Preparation And Property Investigation Of Alumina/Mullite Ceramic Composites

Alumina/0.18⁸.72 vol.% mullite composites were fabricated by reactionsintering of SiC and Al₂O₃ nano-powder in air. Growth behavior of mullite(3Al₂O₃·2SiO₂), composition, microstructure, stress state, mechanical propertiesand wear resistance were investigated.X-ray diffraction was used in the qualitative and quantitative phase analysisas well as the measure of surface residual stress. Scanning electron microscope(SEM) was used to observe the surface topography, fracture surface topographyand abrasive surface. Transmission electron microscope (TEM) was used toanalyze the microstructure. Young's modulus was measured by resonancemethod, Fracture strength was measured through three-point bend tests,hardness and fracture toughness was measured by indentation method, and thenanohardness and nanoscratch characteristics were measured throughnanoindentation.Findings were as follows, SiC particles were oxidated to SiO₂ below 1400 ℃,the SiO₂ together with Al₂O₃ were then entered into the precipitation reaction ofmullite which commenced at 1450¹600 ℃ . The initial temperature ofmullitization as well as its activation energy which range from 867⁸91 kJ/moldeclined as the volume of SiC content increased. The coarse mullite particlesdistributed on the matrix grain boundary while the finer ones mainly embeddedin the matrix grains. The grain growth could be suppressed by mullite particles ifthe mullite content wasn't too low. Compared with that of the alumina, thefracture strength, hardness and nanohardness of the alumina/mullite compositesincreased by 20 %, 15 % and 53 % respectively. The fracture toughness wasdeteriorated appreciably. Wear resistance could be increased significantly inalumina/mullite composites, and it could be 3 times of that for alumina when theload was 2 N.The quantitative relationship between mullite content, matrix stresses andpercentage of transgranular fracture (PTF) was then established. The influenceof composition, stress state, fracture mode and critical flaw size on themechanical properties and wear resistance of alumina/mullite composites wasanalyzed in detail.