Manufacturing High Strength Nanocrystalline Metal Sheets Using a Cold Angular Rolling Process

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The formation of layered structures produced by traditional metalworking has been used to achieve significant strengths in metals for thousands of years. Examples are Japanese swords and Damascus steels. Current manufacturing methods can produce layered structures on a large-scale by bonding separate metals through rolling, but with limited improvements in mechanical properties. Recent studies demonstrated the applicability of severe metal deformation techniques, which introduce high pressure and mechanical shearing to refine the microstructure of metal composites and greatly increase their strength, but the non-continuous nature of these techniques has been a barrier to scale-up and commercialization. This award supports fundamental research needed for the development of a continuous manufacturing process to produce high strength nanocrystalline sheet metals. This project uses a new cold angular rolling processing, which employs a single roller for shearing and compressing metals in a continuous process to create layered nanocrystalline sheets. The value of this process comes through efficient bonding and microstructural modification of low-cost sheet metals in a continuous, energy-efficient process. The project increases U.S. metal manufacturing capability to design and manufacture nanostructured alloys with superior properties for applications requiring lightweight structural metals, promoting the progress of science and advancing national prosperity and economy. University students engaged in this research are being prepared for careers in advanced materials engineering and manufacturing in research laboratories and industries.Non-ferrous metals, including aluminum and magnesium alloys, have a broad range of industrial applications, but they typically suffer from low mechanical strength and poor fatigue resistance. To enable broad use of lightweight ultrafine-grained metals and alloys, there is a critical need for the development of a continuous processing method to simultaneous bond and refine the microstructure of bulk lightweight alloys. This project uses a new cold angular rolling process (CARP) which combines equal-channel angular pressing and single-roller cold rolling in a single-step enabling the production of continuous sheets of hierarchically structured, nanocrystalline alloy sheets without any length limitations. To further improve the refinement of the microstructure and increase in material properties, the project uses layers of dissimilar metals to incorporate interface-induced plastic deformation. By combining CARP, finite element method (FEM), and microstructure and mechanical property characterization, the project provides new fundamental knowledge of (i) relationships between stress-strain state and the microstructure, (ii) interface-induced flow, plastic deformation, and tribomaterial formation, and (iii) microstructure and mechanical properties that develop in layered metallic tribomaterials.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.