Mechanical Properties of Complex Concentrated Alloys: Implications for Structural Integrity

Abstract

Complex concentrated alloys are designed by mixing elements in equiatomic or near equiatomic proportions. The nature of bonding and inter-element interactions of constituents resulting in microstructures that induces superior mechanical properties than for conventional alloys. This disruptive alloy design technique benefits from high configuration entropy and enthalpy of mixing, sluggish diffusion, cocktail or composite properties and severe lattice distortions. These core effects induce notable strengthening and toughening mechanisms such as nanoprecipitation, hierarchical microstructures and nano-twins which promote excellent blend of mechanical properties such as yield strength, toughness, fatigue and creep resistance at ambient and high temperatures. The concept of complex concentrated alloys could address the strength-ductility trade-off. This is evident in equiatomic VCoNi and CrCoNi alloys with strength and fracture toughness of 1GPa and ~200MPa√m at cryogenic and ambient temperatures respectively. These alloys also achieved uniform elongations above 55%. Similar exceptional properties have been achieved for FCC, BCC and multiphase systems by inducing several lattice distortions through atomic size mismatch and alloying with interstitial atoms. Fatigue limits are ~32%–48% of ultimate tensile strengths. Creep resistance are higher than Ni-based superalloys and the mechanisms are dislocation creep with stress component above 3 and activation energies reaching 1000 kJ/mol. This paper presents an overview of the rudimentary mechanical properties of CCAs and their effects on structural integrity. Areas for future research including thermo-mechanical processing and optimization of compositions to tune these properties need are highlighted.