Dimension effect of Y2O3 nanomaterial on microstructure and tensile properties of laser metal deposited stainless steel coatings

Yttrium (Y) is an engineering material used in refinement, and the physical properties of Y2O3 nanomaterials play key roles in thermal-effect of refinement. In this study, the experimental thermal-efficiencies induced by dimension of Y2O3 nanomaterials and their influence on microstructures and tensile performances of graded stainless steel coatings were investigated. To this end, 16Cr2NiSiMo stainless steel coatings were fabricated by laser metal deposition (LMD) technology in the presence of small amounts (<1 wt%) of Y2O3 nanoparticles (diameter 30-50 nm) and Y2O3 nanosheets (thickness 20-30 nm) without additional heat-treatment. Compared to Y2O3 nanosheets-modified coatings, more decline in the interlayer heat-affected zone, dendritic solidification microstructure, pore, microcrack, and taenite phase were all observed for coatings prepared in the presence of Y2O3 nanoparticles. The reason for this difference had to do with the dimension of Y2O3 nanomaterial, which directly influenced the dissociation of Y3+ ions in dendrites by decreasing the melting point of the material and transition temperature of the metastable eutectic. As a result, Y2O3 nanoparticles promoted the hardness and tensile properties of the coatings, while Y2O3 nanosheets increased microcracks and pores but declined the tensile properties. The ultimate tensile strength and elongation of the sample prepared by adding 0.75 wt% Y2O3 nanoparticles enhanced by 17% and 47.9%, respectively.