could have better interfacial bonding between ZTA particle and iron matrix because of the nickel coating on the surface of ZTA particle. Nickel diffuses into the iron matrix during the sintering preparation of composite materials. The interface between ZTA particle and iron matrix presents the evidence of non-chemical bonding.     

Sol-gel-derived hydroxyapatite-carbon nanotube/titania coatings on titanium substrates

In this paper, hydroxyapatite-carbon nanotube/titania (HA-CNT/TiO(2)) double layer coatings were successfully developed on titanium (Ti) substrates intended for biomedical applications. A TiO(2) coating was firstly developed by anodization to improve bonding between HA and Ti, and then the layer of HA and CNTs was coated on the surface by the sol-gel process to improve the biocompatibility and mechanical properties of Ti. The surfaces of double layer coatings were uniform and crack-free with a thickness of about 7 μm. The bonding strength of the HA-CNT/TiO(2) coating was higher than that of the pure HA and HA-CNT coatings. Additionally, in vitro cell experiments showed that CNTs promoted the adhesion of preosteoblasts on the HA-CNT/TiO(2) double layer coatings. These unique surfaces combined with the osteoconductive properties of HA exhibited the excellent mechanical properties of CNTs. Therefore, the developed HA-CNT/TiO(2) coatings on Ti substrates might be a promising material for bone replacement.     

用于电磁屏蔽与吸收材料的镀镍石墨粉的研究

采用阴离子型和非离子型表面活性剂解决石墨粉与水的浸润问题,使用H2SO4和K2Cr2O7溶液对石墨粉末进行氧化,增强镀覆金属与石墨粉的结合力.利用AgNO3和PdCl2溶液对石墨粉末进行活化,在石墨粉表面化学镀铜和化学镀镍;石墨粉末镀铜可以增强其导电性,铜表面再镀镍可以提高其导磁性能.讨论了化学镀铜工艺条件,开发出一种导电导磁性能好、密度小和价格低的镀镍石墨粉类导电填料.     

Effect of adhesive thickness and surface roughness on the shear strength of aluminium one-component polyurethane adhesive single-lap joints for automotive applications

Adhesively bonded technology is now widely accepted as a valuable tool in mechanical design, allowing the production of connections with a very good strength‐to‐weight ratio. The bonding may be made between metal–metal, metal–composite or composite–composite. In the automotive industry, elastomeric adhesives such as polyurethanes are used in structural applications such as windshield bonding because they present important advantages in terms of damping, impact, fatigue and safety, which are critical factors. For efficient designs of adhesively bonded structures, the knowledge of the relationship between substrates and the adhesive layer is essential. The aim of this work, via an experimental study, is to carry out and quantify the various variables affecting the strength of single-lap joints (SLJs), especially the effect of the surface preparation and adhesive thickness. Aluminium SLJs were fabricated and tested to assess the adhesive performance in a joint. The effect of the bondline thickness on the lap-shear strength of the adhesives was studied. A decrease in surface roughness was found to increase the shear strength of the SLJs. Experimental results showed that rougher surfaces have less wettability which is coherent with shear strength tests. However, increasing the adhesive thickness decreased the shear strength of SLJs. Indeed, a numerical model was developed to search the impact of increasing adhesive thickness on the interface of the adherend.     

Effects of HfC/PyC core-shell structure nanowires on the microstructure and mechanical properties of Hf1-xZrxC coating

To elevate the mechanical and anti-ablation properties of Hf_1-xZr_xC coating on C/C composites, HfC/PyC core-shell structure nanowires (HfCnw/PyC) with different PyC layer thickness were synthesized by two steps of CVD. Influences of HfCnw/PyC on the microstructure and mechanical properties of Hf_1-xZr_xC coating were researched. Toughening mechanism of HfCnw/PyC was also investigated. PyC layer exhibited a lamellar structure and combined well with HfCnw. After incorporating HfCnw/PyC, Hf_1-xZr_xC coating structure converted from columnar crystal to isometric crystal. HfCnw improved H, E, K_c and bonding strength of Hf_1-xZr_xC coating, which is ascribed to the nanowire pullout, debonding, bridging and crack deflection mechanism. With the PyC layer thickness increasing, H and E of the coating reduced, K_c and bonding strength of the coating increased. Because of the moderate bonding strength between HfCnw/PyC and coating matrix, lamellar structure of PyC layer and higher K_c of PyC, toughening effectiveness of the core-shell structures gradually enhanced with the PyC layer thickness increasing.