Reaction Mechanism of ZrB(2)-ZrC Formation in Ni-Zr-B(4)C System Analyzed by Differential Scanning Calorimetry

The reaction mechanism of ZrB(2)-ZrC formation in a 30% Ni-Zr-B(4)C system under argon was revealed by using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicated that the reaction mechanism in the Ni-Zr-B(4)C system was complex. Initially, Ni(x)Zr(y) and Ni(x)B(y) intermetallics were formed via solid-state diffusion reactions between Ni, B(4)C and Zr. Then, the eutectic reaction between Ni(2)B and Ni(4)B(3) lead to the formation of Ni-B liquid. The free C atoms dissolved into the Ni-B liquid to form a Ni-B-C ternary liquid, and then part of the Zr powder dissolved into the surrounding Ni-B-C ternary liquid to form Ni-Zr-B-C quaternary liquid. Finally, ZrB(2) and ZrC formed and precipitated out of the saturated liquid. The eutectic liquid plays an important role during the formation of ZrB(2)-ZrC.