Development of Dense Materials by Plasma-Spark Sintering of Oxide–Oxide-Free Components with Different Mixtures of Metal Powders

The effects of Zr, Mo and Zr, Ta powder mixtures during spark-plasma sintering of compositions at pressing loading of 60 MPa in the range 1200 – 1600°C on the phase composition, microstructure, grain sizes of crystalline phases, relative density, linear shrinkage, physical-mechanical properties, and linear correlation of elasticity modulus and fracture toughness of mullite–β-SiAlON–c-BN samples are shown in the present work. Synthesized powders of β-SiAlON and c-BN are characterized by extensive crystallization of β-SiAlON and c-BN, respectively. Sintered samples with Zr, Mo and Zr, Ta mixtures show extensive mullite formation, active growth of β-SiAlON, and less extensive growth of c-BN in the range 1200 – 1600°C. Active growth of crystalline β-Mo, Zr, Mo, and Mo₂Zr phases is noticeable in the sample with Zr, Mo mixtures but extensive growth of crystalline β-Ta, Zr, α-Zr, Ta, β-Ta, Ta₃Zr, and Ta₃Zr₂ is observed in the sample with Zr, Ta mixtures with an increase of temperature. The Zr, Mo mixture favors the formation of a more uniformly and densely sintered microstructure of the ceramic phase, round metallic Mo and β-Mo, Zr particles, more reinforced ceramic-metallic boundary areas, and metallic phases and facilitates the reduction of crystalline-phase grain sizes in the range 1400 – 1600°C. As a result, the composition with a Zr, Mo mixture sinters more uniformly and gradually. The corresponding sample shows larger values of physical-mechanical properties, higher cracking resistance with an insignificant quantity of microcracks, and a larger linear correlation of the elasticity modulus and fracture toughness in the range 1200 – 1600°C.