Melting Behavior Of YSZ@Ni Nanoparticles During Laser Cladding Process

Nano-YSZ coating has shown substantial potential as high temperature materials in industrial field due to its excellent comprehensive performance. However,namopowders prefer to aggregation and spatter during cladding process. In this paper,nano-YSZ particles were modified by plating nickel on their surfaces to reduce aggregation and spatter. Firstly, the preparation process of YSZ@Ni core-shell particles was discussed. Secondly, the effects of different materials on microstructures of the coatings were investigated and the melting behavior of YSZ@Ni nanoparticles was discussed in detail. Finally, the influences of remelting on the melting behavior of YSZ@Ni nanoparticles were discussed and the solidification process was analysed by dynamics.The results show that the optimum reaction conditions are at 60-70 ℃ and a pH=11-12 with a plating solution of CNi=0.12mol/L, CYSZ=0.007mol/L,CN2H4=0.43mol/L. The prepared particles were composed of YSZ(core) and Ni crystals(shell) with a thickness of less than 20 nm. It can be confirmed that the YSZ@Ni is successfully produced by the modified electroless plating process.It is found that YSZ@Ni coating presents a much denser and more continuous surface and stronger bonding with substrate compared with YSZ/Ni and YSZ coating,which infers YSZ@Ni nanoparticles present better processing performance.For YSZ@Ni nanoparticles, in most area of the YSZ@Ni cladding layer, the melted nickel diffused into matrix to form Ni-aggregation transition layer and the melted YSZ solidified into primary YSZ phase and YSZ/(FeCr2O4) eutectic structure containing 200 nm rods-YSZ and lamellars-YSZ with a lamellar space of 400 nm. On edge of the molten pool, the melted nickel solidified into spherical Ni-rich phase and the melted YSZ grew into some equiaxed crystals.The influences of remelting on the melting behavior of YSZ@Ni nanoparticles were studied. The results show that after remelting the coating was consisting of rod-lamellar YSZ-(FeCr2O4) eutectic structure and the primary YSZ phase disappeared.After remelting for three times the lamellar space was 200 nm and it reached about 330 nm after remeling for eight times, which meant that remelting displayed positive and negative effect on the microstructure of YSZ@Ni coating. It can be inferred that remelting can refine grains due to a higher supercooling rate but if thegrowth rate is too high the grains will coarsening owing to multi-melting.