DARPA - Scalable Processing of Nanostructured Cubic Boron Nitride and Its Composites
Abstract
The proposed project will address the challenge of developing a scalable technology to fabricate nanostructured cubic-BN and its composites for structural and functional applications. The approach will consist of two parallel tracks: one on phase-pure c-BN and another on c-BN-based composites (which will have increased fracture toughness with minimal reduction in hardness, strength, and stiffness). For phase-pure c-BN, the approach will be based on nanopowder production by inductively-coupled plasma (ICP) processing, and nanopowder consolidation by high-pressure high-temperature (HPHT) processing. A lab-scale 2kW ICP reactor will be utilized to produce 1-2 gram batches of BN nanopowder by decomposing a volatile precursor, followed by rapid quenching of the hot gas stream, to generate loosely-agglomerated nanoparticles with a narrow particle-size distribution, and preferably with a metastable structure (amorphous or crystalline). High-quality c-BN micropowder (with nanocrystalline structure) will be produced from commercial h-BN powder, using an activator (which is later dissolved out). Concurrently, working with a 300-ton press, disc-shaped test pieces will be fabricated by HPHT processing, using two different pressure-cell designs. One cell will be designed for operation at 0.5-2.0 GPa/1000-1750¼C, yielding disc-shaped samples (1.84 cm dia. ? 0.92 cm thick.; 8.62 gram), and the other cell will be designed for operation at 0.5-5.5 GPa/1000-1750¼C, yielding disc-shaped samples (0.92 cm dia. ? 0.46 cm thick.; 1.08 gram). Different combinations of the c-BN powders produced by the different routes will be investigated. Continuous refinement and cross-validation will occur from parameters extracted from the materials characterization of the small sintered samples. Then, with an optimal set of powders and processing conditions, Rutgers will work with collaborators to produce disc-shaped samples up to 6.5cm dia. ? 0.5cm thick. In parallel, we will use HPHT processing to develop a new class of nanostructured c-BN/Ti composites, in which a high fraction of superhard c-BN particles are cemented together with a tough Ti binder phase. Depending on the processing conditions, Ti can either bond directly to c-BN particles to form Ti-bonded c-BN at high pressures (e.g. 8GPa) or react with c-BN particles to form Ti-bonded TiB2/TiN at lower pressures (e.g. 0.3GPa). In the latter case, it is significant that the reaction products are also hard and stiff, which presents opportunities for new research. Moreover, at 0.3GPa, a significant portion of the nanocrystalline c-BN phase can be preserved (where Ti reacts with the surface of c-BN grains, hindering the conversion of c-BN to h-BN), enabling unlimited scalability. Multi-layered structures will also be produced, alternating superhard and tough phases. In principle, such structures may be designed to satisfy impedance-mismatch requirements in high performance armor, and possibly provide a multi-hit capability. It is particularly noteworthy that the pressure requirements for processing Ti-bonded c-BN, Ti-bonded TiB2/TiN, and their corresponding multi-layered structures are as low as 0.3 GPa, and possibly lower, so that scalability is not an issue.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 10, 2017
- Source ID
- W911NF1510001
Entities
People
- Stephen Da-Yen Tse
Organizations
- Army Contracting Command
- Office of the Secretary of Defense
- Rutgers University