Nanomechanical behaviour of nano-structured BCC high entropy alloys (HEAs)

• Main Author: Nanasekaran, Pritiba
• Other Authors: Upadrasta Ramamurty
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Materials::Nanostructured materials; Engineering::Mechanical engineering
• Online Access: https://hdl.handle.net/10356/150873
• Institution: Nanyang Technological University

The study is devoted to the investigation of the nanomechanical behavior of nanostructured BCC high entropy alloys processed through High-pressure Torsion (HPT). An understanding of the mechanical behavior of nanocrystalline HfNbTiZr HEA with single-phase BCC structure is obtained. Equimolar HfNbTiZr BCC HEA samples were processed through HPT with ¼,1, 2, and 5 number of turns at RT. The microstructure of HPT processed HEA samples were observed through the analysis of SEM, TEM, XRD, Nanoindentation and Vickers Hardness test results. It was found that the mean grain sizes of HfNbTiZr HPT samples decrease as a function of the quantity of HPT turns, and a nanocrystalline microstructure was obtained. XRD results reveal that the HPT processing decreases the grain size of the HfNbTiZr without changing phase, remaining as a single-phase BCC. Vickers Hardness and Nanoindentation experiments reveal that the hardness of the HfNbTiZr HPT samples increases significantly as the number of HPT turns increases, proving the Hall-Petch grain strengthening ability of the HEA. The HfNbTiZr HPT samples also exhibit a comparable deformation mechanism to that of conventional BCC metals. The activation volume, ∗ of the HfNbTiZr samples corresponded to the literature on the BCC metals where the ∗ values are commonly reported to be at the order 10 ³. The HfNbTiZr samples are assumed to have a thermally activated double-kink mechanism as a rate-controlling deformation mechanism. This reveals that the screw dislocations of the BCC HfNbTiZr samples are controlled by a thermally activated kink-pair nucleation process.