News | May 30, 2019

Big lasers need big radiators, Army scientists say strange alloys might change that

News Article Image of Big lasers need big radiators, Army scientists say strange alloys might change that

The Army is evaluating the high-energy laser-equipped vehicles like the Stryker pictured here, which can fry drones in mid-air using a 5-kilowatt laser. More powerful lasers are in development, but they have to be mounted on even larger trucks to be mobile.

C. Todd Lopez/Army

Scientists working at a U.S. Army laboratory are exploring the heat transfer properties of a strange class of metals that can return to their original shape when heated.

They’re called Shape Memory Alloys, and the most common is made of nickel and titanium. They’re already used as braces to move crooked teeth and as stints to open clogged arteries, and recent testing indicated they’ll be great for dealing with all the heat created when powering a high-energy laser.

“In recent years, researchers and companies have attempted to develop smarter, more efficient and environmentally conscientious materials and energy systems,” said Dr. Darin Sharar, principal investigator for the U.S. Army Combat Capabilities Development Command’s Army Research Laboratory.

Directed energy systems, which include lasers, are a hot research topic for the military. The hope is lasers can be used to protect U.S. forces by quickly downing drones and enemy missiles, but designing them to be small and mobile is tough because they have high heat flux and short pulse duration. That means they get hot, extremely fast, and need big cooling units to stop components from cooking and help maintain a precise wavelength and beam quality.

The standard cooling designs require metal fins to provide mechanical support, prevent liquid phase change materials leakage (coolant) and enhance the thermal conductivity of whatever metal (aluminum) that they’re made of. It might be helpful to picture a car’s radiator, which also has heat-dissipating fins.

Those fins make up the bulk of the heat exchangers, leaving less space for energy storage, and that’s making it hard for mobile laser systems to be prototyped.

Architectures using phase change materials (shape memory alloys) are quickly becoming the preferred thermal management solution because of their ability to absorb thermal energy with minimal temperature increase, ensuring the directed energy systems can operate within spec, Sharar said.

“The discovery of thermal energy storage via shape memory alloys provides an unprecedented two order of magnitude improvement in the cooling figure of merit, defined by the product of the material latent heat and thermal conductivity,” Sharar said. “This opens a new paradigm of phase change material design, through which scientists can eliminate the need for heavy/large volume fin structures and fabricate thermal energy storage and heat transfer structures entirely out of metallic shape memory alloys.”

Thermal energy storage figure of merit vs. transformation temperature for the r.t. Martensite and r.t. R-phase NiTi sample characterized herein (green stars), along with values for other solid-solid phase change materials and solid-liquid paraffin. The green band shows the potential range of FOM and transformation temperature for NiTi-based alloys based on thermal conductivity, density and latent heat values from the literature. (U.S. Army graphic)

Sharar said this promises increased duty cycle for directed energy applications, along with the significant size and weight savings, enabling more-capable, compact directed energy assets on smaller platforms, like combat vehicles.

This concept received approval for patenting from the Army and Sharar has received funding to continue the research.

TechLink, in cooperation with the Army Research Laboratory’s technology transfer office, is helping companies evaluate the technology for non-military applications and guiding them through the licensing process; services which are provided at no charge.

Dr. Brian Metzger, a senior technology manager at TechLink, is the point of contact for businesses that want to discuss the technology’s potential.

“There are definitely non-military applications that make this a great candidate for a license agreement,” he said. “Power generation, industrial lasers, and electric vehicles also have unique thermal management issues and we can help companies evaluate the alloy for those purposes.”

Businesses interested in evaluating and licensing the Army technology can contact Brian Metzger at or by telephone at 406-994-7782.