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In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. Herein, we demonstrate that high-temperature lubricity can be achieved with coefficients of friction COF as low as 0. By integrating high-temperature tribological testing, advanced materials characterization, and computations, we show that the formation of spinel-based oxide layers on superalloy promotes sustained self-lubrication due to their lower shear strength and more negative formation and cohesive energy compared to other surface oxides.
To span Ni- and Cr-based ternary oxide compositional spaces for which little high-temperature COF data exist, we develop a computational design method to predict the lubricity of oxides, incorporating thermodynamics and density functional theory computations. Various liquid and solid lubricants have been developed to reduce high-temperature friction and wear on metallic surfaces. So far, only about 20 solid lubricating phases have been identified after decades of experimental study.
The structural origin of these lubricating materials is related to their 2D layered e. Density functional theory DFT calculations show that the decohesion energy in such structures is governed by a shielded Coulomb interaction between the interlayers, whose relatively large distance results in weak coupling and easily plastically deformable structures 5. To minimize the overall material loss at high temperatures, a wear-resistant and self-lubricating surface is desired.
In reality, a high strength, yet abrasive surface is often achieved in refractory metals, whereas soft yet lubricious surface is often achieved in 3d transition metals 4 , 5. Neither is ideal. Incorporating the lubricous phases inside a strong metal matrix could be a convenient way to harness the traits of both. This is demonstrated in the temperature-adaptive chameleon lubricating systems e.
