When you apply mechanical attrition to deformable(plastically) bodies, it is reasonable to obtain a mixture at different scales, i.e., macro scale, micron scale or atomic scale, depending on the experimental parameters you apply. There, all components deform with the effect of the mechanical attrition. However, when the system involves one deformable (like pure metal) and one non-deformable (like an oxide) components, the deformable component one is deformed not only by mechanical attrition but also by non-deformable part. In fact, nano-sized oxide powders contributes the deformation of the microstructure of the deformable component, i.e. grain size refinement, amorphization, introduction of point defects etc. I think, the first stages of this process, inevitably, involve the complete coverage of the non-deformable particles with the deformable component. The last case involves the mechanical attrition of two non-deformable components, i.e., nano-sized oxide powders. This time, it is questionable if the attrition is capable to deform such small particles, and if so what is the extent of this. I think, two effects of attrition for nano-sized oxide particles are the reduction in size and decrease in the crystallinity. Also note that the behavior of the nano-particles could be different than what they possess at micro or macro sizes. Hope to give you some insight.