Addressing the Strength-Ductility Trade-off Using Automated Surface Nanocrystallization
Abstract
Although there has been a growing body of work to address the strength-ductility trade-off in nanocrystalline alloys, one of the most promising methods for near-term commercial deployment is surface mechanical attrition treatment (SMAT), as it can produce a nanostructured surface on an otherwise ÒordinaryÓ metallic component. SMAT has been demonstrated in a range of metallic systems using varied methods, but they all use randomly applied plastic deformation over broad areas, and that restricts direct correlation between impact characteristics and microstructural changes. If SMAT can be precisely controlled in terms of position and energy, new understanding of the microstructural refinement mechanisms and new possibilities in the design of bulk nanocrystalline structures may be realized. The objectives of the project are to 1) Develop and construct a device for precision surface deformation, 2) Apply this device and characterize the resulting surface deformation, and 3) Analyze bulk-scale samples treated by precision nanocrystallization and correlate properties with processing methodology. This will combine hardware and automation systems that are robust and, where possible, readily available. To that end, a device for controlling impact energy and location over a two-dimensional area will be developed by integrating systems for precisely positioning and impacting a surface. This will be accomplished using a computer numerical control (CNC) machine and pneumatic ram system such that the impact location and velocity can be programmed. Redundant sensors to directly measure impact force, velocity, and other parametric conditions will ensure that process-property relationships are accurately coupled. This equipment will allow the direct correlation of microstructural development with impact energy, impact number, and the overlap of neighboring impact zones. This is intended to eliminate the trial-and-error approach to SMAT where a collection of ball bearings with random trajectories and energies are used to study surface refinement. With this new method, samples can be prepared with exact knowledge of the impact characteristics to develop a fundamental understanding of stress, strain and refinement in nanocrystalline surfaces. Producing advanced materials efficiently is of central importance to applying them at scale. This will require multi-scale control and characterization of the materials and the processes used to create them. Consistent with Army interests, this projects assists in the effort to discover and illuminate the governing processing-microstructure-property relationships to enable optimal design and fabrication of nano or micro structural bulk structural materials, provides innovative processing methods capable of fabricating materials with deliberate microstructural architectures and features that advance the materialÕs properties to levels unattainable by conventional processing, and probes fundamental physical laws and the unique phenomena occurring under metastable and far-from-equilibrium conditions to develop revolutionary and disruptive new materials or processing methodologies. This project addresses an underrepresented aspect of producing nanocrystalline and nanostructured alloys. Specifically, many of the processing techniques rely on randomized processes for producing the materials, such that direct control of the microstructure is impractical or impossible at commercial scale. This project simultaneously addresses the lack of control in impact-mediated nanocrystallization and provides a relevant vehicle for scaling these materials up in a meaningful way.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 02, 2022
- Source ID
- W911NF2210170
Entities
People
- Mark Atwater
Organizations
- Army Contracting Command
- Liberty University
- United States Army