In binary alloys, domain walls play a central role not only on the phase transitions but also on their physical properties and were at the heart of the 70’s metallurgy research. Whereas it can be predicted that such defects likely suppressed because they become too costly in energy relative to system size, here we show, with both experimental and numerical approaches how orientational domain walls are formed in CuAu nanoparticles binary model systems. We demonstrate that the formation of domains in larger NPs is driven by elastic strain relaxation which is not the case for smaller NPs where surface effects dominate. Finally, we show how the multivariants NPs tend to form an isotropic material through a continuous model of elasticity. Such multivariant domain structure represents a different morphology from the widely studied nanoparticle configurations such as core-shell or Janus types. Here, we describe this morphology and provide an explanation of its physical origin, which may contribute to a better understanding of chemical ordering phenomena in bimetallic nanoparticles.