ing and distribution. The OEM also has selected a cast iron part to be reproduced using nanotechnology. “Once we have characterized the
material and feel confi dent the process can be controlled, we would make the part and perform durability and other testing on it,” Hathaway said. “Provided it passes those tests, we would look at taking advantage of the weight savings [for a production part].” Currently, strength is the main ben-
efi t of nanoparticles that is driving the casting research. However, Li expects other benefi ts to present themselves as nanoparticles are studied further. “A lot of new phenomenon will
come out For example, we can cast ultra-high strength materials that were traditionally impossile to cast,” he said. “It’s an emerging technology, so new—good—surprises will come up.”
Means to an End One of the earliest challenges of
using nanotechnology in metalcast- ing was fi nding a way to uniformly disperse the minute pieces of material throughout the metal. The tiny particles are drawn together by van der Waals force (an attractive or repulsive force among molecules) and tend to stick together in clumps. The attractive force is so high, keeping the particles apart in order to allow the aluminum or magnesium to bond with them takes a lot of energy. The nano research team’s eureka
moment came when it found that us- ing ultrasonic waves was effective in keeping the nanoparticles apart and uniformly dispersed throughout the metal during solidifi cation. “For the past six years, we’ve been
working on the fundamentals of how to get the nanoparticles to disperse in the metal,” Li said. “Ultrasonic technology is one of the more inexpensive ways.”
Lab to Line Current nanotechnology testing has
been performed with batches of 5 to 10 lbs. of material at a time. In order to use the process in a metalcasting facility, more work is required. “How do we scale up to reason-
able production batches of material, which at Eck is 500 lbs.?” Weiss said. “The whole jist of the TIP money is to be able to scale it up to make real components. The plan is to take it from a laboratory curiosity into
Silicon carbide nanoparticles have many uses beyond casting. These “nano trees” are 3-D nanostructures grown out of silicon carbide nanowires. Researchers are investigating possible applications for these structures, such as water repellant coatings and as a base for a new type of solar cell.
“ Nanotechnology gives us what I call a free lunch. We can increase our mechanical properties
without reducing the ductility or toughness of the material.
something with which we can make metal castings.” To scale up the work, tools to dis-
perse nanoparticles on a larger scale have to be created. Current tools used to do the same thing in polymers can- not withstand the high temperatures of molten metal. The time it takes to add the particles to the melt is also unwieldy. Weiss said it currently takes one hour to add nanoparticles to 10 lbs. of molten aluminum. Different nanoparticles bond bet-
ter with different alloys. The nano research team has tried with success to coat nanoparticles with ceramic to help them bond better with the metal. “We also need specialty nanopar-
ticles,” Li said. “Right now, most are used for the semiconductor industry.
36 Metal Casting Design anD PurChasing ” —Robert Hathaway, Oshkosh Corp.
But that’s not suitable for us on the metal side.” The main challenge, however, will
be to make the method affordable for metalcasters to incorporate into their process. “The cost of nanoparticles continues
to decrease,” Weiss said. “And since we use so little nanoparticle, it’s not tremendously infl uenced by particle cost but by processing time and cost.” That understanding is forefront on
the minds of the nano researchers. “Our mission is to make it inexpen- sive,” Li said.
Go to
www.metalcastingdesign.com to read a paper by Xiaochun Li and David Weiss on ultrasonic cavitation-based dispersion of nanoparticles in aluminum melts.
May/June 2010 METAL
Photo by Ghim Wei Ho and Prof. Mark Welland, Nanostructure Center, University of Cambridge
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