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

A composite powder with a fine homogeneous distribution of the reinforcement phase in the whole particle can be obtained by mechanical alloying. Aluminium PM6061 unreinforced, and matrix composite reinforced with Si 3 N 4 and AlN powder, are milled in a high-energy attritor mill and the powder properties are compared with those of the same composite composition mixed in a horizontal low-energy ball mill. The correlation observed between the apparent densities and the milling time, explained by the morphological and microstructural evolution of the powder particles during the high-energy milling process, is used to determine the steady state of the process. At short milling times, the apparent density decreases as the milling time is extended, due to the deformation dominant at this stage; at longer milling times, it starts to increase with increasing milling time due to the piling up of the flattened particles and fracture of the welded particles. When mechanical alloying reaches the steady state, the apparent density is stabilized. A simple model is proposed to illustrate the mechanical alloying of a ductile–brittle component system. The particle size distribution and the microhardness of the mechanically alloyed particles are determined.

Effect of mechanical alloying on the morphology, microstructure and properties of aluminium matrix composite powders

Materials for thermal conduction

Mechanical properties of Al-based metal matrix composites reinforced with Zr-based glassy particles produced by powder metallurgy

Previously, we reported ultra-high compressive strength (up to 1065 MPa) for a bulk aluminum-based metal matrix nanocomposite [J. Ye, B.Q. Han, Z. Lee, B. Ahn, S.R. Nutt, J.M. Schoenung, Scr. Mater. 53 (2005) 481–486]. The mechanisms that are responsible for this significant strength increase over conventional materials (∼225 MPa, H. Zhang, M.W. Chen, K.T. Ramesh, J. Ye, J.M. Schoenung, E.S.C. Chin, Mater. Sci. Eng. A: Struct. Mater. Prop. Microstruct. Process. 433 (2006) 70–82) and even over other equivalent nanocrystalline materials (∼470 MPa, R.G. Vogt, Z. Zhang, T.D. Topping, E.J. Lavernia, J.M. Schoenung, J. Mater. Process. Technol., 209 (2009) 5046–5053) have not been studied in detail. The material consists of boron carbide reinforcement in a matrix with both coarse-grained and ultrafine-grained Al 5083; the processing introduces secondary phase dispersoids and dislocations. In this work, we systematically investigate the microstructural origins and the strengthening mechanisms, including Hall–Petch, Orowan and Taylor, as appropriate to each phase constituent. To provide insight into the relative contributions of these mechanisms, we calculate overall strength using rule-of-mixtures, modified shear-lag model, and Mori–Tanaka method.

Investigation of aluminum-based nanocomposites with ultra-high strength

Aluminum (Al)-based composite materials which were produced using both powder metallurgical and vacuum plasma spraying (VPS) techniques are presented. The objective was to produce materials with low coefficients of thermal expansion, tailored to approach those of steel (≃13×10 −6 K −1 ), and to improve the mechanical properties of the matrix. Composite materials based on Al are used in different fields where weight and thermal stability are key requirements. Typical applications include aerospace components, electronic packaging, high precision instrumentation, and automobile engine components. The nature, size and the relative quantities of the different reinforcing phases were considered in calculations involving the optimization of the main characteristics of the composites. Fine dispersed powders of Si 3 N 4 , AlN, TiB 2 , B 4 C (5–10 μm) and 3Al 2 O 3 ·2SiO 2 (20–75 μm) were used as the strengthening phases, while pure Al, 6061 and Al–27Si–6Ni alloys were used as the matrix. The dimensional and relaxation stability was investigated for several of the extruded composites. The mechanical properties of the extruded composites and the VPS produced composites were tested. Through a combination of plastic deformation and heat treatment (annealing or quenching with ageing) major improvements in the mechanical properties of the VPS composites were obtained. Varying levels of improvement were seen in the ductility of the VPS composite materials (elongation values ranging from two to ten times greater than the as-sprayed values). The ultimate tensile strengths were also improved by 30–75% compared to the as-sprayed values.

The properties and microstructure of Al-based composites reinforced with ceramic particles

http://dl.asminternational.org/itsc/proceedings-pdf/doi/10.31399/asm.cp.itsc1998p0957/441666/itsc1998p0957.pdf

W and B4C Coatings for Nuclear Fusion Reactors

http://dl.asminternational.org/itsc/proceedings-pdf/doi/10.31399/asm.cp.itsc1998p1229/441795/itsc1998p1229.pdf

Near Net-Shape Forming of Thermal Barrier Coated Components for Gas Turbine Engine Applications

ProTeC has developed a method for forming unique free-standing components. The Vacuum Plasma Spray (VPS) forming process involves the build up of single layer and composite components onto a moving mold. The individual layers may be ceramic, metal, or composites. Complex geometries are possible, depending on the shape of the mold and the spraying program. Examples of structures which have been formed and evaluated are presented herein. 

A. Cavasin

Papers

The properties and microstructure of Al-based composites reinforced with ceramic particles

W and B4C Coatings for Nuclear Fusion Reactors

Near Net-Shape Forming of Thermal Barrier Coated Components for Gas Turbine Engine Applications

The plasma spray forming of near-net-shape component