Reassessment of the Ni–B system supported by key experiments and first-principles calculation

Abstract

Abstract The Ni – B system is reassessed based on critical literature review and the results of key experiments and first-principles calculation. Eight Ni – B alloys are prepared by arc melting the pure elements. The samples are analyzed by means of chemical analysis, X-ray diffraction and differential thermal analysis. NiB12 and NiB2 are not found in the equilibrium condition. Four invariant temperatures are measured: 1098 ± 2 °C for L ↔ fcc(Ni) + Ni3B, 1114 ± 2 °C for L ↔ Ni3B + Ni2B, 1025 ± 2 °C for L ↔ Ni2B + orthorhombic-Ni4B3 and 1044 ± 2 °C for L + βB ↔ NiB. The heat capacity of NiB is determined to be 58.46092 + 0.0012 · T – 1 597 915.59793 · T– 2 (J mol– 1 K– 1, T in Kelvin) in the temperature range from 40 to 950 °C by differential scanning calorimetry. First-principles calculation indicates that the energy of inserting a B atom into the interstitial site of the lattice for Ni atoms is lower than that of substituting for an Ni atom with a B atom. Consequently, the sublattice model (Ni) (B, Va) in which B atoms occupy the interstitial sites is employed for the fcc(Ni) phase rather than the model (Ni, B) (Va) in which B atoms substitute for Ni atoms. In addition, the enthalpies of formation for the five compounds are obtained via first-principles calculation to supplement the modeling. A self-consistent set of thermodynamic parameters for the Ni – B system is finally obtained and the calculated results show good agreement with the experimental data.