Enhanced Microhardness and Corrosion Performance of Additively Manufactured Inconel 718 Specimens through Nanostructuring by Severe Plastic Deformation

Abstract

Severe plastic deformation (SPD) processes, particularly high-pressure torsion (HPT) have been increasingly applied to metallic specimens fabricated by laser powder bed fusion (L-PBF) additive manufacturing (AM) for enhancing their mechanical and functional properties through nanoscale grain refinement (≤ 100 nm). In this study. L-PBF AM-fabricated Inconel 718 (IN 718) specimens are initially subjected to 10 HPT revolutions to produce nanosized grains. Subsequently, microstructural characterisation, as well as hardness and electrochemical tests are conducted to evaluate the evolution of microstructures, hardness, and corrosion performance of the as-received and HPT-processed specimens by using various microscopy, Vickers microhardness (HV) measurements, and corrosion performance, respectively. The results reveal an average grain size of ~ 46 nm, dense dislocation networks, and nanotwins after 10 HPT processing, which contribute to the two-fold hardness increase compared to the as-received condition. Such microstructures also contributed to the overall improved corrosion performance after 10 HPT processing, as quantified by the 83% and 73% reduction in corrosion rate and pitting potential, respectively.