YIP: Elucidating the Role of Flash Heating in Ultrasonic Powder Compaction
Abstract
Ultrasonic powder compaction is a promising approach for synthesizing bulk nanostructured thermites, nanocrystalline alloys, and other thermally unstable materials that are easy to prepare in powder form but challenging to densify. The process resembles standard uniaxial die compaction, except that the upper punch oscillates perpendicular to the loading axis at ultrasonic frequencies. This shearing motion causes rapid consolidation and a brief thennal excursion due to the conversion of plastic work into heat. Key advantages of ultrasonic powder compaction over competing rapid densification technologies (e.g., field assisted sintering) are its scalability, its speed (a typical ultrasonic powder compaction cycle only lasts a couple seconds), and its applicability to additive manufacturing platforms for making net-shaped components. The temperature rise during ultrasonic powder compaction aids densification; however, the peak temperature must be minimized to preserve the structure and properties of thermally unstable powder feedstock like the examples listed above. Thus, there exists a set of optimal processing conditions that fully densifies a given feedstock powder while minimizing thermally activated structural evolution. Unfortunately, predicting such optimal parameter sets for ultrasonic powder compaction remains challenging because the relationships between material properties, process variables, and densification are poorly understood. This proposal will address this knowledge gap and determine the key mechanisms in ultrasonic powder compaction that drive densification, thereby enabling new processing techniques like powder-fed ultrasonic additive manufacturing for the synthesis of bulk net-shaped components with unprecedented properties and functionality. The main scientific goal of this proposal is to test our hypothesis that local flash heating and thermal softening control the growth of interparticle junctions during ultrasonic powder compaction. We will assess this hypothesis through a combination of in situ imaging experiments to determine whether particle contacts form junctions after flash heating; ex situ interrupted ultrasonic powder compaction experiments to characterize individual particle contacts and find structural evidence of flash heating; and physics-based process modeling of flash heating, thermal softening, and junction growth to provide a quantitative test of our hypothesis that flash heating and thermal softening control interparticle junction growth. The scientific insights from this work will dramatically advance the fields of powder metallurgy and granular mechanics, by clarifying how plastically deforming particles flow under oscillatory high-rate high-shear loading. The expected outcomes of this work also have direct relevance to the Army Modernization Priorities, since they will enable predictions of parameter sets that give dense compacts without degrading the structure and properties of thermally unstable powder feedstock. This capability will be useful for consolidating structural materials such as high-strength steels and nanocrystalline alloys, as well as providing fundamental insight into consolidating such exotic functional materials as nanostructured reactive materials and next-generation permanent magnet compounds like Sm2Fel 7N.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jan 04, 2021
- Source ID
- W911NF2110054
Entities
People
- Zachary C. Cordero
Organizations
- Army Contracting Command
- Massachusetts Institute of Technology
- United States Army