Surface Repairing with Homogenous GH4169 Coatings Synthesized by Laser Cladding in N₂-Atmosphere

The homogenous GH4169 coatings were deposited by laser cladding on Ni-based GH4169 substrate,an advanced aircraft engine material.The influence of the N₂-atmosphere on the microstructures,phase-structures and micro-hardness was investigated with scanning electron microscopy and energy dispersive spectroscope.The preliminary results show that the N₂-atmosphere made a big difference.To be specific,the GH4169 coating comprised columnar dendrites and a portion of equiaxed dendrites; the N₂-atmosphere cooled and solidified the molten “pool” of GH4169 much faster than Ar-atmosphere,because of higher heat capacity and greater thermal conductivity.In the solidification,N₂ significantly increased the Nb-content in γ-phased grains,and simultaneously decreased the Nb-content in Laves-phased clusters.In addition,the dual-ageing of GH4169 coatings initiated the formation of γ-phased grains in GH4169 substrate.The higher Nb-content and more precipitation of γ-phased grains accounted for the micro-hardness enhancement.