Microstructural evolution and characteristics of bonding zone in multilayer laser cladding of Fe-based coating

Multilayer coatings were prepared on H13k steel substrate by laser cladding, and Fe-based powders mixed with different Mo and Ni contents were used. The microstructure change between layers in the multilayer deposit process was analyzed. The effects of Mo and Ni contents on the microstructure, phase transformation, element distribution, and microhardness were also systematically investigated. Results showed that dendrite matrix and interdendrite netlike eutectic structure were found in Fe-based cladding layers. Furthermore, the bonding zone was mainly composed of coarse dendrites because of remelting and reheating induced by secondary energy input. Due to the heat accumulation, relatively large dendrites in the bonding zone and thick bonding zone could be formed in the latter layers rather than in the early layers. The phases of sample 1 and sample 3 at room temperature are martensite, residual austenite, residual delta ferrite, M2B and metal carbide (M23C6, and M7C3). The phases of sample 2 at room temperature are austenite, residual delta ferrite, M2B and metallic carbide (M23C6, and M7C3) because more Ni content leads to the change of solidification mode. With increasing Ni content up to 8 wt %, the microhardness of laser cladding layer decreased from 600 HV0.5 to 400 HV0.6 but was distributed homogenously from the interior region to the bonding zone.