Disorder and nanopatterning in ordered binary alloys: in situ ion irradiation and kinetic Monte Carlo simulation

We study the effects of temperature and disordering rate on the ordered microstructures of real and simulated binary alloys. The behavior of Cu3Au, an alloy with L12 chemical order, is investigated experimentally through in situ electron diffraction and dark-field transmission electron microscopy. Under irradiation with 500 keV Ne+ ions, our diffraction analysis reveals a similar, but steeper, trend in disordering rate as previously reported by resistivity. Further investigations by superlattice, dark-field imaging lead to the discovery of temperature and dose rate dependent alterations to the ordered microstructure of the alloy. The process appears to be driven by the nucleation of small, highly ordered domains within the existing microstructure. We attempt to simulate these and other disordering behaviors through a kinetic Monte Carlo method. For simplicity, we focus these investigations on two-dimensional, ordered AB alloys featuring various first and second neighbor ordering energies. Disorder is imposed in these simulated alloys through manipulation of vacancy-atom exchange rates and forced atomic replacement. For certain disordering-temperature conditions and ordering energies 2/1≲0.5, a previously unreported patterning of order is observed, dividing the ordered microstructure into competing, highly ordered domains. This behavior is rationalized in terms of decreased anti-phase boundary energies at the given ordering energies, and a physical picture of the patterning reaction is presented. The application of this picture to Cu3Au is deemed plausible and future work proposed