Improving fracture toughness of alumina with multi-walled carbon nanotube and alumina fiber reinforcements

Alumina has been widely used for personal armour plate due to its relatively low cost, acceptable hardness and fracture toughness. With the increasing threat level, a much improved ceramic material with better ballistic performance and lighter weight is required. In this work, alumina reinforced with 2D and 3D alumina fiber mats has been successfully developed for evaluation. The 2D alumina fiber reinforced alumina composite consists of an alumina matrix reinforced with 18 vol% of alumina fiber mats. And the 3D fiber reinforced alumina composite was made with alumina matrix with a 2D alumina fiber mats along with multi-walled carbon nanotubes vertically grown onto the fiber mats. In comparing with the fracture toughness of commercial alumina of 3.8 MPa.m1/2, the alumina with the 2D and 3D reinforcement offer toughness of 4.4 MPa.m1/2 and 6.6 MPa.m1/2 respectively. The improvement in fracture toughness by the 3D reinforcement in alumina is almost 74%. Detailed examination on fracture surfaces of both 2D and 3D reinforced composites was conducted with scanning electron microscopy to elucidate the contribution of multi-walled carbon nanotubes and alumina fibers in enhancing the fracture toughness of the alumina matrix. Transmission electron microscopy investigation was also conducted on the composite with the 3D reinforcement to provide information on the morphological features at the fiber/matrix regions.