Laser melting of spark plasma sintered zirconium carbide: thermophysical properties of a generation IV very high temperature reactor material

Commercial ZrC(0.96) powder (ABCR, Karlsruhe, Germany) was densified by spark plasma sintering to greater than 96% relative density at temperatures of 1900-2180 degrees C, applied pressures of 40-100 MPa, and soak time of 6-30 min. Effects of process parameters on microstructure were assessed by ceramography. High temperature (>2000 degrees C) was more instrumental in full densification than was high pressure, and excessive ramp rate resulted in high residual porosity. Grain coarsening was promoted by prolonging the isothermal dwell. Laser heating was used to melt sintered ceramics, as part of a novel thermal analysis technique for probing extremely high temperature phase transformations. Temperatures well in excess of the expected melting temperature of ZrC and up to 4000 K were achieved. The feasibility of the technique for detecting melting transitions in zirconium carbide was demonstrated, and solidus and liquidus temperatures within 50-80 K of predicted values were measured. Post-melting analysis of laser-melted specimens revealed dendritic microstructure and composition consistent with single phase ZrC.