Densification And Mechanical Properties Of ZrN Ceramic

As a transition metal nitride, ZrN ceramic is proposed as an attractive candidate material as IMF, for its excellent properties such as high melting point, high thermal conductivity, good corrosion resistance and its superior solubility of minor actinide. Owing to the high melting point, strong covalent bonding and low self-diffusion coefficient of ZrN, high sintering temperature and pressure are require to obtain fully dense ceramics. Present work focus to improve the sinterability and reduce the densificaion temperature of commercial ZrN by doping different additives.Hot-pressed zirconium nitride(ZrN) ceramics respectively doped with Zr, phenolic resin and B4 C are studied in this paper. Densification, diffusion kinetics and microstructures are investigated by Archimedes method, XRD, SEM, EDS and mechanical properties by three-point bending, Vickers hardness and indentation.The densification improvements are attributed to solid solution of Zr into ZrN to form non-stoichiometric ZrN1-x and we discover the Zr2 N as intermediate for defect reaction. Densification temperature decrease by 100 oC as stoichiometric ratio of ZrN1-x reduce 0.1 for that lattice diffusion is mainly influenced by vacancy concentration. Relative density of hot-pressing ZrN at 1600 oC is much higher than pressureless sintering, because chemical potential of vacancy is the function of applied pressure. Large grains existed in ZrN1-x ceramics is the result from increase of grain growth kinetics, which lead to toughness as low as 2.6±0.2 MPa·m1/2 for ZrN0.9,. Two-step sintering leads to coarsening of microstructures as well as the decrease of relative density because of exhausted kinetics for densification.Relative density of ZrN ceramics increase by doped with phenolic resin as additive. We discover that two processes exist in the system. Firstly, carbon atoms diffuse into the matrix of ZrN, which form solid solution ZrCxNy. Secondly, ZrOx‘Ny’ solid solution is formed by nitrogen atoms into ZrO2. Grain growth of ZrN is inhibited by pinning of small ZrOx‘Ny’ grains along the grain boundary. Because of high density and fine microstructures, the flexure strength increase to 333±48MPa when doped with 5mol. % carbon.B4C react with ZrN and ZrO2 impurities to facilitate the densification and fully dense ceramics are prepared. Composites are consisted of non-stoichiometric solid solution ZrCxNy and ZrB2. Value of x and y is calculated in this paper. Due to plate-like ZrB2 grains existed in composites with 10 mol. % B4 C, the flexure strength is enhanced, which is 524±28MPa.