Improvement ductility and corrosion resistance of CoCrFeNi and AlCoCrFeNi HEAs by electroless copper technique

In this study, the effect of copper coated particles on the properties of CoCrFeNi and AlCoCrFeNi high entropy alloys (HEAs) was studied. Mechanical milling is applied to achieve a good homogeneous distribution of an equiatomic CoCrFeNi and AlCoCrFeNi HEAs for 25 h milling time, followed by an electroless copper plating with 5–20 wt.% Cu by 5 wt.%, have been established. The prepared powder alloys were compacted at 800 MPa, then sintered at 1150 °C, 1200 °C, 1250 °C for Cux/(CoCrFeNi)1-x HEA and 900 °C, 950 °C, and 1000 °C for Cux/(AlCoCrFeNi)1-x HEA in a vacuum furnace for 90 min. The correlation between the microstructure, density, hardness, wear behavior and corrosion resistance of the fabricated CoCrFeNi, Cux/(CoCrFeNi)1-x and Cux/(AlCoCrFeNi)1-x HEAs were investigated. The results revealed that, alloys which sintered at 1200 °C for (CoCrFeNi – Cux/(CoCrFeNi)1-x HEAs) and at 950 °C for (Cux/(AlCoCrFeNi)1-x HEA) exhibit the highest relative density. Densification was enhanced as a result of increasing the nano Cu wt.% content. A dramatic decrease in the produced samples’ hardness was observed where it decreased from 189.1 HV to 134.5 HV for Cux/(CoCrFeNi)1-x and from 403 HV to 191 HV for Cux/(AlCoCrFeNi)1-x HEAs by the addition of the nano Cu wt.% content. In addition, Wear rate is increased gradually by the addition of the nano Cu wt.% content. The electrochemical results indicate that an increased nano Cu wt.% content corresponds to an increased corrosion rate from 0.297 mm/year to 1.84 mm/year for Cux/(CoCrFeNi)1-x and from 0.03 mm/year to 0.093 mm/year for Cux/(AlCoCrFeNi)1-x HEAs.