Tech Briefs Magazine - February 2023 - 27

Manufacturing & Prototyping
New Heat Treatment Allows 3D-Printed Metals to
Withstand Extreme Heat
Transforming the microscopic structure of metals may enable energy-efficient 3D printing
of blades for gas turbines or jet engines.
Massachusetts Institute of Technology, Cambridge, MA
A
n MIT-developed heat treatment
aims to transform the microscopic
structure of 3D-printed metals, making
the materials stronger and more resilient
in extreme thermal environments.
The technique also aims to make it possible
to 3D print high-performance blades
and vanes for power-generating gas turbines
and jet engines, which would enable
improved fuel consumption and
energy efficiency.
There is growing interest in manufacturing
turbine blades through 3D printing,
but such efforts have a big hurdle:
creep - a metal's tendency to permanently
deform in the face of persistent
mechanical stress and high temperatures.
In addition, researchers have found that
the printing process produces fine grains
on the order of tens to hundreds of microns
in size - a microstructure that is
especially vulnerable to creep.
" In practice, this would mean a gas turbine
would have a shorter life or less fuel
efficiency, "
said
Zachary
Cordero,
the
Boeing Career Development Professor
in Aeronautics and Astronautics at MIT.
" These are costly, undesirable outcomes. "
Cordero and his team improved the
structure of 3D-printed alloys by adding an
additional heat-treating step, which transforms
the 3D-printed material's fine grains
into much larger " columnar " grains - a
sturdier microstructure capable of minimizing
the material's creep potential. The
researchers noted that the method clears
the way for the industrial 3D-printing of gas
turbine blades.
" In the near future, we envision gas
turbine manufacturers will print their
blades and vanes at large-scale additive
manufacturing plants, then post-process
them using our heat treatment, " said
Cordero. " 3D-printing will enable new
cooling architectures that can improve
the thermal efficiency of a turbine, so
that it produces the same amount of
power while burning less fuel and ultimately
emits less carbon dioxide. "
Tech Briefs, February 2023
A thin rod of 3D-printed superalloy is drawn out of a water bath, and through an induction coil,
where it is heated to temperatures that transform its microstructure, making the material more
resilient. The new MIT heat treatment could be used to reinforce 3D-printed gas turbine blades.
(Image: Dominic David Peachey)
The new method is a form of directional
recrystallization - a heat treatment
that passes a material through a hot zone
at a controlled speed to meld a material's
microscopic grains into larger, sturdier,
and more uniform crystals.
The team tested the method on
3D-printed nickel-based superalloys,
metals typically cast and used in gas turbines.
The engineers placed 3D-printed
samples of rod-shaped superalloys in
room-temperature water placed just below
an induction coil. They then slowly
drew each rod out of the water and
through the coil at various speeds, dramatically
heating the rods to temperatures
varying between 1,200-1,245 °C.
The results showed that drawing the
rods at a particular speed (2.5 millimeters
per hour) and through a specific
temperature (1,235 °C) created a steep
thermal gradient that triggered a transformation
in the material's printed, finegrained
microstructure.
After cooling the rods, the researchers
examined the microstructure and
found that the material's printed microwww.techbriefs.com
scopic
grains were replaced with " columnar "
grains.
The team also exhibited an ability to
manipulate the draw speed and temperature
of the rod samples to tailor the material's
growing grains, creating regions of
specific grain size and orientation. This
level of control can enable manufacturers
to print turbine blades with site-specific
microstructures that are resilient to specific
operating conditions.
Cordero plans to test the heat treatment
on 3D-printed
geometries
that
more closely resemble turbine blades,
while the team is exploring ways to speed
up the draw rate as well as test a heat-treated
structure's resistance to creep.
" New blade and vane geometries will
enable more energy-efficient land-based
gas turbines, as well as, eventually, aeroengines, "
said Cordero. " This could
from a baseline perspective lead to lower
carbon dioxide emissions, just through
improved efficiency of these devices. "
For more information, contact Abby
Abazorius at abbya@mit.edu; 617-2532709.
27

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