Enhanced strength-ductility synergy in a Mo and W co-doping NiCoCr multi-principal element alloy at ambient and cryogenic temperatures

A novel designed Ni48Co33Cr9Mo4W6 multi-principal element alloy (MPEA) with single face-centered cubic (FCC) solid-solution phase was fabricated by casting, homogenization, cold rolling, and various post deformation annealing (PDA) heat treatments. The single-phase FCC structured samples with homogeneous grains exhibited average grain sizes ranging from ∼1.4 to ∼47.8 μm. In addition, a single-phase FCC structured heterogeneous sample consisting of partially un-recrystallized region (∼47.1 vol%) and fully recrystallized region (∼52.9 vol%) was also achieved. Among all the samples with homogeneous grains, the sample processed using PDA treatment at 900 °C for 3 min (named as PDA900-3min) showed an average grain size of ∼1.4 μm, displaying the best mechanical properties. In detail, it exhibited a yield strength of ∼811 MPa and a total elongation of ∼40.2 % at ambient temperature (298 K), and these values were increased to ∼1085 MPa and ∼42.7 % at LN2 (77 K) temperature. Due to heterogeneous deformation induced (HDI) strengthening, the hetero-structured sample (named as PDA900-90s) present markedly higher strength and slightly lower ductility in comparison with the PDA900-3min sample at 298 K and 77 K. These two samples demonstrated synergetic improvement of strength and ductility through Mo/W co-doping and PDA heat treatments both at ambient and LN2 temperatures, attributing to solid solution strengthening and grain boundary strengthening, as well as heterogeneous deformation induced (HDI) strengthening. Additionally, Mo/W co-doping, reduces the stacking fault energy (SFE) of the alloy, facilitates the generation of stacking faults (SFs) and twins, which is prone to maintaining the higher work hardening rate. Therefore, our work suggests that Mo and W co-doping is an effective strategy for achieving enhanced strength-ductility synergy in FCC structured MPEAs.