材料期刊网

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CeO₂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CeO₂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CeO₂粒子对Ni镀层抗磨损的作用。结果表明：在45+80 kHz交变频率超声振荡条件下,电解液中的活性CeO₂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-CeO₂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CeO₂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NiO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。

With industrial developments of aerospace vehicles, marine devices, biomedical and bones, pure Ti and its alloys have gained a great deal of attraction due to their superior properties. Despite having promising properties, limitations of lower hardness, inferior weldability, and poor brittle fracture have restricted their applications. So the objective of this work was to make surface electrodeposition of nanocrystalline Ni coatings on the surface of TA2 substrate using pulsed electrodeposition. Scratch tests was used to compare how effects of two typical HF and DMF activating solutions on modifying interfacial adhesion between TA2 substrate and surface coatings. In order to disclose crystal growth of Ni coating without and with CeO₂ addition, a variety of characterizations such as FESEM, TEM and XRD were employed. A novel decussating-type microhardness with different loading forces attached with nanoindentation tests was conducted to make a comparative study of toughness and strengthening mechanisms between surface coatings and the un-coated TA2 substrate. Besides, wear behaviors of specimens was carried out using the ball-disc dry sliding tests. Results indicated that the addition of CeO₂ nanoparticles into electroplating solution has effectively modified textural growth of Ni grains. This result was attributed to the presence of nano-sized CeO₂ particles that adsorbed onto the preferred locations of crystal Ni growth, leading into an increasing catalytic site of nucleation to reduce Gibbs energy for grain refinement. According to observations of edges for hardness indentations, a smaller size with convergence feature for Ni-CeO₂ coatings was indicative of effects of CeO₂ nanoparticles or its precipiated Ce solute atoms on alloying-dispersion strengthening for completing defective grain boundaries. While for the case of a divergency state of indentations edges within obviously spalling cracks, it exhibited poor surface toughness for pure nickel. Furthermore, An analytic modeling validated here was based on the by-passing Orowan for dislocations pile-up mechanisms, in which this was contributed to the co-existence of Ce-rich worn products and NiO passive film to be expected as solid lubricants and make the self-lubricating effect, thereby improving wear resistance of Ti alloys where subjected to harsh conditions.