A nanoparticle powder is disclosed including a plurality of stabilized nanoparticles having a superalloy composition. At least about 90% of the particles have a convexity between about 0.980-1 and a circularity between about 0.850-1. A method for forming a braze paste is disclosed including mixing the plurality of stabilized nanoparticles with at least one organometallic precursor and up to about 5 wt % binder. A method for modifying an article is disclosed including applying the braze paste to a substrate including at least one crack, removing at least about 70% of the binder in the braze paste, and then applying additional braze paste over the first portion. Under vacuum or inert gas atmosphere, essentially all remaining binder is evaporated. The braze paste is brazed to the article at about 40-60% of the superalloy's bulk liquidus temperature, forming a brazed material and thereby sealing the at least one crack.