In recent years, near-nano (submicron) and nanostructured materials have attracted increasingly more attention from the materials community. Nanocrystalline materials are characterized by a microstructural length or grain size of up to about 100 nm. Materials having grain size of ∼0.1 to 0.3 μm are classified as submicron materials. Nanocrystalline materials exhibit various shapes or forms, and possess unique chemical, physical or mechanical properties. When the grain size is below a critical value (∼10–20 nm), more than 50 vol.% of atoms is associated with grain boundaries or interfacial boundaries. In this respect, dislocation pile-ups cannot form, and the Hall–Petch relationship for conventional coarse-grained materials is no longer valid. Therefore, grain boundaries play a major role in the deformation of nanocrystalline materials. Nanocrystalline materials exhibit creep and super plasticity at lower temperatures than conventional micro-grained counterparts. Similarly, plastic deformation of nanocrystalline coatings is considered to be associated with grain boundary sliding assisted by grain boundary diffusion or rotation. In this review paper, current developments in fabrication, microstructure, physical and mechanical properties of nanocrystalline materials and coatings will be addressed. Particular attention is paid to the properties of transition metal nitride nanocrystalline films formed by ion beam assisted deposition process.

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Nanocrystalline materials and coatings

Of late, nanotechnology seems to be rapidly thrusting its applications in all aspects of life including engineering and medicine. Materials science and engineering has experienced a tremendous growth in the field of nanocomposite development with enhanced chemical, mechanical, and physical properties. A wide array of research has been conducted in the processing of nanocomposites. Consolidation of these systems from loose particles to bulk free form entities has always been a challenge. To name a few, traditional consolidation techniques such as cold pressing and sintering at high temperatures, hot pressing, and hot isostatic pressing have strong limitations of not being able to retain the nanoscale grain size due to the excessive grain growth during processing. This article reviews in detail the results from numerous studies on various methods for manufacturing nanocomposites with improved properties and retained nanostructures. Both challenges and recent advances are discussed in detail in this review.

Challenges and advances in nanocomposite processing techniques

This volume brings together international scientists in the field of solid rocket propulsion. Thirty-nine papers present in-depth coverage on a wide range of topics including: advanced materials and non-traditional formulations; the chemical aspects of organic and inorganic components in relation to decomposition mechanisms, kinetics, combustion and modelling; safety issues, hazards and explosive characteristics; and experimental and computational interior ballistics research, including chemical information and the physics of the complex flow field.

Solid propellant chemistry, combustion, and motor interior ballistics

Dynamic high pressure is 1 GPa (10 kbar) or greater with a rise time and a duration ranging from 1 ps (10−12 s) to 1 µs (10−6 s). Today it is possible in a laboratory to achieve pressures dynamically up to ~500 GPa (5 Mbar) and greater, compressions as much as ~15-fold greater than initial density in the case of hydrogen and temperatures from ~0.1 up to several electronvolts (11 600 K). At these conditions materials are extremely condensed semiconductors or degenerate metals. Temperature can be tuned independently of pressure by a combination of shock and isentropic compression. As a result, new opportunities are now available in condensed matter physics at extreme conditions. The basic physics of the dynamic process, experimental methods of generating and diagnosing matter at these extreme conditions and a technique to recover metastable materials intact from ~100 GPa shock pressures are discussed.Results include (i) generation of pressure standards at static pressures up to ~200 GPa (2 Mbar) at 300 K, (ii) single-shock compression of small-molecular fluids, including resolution of the recent controversy over the correct shock-compression curve of liquid D2 at 100 GPa pressures, (iii) the first observations of metallization of fluid hydrogen, nitrogen and oxygen compressed quasi-isentropically at 100 GPa pressures, (iv) implications for the interiors of giant planets within our solar system, extrasolar giant planets and brown dwarfs discovered recently and the equation of state of deuterium–tritium in inertial confinement fusion (ICF) and (v) prospects of recovering novel materials from extreme conditions, such as metastable solid metallic hydrogen. Future research is suggested.

https://iopscience.iop.org/article/10.1088/0034-4885/69/5/R05/pdf

Dynamic compression of materials: metallization of fluid hydrogen at high pressures

https://apps.dtic.mil/sti/pdfs/ADA192126.pdf

Dynamic Consolidation of Metal Powders.

A model is presented for the deposition of energy at powder particle surfaces during dynamic consolidation. The average energy flux incident on the surface of a powder particle is estimated to be E/τA where E is the specific energy deposited by the shock, τ is the shock rise time, and A the measured powder specific surface area. This flux is assumed to be constant over the rise time of the shock, falling abruptly to zero for times longer than τ. Solution of the thermal transport equation subject to this boundary condition yields the thermal history within a powder particle having the area‐equivalent diameter D=6/ρ0A, where ρ0 is the solid density. The magnitude of the temperatures and the heating and cooling rates indicate likely material transformations. The penetration of a given isotherm provides an estimate of the volume fraction of material transformed. Good agreement is found between model calculations and measurements of the extent of local martensite formation in consolidated 4330V steel powder an...

W. H. Gourdin

Papers

Energy deposition and microstructural modification in dynamically consolidated metal powders