Abstract: Instrumented and Vickers indentation testing and microstructure analysis were used to investigate zirconia toughened alumina (ZTA) and silicon carbide (SiC). Several equations were studied to relate the Vickers indentation hardness, Young's modulus and crack behavior to the fracture toughness. The fracture in SiC is unstable and occurs primarily by cleavage leading to a relatively low toughness of 3 MPa m^1/2, which may be inappropriate for multi-hit capability. ZTA absorbs energy by plastic deformation, pore collapse, crack deviation and crack bridging and exhibits time dependent creep. With a relatively high toughness around 6.6 MPa m^1/2, ZTA is promising for multi-hit capability. The higher accuracy of median equations in calculating the indentation fracture toughness and the relatively high c/a ratios above 2.5 suggest median type cracking for both SiC and ZTA. The Young's modulus of both ceramics was most accurately measured at lower indentation loads of about 0.5 kgf, while more accurate hardness and fracture toughness values were obtained at intermediate and at higher indentation loads beyond 5 kgf, respectively. A strong indentation size effect (ISE) was observed in both materials. The load independent hardness of SiC is 2563 HV, putting it far above the standard armor hardness requirement of 1500 HV that is barely met by ZTA.

Key words: Zirconia toughened alumina, Silicon carbide, Armor, Vickers indentation fracture toughness, Elastic modulus, Vickers hardness