Al₂O₃/ZrO₂ Metastable Powders By Spray Quenching And Properties Characterization Of Sintering Products

On account of the impressive comprehensive properties and advantages,such as high hardness,high thermal resistance,corrosion resistance,excellent electrical insulation,and good chemical durability,the Al₂O₃ ceramics have attracted worldwide attention over the past few decades and are widely used in various industrial areas.However,the Al₂O₃ ceramic usually has poor toughness,which limits further applications in high-end field.It has been demonstrated the fracture toughness of Al₂O₃ can be remarkable improved by the incorporation of ZrO₂ through nano-toughening and phase transformation toughen.At present,ZrO₂ toughened Al₂O₃?ZTA?nanocomposite ceramics and Al₂O₃/ZrO₂ eutectic ceramics have become very prospective materials for toughening Al₂O₃ ceramics.Due to the agglomeration of nanoparticles and grain growth,it is still very difficult to obtain ultra-fine and uniform ZTA nanocomposite ceramics,which weakens the nanotoughening effect,consequently resulting in mediocre performance.To address this issue,in this work,combustion synthesis water atomization?CSWA?was explored for preparing Al₂O₃/ZrO₂ solid solution powders,and the properties of sintering products was systematically studied,which laid the experimental and theoretical foundation for the preparation of ZTA nanocomposite ceramics by solid solution precipitation method.Firstly,we optimized CSWA quenching technique,to in-situ synthesize supersaturated Al₂O₃/ZrO₂ solid solution powders.The powders have regular spherical morphologies with the particle size of ?5 ?m.When ZrO₂ content is 30 mol%,the Al₂O₃ is completely dissolved into ZrO₂ lattice,suggesting that the CSWA greatly improves the solubility of Al³⁺ in ZrO₂ lattice.Based on the theory of metal solidification,the formation mechanism of solid solution can be attributed to solute interception caused by ultra-high cooling rate.During the sintering process,the solid solution powders precipitate ZrO₂ particles and the Al₂O₃ matrix,which forms a fine and uniform nanostructure.The ceramics possess transgranular/intergranular structure: part of nano ZrO₂ is uniformly distributed in Al₂O₃ matrix,while the residuary micron-size ZrO₂ locates at the grain.When ZrO₂ contents are 25-37 mol%,the ceramics exhibits high mechanical properties,the hardness,strength and toughness are between of 17.21±0.25-19.14±0.20 GPa,648±21-728±15 MPa,6.59±0.35-6.75±0.19 MPa·m^1/2,respectively.In order to further improve the mechanical properties,Al₂O₃/ZrO₂?CeO₂?solid solution powders and CeO₂/ZTA nanocomposite ceramics were prepared by adding CeO₂ phase.The precipitation behavior of powders,the structure,mechanical properties,strengthening and toughening mechanism of ceramics,and the influence of sintering mode were investigated in detail.The results show that the CeO₂/ZTA nanocomposite ceramics could achieve controllability on phase composition and microstructure through tuning CeO₂ content: The t-ZrO₂ content increase gradually with the increasing CeO₂ phase,while part of CeO₂ reacts with Al₂O₃.Due to the change of phase structure and microstructure,both of strength and toughness increase first and then decreases with the increase of CeO₂ content.When ZrO₂ content is 25 mol%,the optimal content of CeO₂ in CeO₂/ZTA nanocomposite ceramics is 4 mol%,and its strength and toughness are 832±14 MPa,8.12±0.25 MPa·m^1/2;With the increase of ZrO₂ content to 37 mol%,the optimal content of CeO₂ in CeO₂/ZTA nanocomposite ceramics increases to 6 mol%,and the corresponding strength and toughness reach 865±24 MPa,8.40±0.16 MPa·m^1/2.The spark plasma sintering could refine the microstructure with its bending strength and fracture toughness of 898±18 MPa and 8.75±0.28 MPa·m^1/2,respectively.To solve the contradiction between large size and fine structure of eutectic ceramics,the research of Al₂O₃/ZrO₂ nano-eutectic powders synthesized by combustion synthesis gas atomization?CSGA?and its sintering products are carried out in this paper,which provides a new route for preparing large-size Al₂O₃/ZrO₂ eutectic ceramics with high performance.Based on CSWA quenching technique,a novel CSGA method was established by using air as cooling medium,to in-situ synthesize Al₂O₃/ZrO₂ and Al₂O₃/ZrO₂?Y2O3?nano-eutectic powders.The powders are regular sphere with average particle.In addition,the powders have a fine and homogeneous nano-eutectic structure,which is composed of an Al₂O₃ matrix and a disordered interpenetrating network of ultrafine ZrO₂ phase.ANSYS simulation and BSE results show that the eutectic structure coarsens with the increase of particle size.However,due to the high cooling rate,the interphase spacings of all particles reach nanoscale.The doping of Y₂O₃ could inhibit the transformation of c-t and t-m during the solidification process,which gives rise to a rich variety of ZrO₂ polymorphs.After sintering,the powders form Al₂O₃/ZrO₂?Y₂O₃?composite ceramics with fine and uniform microstructure,whose strength,toughness and hardness are 648±27 MPa,7.39±0.36 MPa·m^1/2 and 19.27±0.55 GPa,respectively.