This August, Georgia Tech professor Sung Kyu Lim joined the Defense Advanced Research Projects Agency (DARPA) as a program manager in the Microsystems Technology Office (MTO). Lim, the Motorola Solutions Foundation Professor in School of Electrical and Computer Engineering (ECE), is the first Georgia Tech ECE researcher to be recruited and serve as a DARPA program manager while teaching at Georgia Tech.

As a prominent researcher in very-large-scale integration (VLSI) systems and design, Lim’s first program at DARPA, dubbed the “3D-EDA (3D Electronic Design Automation) Program,” will develop heterogeneous 3D integrated circuits (IC) design and simulation software to automatically co-optimize the underlying device, circuit, and architecture. The program will use 3D-EDA tools to demonstrate 10x shorter design turnaround time and 10x energy-efficiency improvement.

“We are very proud of Sung Kyu’s appointment to DARPA’s Microsystems Technology Office,” said Arijit Raychowdhury, ECE’s Steve W. Chaddick School Chair. “This is an important recognition of Sung Kyu’s standing in the VLSI field, and also shows how Georgia Tech ECE researchers are leading, on the national level, in developing advanced defense research projects.”

The core mission of DARPA’s MTO is to develop high-performance intelligent microsystems and next-generation components to ensure U.S. dominance in the areas of Command, Control, Communications, Computing, Intelligence, Surveillance, and Reconnaissance (C4ISR), Electronic Warfare (EW), and Directed Energy (DE).

According to DARPA, the office’s work in applying advanced capabilities in areas such as wide-band gap materials, phased array radars, high-energy lasers, complementary metal-oxide-semiconductor (CMOS) circuits, and infrared imaging has helped the U.S. establish and maintain technological superiority for more than two decades.

Lim’s DARPA assignment is supported by the U.S. Department of Defense’s (DoD) Intergovernmental Personnel Act (IPA), which allows for the temporary assignment of skilled personnel between the Federal Government and state and local governments, colleges and universities, Indian tribal governments, federally funded research and development centers, and other eligible organizations.

He will serve for four years at the agency in Washington D.C. before returning to Georgia Tech. Lim’s GTCAD (Georgia Tech Computer-Aided Design) Lab will remain open during his 4-year DARPA term.

Along with the Georgia Tech faculty tapped and reappointed as Regents’ Professors and Researchers at the Aug. 9 University System of Georgia (USG) Board of Regents meeting were five Georgia Tech professors named to the new distinction of Regents’ Entrepreneur.

Georgia Tech faculty named as the first Regents' Entrepreneurs in the USG include Farrokh Ayazi, Ken Byers Professor in Microsystems, School of Electrical and Computer Engineering; Kirk Bowman, professor, Sam Nunn School of International Affairs; Andrei Fedorov, Neely Chair and professor, Woodruff School of Mechanical Engineering and the Petit Institute for Bioengineering and Biosciences; Mark Prausnitz, Regents’ Professor, J. Erskine Love Jr. Chair, School of Chemical and Biomolecular Engineering; and Gleb Yushin, professor, School of Materials Science and Engineering.  

Regents’ Professor First-Time Appointments 
The Board of Regents approved the title of Regents’ Professor to Facundo Fernández, professor and Vasser Woolley Foundation Chair in Bioanalytical Chemistry, School of Chemistry and Biochemistry; Willie Pearson, professor of sociology, School of History and Sociology; Krishnendu Roy, professor, Robert A. Milton Endowed Chair, NSF Engineering Research Center for Cell Manufacturing Technologies, Coulter Department of Biomedical Engineering; and Beril Toktay, professor of Operations Management and Brady Family Chairholder, Scheller College of Business.  

Regents’ Researcher First-Time Appointments 
Those named as Regents’ Researchers include Stephen Balakirsky, principal research scientist, Georgia Tech Research Institute (GTRI); Anton Bryksin, principal research scientist, Petit Institute for Bioengineering and Bioscience; Walter Bradley Fain, principal research scientist, School of Public Policy; and Anita Pavadore, principal research engineer, GTRI. 

First-Time Reappointments 
Receiving a first-time reappointment as Regents’ Professor was Surya Kalidindi, Regents’ Professor, Rae S. and Frank H. Neely Chair, Woodruff School of Mechanical Engineering. Receiving a first-time reappointment as Regents’ Researcher was Margaret Loper, principal research scientist, GTRI. 

Other Reappointments 
Regents’ Professor and Researcher designations only require Institute approval for second-time reappointments. Second-time Regents’ Professor appointments at Georgia Tech include Sy Goodman, Regents’ Professor and professor of International Affairs and Computing, Sam Nunn School of International Affairs; Nicholas Hud, Regents’ Professor, School of Chemistry and Biochemistry; and Vladimir Tsukruk, Regents’ Professor, School of Materials Science and Engineering. Receiving a second-time Regents’ Researcher reappointment was Alexa Harter, director of the Cybersecurity, Information Protection, and Hardware Evaluation Research Laboratory at GTRI. 

New Recognition for Entrepreneurship and Innovation 
The board approved the Regents’ Entrepreneur designation in their February 2022 meeting to recognize and support faculty entrepreneurship and innovation. The Regents’ Entrepreneur designation may be granted by the Board of Regents to an outstanding full-time tenured faculty member who has an established reputation as a successful innovator and who has taken their research into a commercial setting. The Regents’ Entrepreneur designation is bestowed by the board only upon the unanimous recommendation of the USG institution president, the chief academic officer, and the chancellor, and upon the approval of the Committee on Academic Affairs. 

Farrokh Ayazi 
Farrokh Ayazi is director of the Georgia Tech Analog Consortium. His main research interest is in integrated micro and nano electromechanical systems and integrated microsystem design. He is the founder and chief technology officer of Qualtré, which was acquired by Panasonic in 2016. He is currently leading StethX Microsystems, an ATDC company, in commercializing advanced wearable sensors for cardiopulmonary applications.

Kirk Bowman 
Kirk Bowman is the Rise Up & Care term chair in Global Development and Identity. In 2014, Bowman founded Rise Up & Care, a nonprofit corporation that employs an innovative model of international community development, combining global development research; high-level performance organizations in the Global South to transform youth; powerful documentary films by top local directors; and children's books illustrated by local street artists. He directs a Georgia Tech Vertically Integrated Project on Global Social Entrepreneurship with 18 undergraduate students.

Andrei G. Fedorov  
Andrei G. Fedorov’s research covers atomic scale nanomanufacturing; distributed power generation with carbon dioxide management; instrumentation for biomedical research; and thermal management of electronics and medicine. With his students and collaborators, Fedorov started several technology companies to commercialize his inventions in the space of gene/drug delivery; biomarker discovery and quality control in cell therapy manufacturing; and thermal management of high-power generation devices. 

Mark Prausnitz 
Mark Prausnitz has co-founded seven companies that have together raised more than $350 million for commercialization of microneedle technologies developed in his lab at Georgia Tech. Three of the companies have products for sale, including an FDA-approved treatment of ocular inflammation. His technologies have been studied in more than 20 human clinical trials. He has almost 80 issued or pending U.S. patents, with additional international filings. Prausnitz has published more than 300 journal articles and supervised 50 Ph.D. students among a total of almost 350 graduate, postdoctoral, or undergraduate researchers in his lab. 

Gleb Yushin  
Gleb Yushin is a pioneer and globally recognized leader in advanced materials for next-generation Li-ion batteries. He is member of the National Academy of Inventors and fellow of three international professional societies. He has been awarded more than 200 patents, while also being one of the most cited Georgia Tech professors since 2019. He co-founded the most economically successful Georgia Tech startup Sila Nanotechnologies ($3.3B valuation). Yushin has served as a founding faculty advisor for the Entrepreneurs Club at Tech and as an advisor to the Georgia Tech startup CellFE. 

Regents’ Professorships and Regents’ Researcher titles may be granted for a period of three years by the Board of Regents to outstanding faculty members of Georgia Tech, Augusta University, Georgia State University, the University of Georgia, and, in special circumstances, other USG institutions. 

Cancer spreads via circulating tumor cells (CTCs) that travel through the blood to other organs, and they are nearly impossible to track. Now, researchers at the Georgia Institute of Technology have found a detection method that could revolutionize cancer treatment by showing how cancers metastasize and what stage they are. This could lead to earlier and more targeted treatment, beginning with a simple blood test.

When a tumor starts metastasizing, it sheds its cell into the blood. An individual cell often doesn’t survive the bloodstream on its own, but clusters of cells are much more robust and can travel to other organs, effectively pushing the cancer to a metastatic state.

CTCs have proven difficult to study, let alone treat. Blood contains billions of cells per milliliter, and only a handful of those cells would be CTCs in a patient with metastatic cancer. Such intense filtration has been inaccessible using conventional lab methods. Most traditional filtration is too aggressive and would break the cluster back into single cells and ruin the ability to study the effect of a cluster.

“That’s what got engineers like me interested in this because we are really good at creating sensors, or small devices that actually do sensitive analysis,” said School of Electrical and Computer Engineering Associate Professor Fatih Sarioglu. “We started developing technologies to catch these precious cells to help manage cancer better.”

Sarioglu presented the research in “High Throughput, Label-free Isolation of Circulating Tumor Cell Clusters in Meshed Microwells,” recently published in Nature Communications.

Creating the Cluster-Well

Sarioglu’s lab invented a new type of chip called the Cluster-Well, combining the precision of microfluidic chips with the efficiency of membrane filtration to find CTC clusters. Using micron-sized features, microfluidic chips can precisely locate each cell in a blood sample and determine if it’s cancerous.

“Microfluidic chips give you more control as a designer to actually ask whatever question that you want to ask those cells,” Sarioglu said. “It increases the precision and sensitivity, which is what you need for an application like this because you want to find that single cell out of many blood cells.”

To rapidly process a clinically relevant volume of blood, the researchers relied on membrane filtration to make the chip operation more scalable. In effect, the chip looks like a standard membrane filter, but under an electron microscope the microfluidic chip reveals its delicate structure used to capture clusters while letting other blood cells pass through.

Practicality was just as important as functionality to the researchers. Although the chip is initially fabricated with silicon just like a central processing unit in a computer, it is later transferred to polymers to make it accessible, affordable, and single-use, while still retaining its delicacy and precision.

“We really created only the traps that we need to have for recognizing the clusters with the microfluidic chip, and the rest is just a standard filter holder,” Sarioglu said. “Compared to a conventional microfluidic chip, you will get a much more practical assay with orders of magnitude improvement in throughput and a higher sensitivity.”

Analyzing Patient Tumor Cell Clusters

The researchers used the chip to screen blood samples from patients with ovarian or prostate cancers through a partnership with the Emory and Northside Hospitals. They isolated CTC clusters ranging from two to 100 or more cells from prostate and ovarian cancer patients and used RNA sequencing to analyze a subset.

The chip’s unique design means CTC clusters are filtered in microwells and can later be accessed for further analysis. Even a single CTC can contain a significant amount of data on the patient and their specific cancer, which can be critical for managing the disease. For example, the researchers noted hundreds of CTCs in clusters in the blood of ovarian cancer patients, some still alive, a finding that could be consequential to the spread of the disease.

Also, by sequencing the RNA in prostate CTC clusters isolated by the chip, the researchers identified specific genes expressed by these metastasizing cells. Importantly, CTC clusters from different patients were shown to express different genes, which can be potentially utilized to develop personalized, targeted therapies. Sarioglu envisions Cluster-Wells as being a routine part of the treatment process to determine what stage the cancer is at from a simple blood draw.

“Finding these clusters was very elusive,” Sarioglu said. “But this is a technology that allows these precious circulating tumor cell clusters virtually in any cancer to be accessed with precision and practicality that has not been possible before.”

CITATION: Boya, M., Ozkaya-Ahmadov, T., Swain, B.E. et al. High throughput, label-free isolation of circulating tumor cell clusters in meshed microwells. Nat Commun 13, 3385 (2022). https://doi.org/10.1038/s41467-022-31009-9

The award-winning article proposes a novel hierarchical physical design flow enabling the building of high-density and commercial-quality two-tier face-to-face-bonded hierarchical 3D ICs.

Georgia Tech professor Sung Kyu Lim and recent Ph.D. graduate Anthony Agnesina have won the top paper award at the 2022 International Symposium on Low Power Electronics and Design (ISLPED) for their research entitled, “Hier-3D: A Hier archical Physical Design Methodology for Face-to-Face-Bonded 3D ICs.”

Lim is a Motorola Solutions Foundation Professor in Tech’s School of Electrical and Computer Engineering (ECE) and Agnesina is currently a research scientist at NVIDIA and was advised by Lim while at Georgia Tech. Co-authors include eight researchers from the Interuniversity Microelectronics Centre (IMEC), the University of Bremen, ETH Zurich, and the University of Bologna.

The award-winning article proposes a novel hierarchical physical design flow enabling the building of high-density and commercial-quality two-tier face-to-face-bonded hierarchical 3D ICs. Hierarchical very-large-scale integration (VLSI) flows are an understudied yet critical approach to achieving design closure at giga-scale complexity and gigahertz frequency targets.

The authors significantly reduced the associated manufacturing cost compared to existing 3D IC implementation flows and, for the first time, achieved cost competitiveness against the 2D reference in large modern designs.

Experimental results on complex industrial and open manycore processors demonstrate in two advanced nodes that the proposed flow provides major power, performance, and area/cost (PPAC) improvements of 1.2 to 2.2× compared with commercial 2D ICs, where all metrics are improved simultaneously, including up to 20% power savings.

ISLPED was held at the Boston University Electrical and Computer Engineering Department / Photonics Center on August 1-2, 2022. The symposium is the premier forum for presentation of innovative research in all aspects of low power electronics and design, ranging from process technologies and analog/digital circuits, simulation and synthesis tools, system-level design, and optimization, to system software and applications.

The Center for Advancing Sustainable and Distributed Fertilizer Production (CASFER) is a collaborative effort between the National Science Foundation (NSF) and five universities.

Thanks to efforts to combat climate change, many have heard the catchphrase “closing the carbon loop” — a global effort to convert carbon dioxide into something useful to mitigate the damaging effects of pollution on the planet. Another environmental challenge relates not to carbon dioxide but nitrogen. Now, an ambitious plan to close the nitrogen loop is underway, and with it comes the potential to revolutionize agriculture in the U.S. and around the world.

The Georgia Institute of Technology will be part of CASFER, an NSF Engineering Research Center (NSF-ERC), with four other universities. Supported by an initial grant of $26 million from NSF, CASFER seeks to transform the U.S. from nitrogen cycle pollution to a nitrogen circular economy by developing new technologies and programs for capturing, recycling, and producing decarbonized nitrogen-based fertilizers (NBFs). Georgia Tech is joined by Florida Agricultural and Mechanical University, Case Western Reserve University, the Massachusetts Institute of Technology, and Texas Tech University, which will lead the effort and serve as CASFER’s headquarters.

Nitrogen is used in many commercial applications, but one of the most significant uses is in NBFs for growing food. NBFs are put out into fields, but most do not get used — 80% are washed away and wasted, ending up as pollutants in the watershed. With support from NSF, this team of universities will attempt to recover and reuse nitrogen compounds, the principal element in fertilizers.

“By taking pollutants out of the water and converting them for use, we are taking a negative and making a positive out of it,” said Paul Kohl, Regents' Professor and Thomas L. Gossage Chair in the School of Chemical and Biomolecular Engineering (ChBE) and co-lead of the CASFER effort at Georgia Tech, along with Marta Hatzell, associate professor in the George W. Woodruff School of Mechanical Engineering. “This process will both decrease pollution and lower the cost of farming.”

CASFER has three areas of focus it will pursue to achieve its goal. The first involves measuring and analyzing data to identify new opportunities and locations for collecting wasted fertilizer and determining how exactly the fertilizer affects individual environments.

The second area — Kohl and Hatzell’s focus — is the actual collection and separation of nitrogen compounds from the three types of environments where they usually show up: produce farms, livestock farms, and wastewater treatment plants. They will develop specialized separation methods to pull nitrogen pollutants out of the various environments, creating new types of polymer membranes that work to separate and concentrate the compounds into solutions that can be converted for future use. The work will start in the laboratories at Georgia Tech, but later the team will build test beds — portable laboratories the size of small trailers — to test their separation methods on-site.

“All our separations technologies will be modular, electrified, and largely decarbonized,” said Hatzell. “Our overall goal is to design processes that synthesize new or recover used fertilizers from waste at the same or lower price than traditional chemical manufacturing processes.”

The third area is reconverting the concentrated solutions into usable fertilizer. Humans have been making fertilizer the same way for more than 100 years, using an expensive chemical process that requires natural gas — a resource in short supply. CASFER researchers will develop the conversion methods to create new fertilizers and strategies for dispensing it back into fields for growing crops.

“One strength of NSF Engineering Research Centers is their ability to bring interdisciplinary academic teams together in convergent research to identify novel approaches to thorny societal challenges,” said NSF Assistant Director for Engineering Susan Margulies. “With their unique testbeds and industry partners, the centers innovate and translate solutions that are effective and sustainable.” 

CASFER is poised to bring about dramatic changes to the agriculture industry. Since the inception of the Engineering Research Centers program in 1985, the NSF has awarded fewer than 100 grants to open ERCs, which are designed to foster innovation and collaboration between industry leaders, government agencies, and institutions of higher education.

“For decades, NSF Engineering Research Centers have transformed technologies and fostered innovations in the United States through bold research, collaborative partnerships, and a deep commitment to inclusion and broadening participation,” said NSF Director Sethuraman Panchanathan. “The new NSF centers will continue the legacy of impacts that improve lives across the nation.” 

Looking to the future, universities will launch workforce development efforts like training and education to prepare a new generation of farmers and scientists for work in the nitrogen circular economy.

Georgia Tech researchers involved in the grant include Kohl (Co-Thrust Leader), Andrew Medford, and Joseph Scott from ChBE; Peter Hesketh (Co-Thrust Leader) and Hatzell (Thrust Leader/Co-PI) from the Woodruff School; Mary-Lynn Realff from the School of Materials Science and Engineering; Lizanne DeStefano (EWD Lead) from CEISMC; and Jie Xu and Milad Navaei from the Georgia Tech Research Institute.

Alan Doolittle is doing what was once thought impossible: turning an electrical insulator into an ultra-wide bandgap semiconductor. The results have groundbreaking potential for high-power electronics, optoelectronics, and more.

For the past 80 or so years, aluminum nitride (AlN) has been thought of as nothing but an electrical insulator. Because of its high electrical insulating and thermal conductivity properties, it is used frequently in electronic applications to dissipate heat quickly and maintain efficiency.

Researchers at the Georgia Institute of Technology, led by professor Alan Doolittle, are discovering that there is a lot more to AlN than meets the eye, and their promising research shows the material has the potential to transform the semiconductor industry. By leveraging the advantages of AlN, ultra-wide bandgap (UWBG) semiconductors can be used at high-power and high-temperature levels never seen before.

“It’s rare to see such encouraging early results,” said Doolittle, the Joseph M. Pettit Professor in the School for Electrical and Computer Engineering (ECE). “To put things into perspective, AlN has the ability to handle over five times the voltage of other existing wide bandgap semiconductors. It really is the birth of a new semiconductor field.”

For electrical devices, there are two types of semiconducting materials needed: one that carries positive charges (p-type) and one that carries negative charges (n-type). The Doolittle group was able to improve current conduction in p-type AlN by 30,000,000 times and n-type AlN by 6,000 times than prior best results.

The findings, recently published in Advanced Materials and the Journal of Applied Physics, received the Most Valuable Contribution Award at the 2022 Workshop on Compound Semiconductor Materials & Devices, a premier workshop in the U.S. on high performance electronic materials.

Ultra-wide Bandgaps Equal Ultra-wide Applications

Georgia Tech’s AlN-based semiconductor findings represent an emerging new area of interdisciplinary research covering materials, physics, and devices with promising applications for future generations of high-power electronics and optoelectronics, as well as quantum electronics and harsh-environment applications.

Semiconductors can both conduct and insulate electricity, meaning they are necessary for all electronic appliances to operate. Scientists make semiconductor materials by using pure elements (most frequently silicon) and adding intentional impurities to make crystals with the desired electrical, thermal, and optical prosperities.

The bandgap is one of the most important properties of a semiconductor, as it represents the minimum energy required for electrical conduction. It is also the largest factor in determining the voltage at which a device fails (called breakdown), as well as represents the energy/wavelength of light emanating from the semiconductor. UWBG semiconductors can operate at high temperatures, frequencies, and voltages, meaning less semiconductor devices are needed in high voltage circuits which increases performance and efficiency, while reducing costs. Doolittle’s AlN-based semiconductor has the highest bandgap ever demonstrated to have both p and n-type conduction needed for electronics.

“The new AlN-based semiconductor appears to have the ability to withstand voltages at incredibly high levels,” said Doolittle. “Levels that can even withstand some sections of the national utility grid, something no other semiconductor can do.”

With the ability to withstand high voltage and high frequency, AlN-based semiconductors can be utilized in power electronic devices found in automotive, industrial, and consumer applications. The technology could also allow utility grids to more effectively control how much power to transmit and where, a growing demand as old systems integrate with other smart grid innovations and renewable energy sources.

The team used a much lower temperature to grow the AlN crystals than what is normally utilized to create semiconductor materials. The low heat process allows for more precise control of the material’s surface chemistry during creation and is potentially a groundbreaking innovation in its own right.

“That kind of out of the box solution caught a lot of people off guard,” said Doolittle. “It was thought that you couldn’t grow good quality material at this low of temperature, but we’ve shown that it’s possible and has broad applicability.”

AlN’s Impressive Optical Properties

Unlike an incandescent light bulb where a filament is heated to glow and produce light, light-emitting diodes (LEDs) emit light when an electric current flows through a layered semiconductor device. The wide bandgap semiconductor material gallium nitride (GaN) was used to create the first LED blue light in the early 1990s by Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura (for which they won the 2014 Nobel Prize in Physics). Creating the high energy blue LED challenged scientist for decades, as it was the final piece needed to create white light and full-color LED displays that have now revolutionized lighting technology and is predicted to save nearly 20% in energy consumption in the U.S. when fully deployed.

Like GaN, AlN’s wide bandgap means it has enormous light energy which results in the short light wavelengths needed to produce high energy deep ultra-violet (DUV) light beyond the ability of the eye to see. Because AlN has an even larger bandgap than GaN, it produces a DUV light with a wavelength of only 203 nanometers (compared to GaN’s ~365 nm) – nearly twice the energy as light from GaN.

“We're really excited about the optical properties of this material,” said Doolittle. “Researchers have been attempting to get LEDs under 270 nanometer wavelengths for a while now because it opens up an enormous range of applications.”

One such potential application for AlN-based LEDs is light disinfection, a growing focus in research and industry. Unlike current ultraviolet (UV) lights — a light disinfectant plagued by power/efficiency limitations — DUV LEDs use higher energy electromagnetic radiation that is absorbed in the dead layers of human skin instead of being absorbed in live tissue.

“This light gives us a pathway to make light emitters that can kill viruses and bacteria with significantly less — if any — damage to human skin and eyes.” said Doolittle.

Time to Engineer

With the team’s encouraging early studies showing AlN having the potential to be a revolutionary semiconductor material, they now turn to prototyping and optimization. While the new technology is a leap forward and largely solves the most difficult science problems that have roadblocked using AlN as a semiconductor, engineering challenges remain. 

Since such a wide bandgap semiconductor has never been created, a solution to make good electrical contact to the material (for electrical current to be transported to devices) is essential. All known metals are poorly suited to contact AlN, so metal alloys and exotic contacts will be needed, according to Doolittle.

Early prototypes have shown some resistance to current flow that must be improved if AlN is to reach the efficiencies it potentially can achieve. Likewise, thicker devices will need to be engineered to use in the high voltages needed to impact utility grids.

“We have ideas as to how to push this forward and view most of these issues as engineering challenges requiring only time and resources, not fundamental science limitations,” said Doolittle.

***

Citation I: H. Ahmad, J. Lindemuth, Z. Engel, C. M. Matthews, K. Motoki, W. Alan Doolittle, “Substantial P-type Conductivity of AlN Achieved via Beryllium Doping,” Advanced Materials 33 (42), 2104497, September 2021.

DOI: doi.org/10.1002/adma.202104497

Citation II: H. Ahmad, Z. Engel,  C. M. Matthews, S. Lee, and  W. Alan Doolittle, “Realization of homojunction PN AlN diodes”, J. Appl. Phys. 131, 175701 (2022)

DOI: doi.org/10.1063/5.0086314

Funding: This work was supported by the Office of Naval Research (ONR) Multidisciplinary University Research Initiatives (MURI) Program entitled, “Leveraging a New Theoretical Paradigm to Enhance Interfacial Thermal Transport In Wide Bandgap Power Electronics” under Award No. N00014-17-S-F006 administered by Dr. Mark Spector and Lynn Petersen. This work was also in part supported by the Air Force Office of Scientific Research under Award number FA9550-21-1-0318 administered by Dr. Ali Sayir.

Writer: Dan Watson

Photography: Marion Crowder

Media Contact: Dan Watson | dwatson@ece.gatech.edu

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The Georgia Institute of Technology, or Georgia Tech, is a top 10 public research university developing leaders who advance technology and improve the human condition. The Institute offers business, computing, design, engineering, liberal arts, and sciences degrees. Its nearly 44,000 students, representing 50 states and 149 countries, study at the main campus in Atlanta, at campuses in France and China, and through distance and online learning. As a leading technological university, Georgia Tech is an engine of economic development for Georgia, the Southeast, and the nation, conducting more than $1 billion in research annually for government, industry, and society.

A team of researchers at the University of Massachusetts Amherst and the Georgia Institute of Technology has 3D printed a dual-phase, nanostructured high-entropy alloy that exceeds the strength and ductility of other state-of-the-art additively manufactured materials, which could lead to higher-performance components for applications in aerospace, medicine, energy and transportation. The research, led by Wen Chen, assistant professor of mechanical and industrial engineering at UMass, and Ting Zhu, professor of mechanical engineering at Georgia Tech, was published in the August issue of the journal Nature.

Over the past 15 years, high entropy alloys (HEAs) have become increasingly popular as a new paradigm in materials science. Comprised of five or more elements in near-equal proportions, they offer the ability to create a near-infinite number of unique combinations for alloy design. Traditional alloys, such as brass, carbon steel, stainless steel and bronze, contain a primary element combined with one or more trace elements.

Additive manufacturing, also called 3D printing, has recently emerged as a powerful approach of material development. The laser-based 3D printing can produce large temperature gradients and high cooling rates that are not readily accessible by conventional routes. However, “the potential of harnessing the combined benefits of additive manufacturing and HEAs for achieving novel properties remains largely unexplored,” says Zhu.

Chen and his team in the Multiscale Materials and Manufacturing Laboratory combined an HEA with a state-of-the-art 3D printing technique called laser powder bed fusion to develop new materials with unprecedented properties. Because the process causes materials to melt and solidify very rapidly as compared to traditional metallurgy, “you get a very different microstructure that is far-from-equilibrium” on the components created, Chen says. This microstructure looks like a net and is made of alternating layers known as face-centered cubic (FCC) and body-centered cubic (BCC) nanolamellar structures embedded in microscale eutectic colonies with random orientations. The hierarchical nanostructured HEA enables co-operative deformation of the two phases.

“This unusual microstructure’s atomic rearrangement gives rise to ultrahigh strength as well as enhanced ductility, which is uncommon, because usually strong materials tend to be brittle,” Chen says. Compared to conventional metal casting, “we got almost triple the strength and not only didn’t lose ductility, but actually increased it simultaneously,” he says. “For many applications, a combination of strength and ductility is key. Our findings are original and exciting for materials science and engineering alike.”

“The ability to produce strong and ductile HEAs means that these 3D printed materials are more robust in resisting applied deformation, which is important for lightweight structural design for enhanced mechanical efficiency and energy saving,” says Jie Ren, Chen’s Ph.D. student and first author of the paper.

Zhu’s group at Georgia Tech led the computational modeling for the research. He developed dual-phase crystal plasticity computational models to understand the mechanistic roles played by both the FCC and BCC nanolamellae and how they work together to give the material added strength and ductility. 

“Our simulation results show the surprisingly high strength yet high hardening responses in the BCC nanolamellae, which are pivotal for achieving the outstanding strength-ductility synergy of our alloy. This mechanistic understanding provides an important basis for guiding the future development of 3D printed HEAs with exceptional mechanical properties,” Zhu says.

In addition, 3D printing offers a powerful tool to make geometrically complex and customized parts. In the future, harnessing 3D printing technology and the vast alloy design space of HEAs opens ample opportunities for the direct production of end-use components for biomedical and aerospace applications.

Additional research partners on the paper include Texas A&M University, the University of California Los Angeles, Rice University, and Oak Ridge and Lawrence Livermore national laboratories.

Story by Melinda Rose, Associate News Editor at UMass Amherst.