Abstract
Equi-atomic quaternary CoCrFeNi Medium-entropy alloy (MEA) and quinary CoCrFeNiMn high-entropy alloy (HEA) are fabricated by laser energy deposition, followed by 5-pass cold rolling to total reduction of 70 % and annealing at temperatures of 600–1000 °C for 1 h. CoCrFeNi-MEA is severely cracked while CoCrFeNiMn- HEA is slightly cracked after cold rolling. Hardness of as deposited and fully recrystallized (heat treating temperature at 800–1000 °C) CoCrFeNi-MEAs are slightly higher than those of CoCrFeNiMn- HEAs, due to the larger atomic size misfit and lattice strain in CoCrFeNi-MEA than in CoCrFeNiMn-HEA. However, the higher microhardness of CoCrFeNiMn-HEAas-rolled than CoCrFeNi-MEAas-rolled is associated with the higher strain state in CoCrFeNiMn-HEAas-rolled than in CoCrFeNi-MEAas-rolled. With the increase of heat-treating temperature, microhardness of CoCrFeNi-MEA increases first and then decreases due to the precipitation hardening effect of Cr-rich (B2) particles in CoCrFeNi-MEAR-600. Microhardness of CoCrFeNiMn-HEA decreases with the increase of annealing temperature because of the weaker precipitation hardening effect of MnNi phase (L10) and Cr-rich particles (BCC) after annealing at 600 ℃ and higher temperatures. CoCrFeNi-MEAR-700 is much harder than CoCrFeNiMn-HEAR-700 because CoCrFeNi-MEAR-700 is partially recrystallized and CoCrFeNiMn-HEAR-700 is fully recrystallized. Strength behavior of the two alloys is consistent with microhardness behavior. {100}<110> texture component is acquired in both CoCrFeNi-MEAas-rolled and CoCrFeNiMn-HEAas-rolled. <111>//ND texture is observed in both alloys after annealing at 600 ℃. Orientation of recrystallized grains is random in both alloys. Size of recrystallized grains in CoCrFeNiMn-HEA is slightly larger than those in CoCrFeNi-MEA since homologous temperature (T/Tm) of CoCrFeNiMn-HEA is slightly higher than that of CoCrFeNi-MEA.
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