Property enhancement of CoCrNi medium-entropy alloy by introducing nano-scale features

CoCrNi -medium-entropy alloy (MEA) has been widely investigated due to its superior mechanical properties that overcome strength-ductility tradeoff. Here we show further property enhancement of CoCrNi MEA by introducing nano-scale features. Both CoCrNi and oxide dispersion strengthened (ODS) CoCrNi are fabricated by mechanical alloying and spark plasma sintering. Microstructural characterization and mechanical testing of these nanostructured MEAs revealed that the nano-scale features significantly improves the strength of the alloys. In ODS-CoCrNi MEA, Y₂Ti₂O₇ oxides with an average diameter of 7.3 ± 3.2 nm are incoherent with the matrix, and a specific orientation relationship exists between Y₂Ti₂O₇ and the matrix, which is [011]_Y2Ti2O7//[011]_Matrix, (400)_Y2Ti2O7//(200)_Matrix and (22$\bar{2}$)_Y2Ti2O7//(11$\bar{1}$)_Matrix. The recrystallization and grain growth processes are effectively suppressed by the introduction of Y₂Ti₂O₇ nanoparticles. Strengthening mechanism analyses indicate that the strength improvement of ODS-CoCrNi is mainly ascribed to the precipitation strengthening of Y₂Ti₂O₇