Abstract
Energy efficiency is motivating the search for new high-temperature (high-T) metals. Some new body-centered-cubic (BCC) random multicomponent “high-entropy alloys (HEAs)” based on refractory elements (Cr-Mo-Nb-Ta-V-W-Hf-Ti-Zr) possess exceptional strengths at high temperatures but the physical origins of this outstanding behavior are not known. Here we show, using integrated in-situ neutron-diffraction (ND), high-resolution transmission electron microscopy (HRTEM), and recent theory, that the high strength and strength retention of a NbTaTiV alloy and a high-strength/low-density CrMoNbV alloy are attributable to edge dislocations. This finding is surprising because plastic flows in BCC elemental metals and dilute alloys are generally controlled by screw dislocations. We use the insight and theory to perform a computationally-guided search over 107 BCC HEAs and identify over 106 possible ultra-strong high-T alloy compositions for future exploration.
Highlights
Energy efficiency is motivating the search for new high-temperature metals
Our findings are unexpected because screw dislocations are widely understood to control plastic flows in BCC elemental metals and dilute alloys[17,18], there were hints in the literature that edge dislocation motion might be hindered by solutes in some low/ moderate-concentration alloys[19,20,21,22]
Unlike in such dilute alloys, our recent theory shows that edge dislocations in some complex high-entropy alloys (HEAs) can encounter very large energy barriers to glide[23], and enable high strength that is retained at elevated temperatures
Summary
Energy efficiency is motivating the search for new high-temperature (high-T) metals. Some new body-centered-cubic (BCC) random multicomponent “high-entropy alloys (HEAs)” based on refractory elements (Cr-Mo-Nb-Ta-V-W-Hf-Ti-Zr) possess exceptional strengths at high temperatures but the physical origins of this outstanding behavior are not known. We show, using integrated in-situ neutron-diffraction (ND), high-resolution transmission electron microscopy (HRTEM), and recent theory, that the high strength and strength retention of a NbTaTiV alloy and a high-strength/low-density CrMoNbV alloy are attributable to edge dislocations This finding is surprising because plastic flows in BCC elemental metals and dilute alloys are generally controlled by screw dislocations. Our findings are unexpected because screw dislocations are widely understood to control plastic flows in BCC elemental metals and dilute alloys[17,18], there were hints in the literature that edge dislocation motion might be hindered by solutes in some low/ moderate-concentration alloys[19,20,21,22] Unlike in such dilute alloys, our recent theory shows that edge dislocations in some complex HEAs can encounter very large energy barriers to glide[23], and enable high strength that is retained at elevated temperatures.
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