基于双脉冲电沉积技术在活性钛基(TA2)表面制备纳米晶Ni镀层。通过涂层附着力测试对比研究HF体系和DMF改良型活化液对TA2基体与表面镀层界面结合力的影响;借助TEM、FESEM和XRD等表征技术探讨添加纳米CeO_2粒子前后对纳米电沉积层中Ni晶织构生长的影响;通过对纳米压痕及不同载荷下"十字交叉"型环形硬度压痕特征观察,分析复合CeO_2粒子对Ni镀层表面强韧性的影响机制;进一步探讨在高速干摩擦条件下复合CeO_2粒子对Ni镀层抗磨损的作用。结果表明:在45+80 k Hz交变频率超声振荡条件下,电解液中的活性CeO_2粒子能有效吸附在优先生长Ni晶尖端,同时降低了Ni晶生长Gibbs自由能,并演变为Ni晶的催化形核中心来诱发异质形核;纳米压痕测试表明:在500 g高载荷测试条件下,相对于纯Ni镀层试样的硬度压痕边缘的明显开裂和外拓迹象,Ni-CeO_2复合镀层试样则表现为收敛性和连续完整的压痕边缘特征,显示出良好的强韧性。基于干摩擦过程中释放出大量的热,促使部分稀土CeO_2相弥散或少量析出Ce溶质原子,具有对滑移的位错和晶界等缺陷产生钉扎拖拽作用,由此建立以Orowan位错绕过强化和位错塞积的机制模型;干摩擦过程促使部分富Ce磨损产物与Ni O氧化膜机械混合来充当固体润滑剂,能起到良好的减摩作用,弥补了Ti表面耐磨性差等缺陷。
Nano-CeO2 （RE） particles were co-deposited into Ni-P binary composite coatings by applying pulse current （PC） under ultrasonic （U） field. Morphology, chemical content and crystal microstructure were characterized by environmental scanning electron microscopy （E-SEM） with energy dispersive X-ray analysis （EDXA）, XRD diffractometry and transmission electron microscopy （TEM）. Experimental results show that Ni-P coating reinforced with 15g/L nano-CeO2, in amorphous state and with compact structure, can be improved in the microhardness from HV0.2580 to HV0.2780 by annealing at 600 °C for 2 h. The highest content of codeposited Ce and deposition rate can reach 2.3% and 68 μm/h, respectively. Furthermore, the effect of RE adsorption and pulse overpotential on depositional mechanism was investigated. n-CeO2 particles or Ce4＋ ions with strong adsorption capacity acted as the catalytic nucleus to improve densification effectively. During annealing at 600 °C for 2 h, n-CeO2 particles will uniformly adsorb on crystal grain to preferentially pad and heal up gaps of cracking Ni boundaries, promoting dispersion strengthening with refiner-grained structure.
Ni-P and its nano-CeO2 doped coating were electrolessly prepared in acidic condition,and their microstructure and anti-corrosion property were studied and compared.Scanning electronic microscopy（SEM）,transmission electronic microscopy（TEM）,X-ray diffraction spectrometer（XRD）and differential scanning calorimeter（DSC）were used to examine surface morphology and microstructure of coatings.The results showed that Ni-P coating had partial amorphous structure mixed with nano-crystals,while the Ni-P/CeO2 coating had perfect amorphous structure.Upon heating,Ni3P precipitation and Ni crystallization took place in both coatings but at different temperatures of phase change.In addition,the Ni-P/CeO2 coating had sintered phase of NiCe2O4 spinels.The anti-corrosion property and passivity were improved in the CeO2-doped coating because it was less liable to undergo localized corrosion and had a slower corroding rate than its CeO2-free counterpart.During the co-deposition process,some Cen+（n=3,4）ions might be adsorbed to the metal/solution electrical double layer and hinder nickel deposition.Ni-P/CeO2 coating’s perfect amorphous structure was probably due to the hindered crystal-typed deposition of nickel and the promoted deposition of phosphorous.
