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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。 相似文献
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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 相似文献
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三价铬硫酸盐体系快速电沉积可行性探讨 总被引:1,自引:0,他引:1
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. 相似文献
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脉冲参数对氨基磺酸盐镀镍择优取向的影响 总被引:1,自引:0,他引:1
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。 相似文献
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电沉积Ni-Cr合金工艺研究 总被引:2,自引:2,他引:2
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. 相似文献
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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. 相似文献
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Ziliang Li Jianxing Li Zhengke Chen Jinbao Guo Ye Zhu Yu Luo 《Fatigue & Fracture of Engineering Materials & Structures》2021,44(1):141-155
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%. 相似文献
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Cracking in cement paste induced by autogenous shrinkage 总被引:1,自引:1,他引:0
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. 相似文献
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H. J. C. VOORWALD M. P. SILVA M. Y. P. COSTA M. O. H. CIOFFI 《Fatigue & Fracture of Engineering Materials & Structures》2009,32(2):97-104
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. 相似文献
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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. 相似文献
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微等离子体氧化法制备TiO2薄膜的性能研究 总被引:2,自引:1,他引:2
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. 相似文献