Study On Preparation Technology Of Y₂O₃/Sm₂O₃ Co-Doped Al₂O₃-ZrO₂ Eutectic Ceramics By High Temperature Melting Method

Al₂O₃-ZrO₂ eutectic ceramics with excellent corrosion resistance,oxidation resistance and high temperature creep resistance are considered to be ideal ultra-high temperature structural materials for long-term use in oxygen-rich environments above 1400^°C.Improving the mechanical properties by precisely controlling the microstructure of eutectic ceramics was the research focus in the process preparation.Doping the third element into the eutectic system could affect the crystal structure of zirconia and the solidification growth behavior,then influenced the microstructure and properties of eutectic ceramics.In this paper,Al₂O₃-ZrO₂binary eutectic ceramic was selected the research system,and Y₂O₃ and Sm₂O₃ were used as modifiers.The effect of Y/S?Y₂O₃/Sm₂O₃?co-doping content on eutectic microstructure and mechanical properties was studied,the evolution law and mechanism of morphology were explained.The main results are as follows:Different Y/S co-doped Al₂O₃-ZrO₂ eutectic ceramics were prepared by high temperature fusion method,and the microstructure evolution process was studied.The result showed that the eutectic colony structure were observed in all eutectic ceramics.As the Y/S content increased,the solidification structure changed obviously from eutectic cellular to eutectic seaweed,and the ZrO₂ phase inside the eutectic structure was transformed from three-fold symmetric sets of fibers into disordered dispersion of lamellae.Y₂O₃ was easier to dissolve in zirconia phase than Sm₂O₃,therefor the SmAlO₃ phase was identified in boundary region for the higher Y/S co-doping content?4.4 mol%?.Doping of Sm₂O₃ and Y₂O₃ could increase the hardness of Al₂O₃-ZrO₂ eutectic,the maximum hardness reached 16.40±0.51 GPa for 2.2YS sample at ambient temperature,but then the hardness decreased when the co-doping content was further increased.The fracture toughness estimated from the indentation method was 3-4MPa m^-1/21/2 for all Y/S co-doped Al₂O₃-ZrO₂ eutectic at ambient temperature.The fracture toughness was higher at the low co-doping amount,and then decreased as the co-doping amount continues to increase.The eutectic bulk was prepared by using three kinds of different fused precursors:powder cold pressed body,hot pressed sintered body and fused body.The result showed that the hot-pressed sintered body and the fused body after fused eutectic ceramics are eutectic crystal structure,however,but the eutectic crystal group exhibited a strong alignment orientation after re-melting.The eutectic ceramics obtained after the hot-pressed sintered body have better performance,The average hardness and average fracture toughness of eutectic ceramics were16.40±0.51 GPa?3.89±0.21 MPa m^-1/2,respectively.It is worth noting that a large number of hole defects appeared in the central region of the cross section of the sample,which had an adverse effect on mechanical properties.Research on the preparation process of high temperature melting showed that as the melt temperature and the melt holding time increased,the microstructure inside the colony refined.However,the degree of refinement was low,and the mechanical properties of eutectic ceramics were not improved.The average hardness of eutectic ceramics prepared at different melt temperatures and melt holding times at room temperature were about 16 GPa,and the average fracture toughness were about 4 MPa m^-1/2.