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Abstract: Friction and wear contribute to a significant amount of the world’s energy waste and machine failures/damages, making it a priority for industrialized countries to control these two factors through investing in tribological studies. This has been commonly done through material design and exposing materials to different processing conditions to improve their wear resistance. High entropy alloys (HEAs) are strong advanced material candidates for tribological applications because of their wide variety of excellent properties such as high hardness, exceptional mechanical properties, thermal stability, and good corrosion resistance. Interest in achieving better tribological properties in HEAs over traditional alloys has been growing over the past decade. Efforts in alloying, heat treatments, surface modifications, coatings, and composites have been investigated to reduce both friction and wear, especially in harsh environments. However, with each new treatment and new alloy used, wear behaviors experienced by the desired HEA may change drastically. Thus, both identifying and improving understanding of the underlying wear mechanisms is crucial to the advancement of HEAs for a variety of tribological applications.

This work seeks to investigate the tribological properties and specific wear mechanisms experienced by a single-phase FCC 1.1 at% C-doped Fe40. 4Ni11. 3Mn34. 8Al7. 5Cr6 at cryogenic temperatures and after processing by additive manufacturing techniques, specifically laser powder bed fusion and additive friction stir manufacturing, as well as the two-phase Fe28.2Ni18.8Mn32.9Al14.1Cr6 exposed to a surface nitriding treatment. The main guiding question of this work is: Does the different processing of HEAs improve its wear resistance and make them better than a traditionally used 316L stainless steel?

Scanning electron microscopy, energy dispersive x-ray analysis, x-ray photoelectron spectroscopy, atom probe tomography, and scanning transmission electron microscopy are used to characterize the worn pins.

Thesis Committee: Ian Baker (Chair, Advisor), Francis Kennedy, Harold Frost, Wen Chen (U Mass, Amherst)