Mechanical properties and toughening mechanisms of SiC_w Al₂O₃ ceramic composites

Microstructure, mechanical properties and toughening mechanisms of hot pressed SiC_w Al₂O₃ ceramic composites were investigated by means of XRD, SEM, TEM and EPMA. Experimental results show that fracture toughness and Vickers hardness of composites increase with increasing SiC_w content. With 20%(wt) whiskers a fracture toughness of 9 MPa/m was obtained which is nearly twice that of the matrix. Grain size of the matrix has also an influence on fracture toughness and an increment of 1 to 2 MPa/m was obtained when the grain size increased from 0.05 to 0.5 um. TEM observation reveals that in most cases no glassy phase exists along the whisker/matrix boundaries but at certain interfaces small traces of glassy phase containing Al and Si were formed. Whisker pull-out and bridging as well as crack deflection are considered to be the main toughening mechanisms. The existence of glassy phase decreases the interfacial bonding strength and thus facilitates the pull-out of whiskers.