Metal hybrids processed by high-pressure torsion: synthesis, microstructure, mechanical properties and developing trends

The tradeoff between strength and ductility has long been identified as the 'Achilles' heel' of the mechanical properties in engineering applications. Metal hybrids processed by severe plastic deformation (SPD) have gained significant attention in recent years, as they have shown potential for enhancing strength and ductility simultaneously through different heterostructured designs. Among SPD processes, high-pressure torsion (HPT) is considered the most effective in grain refinement and offers excellent versatility for synthesising new materials with a wide variety of experimental setups and processing parameters. This review article describes the current state-of-the-art of metal hybrids processed by HPT, characterised by heterogeneous microstructures (i.e. nanoscale and/or microscale), through a comprehensive study of their synthesis-microstructure-property relationships. The potential of HPT-processed hybrids is highlighted and discussed along with their limitations. Suggestions are provided with the aim to advance current research trends towards future application in high-impact technologies, including the biomedical and microelectronic industries.