超声振荡频率对电沉积纳米晶Ni微织构生长和抗磨性的关联性研究

Influence of Ultrasound with Varying Frequencies on Microstructures and Wear Resistance for Ni Nanocrystals

摘要:

在阳极氧化纳米多孔Ti基体表面电沉积纳米晶Ni镀层，通过界面互扩散和晶体“钉扎”生长来达到冶金结合，旨在解决Ti基与其表面镀层界面结合力差的难题。采用超声辅助脉冲电沉积技术，通过调整超声振荡频率来影响纳米晶Ni生长织构，以揭示不同择优取向的生长织构与微结构和抗磨性的相关性。利用XRD、FE-SEM、TEM等手段来表征纳米晶Ni的生长织构及微结构；借助纳米压痕与摩擦磨损实验来研究其表面强韧性和抗磨性，分析超声作用对碎化晶粒和改善晶体生长织构方向的协同作用机制。此外，探讨超声振荡作用对电沉积过程中纳米晶Ni动态再结晶生长的影响机理，以及不同择优取向的Ni生长织构与其表面力学性能改善的关联性。结果表明：在纳米多孔Ti基体表面预生长Pd原子来诱发后续的电沉积纳米晶Ni进行异质形核生长，成功实现“钻孔钉扎”生长模式，提高了Ti/Ni间的界面结合力，部分界面达到冶金结合效果；纳米压痕测试结果表明，在Ti基体表面电沉积生长纳米晶Ni镀层，显著提高了其表面的强韧性，硬度与弹性模量可分别达15.6与197.2 GPa；同时，大幅度提高了Ti基体表面抗摩性，摩擦系数比Ti基体降低约1/2，其表面磨损形貌由Ti基表面的切削磨损转变为在轻微磨粒磨损条件下的黏着磨损机制，可有效弥补Ti金属在工程上耐磨性差的缺点。

Abstract:

Because of its light weight, high strength and excellent corrosion resistance, titanium and its alloys have been currently used as a brand-new functional material in ships, aviation and other fields. However, it yet exists some defects such as poor surface weldability and wear resistance, especially under the dry-sliding conditions without solid lubricants, so it is essential to enhance its surface properties using surface modification techniques. Herein, this study focused on surface electroplating of nanocrystalline Ni coating on the anodized nanoporous surface of Ti substrate, as well as to achieve a metallurgical bonding interface. In view of this, the objectives of this study are to explore the detailed correlation between growth textures and wear resistance of Ni deposits by means of adjusting ultrasonic frequencies (shorted as “UF”) values. The textural directions and microstructures of the as-deposited Ni nanocrystals were characterized using XRD, FE-SEM and TEM. According to Nanoindentation and wear tests, the synergistic effects from ultrasonic oscillations on both grain refinement and crystallographic texture of Ni nanocrystals were evaluated. Besides the underlying mechanism involved in effects by ultrasonic oscillation on dynamic re-crystallization of Ni textures during the electroplating process, and the relationship between different textural directions of Ni crystals and surface properties were disclosed. The survey results manifested that the pre-adsorbed Pd atoms onto the as-anodized porous Ti surface were acted as nucleation sites for inducing the subsequent Ni growth, having an effective interfacial strength of Ti/Ni composites. Based on Nanoindentation results, it significantly improved its surface toughness by depositing Ni coatings onto the as-anodized Ti matrix, and the hardness and elastic modulus reached 15.6 and 197.2 GPa. Meanwhile its friction coefficient of Ti matrix within Ni coating at UF values of 45+80kHz was much lower, which was reduced by about 2 times relative to that of bare Ti matrix. Ultimately, the wear mechanism was transformed from the originally cutting wear behavior of Ti matrix into the sightly adhesive wear together with grinding abrasion for Ni deposits, effectively compensating the shortcomings of poor wear resistance for Ti alloys used in engineering applications.