Investigation on the interface microstructure and phase composition of laser cladding pure copper coating

Laser cladding is an efficient and clean method that can prepare a corrosion-resistant pure copper coating on the nuclear fuel container surface to ensure service safety. In this study, the single-layer and double-layer pure copper coatings were prepared on 20# steel tubes by laser cladding. The microstructure, elements distribution, phase composition, and interface structure, as well as strain distribution, were characterized by Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM), and transmission kikuchi diffraction (TKD). The results show that the kernel average misorientation (KAM) and geometry necessary dislocation (GND) density at the coating/substrate interface in the double-layer Cu coating decrease compared to the single-layer Cu coating. Under the thermal action during laser cladding of double-layer coating, the phase composition in the substrate transforms completely from austenite, FeO, and ferrite to the entire ferrite. The Cu/Fe interface maintains certain orientation relationships, namely the Kurdjumov-Sachs (KS) and the Nishiyama-Wassermann (NW) relationships, with a mismatch of only 3.01 % for the coherent interface. Thus, the lattice distortion at the interface reduces, slightly alleviating the strain concentration.