Joining Of Ceramics With Structural-functional Properties Combined In Si-Al-O-N System

?-AlON and p-SiAlON ceramics are the typical structure and function composite ceramics in Si-Al-O-N system.Because of high strength,impact resistance and high transparency,?-AlON and ?-SiAlON ceramics are usually used in vehicles,such as ships,helicopters and automobiles.However,it is not only need simple shape ceramics components but also need large sizes,complex geometry shapes or composable ceramic components in practical application.It is hardly to prepare these ceramic components by direct sintered method.Nevertheless,the technology of joining ceramics is a feasible scheme to solve this problem.It will have broad application prospects with this method.AlON-AlON ceramics,SiAlON-SiAlON ceramics and AlON-SiAlON ceramics are joined respectively using AlON powders,SiAlON powders or oxynitride glass raw powders as interlayer materials.And the sintering method is pressureless sintered.The main work and results are shown as followed:(1)High strength and translucency AlON-AlON ceramics samples were prepared by pressureless sintering method using AlON powder as joining materials.Same phase and similar microstructure are observed in eeramies and interlayers.No obvious interfaces and AlON grains growth are observed between AlON ceramics and interlayers.Max bending strength is 229MPa.That is nearly to AlON ceramics,which were prepared at 1880? for 80 min using AlON green bodies as interlayer.The partial transmittance is comparable with AlON ceramics,however,macroscopic transmittance is decreasing because of pores scattering.Comparing with loose powders as interlayer materials,utilizing AlON green bodies as interlayers are beneficial to enhance bending strength and transmittance,because the green bodies could decrease the porosity and pore sizes in interlayer and interface.(2)Using Si-Al-O-N glass raw material powders as joining materials,AION-AION ceramics were successfully joined at 1350?1475? for 30 min by pressureless sintered method.The main phase of AION-AION ceramics interlayers is Si-Al-O-N glass.?-SiAlON is generated in the interlayer when joining temperature is higher than 1450?.which is benefited to increase bending strength.Wettability of oxynitride glass on AlON ceramic surfaces decreased with increasing the content of si3N4,and increased with increasing sintering temperature.Using Y00 as interlayer material,the highest bending strength of 125.2 MPa is obtained.The joining process of AION-AION ceramics include four stages:glass phases generated slowly and liquid phase spread on AlON ceramics surfaces;Si-Al-O-N glass phases generated completed and permeated into AlON ceramics;?-SiAlON formed in the interlayers and AlON disintegrated;AlON dissolute in liquid glass phase.(3)Using three kinds of Si-Al-O-N glass raw materials powders that were mixed with Si3N4 as joining materials,SiAlON-SiAlON ceramics are successful joined at 1350?1475?by pressureless sintering method.The main phases of interlayers are similar with that in AlON-AlON interlayers,and ?-SiAlON is generated in the interlayers,which is benefited to improve bending strength.The wettability of these Si-Al-O-N glass on ?-SiAlON ceramics surfaces are increased with joining temperature increasing.The best wettability is Ce20,one of these Si-Al-O-N glasses,on p-SiAlON is the best.The highest bending strength of 474.4 MPa is obtained by using Ce20 as interlayer materials,which is 61.8%of SiAlON ceramics.The processes of joining SiAlON-SiAlON ceramics include three stages:Si-Al-O-N glass is formed in the interlayer and permeated into SiAlON ceramics;?-SiAlON formed in the interlayer;?-SiAlON ceramics dissolve into Si-Al-O-N glass.(4)Using Si-Al-O-N glass raw materials powders as joining materials,AlON-SiAlON ceramics were joined by pressureless sintering method.However,AlON ceramics with large coefficients of thermal expansion are destroyed because of residual stress.When the interlayer material is single-layer RE00,there are quantity cracks in both of the AlON and SiAlON ceramics.When the interlayers are single-layer RE20 or double-layers RE00/RE20,there are no cracks in the SiAlON ceramics,but there are perpendicular-to-interfaces cracks in the AlON ceramics.Increasing thickness of the interlayer would clearly reduce the cracks in the AlON ceramics,but cannot eliminate the cracks.(5)Other 5 schemes are hardly to effective joined.