Ultra-Refractory Ceramics: the Use of Sintering Aids to Obtain Microstructure Control and Properties Improvement

摘要

The present study focuses on innovative processing for the densification of refractory diborides (ZrB_2, HfB_2) based ceramics, suitable to fabricate UHTC components for structural applications and thermal protection systems. The addition of small quantities (2-5 vol%) of sintering aids allows to overcome the intrinsic low sinterability of zirconium diboride and to improve properties through the micro structural refinement. The introduction of second refractory phases, for instance 20 vol% of SiC in the diboride matrices improves strength, toughness and oxidation resistance. Outstanding properties were measured: fracture toughness 3-5 MPam~(1/2), hardness 9-20 GPa, elastic modulus 350-420 GPa, flexural strength 300 to 750 MPa at R.T and up to 300 MPa at 1500℃. The resistance to oxidation of different materials was compared.