镍-磷-纳米氧化铝化学镀层的激光热处理及其摩擦磨损性能

用化学镀技术在中碳钢基片上制备镍-磷-纳米氧化铝复合镀层,并用CO2激光在多种扫描速度及功率密度下对镀层进行热处理.采用能谱(EDS),扫描电子显微镜(SEM),X射线衍射(XRD)、划痕实验和球盘式摩擦磨损实验对镀层的成分、结构形貌、结合力和摩擦学性能等进行表征,并考察工艺参数对镀层结构和耐磨性能的影响.结果表明,激光热处理后镀层由非晶态变为晶态,析出Ni和Ni3P相,而Al2O3仍呈非晶态;镀层硬度因相变硬化而显著提高,表面粗糙度增加和相结构的改变导致摩擦系数上升,镀层结合力小幅度下降,其主要磨损机制为磨粒磨损.在扫描速度1.5~3.0 m/min,激光功率密度5.0~8.3 kW/cm2范围内,镀层硬度高、耐磨性能优异,最低磨损率为1.21×10-5mm3/(N·m).

Laser Heat Treatment and Wear Resistance of Electroless Plating Ni-P-Nano-Al2O3 Composite Coatings

The Ni-P-nano-Al2O3 composite coatings were prepared onto medium carbon steel substrates by electroless plating method. The transverse-flow CO2 laser was employed for the heat treatment of the coatings at various scan velocities and power densities. The composition, microstructure, morphology, adhesion to the substrate and wear resistance of the coatings were characterized by energy dispersive X-ray spectrum (EDS), scanning electron microscopy (SEM), X-ray diffraction (XRD), scratch test and friction and wear test (ball-on-disk). The effects of process parameters on microstructure and wear resistance of the coatings were investigated. It is found that the laser heat treatment conduces the microstructure from amorphous to crystalline structure, which comprises Ni3P and Ni phase, and Al2O3 phase remaines amorphous; the hardness of the coatings increases obviously for the phase transformation hardening. The friction coefficient increases due to the transformation of phase structure and the raise of surface roughness of the coatings, and the adhesion to the substrate decreases slightly. The main operating wear mechanism is abrasion. By treating with scan velocity 1.5～3.0 m/min, power density 5.0～8.3 kW/cm2, the coatings show high hardness, good wear resistance and a minimum wear rate of 1.21×10-5 mm3/(N·m).