采用横流5 kW CO2激光,在Ni基高温合金表面制备了纳米Al2O3/Ni基合金复合材料激光熔覆层。利用光学显微镜、扫描电镜(SEM)及附件(EDS)分析了熔覆层的快速凝固组织、成分及纳米颗粒的分布。结果表明,未加纳米Al2O3时界面区为垂直于界面、定向生长的柱状树枝晶组织;加入纳米Al2O3后,熔池凝固结晶组织形态发生变化,由细长的柱状树枝晶逐步过渡为较短的树枝晶;当Al2O3的加入量为1%时,熔覆层与基体的界面区不出现定向生长,整个断面呈现等轴枝晶组织;纳米Al2O3促进固液界面前沿形核,纳米Al2O3附着在晶体生长的前沿,阻碍晶体的长大,凝固组织得到显著细化;纳米Al2O3颗粒抑制了熔覆层裂纹的形成。

Composite coatings of Al2O3 nanocrystalline/Ni-based powder produced by transverse flow CO2 laser on Ni-based superalloy were introduced. With Olympus Pme-3 type optical microscope, Philip-XL 30 type scanning electronic microscope (SEM) and energy dispersive X-ray spectroscopy (EDS), the microstructure, chemical composition and distribution of nano particles of the cross-sections of the coatings were analyzed. The results showed that columnar dendrite grew perpendicularly to the interface without nano Al2O3 particles. And the growth morphologies of dendrite transformed from long columnar to short form by adding nano additives. Non-directional dendrite growth at the interface and equaxied dendrite across the section of the clad appeared with the additive amount of Al2O3 particles to 1%. The solidified microstructure was greatly refined because the nano Al2O3 accelerated nucleation ahead of the advancing interface of solid/liquid and held back crystal growth by its concentration. Nano particles prevented the formation of cracks in the coatings.