Study On Thermal Shock Resistance Of Alumina Based Composite Ceramics

Ceramics have excellent mechanical properties,good corrosion resistance at high temperature and excellent chemical stability.However,ceramic/metal composite materials prepared by casting inlay method has been received restrictions on the application,due to the poor thermal shock resistance of ceramics.Therefore,it is very important to study how to improve the thermal shock resistance of ceramics.In this paper,the problem of low strength of Al₂O₃/mullite composite ceramics after thermal shock was solved.By adding AlF₃,MgO and ZrSiO₄ to Al₂O₃/mullite composite ceramics,mullite whiskers,cordierite and ZrO₂ were introduced into the composite ceramics,based on the mechanism of whisker toughening,thermal expansion mismatch and phase transition toughening.The influence of the composition of raw materials,sintering temperature and holding time on the phase composition,sintering properties,micromorphology,mechanical properties and thermal shock resistance of the ceramics were studied,and the control of the thermal shock resistance of Al₂O₃/mullite composite ceramics was realized.The results show that:?1?Al₂O₃/mullite composite ceramics reinforced by mullite whiskers were prepared from Al₂O₃?SiO₂ and AlF₃ by injection molding.With the increase of temperature and AlF₃ content5wt%,the aspect ratio of mullite whiskers decreases and coarsenes.The whiskers which were formed in the composite ceramics with AlF₃ being 5wt%and sintered at 1600?,have the size of 3¹0?m in diameter and a length-diameter ratio of 10¹5.The fracture surface of ceramics mainly showed transgranular fracture characteristics.The bridge effect of mullite whisker improved the fracture toughness of ceramics,and the highest fracture toughness was up to 4.79MPa·m^1/2.Mullite whiskers can effectively enhance the thermal shock resistance of ceramics by hinderringg the propagation of cracks in the process of thermal shock.When the AlF₃ content was 5wt%,the flexural strength loss of the composite ceramics was 3.82%after thermal shock for 10 times.?2?Al₂O₃/mullite/cordierite composite ceramics were prepared by moulding with Al₂O₃,SiO₂ and MgO as raw material and proper amount of PVA solution as plastic agent.With the increase of MgO content,cordierite phase began to appear in the composite ceramics,and the apparentporosityincreased.Theflexuralstrengthandfracturetoughnessof Al₂O₃/mullite/cordierite composite ceramics decreased with the increase of MgO content.Based on the heat mismatch mechanism,the flexural strength loss of composite ceramics after thermal shock for 10 times was 7.42%.?3?Al₂O₃/ZrO₂/mullite composite ceramics were prepared by molded molding with Al₂O₃,ZrSiO₄ and MgO as raw materials and proper amount of PVA solution as plastic agent.The content of t-ZrO₂ was increased with the increase of MgO content.Magnesia-aluminum spinel was formed because of excessive MgO addition.Based on ZrO₂ phase transition enhancement,the flexural strength and fracture toughness of composite ceramics were up to 365.21 MPa and 5.31MPa·m^1/2.The lowest loss of flexural strength of ceramics was 5.61%after thermal shocksb for 10 times.