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 degrees 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 similar to 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.