The Effect of Copper on the Microstructure, Wear and Corrosion Resistance of CoCrCuFeNi High-Entropy Alloys Manufactured by Powder Metallurgy

Abstract

This paper focuses on the microstructure, phase composition, mechanical, tribological and corrosion properties of high-entropy alloys (HEAs) in the CoCrCuFeNi system depending on copper content, which was varied from 0 to 20 at. % with an increment of 5%. CoCrCuFeNi alloys were manufactured by powder metallurgy methods: mechanical alloying and hot pressing of element mixtures. The solubility limit of copper in CoCrFeNi solid solution was found to be 9 at. %. Segregation of irregularly shaped copper grains sized 1–30 μm is observed at concentrations above this solubility limit. As copper concentration increases, the phase composition of CoCrCuFeNi alloys changes from the single phase based on FCC1 solid solution (Cu = 0–5 at. %) to the dual-phase FCC1 + FCC2 alloy (Cu = 10–20 at. %), where FCC1 is the main phase and FCC2 is the secondary copper-rich phase. Tribological tests have shown that doping the CoCrFeNi alloy with copper increased wear resistance by 23% due to solid solution hardening. As copper content rises above 20%, the content of the secondary FCC2 phase increases, while wear resistance and alloy hardness decline. An analysis of wear tracks and wear products has shown that abrasion of CoCrCuFeNi alloys occurs via the abrasive-oxidative wear mechanism. The corrosion tests of CoCrCuFeNi HEAs in 3.5% NaCl solution had demonstrated that doping the alloy with copper at low concentrations (5–10%) leads to decreasing of corrosion resistance, possibly due to the formation of undesirable oxide Cu2O along with protective Cr2O3. At high copper concentrations (15–20%) galvanic corrosion is suppressed due to coarsening of FCC2 grains and thus decreasing the specific contact surface area between the cathode (FCC2) and the anode (FCC1).

Microstructure and tribological behaviour of CoCrCuFeTi high entropy alloy reinforced SS304 through friction stir processing

“…This in turn reduces the SWR of the samples. The Cu and Ti present in the reinforced HEA tends to form oxides rapidly and advance the third body layer formation which eventually increases the wear resistance 53 . At intermittent sliding velocity, the local heat at the contact surface raised and debilitated the bond between the reinforcement and the matrix leading to easy material removal.…”

Oxidative and abrasive wear of multiphase AlSi0.75TiMnFeCux (X = 0, 0.25, 0.5) high entropy alloy under non-lubricating reciprocating motion

“…Overall, the superior wear resistance of AlSi 0.75 TiMnFeCu 0.25 and AlSi 0.75 TiMnFeCu 0.5 HEA/WC pairs can be attributed to their multiphase microstructures containing Al-, AlCu rich with harder IMCs and Laves phases in the BCC matrix. In contrast, the AlSi 0.75 TiMnFe HEA had a higher fraction of brittle IMCs and Laves without soft Al-, Cu-rich particles, which acted as scratching centres during reciprocating motion and wear out the tracks easily [31,42,46,49].…”

High entropy Fe–Mn–Ni–Co–Al–C alloys from an industrial steel

“…28,29 Their wear resistance and corrosion properties were also studied. 30 A porous high-entropy alloy was also produced by partial liquid metal dealloying. 31 Lightweight steels with Mn and Al possess good ductility and low density, especially alloys with high content of Mn (up to 30 mass%) and Al (up to 10 mass%).…”

“…28,29 Their wear resistance and corrosion properties were also studied. 30 A porous high-entropy alloy was also produced by partial liquid metal dealloying. 31…”