激光处理Ni-P-Al2O3纳米化学复合镀层的微观组织

为了获得性能优良的镀层,在Fe-C合金表面制备了均匀的化学镀层,然后通过高功率连续CO2激光处理镀层表面,利用透射电子显微镜(TEM)观察了沉积Al2O3粒子的微观形貌,采用光学显微镜(OM)和扫描电子显微镜(SEM)观察了镀层处理前后表面及截面形貌,用X射线能谱仪(EDS)对处理前后的镀层进行了元素分析,用X射线衍射仪(XRD)进行物相分析,测试了处理前后镀层物相的变化,用微观硬度仪测量了激光处理后截面的硬度分布.结果表明,激光处理后,强化层表面平整光滑,与基体形成冶金结合,成分均匀,组织细密;处理层物相明显栽从镀态的非晶态向晶态转变,出现了Ni3P和其他一些非平衡强化相.截面处理层由表及里可分为四层:激光作用层、过渡层、热影响区(HAZ)以及基体.纳米Al2O3颗粒均匀分布在过渡区,激光处理层显微硬度约提高3倍,这主要是由于Al2O3颗粒的弥散强化作用以及生成新的强化相磷化物所致.

Microstructure Characterization of Ni-P-Al2O3 Electroless Composite Plating on Fe-C Alloy Treated by Laser Beam

The uniform Ni-P-Al_2O_3 eletroless plating was produced on Fe-C alloy,and treated by high power continuous-wave(CW)CO_2 laser.Transmission electron microscope(TEM)was applied to observe the morphology of the Al_2O_3 particles.Optical microscope(OM)and scanning electron microscope(SEM)were used to observe the morphologies of the coating.X-ray diffraction(XRD)and X-ray energy dispersive spectroscopy(EDS)were employed to analyze the phases and elements of the coating.The changes of micro-hardness before and after laser processing were tested respectively.The results reveal that the strengthened coating has good performances with smooth surface,uniform components and fined microstructure.The phases in strengthened layer obviously changes from amorphous state to crystalline state and the main phase is Ni_3P with some non-equilibrium phases.Al_2O_3 particles are homogeneously dispersed in the grain boundaries,which can greatly improve the material properties. The whole coating is divided into four regions from surface to inner as follows:laser strengthed region,transition zone,heat affected zone(HAZ)and substrate.The microhardness of strengthened region is about 3 times of substrate owing to the dispersion of the Al_2O_3 particles and the phosphide as strengthening phase.