Thermal Shock Resistance And Corrosion Resistance Against Molten-Ce Of Y₂O₃-Nb Composites

The material of crucible is the key to purity of melting metal and superalloy.Although the excellent corrosion resistance and high-temperature stability guarantee Yttrium oxide wide potential applications in the field of high temperature alloy melting crucible materials,the poor mechanical properties and thermal shock resistance limit its development and industrial applications.Niobium has high melting point,excellent ductility and thermal expansion coefficient similar with yttrium oxide.Hence,aimed to reduce the thermal stress generated under high temperature thermal cycling conditions,a series of Y₂O₃-Nb composites are fabricated by hot-press sintering to meet the requirements of metal and superalloy smelting.Effect of Nb content on compositions,microstructure,mechanical properties,thermophysical properties,thermal shock resistance and molten-Ce corrosion resistance of Y₂O₃-Nb composites were systematically analyzed by X-ray diffractometer,scanning electron microscope,mechanical testing machine and the laser flash thermal analyzer.The results show that the addition of Nb improves the sintering ability and mechanical properties of Y₂O₃ ceramics.When adding 5vol.%Nb,the composites exhibits the highest relative density and hardness of 98.46%and 8.28 GPa,respectively.With the increase of Nb,the elastic modulus,flexural strength and fracture toughness of the composites are significantly improved.With the addition of 20 vol.%Nb,the highest elastic modulus of 205 GPa,flexural strength of 227 MPa and fracture toughness of3.24MPa·m^1/2are 1.4,1.3 and 2.3 times higher than those of the monolithic yttrium oxide.With the increase of experiment temperature,the isothermal heat capacity increases first and then decreases,thermal diffusion coefficient and thermal conductivity shows a decreasing trend,while the thermal expansion coefficient increases.The surface layer of Y₂O₃ ceramic and Y₂O₃-Nb composites are intact without cracks after 10,20,40 cycles of thermal shocks in 1200-1600℃,respectively.After 40 cycles of thermal shocks,the residual flexural strength of Y₂O₃-10 vol.%Nb composite increase from 212 MPa to 348 MPa and increase by 64%compared with original flexural strength,which unfold the best thermal shock resistance.When the specimen suffered molten Ce corrosion at 1300°C,obvious corrosion reaction layer isn’t observed in the interface between Y₂O₃ ceramic and molten Ce.With the increase of Nb content,erosion reaction layer appears and thickness shows a increasing trend.The thickness of erosion layer in the early period grows faster than that in later period.The thickness of the erosion layer positively correlated with erosion temperature while the specimen was eroded by same time.