Ion-irradiation-induced transformations in intermetallic alloys: formation and stability

Ion irradiation has been used to examine phase stability and phase formation in intermetallic alloys. An ion-irradiation-induced phase transformation from Ni2Al3 to NiAl was investigated by transmission electron diffraction. Detailed examination of the closely related equilibrium NiAl and Ni2Al3 structures permits explanation of this transformation based on the structural similarity of the two phases and using a model built around radiation disordering of vacancies. Compound samples of NiAl3 as well as Ni23Al77 multilayered samples were on irradiated by either Xe or Ne ions. Formation of NiAl3 by ion mixing Ni/Al multilayers was not affected by the mass of the irradiating ion and appears to be limited by nucleation. Results of the ion-irradiation stability of metallic CsCl phases indicate that CsCl compound stability under ion irradiation is strongly correlated with atomic mobilities and the width of the phase field. Immiscible alloy systems of Cu/W and Cu/Ta were used to examine the response of coevaporated amorphous alloys to thermal annealing and ion irradiation. Results show that the crystallization temperature, T/sub c/, is not predicted equally well for systems with a positive or negative heat of formation