無電解Ｎｉ‐Ｂ合金の作製とその熱的構造変化

Abstract

Electroless Ni-B alloys composed of from 7 to 25at% B were prepared using a nickel-chloride plating bath containing dimethylamine borane (DMAB) as a reducing agent. The influence of conditions of preparation such as bath temperature (50-80°C), pH (5-8) and nickel-ion complexing agents (Na-succinate, Na-malonate and Na·K-tartrate) on the deposition rate and the boron content of the deposits was examined. Heat-induced structural changes in the deposited Ni-B alloys were also investigated by means of differential scanning calorimetry, evolved gas analysis, X-ray diffraction and transmission electron microscopy. The results are summarized as follows: (1) Boron content in the deposits was influenced by the species of complexing agent, with deposits from Na-succinate baths containing about 7 to 17at% B, those from Na-malonate baths containing about 16 to 21at% B and those from Na·K-tartrate baths containing about 21 to 25at% B. (2) Deposited alloys with about 7 to 10at% B were supersaturated solid solutions of fccNi with boron occluded, and those with about 15 to 25at% B were amorphous solids. (3) The process of crystallization of electroless Ni-B alloys can be classified into two types depending on boron content. In alloys with about 7 to 18at %B (region I), fine fccNi particle precipitated from an amorphous (or supersaturated solid solution) matrix at about 200°C and upon further heating the remained matrix was transformed into a stable phase of (Ni+Ni3B) by eutectic crystallization at 300-400°C. In alloys with about 20 to 25at% B (region II), the amorphous solid converted directly into stable crystal phases of Ni3B and Ni at 300-350°C.