Multiphase ceramic composites derived by reaction of Nb and SiCN precursor

In this work multiphase Nb(C,N)/Nb5Si3 ceramic composites containing niobium silicide, nitride and carbide phases were designed by using the polymer derived ceramic (PDC) route to avoid the complicated shaping of refractory metal compounds. Starting from polycarbosilazane (PCSZ) precursor powder and metallic niobium as reactive filler green compacts were manufactured by uniaxial warm pressing and stabilized by subsequent crosslinking. Due to the reactivity of both the Nb and the rearrangements within the forming amorphous SiCN phase a porous ceramic material is generated via solid-state reaction during thermal treatment. Depending on the amount of PCSZ as well as on the pyrolysis conditions the particles within this network reveal a core/rim structure containing submicron-sized Nb2CN, NbC as well as coarse-grained Nb2N phases in the core and Nb5Si3 or alternatively metastable Nb5Si4C phase at the particle surface.