Synthesis of In Situ ZrB_2/ZrN composite

摘要

In situ ZrB_2/ZrN composite was fabricated from Zr/BN powder blends by pressureless firing above 1600°C with a pre-treatment in vacuum at 450 °C. The synthesis mechanism of ZrB_2/ZrN composite was investigated by XRD and SEM technologies. ZrN in the needle-like shape forms firstly in the matrix at ca 900 °C, followed by the appearance of ZrB which is an intermediate phase in this reaction and will transform to ZrB_2 later at a relatively high temperature. The initially formed ZrN is most probably a non-stoichiometric compound with vacancies in the nitrogen site, noted as ZrN_(1-x), which incorporate then the nitrogen elements from the remains of BN and eventually transform to stoichiometric ZrN. A long time holding at the formation temperature of ZrN may promote the grain growth of needle-like ZrN and thus be favorable to the improvement of mechanical properties of ZrB_2/ZrN composite.