Laser shock peening-induced nanostructure evolution and mechanical response of LDED-Fabricated CoCrNi medium-entropy alloy

The present study investigates the effects of Laser Shock Peening (LSP) on the mechanical behaviour and nanostructure formation of equiatomic CoCrNi medium-entropy alloys (MEAs) that were produced through Laser Directed Energy Deposition (LDED) following processing. It systematically examines the impact of varying numbers of LSP passes (1-LSP, 2-LSP, and 3-LSP) on the mechanical response, dislocation density, and surface integrity. Scanning electron microscopy (SEM) demonstrated that the depth of the LSP-affected area increased significantly with the number of impacts. The 1-, 2-, and 3-LSP samples exhibited a depth of 4 µm, 8.5 µm, and 21 µm, respectively. X-ray diffraction (XRD) analysis demonstrated a significant peak broadening following LSP, which was the consequence of the accumulation of surface compressive stresses and the increase in dislocation density. Kernel Average Misorientation (KAM) maps from Electron Backscatter Diffraction (EBSD) demonstrated minimal misorientation in the 1-LSP condition, whereas the 3-LSP sample exhibited the highest local misorientation and strain accumulation.

The relationship between LSP intensity and material hardening was clearly demonstrated by mechanical testing using tensile, nanohardness, and microhardness tests. Hardness was highest near the surface and gradually decreased with depth. Although the 1-LSP sample underwent minimal modifications in its properties, the 2-LSP and 3-LSP samples achieved yield strengths of approximately 500 MPa. More LSP passes increased strength, but in the 3-LSP condition, excessive peening reduced ductility by about 27%. These results confirm that the right LSP parameters can effectively improve the balance between strength and ductility of LDED-built CoCrNi MEAs by refining the microstructure and controlling dislocation distribution.

Dr. Dan Sathiaraj is currently an Associate Professor in the Department of Mechanical Engineering at Indian Institute of Technology (IIT) Indore. Before joining IIT Indore, he worked as a Postdoctoral Researcher at Technische Universität (TU) Dresden, Germany, from May 2017 to November 2019. His postdoctoral research was supported by the prestigious Alexander von Humboldt Foundation.

Dr. Sathiaraj’s research interests include advanced multi-component alloys (High-Entropy Alloys, HEAs), surface engineering, and fundamental deformation mechanisms in metallic materials processed through conventional routes. He has authored and co-authored over 50 research publications in reputed international journals and conferences.