Synthesis, Preparation And Properties Of Two Kinds Of Machinable Ceramics Ti₃SiC₂, Y₄Al₂O₉

Ti₃SiC₂has attracted considerable attention due to the combination of manysalient characteristics both in metals and ceramics, including excellent thermal andelectronically conductivities, damage tolerance, low density, high Young’s modulusetc.. Some undesirable TiC may exist in the final product during the synthesis ofTi₃SiC₂. It was found that adding in some Al can alleviate this problem considerably.However, the properties of materials may deteriorate under some specificcircumstances. Consequently, it is primary to find out an efficient way to synthesisTi₃SiC₂and without making any deterioration to the properties of materials. Theresearch work on pressureless sintering makes it is possible that special-shapedcomponents that prepared by extrusion and slip casting may be employed in actual.While the work concerning YAM was based on the relatively low thermalconductivity and it is also believed that the metastable YAM phase may possess somepotential special characteristics.Based on the above scientific facts, we then carried out some work on thesynthesis of high purity Ti₃SiC₂with microwave sintering, pressureless sintering ofTi₃SiC₂as well as related work of YAM ceramic.The reaction tracks of synthesis of Ti₃SiC₂by microwave heating were examinedby XRD, SEM and EDS. Under the guidance of as-proposed mechanisms, Ti₃SiC₂with a high purity of98vol.%was synthesized successfully with Ti, Si and flakegraphite.The relative density of green bodies reached95%both in the conventionalpressureless sintering and microwave sintering. However, the sintering temperaturewas200oC higher in conventional pressure at highest relative density. The optimalsoaking time was determined as1h.Single phase Y₄Al₂O₉powders first were synthesized by a solid-state reaction.Dense YAM bulks with the relative density99.5%was achieved by SPS.Microstructure and part of the mechanical properties of YAM were examined.Fracture morphology revealed that the main fracture mode is trans-granular. Cleavagezones were observed widely distributed among the fracture surfaces. The intrinsicVickers hardness of YAM is4.3GPa. For the first time, we proposed that YAM was a sort of damage tolerant machinable ceramic after examining the mechanical feedbackbehaviors as well as the machinability tests of YAM.