汽车减振器连杆的耐蚀性研究

对用两种不同的电镀工艺制备的汽车减振器连杆进行了电解腐蚀试验,探讨了减振器连杆镀铬层点蚀的形成机理及其对连杆表面耐腐蚀性的影响。运用金相显微镜及扫描电镜观察腐蚀前后连杆的镀铬层组织,证实连杆的表面镀层缺陷是影响其耐腐蚀性的主要原因。电镀工艺中减小电流密度可以减小镀层裂纹宽度和深度,从而提高镀层的耐蚀性。     

汽车减振器连杆电镀铬及耐蚀性研究

汽车减振器连杆耐蚀性是影响汽车减振器质量和寿命的主要因素之一。连杆电镀工艺参数的选择决定了其镀铬层的质量及其耐腐蚀性能。通过对汽车减振器连杆电流密度与镀铬层组织形态的研究找到其对应关系，进行盐雾试验得到了优化的电流密度参数。不同表面质量的连杆盐雾试验对比表明：镀前对汽车减振器连杆进行表面超精加工可显著提高连杆的耐蚀性。研究结果为优化企业电镀生产工艺并提高汽车减振器的制造水平提供了一条有效途径。     

电沉积钯钴合金形貌及其耐蚀行为研究

为更好地了解Pd-Co合金的材料特性,采用电沉积法制备了Pd-Co合金镀层．通过扫描电镜（SEM）和动电位扫描（Tafel）对Pd-Co合金镀层的表面形貌和耐蚀性进行了考察。结果表明,Pd-Co合金镀层的晶粒尺寸和表面形貌受镀液中Co^2＋浓度和电流密度的影响较大,随着镀液中Co^2＋浓度的增加,镀层的晶粒尺寸逐渐减小,晶粒从片状变为球状;随着电流密度的增大,Pd-Co合金镀层的晶粒从粒状变为块状,晶粒尺寸呈先减小后增大的趋势。当电流密度小于1.0A／dm^2时,Pd—Co共沉积过程受阴极极化控制;当电流密度大于1．0A／dm^2时,其沉积过程受浓差极化控制。Pd-Co合金镀层的耐蚀性按腐蚀介质为中性、酸性、碱性的顺序逐步降低。     

经阴极极化的微裂纹铬与预镀高应力镍层的微裂纹铬

一、引言自1928年以来,人们一直认为装饰性镀铬层最合适的厚度范围是0.25～0.5微米.但是由于镀铬层具有较大的内部应力,使镀层产生较大的裂纹,裂纹所在的底镀层(镍镀层),被剧烈地腐蚀. 基于上述原因,后来发明了无裂纹镀铬工艺,但在实际生产中发现,镀层仍然产生与以前一样的大裂纹,耐腐蚀性能没有得到提高.近年来,研究开发的结果,与以前的设想正好相反,认为镀铬层产生大量的微裂纹,能显著地提高其耐腐蚀性能.微孔铬、微裂纹铬等工艺,统称为微观不连续性镀铬工艺. 保加利亚科学院理化室1983年发表了一     

双向脉冲镀铬占空比对镀层微观组织及硬度的影响

为了了解占空比对双向脉冲镀铬层微观组织及硬度的影响,采用标准镀铬溶液,镀液温度为55℃,用自制双向脉冲电源装置,频率为100 Hz,峰值电流密度为50 A/dm2,在各种占空比下制备了5种镀层,并考察了其微观组织及硬度。结果表明:随着占空比的升高,镀铬层的硬度增加,延迟裂纹减少,致密度增大,表面粗糙度降低,当占空比大于70%时,镀铬层的硬度减小,延迟裂纹增加,致密度减小,表面粗糙度增加;占空比为70%的镀铬层各项性能最好。     

纳米SiC复合镀层制备工艺的研究

在A3钢板上制备了含有纳米SiC的镍基复合镀层，在MM－200摩擦磨损试验机上对镀层进行磨损试验，研究了阴极电流密度、镀液温度、SiC浓度和pH值等主要工艺参数对镀层耐磨性能的影响，以确定工艺参数范围，并采用正交试验方法分析得到最佳的工艺参数。结果表明，纳米SiC复合镀层的最佳工艺参数为：电流密度3A／dm^2，温度30℃，SiC含量5g/L,pH=3.5。     

钕铁硼磁体的有机溶液电镀铝研究

对钕铁硼磁体自AlCl LiAlH4的四氢呋喃－苯溶液中电镀铝进行了研究,结果表明：在电流密度为1－5A／dm^3时得到的镀层最为致密均为;当电流密度为10A／dm^3时,电镀速度可达到72μm/h;镀铝磁体在3．0％氯化钠溶液中的耐腐蚀性能优于电镀镍、锌磁体,经阳极氧化和铬酸盐处理后,性能进一步提高;有机溶液电镀铝方法是钕铁硼磁体有效的防腐蚀手段。     

A100钢镀Cr防护技术在海洋环境下的腐蚀行为研究

通过海南户外暴露实验研究了A100钢表面镀铬层的腐蚀行为.使用扫描电镜观察了腐蚀后镀层的表面和截面形貌,利用交流阻镜技术表征了镀层在不同腐蚀阶段的特征;并讨论了腐蚀对力学性能的影响.结果表明:镀层表面存在的显微裂纹是腐蚀发生、发展过程中的主要影响因素,腐蚀对镀层力学试样的力学性能影响很大,导致抗拉强度降低,断口呈脆性断...     

三价铬硫酸盐体系快速电沉积可行性探讨

三价铬镀铬是替代六价铬镀铬理想的清洁生产工艺.研究了电流密度、电镀时间和不同基体金属对三价铬硫酸盐镀液中快速镀铬的影响.结果表明:采用三价铬硫酸盐镀液在铜、镍和低碳铜基体上进行快速镀铬都可得到表面连续致密、结构为非晶态的铬镀层,镀速在铜基体上比在镍和低碳钢基体上快很多;电流密度10 A/dm2下电镀10 s,铜基体上可得到0.40μm以上的铬镀层,平均镀速可达2.50μm/min;镍和低碳钢基体上只能得到0.10μm的铬镀层,平均镀速为0.50 μm/min;快速镀铬的电流效率与电流密度有关,电流密度为10～12 A/dm2时可达25.0%以上;三价铬硫酸盐镀液长时间连续快速镀铬时镀液体积明显减少、pH值降低.     

脉冲参数对氨基磺酸盐镀镍择优取向的影响

采用脉冲电镀在氨基磺酸盐镀液中以相同的平均电流密度不同脉冲导通／间歇时间制备镍镀层，用X射线衍射仪(XRD)研究了镀层结构及脉冲参数对镀层择优取向的影响。结果表明，所有镍镀层皆为面心立方结构，在(200)面有明显择优取向；脉冲间歇时间(toff)为9ms时，(200)面的相对取向密度(J200)随脉冲导通时间(ton)的增加而减小；ton为0．1ms时，J200随toff的增加而增大；当脉冲峰值电流密度(ip)大于19A／dm^2时，J200随ip的增大而增大；(200)面择优取向密度受过电位、镍离子的还原速度和氢氧化镍在阴极表面吸附的共同作用。     

电沉积Ni-Cr合金工艺研究

含有一定量Cr的Ni-Cr镀层具有良好的耐磨、耐腐蚀性能.选取柠檬酸钠作为配位剂,用动电位扫描法研究了电沉积Ni-Cr合金时的阴极行为,同时对镀层的耐腐蚀性进行了试验.试验结果表明:镀液中加入配位剂柠檬酸钠可以提高阴极极化;pH值、阴极电流密度、配位剂对镀层中铬含量影响较大,在一定范围内增大pH值,增加配位剂的用量,提高电流密度,有利于提高镀层中铬的含量,最佳工艺条件为pH值为2.5,阴极电流密度为25A/dm2,镀液中柠檬酸钠的含量为35g/L,镀层中铬质量分数为20%左右时,Ni-Cr合金镀层的耐腐蚀性能最好.     

超细晶镍钴合金的电铸工艺

为了进一步提高金属的硬度和强度,采用电铸工艺通过添加剂TN2提高阴极过电位,抑制晶粒生长,制备了超细晶镍钴合金层,研究了电流密度和添加剂TN2对铸层晶粒大小的影响.结果表明:提高电流密度可以细化晶粒,当电流密度从5 A/dm~2 增加到15 A/dm~2 时,晶粒大小从5μm 细化到500 nm;添加0.15 g/L TN2 时,铸层表面半光亮,晶粒进一步细化(小于500 nm),硬度高达60 HRC.     

Cracks,microcracks and fracture in polymer structures: Formation,detection, autonomic repair

Polymers and polymer composites are susceptible to premature failure due to the formation of cracks and microcracks during their service time. Evolution of cracks and microcracks could induce catastrophic material failure. Therefore, the detection/diagnostics and effective repair of cracks and microcracks are vital for ensuring the performance reliability, cost effectiveness and safety for polymer structures. Cracks and microcracks, however, are difficult to detect and often repair processes are complex. Biologically inspired self-healing polymer systems with inherent ability to repair damage have the potential to autonomically repair cracks and microcracks. This article is a review on the latest developments on the topics of cracks and microcracks initiation and propagation in polymer structures and it discusses the current techniques for detection and observation. Furthermore, cracks and microcrack repair through bio-mimetic self-healing techniques is discussed along with surface active protection. A separate section is dedicated to fracture analysis and discusses in details fracture mechanics and formation.     

镀铬层气密性研究

活塞杆镀铬层的气密性问题，是航空工厂长期存在的的一个老大难问题，为了解决一这问题，本文从消除或减少铬层裂纹（治本）和封闭或碾压裂纹（治标）两个方面进行了研究，证明采用脉冲镀铬＋铬层金刚石碾平工艺，保证铬层的气密性达到设计要求。     

Experimental and computational study on thermo‐mechanical fatigue life of aluminium alloy piston

To assess the life of a new diesel aluminium alloy piston under thermal shock loads, thermo‐mechanical fatigue (TMF) testing was conducted to characterise the TMF properties of the piston alloy, and an empirical model based on the constraint ratio concept was proposed to predict the TMF life of the piston. Considering that the empirical model required expensive experimental support, a platform with high‐frequency induction heating was established to simulate the force on the piston under thermal shock loads to calculate the piston life using the thermal shock test. Additionally, a finite element method was developed to compute the distributions of temperature, strain, and stress during this process. The characteristics of crack initiation and propagation in TMF test rods and piston mock‐ups were also investigated. The results showed that the TMF test rod suffered brittle fracture with brittle quasi‐cleavage features. The microcracks mainly occurred in primary Si particles due to stress concentration around the primary Si particles induced by the difference between the thermal expansion coefficients of Si and Al. From a macro perspective, the piston initially cracked at the rim above the pinhole, where the stress is larger than that along other directions. From a micro perspective, the protrusions of various sizes on the piston rim were induced by the compression stresses at high temperature. The piston cracks usually initiate around primary Si particles, propagate along the edge of primary Si in a straight line, bifurcate and then stop at a certain depth. If the piston was only heated, cracks or plastic deformations were not produced. The piston life can be assessed using the proposed empirical model based on the constraint ratio concept or thermal shock testing based on the developed platform. The difference between the predicted and experimental life was not greater than 7%.     

Cracking in cement paste induced by autogenous shrinkage

Detection and quantification of microcracks caused by restrained autogenous shrinkage in high-performance concrete is a difficult task. Available techniques either lack the required resolution or may produce additional cracks that are indistinguishable from the original ones. A recently developed technique allows identification of microcracks while avoiding artefacts induced by unwanted restraint, drying, or temperature variations during sample preparation. Small cylindrical samples of cement paste are cast with steel rods of different diameters in their centre. The rods restrain the autogenous shrinkage of the paste and may cause crack formation. The crack pattern is identified by impregnation with gallium and analyzed by optical and scanning electron microscopy. In this study, a non-linear numerical analysis of the samples was performed. Autogenous strain, elastic modulus, fracture energy, and creep as a function of hydration time were used as inputs in the analysis. The experimental results and the numerical analysis showed that samples with larger steel rods had the highest probability of developing microcracks. In addition, the pattern and the width of the observed microcracks showed good agreement with the simulation results.     

Improvement in the fatigue strength of chromium electroplated AISI 4340 steel by shot peening

In landing gear, an important mechanical component for high responsible applications, wear and corrosion control is currently accomplished by chrome plating or hard anodising. However, some problems are associated with these operations. Experimental results have also shown that chrome‐plated specimens have fatigue strength lower than those of uncoated parts, attributed to high residual tensile stress and microcracks density contained into the coating. Under fatigue conditions these microcracks propagate and will cross the interface coating‐substrate and penetrate base metal without impediment. Shot peening is a surface process used to improve fatigue strength of metal components due to compressive residual stresses induced in the surface layers of the material, making the nucleation and propagation of fatigue cracks difficult. This investigation is concerned with analysis of the shot peening influence on the rotating bending fatigue strength of hard chromium electroplated AISI 4340 steel. Specimens were submitted to shot peening treatment with steel and ceramic shots and, in both cases, experimental results show increase in the fatigue life of AISI 4340 steel hard chromium electroplated, up to level of base metal without chromium. Peening using ceramic shot resulted in lower scatter in rotating bending fatigue data than steel shots.     

阴/阳极电流密度对铝合金微弧氧化陶瓷膜耐蚀性的影响

为了弄清铝合金微弧氧化重要参数对其耐点蚀和微硬度的影响,在氢氧化钠和硅酸钠溶液中,保持阳极电流密度为15A/dm2,制备了阴/阳极电流密度比在0.6～0.8之间的铝合金微弧氧化陶瓷膜.结果表明:阴/阳极电流密度比对陶瓷膜的抗点腐蚀性和硬度有很强的影响;不同阴/阳极电流密度比所制备的陶瓷膜微观结构差异较大,陶瓷膜抗点腐蚀性和硬度的不同是由这种微观结构差异所引起的.     

Electroplating characteristics of eutectic Sn-Cu ions for micro-solder bump on a Si chip

The fabrication of fine bumps on a Si chip is an important issue due to the trend of smaller sized and multi-functioning electronics. In this study, a Sn-Cu near eutectic solder bump was fabricated by electroplating. A Si wafer was used as a substrate, while layers of the Under Bump Metallization (UBM) of Al/Cu/Ni/Au (400/300/400/20 nm in each) were coated onto the Si wafer by electron beam evaporation. The bumps on the UBM were plated by a direct current, and the bump size was 20 x 20 x 10 microm with a 50 microm pitch. Characteristics of the electroplated bumps were examined by XRD, EDS and EPMA. A polarization curve was established to find a potential range of electrodeposition of Sn-Cu. By plating with a reduction current density of 1 A/dm2 for 23 min, a near eutectic Sn-Cu bump was obtained. The bump height increased in current density, namely from 2.25 microm at 0.5 A/dm2 to 6.58 microm at 2 A/dm2 from 10 min of plating. In the electroplated state, a beta-Sn and Sn-Cu intermetallic compound (IMC) coexisted in the bumps. Cu3Sn and Ni3Sn4 IMCs were discovered by XRD analysis along the interface between the bump and the UBM.     

微等离子体氧化法制备TiO2薄膜的性能研究

选用TA1钛合金,运用微等离子体氧化技术在其表面原位生长TiO2薄膜.在(Na3PO4-Na2B4O7)电解液体系中,采用XRD、SEM对钛合金表面成膜的微观结构进行测试研究,结果表明:当配比为4:1,成膜时间60min,电流密度10A/dm2条件下制得的薄膜,该膜层中TiO2主要为锐钛矿晶型,膜层均匀,表面粗糙多孔,孔洞大小适中;同时,在电解液中掺杂一定浓度的Fe3 、Si4 离子,当掺杂量分别为0.1～0.2g/L、0.5～1.0g/L条件下制备的薄膜,用于光催化氧化降解水中的罗丹明B,可以提高其光催化活性.