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The reaction mechanism of ZrB₂-ZrC formation in a 30% Ni-Zr-B₄C 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-B₄C system was complex. Initially, Ni_xZr_y and Ni_xB_y intermetallics were formed via solid-state diffusion reactions between Ni, B₄C and Zr. Then, the eutectic reaction between Ni₂B and Ni₄B₃ 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, ZrB₂ and ZrC formed and precipitated out of the saturated liquid. The eutectic liquid plays an important role during the formation of ZrB₂-ZrC.