Bulk monolithic zirconium and tantalum diborides by reactive and non-reactive spark plasma sintering

• Standard and Reactive SPS to obtain binderless dense ZrB2 and TaB2.
• Non-reactive SPS process made use of ceramic powders synthesised by SHS.
• Both processing routes enabled to achieve nearly full dense ceramics.
• The SHS–SPS method generally provided more homogeneous microstructures.
• ZrB2 displayed higher performances with strength basically maintained up to 1200 °C.

Monolithic ZrB2 and TaB2 were produced starting from the precursors through Self-propagating High temperature Synthesis followed by Spark Plasma Sintering (SHS–SPS) and by means of Reactive Spark Plasma Sintering (RSPS). Both methods enabled to achieve almost fully dense ceramics with mean grain size typical of pure bulks. ZrB2 materials displayed significant differences in the final mean grain size of the products obtained by the two routes, while a satisfactory homogeneity was reached in both cases. This was confirmed by good mechanical strength values, about 400 MPa at room temperature, basically maintained up to 1200 °C. On the other hand, TaB2 sintered materials were quite diverse, in particular TaB2/RSPS showed a dual distribution of mean grain size, along with an almost no residual porosity, whilst TaB2/SHS–SPS had more homogeneous grain size distribution and diffused trapped porosity which corrupted the mechanical and oxidation performances.