High Pressure Compressive Reverse Shearing: A New Severe Plastic Deformation Process

Abstract

Metalworking has been a cornerstone of human advancement, enabling the creation of tools, structures, and machinery that drive modern industries. It plays a pivotal role in manufacturing and engineering, ranging from large-scale industrial production to artisanal craftsmanship. The continuous evolution of metalworking techniques has focused on enhancing material properties to meet demanding applications. Among these, severe plastic deformation (SPD) has emerged as a transformative approach to refine microstructures and improve the mechanical properties of metals and alloys. Despite the development of over 50 SPD techniques, including high-pressure torsion (HPT), equal channel angular pressing (ECAP), and accumulative roll bonding (ARB), these methods face limitations such as low processing speeds, inability to produce large components, and restricted strain impartation in a single step. To address these challenges, this study proposes and develops a novel SPD technique, termed High-Pressure Compressive Reverse Shearing (HPCRS). The process applies large accumulated shear strain in a reciprocating manner along with compressive strain within a channel, enabling the processing of bulk metals and pre-compacted powders into metallic sheets. For an 83% thickness reduction, the obtained values for accumulative equivalent strain, shear strain, and compressive strain were approximately 42, 73, and 1.8, respectively. The HPCRS process has been demonstrated on materials with diverse crystal structures, including FCC (commercially pure aluminum, OFHC copper), BCC (interstitial-free steel), and HCP (commercially pure zinc), as well as on pre-compacted Al and Mg powders. Experimental results on commercially pure aluminum reveal the achievement of ultra-fine grain microstructures in the sub-micron range together with a unique crystallographic shear texture. A shear texture in sheet metals is known to improve formability. Along with all the ideal shear texture components, HPCRS samples exhibit predominantly B and Bb components. The process showed the capability to tune the strength-ductility combination through variations in processing frequency and amplitude. At a lower processing frequency of 0.1 Hz, the tensile results showed a threefold increase in strength than that of the starting material. However, with the increase in frequency (from 0.1 Hz to 20 Hz) an increase in ductility (from 20 % to 33 %) has been found with a gradual drop in strength (from 230 MPa to 100 MPa). Notably, the metal-forming speed in this process can be exceedingly high. At a processing frequency of 20 Hz, samples were processed in less than 15 seconds. Perhaps the most important characteristic of HPCRS is the exceptional high-temperature grain stability on commercially pure aluminum for 100 hours. This is attributed to special grain boundaries having ledge-shape patterns and unique sub-microstructural features, that evolved during heat treatment. Therefore, the key features of the HPCRS process make it highly relevant for industries such as automotive, aerospace, and electronics. This study establishes HPCRS as a revolutionary SPD technique with significant potential to advance materials manufacturing and industrial applications.