Fracture behavior improvement of TaC-based ceramic composites by fibrous structure

Tantalum carbide (TaC) has monopolized properties making it suitable for aerospace applications. However, its extensive usages have been confined by its catastrophic fracture as a ceramic material. Accordingly, in this research, a fibrous monolithic structure based on TaC-20 vol% HfC composite as cell materials and porous graphite as cell boundary phase was produced by co-extrusion processing. Then, fibrous specimens were sintered using hot pressing at the temperature of 1800 °C for 1 h at a pressure of 40 MPa. Monolithic TaC- HfC composites also with the cell composition were manufactured by hot pressing at the same conditions and their fracture behavior and mechanical properties were compared to fibrous specimens. TaC-based fibrous monoliths showed graceful failure in flexural testing because of sufficient difference in strength between the cell and the cell boundary phases. In addition, fibrous monolithic specimens with three values of 25:75, 30:70, and 35:65 cell boundary to cell (CB:C) volume ratios were prepared and its influence on the mechanical properties was investigated. On increasing the cell boundary to cell volume ratio, the work of fracture (WOF) and the fracture toughness enhanced remarkably and reached maximum values of 2145 ± 56 J/m2 and 6.6 ± 0.4 MPam1/2, respectively in ratio of 30:70, because the wide crack interactions with the weak and porous graphite such as crack deflection and delamination occurred. Crack propagation patterns were also studied by scanning electron microscopy.