Preparation And Properties Of Directional Solidified AL2O3/ER3AL5012 Eutectic Ceramics

Al2O3/EAG binary eutectic composite ceramic is good structural material and functional material with excellent high temperature resistance,corrosion resistance and high strength.In this experiment,high purity Al2O3 and Er2O3 powders were used as raw materials and eutectic composite ceramics were prepared with smooth surface and low porosity by Bridgman and Zone Melting after Natural Cooling Solidified(ZMN)methods.Then,the effects of growth rates(0-24 mm/h)on the phase composition,microstructure and mechanical properties were stucdied and finally the toughening mechanisms of Al2O3/EAG solidified ceramics were also analyzed.The main experiment contents and results are as follows:(1)Preparation and characterization of sintered ceramics:powder was under the condition of the ball milling rate of 350r/min for 4 hours and rod-like pre-sintered ceramics with size of ?10 mm×15 mm were prepared under the pressure of 10 MPa.Pre-sintered ceramics were kept at 1500 ? for 2 hours,and the sintered ceramics were obtained.Volume density,apparent porosity and hardness of the sintered ceramics were 5.047 g/cm3,8.645%and 2.42 GPa,respectively.(2)Experimental parameters and preparation of solidified ceramicsl:the tungsten crucible with a diameter of 14 mm and a wall thickness of 2 mm have been determined.Induction coils of Bridgman method and ZMN are cylindrical and saucer,and the heating temperature was selected at 2200 ? and 2100 ?respectively.(3)Characterization of solidified ceramics:through XRD and EDS test and analysis,they show that the phase composition of Al2O3/EAG solidified ceramics before and after melting have not changed,which are composed of Al2O3 phase and Er3Al5O12(EAG)phase.The microstructure of the solicdified ceramics was observed by SEM.It is found that the microstructure of the solidified ceramics is homogeneous,and there are no pores and other amorphous phases.With the increase of growth rate,the microstructure and size of the solidified ceramics decrease gradually,and the eutectic spacing(?)and growth rate(?)satisfy the ?2??60(constant)relationship.(4)Mechanical properties of solidified ceramics:the hardness and fracture toughness of Bridgman and ZMN directional solidified ceramics were tested by the indentation method,it is found that with the increase of growth rates,hardness and fracture toughness are slowly increased.When the growth rate is the same,the hardness and fracture toughness of ZMN solidified ceramics are basically greater than those of Bridgman solidified ceramics.(5)Toughening mechanism of solidified ceramics:the toughening mechanism of Al2O3/EAG solidified ceramics was analyzed and found that the diffusion way of two kinds of methods is mainly transgranular extension.On the one hand,there are crack deflection and branching toughening mechanisms in the microstructure of Bridgman and ZMN Al2O3/EAG solidified ceramics,which improve the toughness of Al2O3/EAG solidified ceramics.On the other hand,under the condition of high growth rate,the microstructure of solidified ceramics is dense,the interface becomes more tortuous,and the phenomenon of stress concentration is reduced,which prevent the expansion of cracks.Therefore,the toughness of Al2O3/EAG solidified ceramics is improved.