Physico-mechanical, microstructure, and chemical properties of Si/Ti/Nb additions to CoCrMoW medium entropy alloys

Abstract

CoCrMoWSi, CoCrMoWTi, and CoCrMoWNb medium entropy alloys (MEAs) were manufactured by powder metallurgy technique. The MEAs were sintered in a vacuum furnace followed by a hot isostatic press (HIP) as a secondary process. Optical microscope, scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDX), and mapping for elemental distribution were investigated. They indicated a homogenous distribution for all the elements with each other. Both the XRD patterns and calculated thermodynamic parameters indicated the formation of new phases including Co7Mo6 and Co7W6, CoCrTi, CoCrNb, and CrSi, with a dual FCC and BCC phase during the sintering process. Density and hardness measurements recorded the highest value for the HIP-sintered samples compared to the vacuum-sintered ones. CoCrMoWSi recorded the highest density and hardness followed by CoCrMoWNb and finally CoCrMoWTi MEAs. The wear resistance results are in complete agreement with the density and hardness results for both sintering samples. The corrosion resistance of the investigated Co-based MEAs was also studied in 3.5% NaCl which recorded the highest corrosion resistance for CoCrMoWNb alloy than the other investigated ones. Uniform, localized and even galvanic corrosion in CoCrMoWTi MEA was noticed on the surface morphologies of the corroded MEA samples.