Influence of the heating rate on the in situ synthesis and consolidation of ZrB2 by reactive Spark Plasma Sintering

The effect of the heating rate during reactive SPS to obtain dense ZrB2 from elemental reactants is investigated. When the temperature is increased at 500 °C/min or faster, the synthesis reaction evolves under combustion regime. In contrast, if heating rates equal or lower than 200 °C/min are considered, a gradual solid-state diffusion mechanism is established. In both cases, the synthesis reaction goes to completion during the non-isothermal heating step, although samples have to be processed for 20 min at 1850–2000 °C and 50 MPa to reduce residual porosity. Despite of the combustion synthesis route allows to obtain pure dense products at milder temperature conditions, safety problems and product inhomogeneity make its exploitation not convenient. On the other hand, safety conditions are preserved during the gradual formation of ZrB2 by SPS. Correspondingly, 96% dense monolithic products can be obtained at temperature levels of about 2000 °C within 20 min dwell time.