STRATIFICATION MECHANISM AND INTERFACE CHARACTERIZATION OF (TiN), (TiC)/NiCrBSi COMPOSITE COATINGS SYNTHESIZED BY LASER REMELTING

Abstract

TiC / TiN -reinforced composite coatings were fabricated on the substrate of Ti – 6Al – 4V alloy using laser remelting. X-ray diffraction (XRD) was used to identify the phases in the laser-clad composite coating; the interface characterization of the dilution zone-clad zone (IDC) and the dilution zone-heat-affected zone (IDH) was observed with a scanning electron microscope (SEM). The results show that the microstructure of a cross-section has stratification characterization, and consists of the clad zone (CZ), the dilution zone (DZ), the diffusion layer (DL) and the heat-affected zone (HAZ). The layer-by-layer microstructure results from the boundary layer phenomenon of viscous melt-fluid and diffusion. The kind of reinforced particle has an effect on the interface morphology, microstructure and flow characterization of the melt-fluid. The phase constitution in the clad zone consists of ( Cr – Ni – Fe ), TiC , Ni 4 B 3, Ti 2 Ni , Cr 2 B and M 23 C 6 for TiC + NiCrBSi coating, and ( Cr – Ni – Fe ), TiN , NiB , Cr 2 Ti and Ti 2 Ni for TiN + NiCrBSi coating. The interfaces of the IDC in the NiCrBSi -clad layer is clear and clean; those of TiC + NiCrBSi and TiN + NiCrBSi are illegible. Ti – Ni phases with acicular microstructure link dilution zone and clad zone, and two kinds of phase with acicular microstructure, are similar in composition and shape.