A metal matrix nanocomposite is formed by heating a metal above its liquidus temperature, adding nanoparticles, and then agitating the mixture with high-frequency (and preferably ultrasonic) vibration. The mixture can then be cooled below the liquidus of the metal to a semisolid state, and placed in a mold to form it into some desired shape. The formed mixture can then be quenched or otherwise allowed to cool to provide an article in finished (or nearly so) form.