Chemical Engineering March 2016 - 24

UCLA
2 μm
FiGure 6. Uniform distribution of dispersed nanoparticles in a magnesium matrix gives this material
unique qualities
ducing silicon carbide (SiC) ceramic
fibers, and the other applying proprietary
coatings to the fibers and forming
them into a matrix to produce what is
known as CMC tape. The CMC tape
will then be sent to another gE site
in Asheville, N.C., which is currently
the only site in the world where CMC
components are mass produced,
according to gE.
until the Huntsville plants start up
in 2018, the Asheville site, which
opened in late 2014, will continue
to receive raw materials from NgS
Advanced Fibers Co. (NgS), a company
in Japan jointly owned by Nippon
Carbon, Herakles Safran France
and gE. According to gE, the Huntsville
plants will be the first in the u.S.
to mass-produce SiC fibers, and
more CMC tape will be made there
than anywhere else in the world.
NgS is also currently constructing a
new factory for SiC fibers in Japan to
meet global demand, which gE projects
will grow tenfold by 2020.
in the past, CMCs were difficult
to produce at a large scale and
were only able to be used in large
structures - the ability to produce
smaller, more complex components
is a breakthrough. At present, the
main end-use for gE's CMCs is to
replace metal composites in components
for the company's lEAp jet
engines, specifically high-pressure
turbine shrouds (Figure 4).
When compared to other materials
used in jet-engine components,
CMCs are more lightweight (reportedly
one-third the density of metal alloys)
and resist higher temperatures,
leading to better fuel efficiency. The
CMCs are said to operate at temperatures
as high as 2,400ºF, which
is 500ºF hotter than superalloys
can handle. " Withstanding higher
temperatures means we can push
more air through the engine instead
of diverting some to cool off metal
parts and keep them from melting, "
explains a representative from
gE Aviation. " CMCs are also stronger
than some metal parts and will
HRL Laboratories
last longer, resulting in less time and
money spent on maintenance, repair
and overhaul. " gE Aviation has also
demonstrated the use of rotating
CMC components in a low-pressure
turbine (Figure 5), said to be an industry
first. gE emphasizes that the
applications for CMCs go beyond jet
engines - the company's power and
Water business has tested CMCs in
air-cooled gas turbines and also used
prototype CMC parts to replace superalloys
in large gas turbines.
Beyond CMCs, SiC is an important
part of other composites. A new
metal nanocomposite developed by
researchers from the university of
California, los Angeles (uClA; www.
ucla.edu) has garnered a great deal of
attention due to its very high strength,
lightweight structure and mechanical
stability at temperatures up to 400ºC.
Composed of a magnesium-zinc alloy
infused with SiC ceramic nanoparticles,
the key to this material's unique
properties is the ability to uniformly
disperse the dense SiC nanoparticles
throughout the magnesium (Figure 6)
- a task that has not been achievable
at this scale until now. The attractive
forces between nanoparticles
tend to form clusters within the metal
matrix, but uClA's method leverages
the small van der Waals attractions
between the particles and the molten
metal and high thermal-motion energy
to stabilize the dispersion.
The research team, led by Xiaochun
li, Raytheon Chair in Manufacturing
and professor of materials science
and engineering at uClA, injected the
SiC nanoparticles into a molten bath
of the magnesium alloy, and incrementally
concentrated the nanoparticles
in the mixture by partially evaporating
the molten metal in a vacuum
furnace. once solidified, the resulting
composite contained 14 vol.% SiC,
and after mechanical processing, it
boasted a record-high yield strength
of 710 Mpa for magnesium alloys.
FiGure 7. Following 3-D printing, ceramic-composite parts are sent into a conventional firing process
24
" in our lab, samples of a few grams
of magnesium were used. But the
process is solidification-based and
would be scaled up without much difficulty, "
says li. potential applications
for the new metal are wide-ranging,
spanning the automotive, aerospace,
medical and electronics industries.
in fact, according to li, industrial inChemiCal
engineering www.Chemengonline.Com marCh 2016

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Chemical Engineering March 2016

Table of Contents for the Digital Edition of Chemical Engineering March 2016