| It is well known that alloys with a moderate, positive heat of mixing (e.g., Ag-Cu, Cu-Fe, Au-Ni) can be rendered miscible by heavy-ion irradiation. The experimental evidence shows that the underlying phenomenology is one of competing dynamics, where atomic mixing in collision cascades operates in opposition to thermal decomposition by radiation enhanced diffusion. In this Thesis, we perform theoretical and experimental studies of ion-beam mixing in immiscible binary alloys, focusing on the long-time regime. In this nonequilibrium dynamical steady state, the resulting phases and microstructures depend explicitly on the interplay between the two main kinetic actors.; In the theoretical part, we perform kinetic Monte Carlo simulations to investigate the dynamical steady state. Using first simple irradiation models, we construct dynamical phase diagrams that are then compared to existing theoretical models based on effective thermodynamics descriptions. When we improve upon the irradiation model, our simulations show that immiscible alloys under irradiation can spontaneously form compositional patterns at the nanometer scale. We obtain the same behavior by building continuum models that we solve by the construction of effective free-energy functionals. Interestingly, such irradiation-mixing models share similarities with the description of block-copolymer melts. This analogy helps to rationalize the spontaneous pattern formation. We also extend our models to include fluctuations, which allows us to derive the nonequilibrium structure factor.; In the experimental part, we investigate the microstructures resulting under ion-beam mixing in Ag-Cu multilayers. We find that, regardless of the irradiation temperature, extensive grain growth takes place. In the regime when thermal decomposition is in dynamic balance with irradiation mixing, phase separation takes place at a finite-length scale, of the order of the nanometer, in agreement with our theoretical predictions. This spontaneous nanoscale decomposition demonstrates that ion-beam mixing can be used as a processing tool for the synthesis of nanocomposite materials. |
