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Under the long-term collaboration with Prof. Yeh at National Tsing Hua
University (NTHU), Dr. Chang and coworkers developed a new material
system, the high-entropy alloys with multi-principal components
incorporated but simple crystal structures formed. Some of the
high-entropy alloys exhibited excellent mechanical properties and high
elevated-temperature strengths, while some presented high ductility.
The first four papers that Dr. Chang wrote (when working as a
postdoctoral research fellow at NTHU) have received more than 1,300
citations. Dr. Chang further developed multi-component high-entropy
alloys and nitrides for applications to protective hard coatings and
diffusion barriers, and found that multi-component high-entropy
materials possessed a special nanocomposite structure (nanocrystalline
precipitations within an amorphous matrix) as well as an excellent
mechanical property and a high thermal stability. Their nanocomposite
structure and high strengths remained even after high-temperature
annealing at 900°C, and a thin quinary-nitride layer of only 10 nm
thick successfully resisted the interdiffusion of Cu and Si at 900°C as
well. The excellent diffusion resistance of high-entropy materials was
confirmed by an ultrathin senary-alloy/nitride multilayered structure
with a thickness of only 4 nm that endured the interdiffusion of Cu and
Si at 800°C. The breakthroughs in developing new diffusion barrier
materials were published in several scientific journals including
Applied Physics Letters as well as in JOM and Entropy (Invited Papers).
Recently, Dr. Chang further investigated the sluggish diffusion
kinetics in multi-component materials, based on the fundamentals of
crystal structure and thermodynamics, and published a paper in
Scientific Reports (Nature Publishing Group).
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Left to right: quinary-nitride
structure and elemental distributions after annealing at 900°C;
senary-alloy/nitride multilayered structure of 4 nm thick.
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