激光强化NiAl/纳米Al_2O_3复合镀层的显微组织与显微硬度

Microstructure and microhardness of NiAl/nano Al_2O_3 electroless composite plated coating by laser hardening

用化学复合镀技术在45钢基体上制备NiAl/Al2O3复合镀层,并用高功率连续CO2激光在多种扫描速度及功率密度下对镀层进行强化。采用光学显微镜(OM)、能谱(EDS)、扫描电子显微镜(SEM)、X射线(XRD)和显微硬度仪(载荷200 g、加载时间15 s)分别对镀层强化前后表面及截面形貌、元素、物相、显微硬度等进行分析。结果表明:用高功率、快扫描、大光斑的工艺直接合成了Ni30Al20Fe金属间化合物,并制备出无裂纹和气孔,连续完全致密,与基体形成冶金结合的涂层,截面由表及里可分为4层:激光作用层、过渡层、热影响区(HAZ)以及基体,Al2O3颗粒均匀分布在过渡区,激光强化层显微硬度约是基体的4倍,这主要是由于Al2O3的弥散强化作用和强化相Ni0.77AlFe0.23、Fe0.64Ni0.36的存在共同提高了镀层的硬度。

NiAl/Al2O3 composite coatings were prepared on 45 steel substrates by electroless composite plating.The transverse-flow CO2 laser was employed for strengthening the coatings at various scanning velocities and power densities.The surface section pattern,composition,phase and microhardness of the plated coatings before and after laser hardening were analyzed by optical microscope（OM）,energy dispersive X-ray spectrum（EDS）,scanning electron microscopy（SEM）,X-ray diffraction（XRD） and microhardness tester（load of 200 g and loading time of 15 s）.The high laser power,fast scanning velocity and big beam diameter were employed to directly synthesized Ni30Al20Fe.Moreover,the coatings with fully dense,free of cracks and porosity were fabricated,with the metallurgical bonding with the substrate.The coating from surface to inner consists of four regions as follows： laser strengthed region,transition zone,heat affected zone（HAZ） and substrate.The microhardness of hardening zone is about 4 times of substrate for the strengthened dispersion of the Al2O3 particles,strengthening phase of Ni0.77AlFe0.23 and Fe0.64Ni0.36.