Lightweight metal matrix nano-composites (MMNCs) (metal matrix with nano-sized ceramic particles) can be of significance for automobile, aerospace and numerous other applications. It would be advantageous to produce low-cost as-cast bulk lightweight components of MMNCs. However, it is extremely difficult to disperse nano-sized ceramic particles uniformly in molten metal. This paper presents a new method for an inexpensive fabrication of bulk lightweight MMNCs with reproducible microstructures and superior properties by use of ultrasonic nonlinear effects, namely transient cavitation and acoustic streaming, to achieve uniform dispersion of nano-sized SiC particles in molten aluminum alloy A356. Microstructural study was carried out with an optical microscope, SEM, EDS mapping, and XPS. It validates a good dispersion of nano-sized SiC in metal matrix. It also indicates that partial oxidation of SiC nanopartilces results in the formation of SiO2 in the matrix. Mechanical properties of the as-cast MMNCs have been improved significantly even with a low weight fraction of nano-sized SiC. The ultrasonic fabrication methodology is promising to produce a wide range of other MMNCs.

Study on bulk aluminum matrix nano-composite fabricated by ultrasonic dispersion of nano-sized SiC particles in molten aluminum alloy

In this study, 0.75, 1.5, 2.5, 3.5, and 5 vol.% of alumina nanoparticles were incorporated into the A356 aluminum alloy by a mechanical stirrer and then, cylindrical specimens were cast at 800°C and 900°C. A uniform distribution of reinforcement, grain refinement of aluminum matrix, and presence of the minimal porosity was observed by microstructural characterization of the composite samples. Characterization of mechanical properties revealed that the presence of nanoparticles significantly increased compressive and tensile flow stress at both casting temperatures. The highest compressive flow stress was obtained by 2.5 vol.% of Al2O3 nanoparticles. It is then observed that the flow stress decreases when Al2O3 concentration increased further to 5 vol.% irrespective of the amount of deformation and casting temperature. It was revealed that the presence of nano-Al2O3 reinforcement led to significant improvement in 0.2% yield strength and ultimate tensile stress while the ductility of the aluminum matrix is ...

Investigation on mechanical properties of nano-Al2O3-reinforced aluminum matrix composites:

Mechanical properties of tri-modal Al matrix composites reinforced by nano- and submicron-sized Al2O3 particulates developed by wet attrition milling and hot extrusion

Pure aluminum Nano composite reinforced with Nano titanium dioxide was produced by powder metallurgy route. Measurements of tensile strength, hardness, and density showed that the porosity and the tensile strength of composites increased with an increase in volume fraction of nanoparticles; however ductility of aluminum was decreased. Wear test revealed that composites offer superior wear resistance compared to alloy.

Properties of aluminum matrix Nano composites prepared by powder metallurgy processing

The processing of 3 mol% yttria partially stabilised zirconia nanopowder into components has been investigated via slip casting low viscosity but high solids content nanosuspensions and subsequent pressureless sintering via one and two stage sintering involving both pure conventional heating and hybrid conventional-microwave heating. Very homogeneous and uniform green bodies with densities up to ∼54% of theoretical could be produced, the major limitation being cracking on drying when the highest solid content suspensions were used. This could be partially overcome via the use of humidity drying. The pressureless sintering of the bodies revealed that the two stage sintering process allows a much finer average grain size to be retained than conventional single stage firing, whilst the use of hybrid heating gave further improvements. Greater than 99% dense ceramics with average grain sizes of ∼65 nm could be produced from a powder with an average particle size of ∼16 nm.

Dense nanostructured zirconia by two stage conventional/hybrid microwave sintering

The use nanocrystalline materials for novel applications requires the development of cost effective consolidation methods to generate engineering components. Full consolidation of nanoparticles is a sensitive compromise between initial nanopowder characteristics, the several processing conditions in sintering such as pressure, temperature and time, and microstructural changes such as pore elimination and grain growth. This paper reviews lesses in nanopowder densification and discusses which affer commercial potential for the commercial production of components with nanosize grains.

J. R. Groza

Papers

Sintering of nanocrystalline powders