Effect of molybdenum addition on microstructure and behavior of AlCoCrFeNi high-entropy alloys in wet environments

The materials used for the components operating in harsh fluid environments are required to have excellent resistance to various forms of wear (sliding wear, cavitation and corrosion). High-entropy alloys (HEA) appear to be quite the promising materials in this respect of applications. In this work, influences of Mo on corrosion, cavitation and wear of AlCoCrFeNi HEAs in fluid environments were investigated. AlCoCrFeNi- x Mo ( x = 0, 1, 2, 3, 4, 5 at.%) HEAs were manufactured by vacuum arc melting. In addition, influences of Mo on corrosion, cavitation and wear of AlCoCrFeNi HEAs in fluid environments were investigated and compared with stainless steel AISI 304L. Tribological tests were carried out using the ball-on-disc method in 3.5% NaCl solution, and the surfaces that showed traces of abrasion to identify the wear mechanisms were subjected to SEM and EDS analyses. The potentiodynamic polarization tests were carried out in 3.5% NaCl solution in a three-electrode electrochemical system. Cavitation erosion resistance was estimated using the ASTM G32 standard. In general, molybdenum can improve the cavitation resistance and the wear ability of AlCoCrFeNi alloy with increased hardness and higher corrosion resistance. However, as the Mo content exceeded a certain level (4 and 5 at.% Mo), the cavitation erosion of Mo containing alloys was accelerated which led to a negative effect on the cavitation resistance, although the alloys showed higher hardness. The results of corrosion studies confirm that molybdenum-modified HEAs have a better resistance than stainless steels for preventing fluid environment damage to the metallic components.