Characterization of Hf-Doped CoCrAlYSi Coatings Synthesized by Laser Cladding on Ni-Based GH586 Alloy

The Hf-doped CoCrAlYSi coatings were synthesized by laser cladding on substrate of Ni-based GH586 super-alloy. The influence of the Hf-content on the microstructures and oxidation resistance was investigated with X-ray diffraction, energy dispersive spectroscopy, scanning electron microscopy and oxidation-test at 1100℃ for 100 h. The results show that the Hf-content had a major impact. For instance, the crack-free reticular structures and many pores at the grain-boundary co-exist on the surfaces of laser cladded CoCrAlYSi coating. As the Hf-content increased from 0.1 to 0.3 in the CoCrAlYSiHf_x coatings, dominated by γ-Co phase, the pore and micro-crack densities increased, possibly because the laser induced degassing and oxidation at grain-boundary. In oxidation test, 6 and 12 μm thick oxide-layers formed on CoCrAlYSi and CoCrAlYSiHf_x surfaces, respectively, and the 12 μm thick, compact porous Cr₂O₃-layer was found to display strong oxidation-resistance even at 1100℃.