Synthesis of Bulk Metal Matrix Nano Composites by Full Cavitation Solidification Method

摘要

There are several methods for the production of metal matrix nano composites including mechanical alloying, vertex process and spray deposition. However, the above processes are expensive. Solidification processing is a relatively cheaper route. However, during solidification processing nano particulates tend to agglomerate as a result of van der Waals forces and thus proper dispersion of the nano-particulate in metal matrix is a challenge. Many researchers have dispersed nanoparticles in metal matrices by ultrasonic casting. However their technique has several drawbacks such as the oscillating probe, which is in direct contact with liquid metal, may dissolve in the liquid metal and contaminate it. Moreover, the extent of dispersion is not uniform. It is maximum near the probe and gradually decreases with distance away from the probe. The oscillating probe is also removed from the liquid metal before cooling and solidification begins leading to partial reagglomeration of nanoparticles. To overcome these difficulties a non-contact method, where the ultrasonic probe is not in direct contact with the liquid metal, was used in an attempt to disperse nano-sized Al_2O_3 particulates in an aluminium matrix. In this method the mold was subjected to ultrasonic vibration. The crystallite size of Al_2O_3 was mostly below 10 nm. Nano composite having 1-1.5 wt. % of Al_2O_3 was cast. From HRTEM studies it is observed that the Al_2O_3 particles are distributed uniformly except at the grain boundaries, hi micro scale the hardness is uniform throughout the samples. This is due to cavitation process as well as pushing of the nanoparticles during the growth of the grains, hi the present study the process of cavitation accounts all first-order effects i.e., phase change, bubble dynamics, turbulent pressure fluctuations, and noncondensable gases for deaglomeration and distribution of particles throughout the domain to get uniform distributions.