Shape Memory Alloys Offer Efficient, Eco-Friendly Cooling Technology

Metal Alloy Cooling Material Artists Impression

A team of researchers from the University of Maryland has created a new type of elastocaloric material for cooling that boasts high efficiency, is environmentally friendly, and can be easily expanded for commercial purposes.

Used in refrigeration and HVAC systems around the world, current cooling technology has plateaued in both efficiency and environmental impact.

An international research team led by the University of Maryland has developed a novel elastocaloric cooling material that is highly efficient, eco-friendly, and easily scaled up for commercial use.

The researcher’s new cooling material is a nickel-titanium alloy that was sculpted using additive technology (3-D printing). Their work is published in the November 29, 2019, issue of Science.

Cooling technology, used in refrigeration and HVAC systems around the globe, is a multi-billion dollar business. Vapor compression cooling, which has dominated the market for over 150 years, has plateaued in efficiency, and uses chemical refrigerants with high global-warming potential. Solid-state elastocaloric cooling, in which stress is applied to materials to release and absorb (latent) heat, has been under development for the last decade and is a front-runner for alternative cooling technologies. Shape-memory alloys are found to display a significant elastocaloric cooling effect; however,  hysteresis – work lost in each cycle, which causes fatigue and eventual failure of such materials – remains a challenge.

The international team of collaborators led by UMD Materials Science and Engineering (MSE) Professor, Ichiro Takeuchi, has developed an improved elastocaloric cooling material using a blend of nickel (Ni)-titanium (Ti) metals, forged using a 3D printer, that is not only potentially more efficient than current technology, but is completely ‘green.’ Moreover, it can be quickly scaled up for use in larger devices.

“In this field of alternative cooling technologies, it’s very important to work on both the materials end, as well as the systems end – we are fortunate to have a highly-qualified team of experts at the University of Maryland, College Park to work on both ends,” said Professor Takeuchi. “It’s only when these two efforts closely align that you make rapid progress, which our team was able to do.”

Comparatively speaking, there are three classes of caloric cooling technology – magnetocaloric, electrocaloric and elastocaloric – all of which are ‘green’ and vapor-less. Magnetocaloric, the oldest of the three, has been under development for 40 years and is just now on the verge of being commercialized.

“The need for additive technology, otherwise known as 3D printing, in this field is particularly acute because these materials also act as heat exchangers, delivering cooling to a medium such as water,” said Takeuchi.

Takeuchi has been developing this technology for almost a decade – he received the UMD Outstanding Invention of the Year for this research in 2010, and the DOE ranked elastocaloric cooling, also known as thermoelastic cooling, #1 as the ‘most promising’ of alternative cooling technology in 2014 – and it is one step closer to commercialization.

“The key to this innovation that is fundamental, but not often discussed, is that materials fatigue – they wear out,” said Takeuchi. “This is a problem when people expect their refrigerators to last for a decade, or longer. So, we addressed the problem in our study.”

The team tested their creation heavily over a four-month period and still maintained its integrity. “Some known elastocaloric materials start showing degradation in cooling behavior after just hundreds of cycles. To our surprise, the new material we synthesized showed no change after one million cycles,” said, UMD’s Huilong Hou, who is the first author of the work and a post-doctoral researcher in the Department of Materials Science and Engineering.

The metal additive manufacturing uses a laser to melt, and then mix, metals in powder form. By controlling the powder feed, the team was able to produce nanocomposites which gave rise to the robust mechanical integrity in the material.

The research team also included scientists at the U.S. Department of Energy Ames Laboratory in Ames, Iowa, where the 3D printing was carried out, and researchers from the Colorado School of Mines in Golden, Colorado, who helped investigate the internal structure of the printed materials.

Funding was provided by the Advanced Research Projects Agency-Energy (ARPA-E) of the U.S. Department of Energy (DOE) supported the original characterization of shape memory alloys at the University of Maryland under grant ARPA-E DEAR0000131. The use of the laser-engineered net shaping (LENS) equipment was supported by the Critical Materials Institute, an Energy Innovation Hub funded by the Advanced Manufacturing Office of the Office of Energy Efficiency and Renewable Energy of the DOE. The work at Ames Laboratory was also supported by the Division of Materials Science and Engineering of the Basic Energy Sciences Programs of the Office of Science of the DOE under contract DE-AC02-07CH11358 with Iowa State University.

Reference: “Fatigue-resistant high-performance elastocaloric materials made by additive manufacturing” by Huilong Hou, Emrah Simsek, Tao Ma, Nathan S. Johnson, Suxin Qian, Cheikh Cissé, Drew Stasak, Naila Al Hasan, Lin Zhou, Yunho Hwang, Reinhard Radermacher, Valery I. Levitas, Matthew J. Kramer, Mohsen Asle Zaeem, Aaron P. Stebner, Ryan T. Ott, Jun Cui and Ichiro Takeuchi, 29 November 2019, Science.
DOI: 10.1126/science.aax7616

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