Comparative Evaluation of Microstructural and Mechanical Properties of Microwave and Spark Plasma Sintered ZrB2-SiC-TiC Composites

A comparative study was carried out on the synthesis of ZrB2-25 vol.% SiC-(5, 10 and 15 vol.%) TiC composites through microwave sintering (MS) and spark plasma sintering (SPS). The effects of TiC inclusion on sinterability, microstructures, phase analysis and mechanical characteristics of ZrB2-SiC composites processed through MS and SPS were examined and compared. The structural integrity of ZrB2-based composites was enhanced by TiC addition due to generation of lower tensile residual stresses in the matrix phase and higher compressive residual stresses in the reinforcement phase. The composites developed by SPS exhibited higher relative density, hardness and compressive strength, whereas higher fracture toughness was observed for composites developed by MS. Results indicated that SPS sintered Z25S10T composite exhibited maximum relative density, microhardness, compressive strength and minimum open porosity of 99.38 +/- 0.26%, 24.78 +/- 1.06 GPa, 349.01 +/- 16.72 MPa and 0.37 +/- 0.11%, respectively. The maximum fracture toughness of 6.36 +/- 0.296 MPa m(1/2) along with maximum critical energy release rate of 93.275 +/- 4.64 J/m(2) was obtained for Z25S15T composite developed through MS. The higher fracture toughness of microwave sintered composites could be attributed to the activation of several strengthening mechanisms like deflection, bridging and impeding of cracks.