Fracture and property relationships in the double diboride ceramic composites by spark plasma sintering of TiB 2 and NbB 2

Bulk titanium diboride–niobium diboride ceramic composites were consolidated by spark plasma sintering ( SPS ) at 1950°C. SPS resulted in dense specimens with a density exceeding 98% of the theoretical density and a multimodal grain size ranging from 1 to 10 μm. During the SPS consolidation, the pressure was applied and released at 1950 and 1250°C, respectively. This allowed obtaining a two‐phase composite consisting of TiB 2 and NbB 2 . For these ceramics composites, we evaluated the flexural strength and fracture toughness and room and elevated temperatures. Room‐temperature strength of thus produced bulks was between 300 and 330 MPa, at 1200°C or 1600°C an increase in strength up to 400 MPa was observed. Microstructure after flexure at elevated temperatures revealed the appearance of the needle‐shape subgrains of NbB 2 , an evidence for ongoing plastic deformation. TiB 2 –NbB 2 composites had elastic loading stress curves at 1600°C, and at 1800°C fractured in the plastic manner, and strength was ranged from 300 to 450 MPa. These data were compared with a specimen where a (Ti,Nb)B 2 solid solution was formed during SPS to explain the behavior of TiB 2 –NbB 2 ceramic composites at elevated temperatures.