为了提高碳钢的表面性能,在45#钢表面制备Ni-P-纳米Al₂O₃化学复合镀层,再通过脉冲Nd:YAG激光对镀层表面进行强化处理。利用光学显微镜(OM)和扫描电子显微镜(SEM)观察镀层在脉冲激光处理前后的表面形貌与截面微观组织,利用X射线能谱仪(EDS)对截面进行元素分析,用X射线衍射仪(XRD)对脉冲激光处理前后镀层进行物相分析,用显微硬度计测量镀层截面硬度分布。结果表明,镀层经脉冲激光处理后,由表及里分为树枝晶区、胞晶区、柱状晶区、熔合区、热影响区(HAZ),并与基体形成冶金结合;镀层由非晶态转变为晶态,生成Al5FeNi,FeNi及Fe0.64Ni0.36等金属间化合物;强化层最高硬度较未经激光处理的复合镀层提高1.7倍,较基体提高4.5倍,这是硬质相粒子弥散强化及马氏体相变强化综合作用的结果。

To strengthen the surface performance of medium steel,Ni-P-Al₂O₃ electroless composite plating was produced on 45# steel,and then treated by pulsed Nd:YAG laser beam. Optical microscope (OM) and scanning electron microscope (SEM) were used to observe the microstructure of the coating. X-ray energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) were employed to analyze the phases and elements of the coating. The micro-hardness of pulse laser processing was tested. The results reveal that the hardened coating has good performance with uniform components and fined microstructure. The phases in hardened layer obviously change,the coating is divided into five regions from the surface to inner as follows:dendrite region,cystiform crystal zone,columnar crystal zone,fusion zone,heat affected zone (HAZ) and substrate. After laser process,the coating obviously transits from amorphous state to crystalline state,where non-equilibrium phases such as Al5FeNi,FeNi and Fe0.64Ni0.36 were found. The microhardness of hardened region is about 1.7 times of as-deposited layer and 4.5 times of the substrate owing to dispersion and transformation strengthening.