TECHNOLOGY AREA(S): Materials/Processes
The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), which controls the export and import of defense-related material and services. Offerors must disclose any proposed use of foreign nationals, their country of origin, and what tasks each would accomplish in the statement of work in accordance with section 5.4.c.(8) of the solicitation.
OBJECTIVE: Develop a new high-strength nanostructured Ag or Ag alloy for shape charge and Explosively Formed Penetrator (EFP) liner applications.
DESCRIPTION: The U.S. Army requires a high strength Ag or Ag alloy for use as liners in explosively formed penetrators (EFPs) and shaped charges. Currently Ta has most commonly been selected for these applications because of its appealing combination of strength, density, ductility at high strain rates and relative safety in handling. However, Ta is challenging to manufacture into appropriate shapes and is quite expensive as a result. Improved performance is also desired. Ag is used routinely in commercial shape charge applications, but rarely in EFP applications due primarily to insufficient strength. Recent work at the Army has suggested that a higher strength Ag could outperform Ta as a liner material. Nanostructured (NS) and ultra-fine-grained (UFG) metals, in which grain sizes are usually in the range of 1-1000 nm, are well known to have substantially improved strength relative to coarser-grained metals, and Ag or Ag alloy with such a structure may have sufficient strength for EFP applications. For example a traditional microcrystalline Ag might have a yield strength of 50-150 Mpa, while a UFG or NS Ag might have a yield strength of 250 to 500 Mpa. However, even when demonstrated to have appropriate properties, the manufacturing of NS or UFG materials in monolithic form to the geometries and length scales required for EFP liner applications has not traditionally been possible. The desirable grain structures are lost during the consolidation, forming, and/or melting and casting processes required to achieve full density and shape. The contractor shall demonstrate the feasibility of creating an Ag alloy with a hardness of at least 100 VHN and tensile strength of at least 300 Mpa after consolidation, and of forming the new material into a final piece with at least 2.5 cm-scale dimensions on all axes while maintaining appropriate properties. The density of the resultant alloy shall not be less than 90% that of pure Ag, and an increase in density relative to Ag will be preferred. Appropriate strength, high-rate performance, density and manufacturability will all be demonstrated as part of this work.
PHASE I: Develop NC or UFG Ag alloy. Demonstrate a hardness of at least 100 VHN with a density of at least 90% that of pure Ag in this alloy. Demonstrate ability to form this alloy into monolithic pieces with minimum of 5 mm dimension on each side. Provide at least 2 samples to the Army for independent characterization.
PHASE II: Optimize new alloy to maximize hardness and density. Produce monolithic pieces of preferred alloy(s) with minimum 8.2 cm in diameter by 0.5 cm thick, including appropriate test specimens for uniaxial mechanical tests, Split Hopkinson Bar testing, and standard Army Shaped Charge Jet testing (see reference 4). Perform uniaxial mechanical testing and Split Hopkinson Bar testing of optimized alloy, and demonstrate uniaxial yield strength of at least 300 Mpa. Demonstrate ability to make multiple characteristic plate and dish geometries at these length scales. Provide at least 5 samples each to the Army for uniaxial mechanical testing, Split Hopkinson Bar testing, Shaped Charge Jet and EFP testing.
PHASE III DUAL USE APPLICATIONS: The developed technology will be transitioned to prototype scale and tested at high strain rates. Partnerships with major materials manufactures will be formed to transition the technology to full-scale manufacturing for military sector applications. Dual use applications in the civil sector are anticipated, including in industrial and commercial electronics and electricity transmission.
- Conrad, Hans, and Kang Jung. "Effect of grain size from millimeters to nanometers on the flow stress and deformation kinetics of Ag." Materials Science and Engineering: A 391.1 (2005): 272-284.
- Trelewicz, Jason R., and Christopher A. Schuh. "The Hall-Petch breakdown at high strain rates: Optimizing nanocrystalline grain size for impact applications." Applied Physics Letters 93.17 (2008): 1916.
- Marek, Ivo, et al. "High-strength bulk nano-crystalline silver prepared by selective leaching combined with spark plasma sintering." Materials Science and Engineering: A 627 (2015): 326-332.
- Baker, Ernest L., et al. "Shaped Charge Jet Characterization and Initiation Test Configuration for IM Threat Testing." Procedia Engineering 58 (2013): 58-67.
KEYWORDS: silver, shape charge, explosively formed projectile, nanostructured, warhead
- TPOC-1: Peter Rottinger
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