Tech Briefs Magazine - May 2021 - 42

Materials & Coatings
in the presence of water vapor, the paper
starts to bend and under dry conditions, it
unbends. Repeated cycles of humid and
dry conditions cause the paper to perform a flipping motion over time.
To show that it is possible to customize
the water vapor responsiveness of pollen
paper, the team adjusted processing
parameters - chiefly, the alkaline incubation time of the pollen grains. They joined
two pollen paper samples, each prepared
under different incubation times (3 hours
and 12 hours), to form a strip of bi-material pollen paper with a visible boundary.
When the bi-material pollen paper was
exposed to a humid-dry cycle, the two
pollen paper samples' different reactions
to humidity caused the paper to " walk "
like a caterpillar that moves by alternatingly expanding and contracting its soft body.
For more information, contact Foo Jie
Ying at jieying@ntu.edu.sg.

Desorption
of Water
One
Dehydration
and
Hydration
Cycle
Adsorption
of Water

12 hr

3 hr

A bi-material pollen strip is able to " walk " with the adsorption and desorption of water.

Oxide Dispersion Strengthened Medium Entropy Alloy
This additively manufactured alloy is tailored for high-temperature applications.
John H. Glenn Research Center, Cleveland, Ohio

N

ASA Glenn researchers developed a
new oxide dispersion strengthened
medium entropy alloy (ODS-MEA) via
additive manufacturing (AM). ODS alloys, in which nanoscale ceramic particles are distributed within the metal,
were originally developed to enhance
mechanical properties (e.g., creep resistance, tensile strength, microstructure
integrity) at extreme temperatures. Such
alloys show promise for metal components of gas turbines, rocket engines,
nuclear reactors, and other high-temperature applications; however, the conventional mechanical alloying process to
produce such alloys is highly inefficient,
time-consuming, and costly.
ODS-MEA is designed for production
via selective laser melting. The alloy can
be fabricated into complex geometries
and is resistant to stress cracking and
dendritic segregation. It is not susceptible to deleterious phase changes when
exposed to extreme temperatures and
requires limited post-processing.
The alloy maintains properties up to
1100 °C and is not susceptible to deleterious phase changes when exposed to
extreme temperatures - an issue ubiquitous to Ni-based superalloys such as
Inconel-625 and Inconel-718. Yttria particles are dispersed throughout the alloy to

Laser or E-Beam

(a)
Dispersed
Y2O3

Y2O3 coated
HEA powder

Turbulent
melt pool

Build plate
(c)

(b)

SE

5 um

Y

2 um

Co

O

(a) A schematic demonstrating the incorporation of nanoscale yttria particles into the AM part
using novel, oxide-coated powder feedstock. (b) SEM micrograph revealing the dispersion of
oxides in the AM component. (c) Chemical maps confirming the dark particles shown in (b) are
nanoscale yttria dispersoids.

maximize strength and creep resistance at
high temperatures using a novel fabrication technique. This technique employs
an acoustic mixer to stir nanoscale yttria
oxide powder within a metallic matrix
powder, creating a film of yttria surrounding the larger metallic powder particles.

42

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Cov

ToC

Solid components are then produced
from this mixture via SLM, during which
the laser disperses the yttria particles
throughout the microstructure.
Ultimately, the process eliminates the
many expensive and time-consuming steps
in the production of ODS alloys via tradiTech Briefs, May 2021


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Tech Briefs Magazine - May 2021

Table of Contents for the Digital Edition of Tech Briefs Magazine - May 2021

Tech Briefs Magazine - May 2021 - Intro
Tech Briefs Magazine - May 2021 - Sponsor
Tech Briefs Magazine - May 2021 - Cov1
Tech Briefs Magazine - May 2021 - Cov2
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