The Influence of Chemical Composition on Shape Memory Effect of TiNi Bulk Alloy Produced by Mechanical Alloying

抄録

Three kinds of elemental powders consisted of Ti and Ni, with different chemical compositions, Ti₅₀Ni₅₀, Ti₄₅Ni₅₅ and Ti₅₅Ni₄₅, were mechanically alloyed for 30h by a planetary ball mill, compacted, sintered at 973K and annealed at several temperatures, 673K, 773K and 873K, and the martensitic transformation behaviors for those bulk samples were investigated. All three samples turned into amorphous state after mechanical alloying for 30h. After compacting, sintering and annealing, however, TiNi (B2) phase with a small amount of Ti₂Ni phase formed in the Ti₅₀Ni₅₀ sample, while TiNi (B2), Ti₂Ni and TiNi₃ phases formed in Ti₄₅Ni₅₅, and TiNi (monoclinic), Ti₂Ni and Ti₃Ni₄ phases in Ti₅₅Ni₄₅. The fraction of Ti in all the samples was reduced by approximately 1at% after a series of fabrication processes, suggesting that mechanical alloying (MA) process contributed to the phenomenon. Martensitic transformation behavior was observed in all the samples after a series of fabrication processes. Several precipitated phases influenced the martensitic transformation behavior, temperature and enthalpy for the transformation, suggesting that the precipitated phases have possibility to control martensitic transformation temperature. The martensitic transformation behavior was also dependent on annealing temperature.