Evidence of Inverse Hall-Petch Behavior and Low Friction and Wear in High Entropy Alloys

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

doi:10.1038/s41598-020-66701-7

Evidence of Inverse Hall-Petch Behavior and Low Friction and Wear in High Entropy Alloys

Sci Rep. 2020 Jun 23;10(1):10151. doi: 10.1038/s41598-020-66701-7.

Authors

Morgan R Jones¹, Brendan L Nation¹, John A Wellington-Johnson¹, John F Curry¹, Andrew B Kustas¹, Ping Lu¹, Michael Chandross¹, Nicolas Argibay²

Affiliations

¹ Material, Physical, and Chemical Sciences Center, Sandia National Laboratories, Albuquerque, NM, 87123, USA.
² Material, Physical, and Chemical Sciences Center, Sandia National Laboratories, Albuquerque, NM, 87123, USA. nargiba@sandia.gov.

Abstract

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^-6 mm³/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/m²). This value was used to explain cavitation-induced nanoporosity found in the highly deformed surface layer, a phenomenon that has been linked to superplasticity.