Revolutionary lubricant prevents friction at high temperatures

Limits of lubricants

Friction is the basis of movement. However, in various industrial applications — such as advanced manufacturing, transportation, and aerospace — too much friction causes machines to wear down. Lubricants, or substances that reduce friction between two surfaces that come into contact with each other, are key to safe operating conditions and optimal performance, but developing materials that resist wear above 600 degrees Celsius, or 1,000 degrees Fahrenheit, remains a challenge.

In fact, it took many years, minds, and institutions, to achieve these novel findings on a solid lubricant. 

“Collaborative work with other universities brought many knowledgeable people together to share resources, which is crucial in this discipline,” said then-Ph.D. student and first author Zhengyu Zhang. “The future of many industries will depend on advances in materials science, and such a wide topic requires varied expertise.”

The discovery also depended on a device called a high temperature tribometer, which Cai procured for her lab in 2019. The cutting-edge device measures friction, wear, and other tribological properties between two surfaces in contact at high temperature. At the time, Virginia Tech was a pioneer in housing this technology and making it available to faculty and graduate student researchers. The machinery set the groundwork that made the discovery possible for its testing capabilities at temperature thresholds well above traditional equipment. 

Solid findings

The team used high-temperature testing, advanced materials analysis, and computational methods to show that spinel oxide layers – a specific class of minerals that act as a coating – can form naturally on the surface of additively manufactured metal’s surface during high temperature oxidation, enabling self-lubrication. This is possible from the spinel oxide’s low shear strength, or the weakness of the bonds between its molecules, which allows them to easily slip past each other under stress, and its high stability, allowing it to maintain its properties under those stressful and high temperature conditions. 

First, the researchers used advanced computers to predict which kinds of oxides would work best. Then, by carefully tweaking the metal surface that formed a special layer of oxide, Cai and Zhang discovered that spinel oxides are much better at withstanding high temperatures than the materials used before.

Each collaborator provided a key component of the study: 

• University of Florida completed calculations using 4D transmission electron microscopy characterization to identify crystallized structures of very complex oxidized surfaces.
• Jackson State provided the initial samples of the additively manufactured metals.
• Arizona State collaborated on acquiring funding and completing calculations.
• Iowa State completed calculations to simulate mechanical properties of the key oxide.
• Nebraska-Lincoln conducted the high temperature harness tests.
• Virginia Tech led the entire project, conceptualized the idea, conducted high-temperature tribological tests, analyzed surface characterization, carried out calculations of key thermal and mechanical properties for all oxides, and executed phase prediction analyses. 

“This is a great achievement scientifically, and we are thankful to our collaborators who made it possible,” Cai said. “Without Virginia Tech’s resources and strong partnerships with fellow scientists at universities around the country, we would not have discovered this new family of solid lubricant. These findings highlight a promising approach to designing self-lubricating alloys for extreme temperatures.”