• Nation, Brendan
• Lu, Ping
• Wellington-Johnson, John A.
• Curry, John F.
• Jones, Morgan R.
• Chandross, Michael
• Kustas, Andrew B.
• Argibay, Nicolas

Abstract

<jats:title>Abstract</jats:title><jats:p>We present evidence of inverse Hall-Petch behavior for a single-phase high entropy alloy (CoCrFeMnNi) in ultra-high vacuum and show that it is associated with low friction coefficients (~0.3). Grain size measurements by STEM validate a recently proposed dynamic amorphization model that accurately predicts grain size-dependent shear strength in the inverse Hall-Petch regime. Wear rates in the initially soft (coarse grained) material were shown to be remarkably low (~10<jats:sup>–6</jats:sup> mm<jats:sup>3</jats:sup>/N-m), the lowest for any HEA tested in an inert environment where oxidation and the formation of mixed metal-oxide films is mitigated. The combined high wear resistance and low friction are linked to the formation of an ultra-nanocrystalline near-surface layer. The dynamic amorphization model was also used to predict an average high angle grain boundary energy (0.87 J/m<jats:sup>2</jats:sup>). This value was used to explain cavitation-induced nanoporosity found in the highly deformed surface layer, a phenomenon that has been linked to superplasticity.</jats:p>

Topics

• impedance spectroscopy
• surface
• grain
• grain size
• phase
• grain boundary
• wear resistance
• strength
• grain boundary energy