Method of consolidating precipitation-hardenable alloys to form consolidated articles with ultra-fine grain microstructures

Abstract

A method by which consolidated articles can be produced from nanocrystalline materials to have mechanical properties that can be improved through thermal treatment. The method entails machining a body to produce polycrystalline chips having nanocrystalline microstructures, and then consolidating the chips to form a consolidated article having mechanical properties that exceed that of the body from which the chips were formed. In particular, consolidation of nanocrystalline chips formed by machining a supersaturated solid-solution body causes precipitation of a fine dispersion of precipitates in the consolidated article, with the potential for certain properties to even improve during consolidation or subsequent thermal treatment of the consolidated article.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This patent application claims the benefit of U.S. Provisional Application No. 60 / 677,246, filed May 3, 2005, and is a continuation-in-part patent application of co-pending U.S. patent application Ser. No. 10 / 707,999, filed Jan. 30, 2004, which is a division application of U.S. Pat. No. 6,706,324, which claimed the benefit of U.S. Provisional Application No. 60 / 244,087, filed Oct. 28, 2000. The contents of these prior applications are incorporated herein by reference.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH [0002] This invention was made with Government support under Agreement No. DE-AC05-000R22725, awarded by the U.S. Department of Energy. The Government has certain rights in the invention.BACKGROUND OF THE INVENTION [0003] The present invention generally relates to methods of producing materials and articles with nanocrystalline microstructures, and more particularly to producing such materials and articles by machining and th...

AI Technical Summary

Benefits of technology

[0011] According to a preferred aspect of this invention, a consolidated article can be formed from the nanocrystalline chips to have mechanical properties that exceed that of the body from which the chips were formed. In particular, consolidation of nanocrystalline chips formed by machining a supersaturated solid-solution body has been found to cause precipitation of a fine dispersion of precipitates in the resulting consolidated article, with the potential for certain properties to even improve during consolidation or subsequent thermal treatment of the consolidated article. Such a capability has the potential to lead to more widespread use of nanocrystalline materials in applications where improved strength-to-weight ratio is important. Furthermore, in this processing route, the nanocrystalline microstructure is preserved during consolidation and the resulting bulk component is stronger than both the precursor and any component produced by bulk processing techniques in the material.

[0013] In view of the above, the present invention provides a controllable and low-cost method for synthesizing nanocrystalline solids that can be used to produce monolithic, composite, and consolidated products. The method of this invention also makes possible the capability of producing nanocrystalline solids from materials that have been difficult or impossible to process using prior art techniques, such as very hard materials that cannot be processed by multi-stage deformation processes, and alloys that cannot be processed by the condensation method.

Problems solved by technology

However, there are significant limitations and disadvantages with this processing technique.

A significant limitation is the inability to induce large strains in very strong materials, such as tool steels.

Other limitations include the inability to impose a strain of much greater than one in a single stage of deformation, the considerable uncertainty of the deformation field, and the minimal control over the important variables of the deformation field—such as strain, temperature, strain rate and phase transformations—that are expected to have a major influence on the evolution of microstructure and material properties.

While suitable for making powders and small compacted samples with excellent control over particle size, the condensation method is at present not practical for most applications other than experimental.

A particularly limiting aspect of the condensation method is the inability to form nanocrystalline materials of alloys because of the difficulty of controlling the composition of the material from the vapor phase.

Another limiting aspect of the condensation method is that high green densities are much harder to achieve as a result of the nano-size particles produced.

However, these techniques cannot produce nanocrystalline materials at a cost acceptable for practical applications.

Another complication in producing articles from nanocrystalline and ultra-fine grained particulates is the difficulty of consolidating such particulates through thermo-mechanical processing while maintaining mechanical properties and retaining the fine microstructure.

Typically, consolidation of ultra-fine (including nanocrystalline) grained particulates results in loss of strength and grain coarsening during thermal treatment.

This problem has not generally been solved, but rather partially circumvented through attempts at consolidation at room temperature.

However, the limited flow properties with these techniques and the associated costs have prevented any significant progress.

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