纳米A_2lO_3对激光熔覆钴基合金涂层组织的影响

Effect of nano-Al2O3 on microstructure of cobalt based alloy coating by laser cladding

利用5kWCO2激光器,在镍基高温合金表面熔覆纳米Al2O3/钴基合金复合材料,制备了涂层。利用光学显微镜、扫描电镜和透射电镜分析了熔覆层的组织结构。结果表明,加入纳米Al2O3,界面的生长形态发生变化,由细长的柱状树枝晶转变为较短的树枝晶;纳米Al2O3含量大于1%时整个断面获得等轴枝晶组织;纳米Al2O3作为异质形核的核心,细化了组织;纳米Al2O3在熔覆层中分布不均匀,促进了γ-Co向ε-Co的转变;熔覆层的亚结构为层错。对熔覆层的组织形成机理进行了分析。

Composite coatings of nano-Al2O3/Cobalt-based alloy are formed by laser cladding with a 5 kW CO2 laser on Ni-based superalloy. Cross-section of the coatings has been examined to reveal their microstructure, phase composition and sub-microstructure using optical, scanning electron microscope (including energy dispersive spectroscope), transmission electron microscope and X-ray diffraction. The results showed that fine dendrite microstructure occurred by adding nano-Al2O3. When the additive amounted to 1%, fully equiaxed crystallization appeared. There existed some equilibrium and non-equilibrium phases in the coatings, such as γ-Co, Cr23C6, CoAl2O4, Al2O3 and Ε-Co. These were contributed to that nano-Al2O3 acting as new nucleation site and rapid solidification of the melting pool. The results also showed inhomogeneous dispersion of nano-Al2O3 at the grain boundary and stacking fault of sub-microstructure in the coatings. The mechanism of formation of microstructure was analyzed.