Shown are nanoparticles dispersed in a cast magnesium test ingot.
be created. Current tools used to do the same thing in polymers can not with- stand the high temperatures of molten aluminum and magnesium. 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 better
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. 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.
Nano in the Field
Oshkosh is interested in nano- technology to help cut weight in its products, particularly defense vehicles. Hathaway recalled a vehicle his com- pany worked on 12 years ago for the military. The vehicle had to be lifted by a helicopter, so the weight guidelines were strict and challenging. The team was counting pounds and ounces to
Go to
www.moderncasting.com to read a paper by Xiaochun Li and David Weiss on ultrasonic cavitation-based dispersion of nanoparticles in aluminum melts.
30
These silicon carbide nanoparticles used with magnesium casting alloys have an average particle size of a little less than 50 nanometers.
meet the limit, he remembered. Osh- kosh found a way to meet the challenge without nanotechnology at the time, but the tiny pieces of matter could open up new and easier ways to lighten the load for future applications. Weight-saving through the use of nanoparticles will infl uence the com- mercial sector, as well. “Every pound saved [in the weight
of the vehicle] is a pound more of re- fuse or concrete a customer can haul,” Hathaway pointed out. “Lightweight components may be more expensive, but if it means fewer trips to the
“Nanotechnology gives us what I call a free lunch. We can increase our mechanical properties without reducing the ductility or toughness of the material.”—Robert Hathaway, Oshkosh Corp.
plant or fi eld, it pays for itself.” As part of the nano-research, Osh-
kosh’s role is to assist in characterizing the material. The company’s research team is studying tensile samples sent to its lab to look at how the samples fracture and measure particle spacing and distribution. The OEM also has se- lected 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.” MC
MODERN CASTING / March 2010
Photos on this page courtesy of Xiaochun Li, Univ. of Wisconsin-Madison
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