Spark plasma sintering of fine-grained alumina ceramics reinforced with alumina whiskers

Densification of alumina whisker-reinforced alumina ceramics by spark plasma sintering (SPS) has been investigated with the aim of obtaining a fine-grained microstructure and also studying the effect of whisker addition on the room-temperature mechanical properties. It was found that whisker addition retards slightly the sinterability of alumina by whisker hindering of particle rearrangement. Besides, the internal stress on the alumina matrix particles reduced due to the presence of a whisker network structure of strong rigid boundaries. Nevertheless near fully-dense and fine-grained alumina ceramics with alumina whisker content between 3 wt% and 10 wt% could be obtained under appropriate SPS conditions. The hardness of alumina ceramics with 3 wt% was comparable to that of pure alumina ceramics (∼26 GPa) whereas its fracture toughness (5.6 MPa m1/2) was higher (4.2 MPa m1/2). Crack bridging by well-dispersed whiskers and whiskers pull-out were identified as the main toughening mechanisms.