Strengthening mechanisms in high-entropy alloys: Perspectives for alloy design
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INVITED REVIEW This section of Journal of Materials Research is reserved for papers that are reviews of literature in a given area.
Strengthening mechanisms in high-entropy alloys: Perspectives for alloy design Pedro E.J. Rivera-Díaz-del-Castilloa) and Hanwei Fu Department of Engineering, Lancaster University, LA1 4YW Lancaster, U.K. (Received 17 April 2018; accepted 20 August 2018)
High-entropy alloys (HEAs), originally introduced to the literature due to their ability to stabilize a single phase across large temperature ranges, have recently demonstrated to display multiphase systems undergoing a variety of strengthening mechanisms. Previous reports have focused on solid solution strengthening and precipitation hardening; however, other hardening mechanisms such as twinning and martensite formation have been reported to play a key role in controlling their mechanical behavior. Such deformation mechanisms display significant variations with temperature and strain rate. The present contribution provides an outline of the various hardening mechanisms reported in the literature for HEAs. For each mechanism, a modeling strategy is proposed to describe the associated mechanical behavior. The mechanisms are combined into a single framework to discover new HEAs of improved mechanical behavior. A strategy for HEA design is presented, and the advantages of adopting additive layer manufacturing to improve mechanical behavior are discussed.
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2018.328
computing4 and the so-called fourth industrial revolution.4 The attractive properties of HEAs combined with their affinity with highly automatized production technologies can lead to a technological breakthrough of broad implications. The most attractive aspect of HEAs lies on their combination of mechanical properties. As reviewed by Zhang et al.,5 the alloy improvement of HEAs in comparison with regular systems is significant. The combination of properties, especially at high temperatures, has no counterpart in present alloying systems. HEAs exceed regular systems with one principal element in terms of their fatigue, high temperature strength, ductility, corrosion, and irradiation resistance properties.5 As opposed to the original ambition of displaying a single phase, they show often several phases, but still a certain microstructural simplicity not expected in systems where the Gibbs phase rule would dictate the appearance of several phases. The associated hardening mechanisms include grain refinement, solid solution, precipitation, and dynamic Hall–Petch effect (wherein twinning is increasingly formed upon deformation). For instance, AlCuCrFeNiCo grain refinement has led to superplastic behavior in the 800–1000 °C temperature range after hot working and grain size reduction,7 and this alloy has been characterized in detail by Shaysultanov et al.8 A behavioral transition between CoCrFeNi, CoCrFeNiV, and CoCrFeNiMnV has been reported by Salishchev et al.9; the V-containing alloy showed
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