In the last two decades, metal matrix nanocomposites have witnessed tremendous growth. Particulate-reinforced nanocomposites have been extensively employed in the automotive industry for their capability to withstand high temperature and pressure conditions. Several manufacturing approaches have been used to fabricate them. Non-homogeneous particle dispersion and poor interface bonding are the main drawbacks of conventional manufacturing techniques. A critical review of nanocomposite manufacturing processes is presented; the distinction between ex-situ and in-situ processes is discussed in some detail. Moreover, in-situ gas/liquid processes are elaborated and their advantages are discussed. The thermodynamics and kinetics of the reaction between the precursor gas and the liquid metal have been analyzed and their role on particle formation studied. This critical review will provide the reader with an overview of nanocomposite manufacturing methods along with a clear understanding of advantages and disadvantages.
Research Summary aluminum: cast shop and alloys How would you… …describe the overall signifi cance of this paper? This paper describes a methodology and a conceptual framework to manufacture Al-based nanocomposites in a cost-effective way. It gives a pathway to make nanocomposites directly from melt. …describe this work to a materials science and engineering professional with no experience in your technical specialty? Al-based alloys cannot be used above 285°C as the precipitation hardening mechanism falls apart. Nano-composite Al alloys can be utilized at temperatures above 300°C which gives the opportunity to use them for a variety of elevated temperature applications. …describe this work to a layperson? Diesel engines are quite effective in that energy usage is less. Diesel is quite effective and gets excellent mileage (miles/gallon). However, diesel engines operate at higher temperatures than internal combustion engines. Al alloys fall short for many diesel applications as the Al does not maintain its strength at elevated temperatures. Nanocomposites open up a way for us to use Al for diesel applications.
Aluminum nitride (AlN) possesses superior thermal and electrical properties and is an ideal candidate for high-temperature, as well as for packaging and optoelectronic applications. Aluminum based composites reinforced with AlN have been manufactured via an in situ gas-assisted process, where a nitrogen-bearing gas is injected in the molten aluminum at 1273-1323 K. The process is carried out in an inert atmosphere in order to avoid oxygen contamination. Addition of Mg lowered the oxygen content in the melt by forming MgO and thus favoring the nitridation reaction. Particle size formed in the matrix varied from 1- 3 μm to sub-micron scale depending on the gas injection time. Longer bubbling times give rise to improved reinforcement dispersion. Addition of Si is detrimental for the synthesis of AlN; Mg2Si phase precipitates, replacing the formation of MgO and hindering the nitridation reaction. The challenges of controlling the kinetics are discussed.
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