High-pressure and high-temperature induced densely discontinuous nanoprecipitates in multi-principle element alloy

Knowledge of pressure-related microstructural evolution could be beneficial for directionally tuning mechanical performance of materials. Therefore, in this work, a comparison on the precipitates characteristics and mechanical performance of Ni1.5Co1.5CrAl0.2Ti0.1 multi-principle element alloy (MPEA) aged at 800 °C under high-pressure (HP800) or ambient-pressure (AP800) was systematically studied. Results demonstrate both HP800 and AP800 samples exhibit a heterogeneous microstructure consisting of discontinuous precipitate (DP) regions near grain boundaries and continuous precipitates regions in grain interior. However, the volume fraction of DP regions in the HP800 is ∼25.83% higher than that in the AP800. For revealing the intrinsic mechanism, the fully recrystallized matrix Ni1.5Co1.5Cr MPEA was treated by high-pressure. It is found that the plastic deformation occurs, as well as Ni1.5Co1.5Cr MPEA achieves grain refinement via high-pressure and high-temperature (HPHT) because pressure inhibits grain growth and dynamic recrystallization (DRX) process forms the new fine grains. Similarly, in the Ni1.5Co1.5CrAl0.2Ti0.1 MPEA, the grain refinement is also induced by DRX process during HPHT, so as to promote the formation of DP regions. Besides, HP800 reveals a good combination of a yield strength of 801 ± 33 MPa and an ultimate tensile strength of 1249 ± 53 MPa at a good uniform elongation of 41.85 ± 4.03%, owing to high-density stacking faults and Lomer-Cottrell locks. The present finding might provide a fundamental understanding of DRX process under HPHT and a significant guidance for optimizing nano-precipitates via pressure to develop high-performance strengthened MPEAs. •The aged Ni1.5Co1.5CrAl0.2Ti0.1 MPEA under AP or HP (4 GPa) both exhibit a heterogeneous structure, including DP and CP regions.•The volume fraction of DP regions aged under HP is ∼25.83% higher than that aged under AP.•The nano-lamellar precipitates are distributed in DP regions near GBs and nano-spherical precipitates are distributed in CP regions in grain inner.•High-pressure could effectively restrain grain growth and DRX process during HPHT could produce new fine grains, leading to the higher volume fraction of DP regions.•The MPEA aged under HP obtains a good mechanical performance of 801 ± 33 MPa (YS), 1249 ± 53 MPa (UTS) and 41.85 ± 4.03% (UE), attributed to high-density SFs and L-C locks.