Dean Pierce of the Department of Energy’s Oak Ridge National Laboratory and a research team led by ORNL’s Alex Plotkowski were honored by DOE’s Vehicle Technologies Office for development of novel high-performance alloys that can withstand extreme environments.
At this year’s Vehicle Technologies Annual Merit Review, held virtually on June 12, VTO recognized Pierce, an R&D staff scientist in the Physical Sciences Directorate, and the DuAlumin-3D research team under Plotkowski.
VTO honored Pierce, a member of ORNL’s Alloy Behavior and Design group, with a Distinguished Achievement award in recognition of his leadership in the development of the new Three Chromium-eXtreme High-Temperature Strength, or 3Cr-XHTS, steel. The steel alloy is made of chromium, which comprises nominally 3% of the material’s mass as reflected in its name, and other alloying elements.
Through the VTO LightMAT program, the ORNL team worked in close collaboration with Cooperative Research and Development Agreement partner Cummins to develop the more durable steel alloy in less than four years.
“We’ve had a great collaboration with Cummins, and working with them has allowed us to bring together the unique expertise at both ORNL and Cummins to develop 3Cr-XHTS,” Pierce said. “I was excited for our whole team that, after four years of hard work and some exciting results, we were recognized.”
3Cr-XHTS steel was created for use in pistons capable of enduring high temperatures, high stress and long periods of wear for next-generation, higher-efficiency, heavy-duty internal combustion engines. The current state-of-the-art steel alloy for heavy duty engine pistons, 4140 steel, is limited to applications where peak metal temperatures are below 500 C, making the material insufficient for use in future, higher-temperature engines.
“For the piston application, we needed to design a steel that is not only strong and oxidation resistant at high temperatures, but it also has to conduct heat well. One of the purposes for conducting heat is to keep the temperature at the combustion surface of the piston low enough so that the material doesn’t fail during operation,” Pierce said. “These properties are often in conflict with one another, meaning that when one property is improved, others can be degraded, and our team needed to overcome this metallurgical design challenge.”
The new high-strength, medium-carbon steel is optimized for superior fatigue and oxidation resistance. Compared with 4140, 3Cr-XHTS steel demonstrated a 143% increase in fatigue strength and about a 75 C increase in high-end operating temperature. The steel also demonstrated a 46% improvement in high cycle, high-temperature fatigue strength compared with H11 tool steel, another chromium-containing high-temperature alloy.
Using 3Cr-XHTS steel, researchers manufactured full-size piston crowns, engine parts that are located at the top surface of pistons and exposed to high-temperature gases and high-pressure during combustion. The new alloy successfully passed Cummins’ most rigorous engine test, a 500-hour modified peak power output test, within a six-cylinder, 15-liter heavy duty engine.
In addition to the steel’s advantageous material properties, 3Cr-XHTS steel is affordable and may potentially be a replacement for higher-cost tool steels. The alloy could have applications in various vehicle sector decarbonization efforts and is compatible with low-carbon fuels that may be adopted for heavy-duty vehicles in the future, such as natural gas, hydrogen, synthetic diesel, renewable diesel and biofuel.
At the Annual Merit Review, ORNL’s DuAlumin-3D research team received a Team Award recognizing their development of DuAlumin-3D, a lightweight aluminum alloy developed under the VTO Powertrain Materials Core Program in a joint effort with the DOE Advanced Materials and Manufacturing Office, or AMMTO. Work was performed in part at the Manufacturing Demonstration Facility at ORNL, home to the MDF Consortium, a nationwide group of collaborators working with the lab to advance the state of the art in U.S. manufacturing technology under the guidance of AMMTO.
The team began developing the alloy in response to a need for resilient, lightweight aluminum alloys that could be used in additive manufacturing, or 3D printing.
“Aluminum alloys were a really interesting problem space for us to work in,” said Plotkowski, senior R&D staff member and the project’s principal investigator. “The major challenge is that conventional wrought aluminum alloys, the ones that we use the most around the world as well as the ones that have the most attractive properties, are challenging to process with additive manufacturing.”
DuAlumin-3D overcomes this hurdle and other material problems with its extraordinary fatigue strength and creep resistance — the best creep resistance, in fact, of any known aluminum alloy at 300 C and above. The printable material was designed for use in laser powder bed additive manufacturing and can withstand AM’s extreme thermal conditions. The alloy retains more than half its strength at temperatures of 300 to 315 C, with microstructural stability up to 400 C.
DuAlumin-3D takes its name from its dual strengthening mechanisms, made possible by the rapid solidification characteristics of 3D laser printing combined with a brief heat treatment.
In less than three years, the technology evolved from a concept into its current state as a viable material for additively manufactured prototypes and products.
“It was necessary to collaborate in order to make this project happen,” Plotkowski said. “It’s, in my opinion, an example of the kind of unique thing that ORNL can do that few other organizations in the world can do because we’re bringing together this diverse skillset. We’re able to easily pull people from all across the organization to contribute.”
Using DuAlumin-3D, researchers have already printed pistons that successfully completed a severe four-cylinder engine test demonstration at ORNL in January. The team is also working alongside commercial partners, including General Motors and Honda Performance Development, to further develop the alloy for use in specific vehicle components. GM is scheduled to test a set of pistons printed from the alloy in a new lightweight, high efficiency V8 medium duty truck engine.
DuAlumin-3D could also be applicable in the aerospace sector, Plotkowski said, where a lightweight material like the new alloy could replace titanium parts to significantly reduce an aircraft’s weight and improve energy efficiency.
The ORNL team, alongside collaborators General Motors and Beehive Industries, also received a 2022 R&D 100 Award for DuAlumin-3D.