Al 2 O 3 /ZrO 2 Eutectic Ceramics Were Prepared By Zone Melting Directional Solidification

Directional solidification technology can control the grain orientation of solidification structure,eliminate the transverse grain boundary,get single crystal structure,and improve the mechanical properties of the material.Oxide eutectic ceramics with high temperature mechanical properties of corrosion resistance and oxidation resistance,high strength,high hardness and excellent and attracted widespread attention,become a new generation of ultra high temperature structural material candidate,has important application prospect in the ultra high temperature aerospace engine.In this study,Al2O3/ZrO2 two eutectic ceramics were prepared by high frequency induction zone melting and directional solidification.The main research contents and conclusions are as follows:(1)Preparation of pre-sintered ceramic.Through the analysis of the density and apparent porosity of the calcined ceramic,the optimum sintering parameters were determined.With the increase of sintering temperature,the bulk density of the material increases,the porosity decreases,sintering time on the bulk density and porosity of the impact of small molding pressure is small,the sintering will occur when the softening,molding pressure is too high,the sintered ceramic surface will crack.The bulk density was 3.87 g/cm3,the apparent porosity was 2.43%,the hardness was 9.51GPa,and the fracture toughness was 3.17MPa·m1/2 after 2 ? s furnishing at 1500 ?.(2)Determination of Directional Solidification Process Parameters.After analyzing the influence of the shape and number of turns on the temperature gradient,combined with the actual test,the induction coil is made into three turns of the coil induction coil.The temperature of the zone was 2200 ?,and the temperature of the zone was 2000 ?.2200 ? and 2350 ?.The XRD patterns show that the eutectic ceramics are composed of Al2O3 phase and ZrO2 phase,and no new phase is formed,and the preferential orientation occurs.When the growth rate is 3mm/h,the Al2O3 phase is the matrix phase in the Al2O3/ZrO2 eutectic ceramics after directional solidification.Most of the ZrO2 phase is uniformly embedded in the Al2O3 phase with the rod shape,and the small part is lamellar.(3)Effect of growth rate on micro structure of eutectic ceramics.In the case of low solidification rate,the microstructures of eutectic ceramics show a large number of bar-like regular eutectic morphology,a small part of the lamellar.As the rate of solidification increases,most of the rod-like eutectic changes to lamellar regular eutectic.With the increase of the growth rate,the microstructure of the eutectic ceramics is refined gradually,and ?2v?1 is calculated and ?2v=constant.(4)Effect of growth rate on mechanical properties of eutectic ceramics.With the increase of growth rate,the mechanical properties of eutectic ceramics increase gradually,the maximum hardness of eutectic ceramics is 16.64GPa,the maximum fracture toughness is 5.04MPa m1/2,which is 1.75 times and 1.59 times of pre-sintered ceramics respectively.The disappearance of the pores and the interface amorphous phase and the single crystal phase effectively improve the hardness and fracture toughness of the material.The dispersion of ZrO2 phase plays a role in tuffing and crack propagation,which is an important factor for the increased fracture toughness of eutectic ceramics.With the increase of growth rate,the microstructure of eutectic ceramics gradually refined,ZrO2 phase distribution is more uniform,so the toughening effect is better.