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? with a pre-treatment in vacuum at 450 deg 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 deg 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.