Characterization on the coatings of Ni-base alloy with nano- and micron-size Sm2O3 addition prepared by laser deposition

The coating materials are the powder mixture of micron-size Ni-base alloy powders with both 1.5 wt.% micron-size and nano-size Sm2O3 powders, which are prepared on Q235 steel plate by 2.0 kW CO2 laser deposition. The results indicate that with rare earth oxide Sm2O3 addition, the width of planar crystallization is smaller than that of the Ni-base alloy coatings. Micron- and nano-Sm2O3/Ni-base alloy coatings have similar microstructure showing the primary phase of γ-Ni dendrite and eutectic containing γ-Ni and Cr23C6 phases. However, compared to micron-Sm2O3/Ni-base alloy, preferred orientation of γ-Ni dendrite of nano-Sm2O3/Ni-base alloy is weakened. Planar crystal of several-μm thickness is first grown and then dendrite growth is observed at 1.5% micron-Sm2O3/Ni-base alloy coating whereas equiaxed dendrite is grown at 1.5% nano-Sm2O3/Ni-base alloy coating. Hardness and wear resistance of the coating improves with decreasing Sm2O3 size from micron to nano. The improvement on tribological property of nano-Sm2O3/Ni-base alloy over micron-Sm2O3/Ni-base alloy coatings can be attributed to the better resistance of equiaxed dendrite to adhesion interactions during the wear process. In 6 M HNO3 solution, the corrosion resistance is greatly improved with nano-Sm2O3 addition since the decrease of corrosion ratio along grain-boundary in nano-Sm2O3/Ni-base alloy coating contributes to harmonization of corrosion potential.