Formation of metastable solid solutions of boron in nickel under mechanochemical synthesis from Ni-B and Ni-Nb-B mixtures

Abstract

Using high-energy ball milling of Ni87B13 and Ni87 − x Nb x B13 component mixtures (x = 7, 10, 12, 14) for 2 h, nanocrystalline alloys containing fcc solid solutions of Ni〈B〉 and Ni〈Nb,B〉 were obtained. According to the results of X-ray analysis, oversaturated solid solutions of Ni〈B〉 are interstitial solutions; those of Ni〈Nb,B〉 are substitutional solutions or mixed substitutional-interstitial solutions. Upon heating of the alloys, exothermal effects appear on differential scanning calorimetry (DSC) curves; they are attributed to decomposition of metastable solid solutions and to crystallization of the amorphous phase appearing in mechanical alloying. After heating to 720°C, the Ni87B13 alloy contained stable phases of Ni and Ni3B; the Ni75Nb12B13 alloy contained a τ phase (Ni21Nb2B6) and a metastable solid solution of Ni〈Nb〉.