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A D V A N C E D
M A T E R I A L S
&
P R O C E S S E S |
N O V E M B E R / D E C E M B E R
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Artistic interpretation of cold sinter-
ing of ceramic particles (white) and
polymer strands (green) using low
heat to evaporate added water mol-
ecules (blue). Courtesy of Jennifer M.
McCann/MRI.
COLD SINTERING PROCESS
MIXES THINGS UP
Researchers at Penn State, Univer-
sity Park, Pa., developed a new method
for producing compounds of previously
incompatible materials that could also
lower energy costs for many types of
manufacturing. The low temperature
method, called cold sintering process
(CSP), uses significantly less energy
than traditional methods, and can
Shear band formation is a long-standing
problem in metals manufacturing. At
left, the phenomenon appears as a wavy
structure in a titanium strip. Top right, a
“micromarker” was traced across a shear
band (yellow). Bottom right, an electron
backscatter image reveals the band as a
severely deformed, dark region about
4 µm thick. Courtesy of Purdue.
densify some materials to over 95% of
their theoretical density in 15 minutes.
For example, researchers used CSP to
co-sinter ceramic and thermoplastic
polymer composites to high density at
120°C in 15-60 minutes.
In CSP, water or acid is applied to
ceramic powder, causing particle sur-
faces to partially dissolve and produce
a liquid phase at particle-particle inter-
faces. With temperature and pressure,
the solid particles begin to densify and
clusters of atoms or ions leave the inter-
faces. This aids diffusion, minimizes
surface free energy, and allows parti-
cles to pack together. The key is a pre-
cise combination of moisture, pressure,
heat, and time required to capture the
reaction rates so the material fully crys-
tallizes and achieves very high density.
The team has verified 50 unique com-
binations so far, including formulas for
ceramic-ceramic and ceramic-nanopar-
ticle
composites,
ceramic-metals,
and ceramic-polymers. Applications
include thermal insulation, biomedical
implants, and electronic components.
psu.edu.
SHEAR GENIUS
An international team led by
researchers at Purdue University, West
Lafayette, Ind., discovered microscopic
details of the process of shear banding
and developed a simple method to con-
trol the defect in metals manufacturing.
The team studied the displacement
profiles created when metal was etched
with tiny marks, then processed. The
resulting groove-like “micromarkers”
revealed large serrated deformations
that, surprisingly, resemble liquid
flowing past an interface. Turning to
mathematical equations typically used
to analyze viscous fluid flow, the team
determined that shear bands form in
two phases. The first occurs within just
a few microseconds of cutting when a
weak interface is created in the metal.
In the second, more gradual phase,
metal slides along the weak interface
then shears, producing the wave shape.
To suppress shear banding,
researchers added a wedge-shaped
die opposite the cutting tool, channel-
ing the chip from the machined metal
between the two tools. The die con-
strains the metal, forcing it to deform
more uniformly and eliminating the
sliding phase.
purdue.edu.
Norsk Titanium US Inc.,
Platts-
burgh, N.Y., a subsidiary of
Norsk
Titanium AS,
Norway, will open a
70,000-sq-ft production and train-
ing facility later this year.
The Plattsburgh Demonstration
and Qualification Center will
incorporate Norsk’s “ultra lean
cell,” featuring a 120-ft production
line that turns CAD files into fin-
ished aerospace parts and allows
for 3D printing, heat treatment,
nondestructive testing, and final
machining in less than 40 hours.
norsktitanium.com.
BRIEFS
Sandia National Laboratories,
Albuquerque, N.M., and
The University
of Akron,
Ohio, approved a master research agreement to collaborate
on additive manufacturing and advanced materials research. Areas of
interest include the roles of adhesion, friction, and wear in coatings,
lubricants, and adhesives, as well as the use of carbon nanotube-based
coatings to reduce drag, inhibit ice formation, and provide better heat
transfer. In addition, biomimicry will be studied in the context of
advanced adhesives for engineering and biological applications.
sandia.gov, uakron.edu.
PROCESS TECHNOLOGY