Cold spray formation of thin metal coatings

Abstract

The invention relates to an adaptation of the cold spray process to provide a method of coating fine metal particles, including aluminum and copper, onto a work piece. In one embodiment, the invention is a metal agglomerated hard sphere composition capable of providing about a 1 micron or thicker coating of a metal on a work piece in a cold spray process. In another embodiment the invention is a method of coating metal particles, including metal particles having a particle size of about 0.01 to about 10 micron, onto a work piece. The method of the invention circumvents many of the problems associated with cold spray processing of very fine particles.

Description

[0001] This invention was made with United States Government support under Agreement No. N00421-04-P-0625 awarded by Navy Air System Command. The United States Government has certain rights in the invention.BACKGROUND OF INVENTION [0002] 1. Field of Invention [0003] The present invention relates to metallurgy and more specifically to cold spray processing of metal powders to form thin metal coatings onto a work piece. [0004] 2. Description of Related Art [0005] U.S. Pat. No. 5,302,414 dated Apr. 12, 1994, incorporated herein by reference, and related re-examination certificate U.S. Pat. No. B1 5,302,414 dated Feb. 25, 1997, describe a cold gas dynamic spraying method for applying a coating, also referred to as cold spraying. That patent describes a process and apparatus for accelerating solid particles having a size from about 1-50 μm to supersonic speeds in the range of 300-1,200 m / sec and directing the particles against a substrate surface. When the particles strike the substrate ...

AI Technical Summary

Benefits of technology

[0012] One object of the invention is to adapt the cold spray process to provide a method of coating fine metal particles, of less than 5 μm average particle size, to a work piece. Another object of the invention is to provide a refurbishing method for applying thin metal coatings, of about 1 to about 10 μm in thickness, to a work piece. Another object of the invention is to provide metal coatings characterized by very small grain size, densely packed and work-hardened, to give wear resistant coatings.

Problems solved by technology

An inherent disadvantage is that a vacuum chamber is required.

There apparently is insufficient mass, and thus momentum, to propel the particle through the bow shock region.

This lower limitation on particle size may be the reason that cold spray processing has not been demonstrated useful in preparing thin metal coatings, for instance, films less than about 8 microns.

Thin metal coatings are typically achieved with physical or chemical vapor deposition methods under vacuum and high temperature conditions, usually 250-1200° C. For repair of work pieces in the field, where a thin coating is required, vacuum or high temperature processing is not suitable.

Other methods such as electroplating and brush-plating can be used to prepare thin coating, but they have toxicity and environmental issues associated with them.

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