Stir Casting: An Economical Method for Producing Composite Materials

Being liquid-state process, stir casting is a simple and most economical method for manufacturing of composite materials. It also offers better matrix-particle bonding, vivid selection of base materials and reinforcements, requisite operational flexibility and capability for large quantity production of structural components of complex geometry However, one of the serious drawbacks of stir casting route for processing composite is the difficulty in achieving a uniform distribution of reinforcing particles in the liquid due to different densities among other reasons. This problem is aggravated when the size of the reinforcing particles is reduced to the nanometric range because of their large surface-to-volume ratio, higher viscosity and poor wettability in melts.

Finer particles agglomerate more due to enhanced inter-particles van der Waals attractive forces. Dispersion of nanoparticles in the liquid will thus require a large amount of force to break the bonds in-between the particles. The mechanical stirring arrangement, used in the conventional stir casting methods, is often insufficient to provide the requisite level of force.

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It has been established recently that ultrasonic cavitation is the most effective technique to overcome the common problems relating to the dispersion of nanoparticles in the liquid metal.

The ultrasonic assisted stir casting processing involves mainly two important phenomena, i.e., transient cavitation and acoustic streaming. The development of acoustic cavitation in the liquid is one of the prime conditions of the ultrasonic process. The alternating pressure i.e., positive and negative pressure above the cavitation threshold, causes the formation of numerous cavities in the melt. During the negative pressure cycles, micro air bubbles, which tend to be trapped inside particle clusters, collapse under the compression stresses of the sound wave.

The energy released due to the collapse is transformed into pressure pulses above 1000 atms and into cumulative jets up to 100 m s-1 resulting in the formation of transient (in the order of nanoseconds) micro 'hot spots'. These hot spots generate the temperature of about 5000 ?C, and heating and cooling rates above 1010 K s-1.The development of acoustic cavitation initiates heat and mass transfer processes such as diffusion, wetting, dissolution, dispersion, and emulsification etc. Acoustic streaming helps to circulate particles all over the melt (Fig. 1). The acoustic cavitation starts to develop in the melt when the acoustic pressure exceeds the cavitation threshold.

Rewrite

Being liquid-state method, stir casting could be a easy and most economical technique for producing of composite materials. It conjointly offers higher matrix-particle bonding, vivid choice of base materials and reinforcements, requisite operational flexibility and capability for giant amount production of structural parts of advancedgeometry but, one among the intense drawbacks of stir casting route for process composite is that the problem in achieving an even distribution of reinforcing particles within the liquid due to completely different densities among different reasons. This drawback is aggravated once the dimensions of the reinforcing particles is reduced to the nanometric range due to their massive surface-to-volume ratio, higher viscosity and poor wettability in melts.

Finer particles agglomerate additional due to increased inter-particles van der Waals engaging forces. Dispersion of nanoparticles within the liquid will thus need an oversized quantity of force to break the bonds intermediate the particles. The mechanical stirring arrangement, utilized in the traditional stir casting methods, is usuallyinadequate to produce the requisite level of force. it's been established recently that ultrasonic cavitation is that the best technique to beat the common issues about the dispersion of nanoparticles within the liquid metal.The ultrasonic aided stir casting process involves primarily two necessary phenomena, i.e., transient cavitation and acoustic streaming. the event of acoustic cavitation within the liquid is one among the prime conditions of the ultrasonic method. The alternating pressure i.e., positive and negative pressure above the cavitation threshold, causes the formation of diverse cavities within the melt. during the negative pressure cycles, small air bubbles, that tend to be unfree within particle clusters, collapse under the compression stresses of the wave. The energy released due to the collapse is transformed into pressure pulses higher than one thousand atms and into accumulative jets up to a hundred m s-1 resulting in the formation of transient (in the order of nanoseconds) small'hot spots'. These hot spots generate the temperature of concerning 5000 ?C, and heating and cooling rates higher than 1010 K s-1.The development of acoustic cavitation initiates heat and mass transfer processes like diffusion, wetting, dissolution, dispersion, and emulsification etc. Acoustic streaming helps to flow into particles everywherethe melt (Fig. 1). The acoustic cavitation starts to develop within the melt once the acoustic pressure exceeds the cavitation threshold.

Final

Being liquid-state method, stir casting could be an easy and most economical technique for producing of composite materials. It conjointly offers higher matrix-particle bonding, vivid choice of base materials and reinforcements, requisite operational flexibility and capability for giant amount production of structural parts of advanced geometry but, one among the intense drawbacks of stir casting route for process composite is that the problem in achieving an even distribution of reinforcing particles within the liquid due to completely different densities among different reasons. This drawback is aggravated once the dimensions of the reinforcing particles are reduced to the nanometric range due to their massive surface-to-volume ratio, higher viscosity and poor wettability in melts.

Finer particles agglomerate additional due to increased inter-particles van der Waals engaging forces. Dispersion of nanoparticles within the liquid will thus need an oversized quantity of force to break the bonds intermediate the particles. The mechanical stirring arrangement, utilized in the traditional stir casting methods, is usually inadequate to produce the requisite level of force. it's been established recently that ultrasonic cavitation is that the best technique to beat the common issues about the dispersion of nanoparticles within the liquid metal.

The ultrasonic aided stir casting process involves primarily two necessary phenomena, i.e., transient cavitation and acoustic streaming. the event of acoustic cavitation within the liquid is one among the prime conditions of the ultrasonic method. The alternating pressure i.e., positive and negative pressure above the cavitation threshold, causes the formation of diverse cavities within the melt. during the negative pressure cycles, small air bubbles, that tend to be unfree within particle clusters, collapse under the compression stresses of the wave. The energy released due to the collapse is transformed into pressure pulses higher than one thousand atms and into accumulative jets up to a hundred m s-1 resulting in the formation of transient (in the order of nanoseconds) small'hot spots'. These hot spots generate the temperature of concerning 5000 ?C, and heating and cooling rates higher than 1010 K s-1.The development of acoustic cavitation initiates heat and mass transfer processes like diffusion, wetting, dissolution, dispersion, and emulsification etc. Acoustic streaming helps to flow into particles everywhere melt (Fig. 1). The acoustic cavitation starts to develop within the melt once the acoustic pressure exceeds the cavitation threshold.