Characterization on the coatings of Ni-base alloy with nano- and micron-size Sm 2O 3 addition prepared by laser deposition

Abstract

The coating materials are the powder mixture of micron-size Ni-base alloy powders with both 1.5 wt.% micron-size and nano-size Sm 2O 3 powders, which are prepared on Q235 steel plate by 2.0 kW CO 2 laser deposition. The results indicate that with rare earth oxide Sm 2O 3 addition, the width of planar crystallization is smaller than that of the Ni-base alloy coatings. Micron- and nano-Sm 2O 3/Ni-base alloy coatings have similar microstructure showing the primary phase of γ-Ni dendrite and eutectic containing γ-Ni and Cr 23C 6 phases. However, compared to micron-Sm 2O 3/Ni-base alloy, preferred orientation of γ-Ni dendrite of nano-Sm 2O 3/Ni-base alloy is weakened. Planar crystal of several-μm thickness is first grown and then dendrite growth is observed at 1.5% micron-Sm 2O 3/Ni-base alloy coating whereas equiaxed dendrite is grown at 1.5% nano-Sm 2O 3/Ni-base alloy coating. Hardness and wear resistance of the coating improves with decreasing Sm 2O 3 size from micron to nano. The improvement on tribological property of nano-Sm 2O 3/Ni-base alloy over micron-Sm 2O 3/Ni-base alloy coatings can be attributed to the better resistance of equiaxed dendrite to adhesion interactions during the wear process. In 6 M HNO 3 solution, the corrosion resistance is greatly improved with nano-Sm 2O 3 addition since the decrease of corrosion ratio along grain-boundary in nano-Sm 2O 3/Ni-base alloy coating contributes to harmonization of corrosion potential.