FREE-ENERGIES OF THE TI-NI, FE-NI AND MO-NI ALLOYS IN RELATION TO THEIR BEHAVIOR UNDER PARTICLE IRRADIATION

The metastable free-energy diagrams of the Ti-Ni, Fe-Ni and Mo-Ni syst ems were calculated at room temperature using a semiempirical theory b ased on thermodynamic considerations. Ti-Ni and Mo-Ni form equilibrium -ordered compounds that are destabilized by particle irradiation. Effe ctively, Ti2Ni, TiNi, MoNi and MoNi3 amorphize after irradiation. In t he present work, this experimental behaviour is understood by consider ing the modification of the free-energy diagrams after particle irradi ation. Conversely, in the Fe-Ni system, a metastable fee solid solutio n evolves under irradiation towards ordered FeNi. In this system, acco rding to our calculation, the free-energy of the amorphous phase is mu ch higher than the free-energy of any other competing phase, so the am orphous phase cannot be produced. Each selected alloy has an intermeta llic compound (TiNi3, FeNi3 and MoNi4) which does not amorphize by par ticle irradiation and whose composition is close to the nickel-rich en d of the phase diagram. According to the calculated free-energy diagra ms, the reason for this impossibility of amorphization would be the co mpetition of the terminal solid solution with the amorphous phase.