Study On Strengthening And Toughening Mullite Ceramics With Whisker Frame

Mullite ceramics have been widely studied and used for their excellent corrosion resistance and thermal shock resistance.Because of its brittleness,its application in engineering is limited,further improving its mechanical properties has obvious engineering significance to the application of mullite ceramics.Fiber（whisker）reinforcement is an effective method to strengthen and toughen ceramic materials.This study by gas-solid reaction preparation high porosity whisker framework,by impregnation introducing mullite sol whisker framework,after drying,respectively by pressureless sintering and hot pressing sintering whisker was prepared by frame strength of porous mullite ceramics and relative density of mullite ceramic,based on the mechanism of whisker pulled up,bridge and crack deflection,in order to achieve the purpose of mullite ceramic toughness.The effects of raw material composition and sintering temperature on ceramic phase composition,sintering properties,microstructure and mechanical properties were studied.The results show that:（1）Mullite whisker raw powder was prepared by sol-gel method with Al₂O₃,TEOS（Si O₂ source）,Al F₃,H2_O and ethanol as raw materials.A whisker frame with high porosity（60%～70%）was prepared by gas-solid reaction.When the amount of Al F₃ in all the raw powder（20wt.%）and the molar ratio of Al₂O₃ to Si O₂ in the reaction system were 3:3,pure mullite whiskers were generated.With the increase of sintering temperature,the weight loss ratio of whisker sample gradually increases,the porosity decreases,the size of rod whisker increases,and the sintering neck appears between whiskers at 1200℃.（2）Porous mullite ceramics with strong and tough whisker frame were prepared by non-pressure sintering.The mullite whisker of frame structure has a strong effect on porous mullite ceramics.The best reinforcing effect was achieved with 43.5%porosity,and the bending strength was up to 75MPa.The results of fracture toughness test by unidirectional compression method showed that the fracture toughness of porous ceramics increased with the increase of porosity.（3）Whisker strength is obtained by hot-pressing sintering preparation of mullite ceramic,along with the sample of whisker accounted in the line in the process of sintering shrinkage rate is reduced,unilateral gap beam method of fracture toughness show that the whisker content was 69.5 wt.%of mullite ceramics fracture toughness is highest,reached 2.4MPa·m^1/2,whisker content is 69.5 wt.%of mullite ceramics bending strength is the highest,reached 325 MPa,with the improvement of whisker content,high porosity change results in the decrease of bending strength of mullite ceramics quickly.