Precipitate-hardened aluminum alloys formed using pulsed laser deposition

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Abstract
Very high‐strength alloys of Al have been formed by pulsed laser deposition (PLD) from Al and Al2O3 targets. The deposition is alternated between the two targets, with the ratio of pulses per target controlling the O content, and the amount of each element deposited in a cycle kept low enough that the final material is uniform in composition and has a highly refined microstructure. A fine, uniform dispersion of ∼1‐nm‐diam γ‐Al2O3 precipitates is formed in fcc Al, with an overall composition of up to 33 at. % oxygen. This microstructure is very similar to one that we previously synthesized by using ion implantation of O into Al, where nanoindentation testing revealed yield stresses of ∼1 GPa or more. Nanoindentation testing of these new PLD materials shows yield stresses as high as 5.1 GPa, greatly exceeding the strengths of aerospace Al alloys and even high‐strength steels. The key to the properties of these materials is the dispersion of small, hard precipitates spaced only a few Burgers vectors apart; dislocations are apparently unable to cut through and must bow around them. While the nature of ion implantation limits both its cost effectiveness and the thickness of the layers that can be formed, PLD is a completely new approach with major advantages over implantation, including greater control of the composition versus depth, deposition on arbitrary substrates to any thickness, and scalability of the process to larger areas.

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