Effects of hot isostatic processing and hot rolling on direct energy deposited CoCrNi medium entropy alloy – Microstructural heterogeneity, wear behaviour and corrosion characteristics

Metal additive manufacturing, particularly the direct energy deposition (DED) method, has rapidly evolved over the last decade and become a prime technique to revolutionize the fabrication sector, particularly for aerospace, automotive, and biomedical industries. In this study, the DED-printed CoCrNi medium entropy alloy has been subjected to two alternative processing methods: hot rolling and hot isostatic pressing. The effects of processing routes on microstructural evolution, defect minimization such as porosities, dislocations, and their cumulative impact on mechanical properties and wear response have been studied. The diverse responses of the material surface parallel and perpendicular to the build direction were rationalized based on the repetitive and complex heating of selective surfaces during deposition. Compared to the hot isostatic processed specimen, the hot rolled specimen illustrates a ∼ 40% increase in hardness and subsequent ∼21% reduction in wear rate for the material parallel to the build direction, whereas ∼34% increment in hardness and ∼ 19% reduction in wear rate for the material perpendicular to the build direction. Further, the effect of processing routes on the corrosion behaviour was recorded in 3.5 wt% NaCl solution using potentiodynamic polarization test. Hot isostatic pressed specimen demonstrates better corrosion resistance (∼37%) than hot rolled specimen due to the lesser number of grain boundaries or corrosion nucleation sites.