Combined effects of solute drag and Zener pinning on grain growth of a NiCoCr medium-entropy alloy

Coarse grains are formed during thermomechanical processing for the widely studied NiCoCr medium-entropy alloy (MEA) due to the lack of effective approaches to restrain grain growth. Here, a novel integrated method combing solute drag and Zenner pinning effects are proposed. The 0.5 at.% C was added to precipitate carbides which generates pinning of the grain boundaries; while solute drag is implemented by 3 at.% addition of Mo with low self-diffusion coefficient. Results show that most of Mo is dissolved in the matrix and M23C6 carbides uniformly precipitated after aging. The combined method shows a significant effect on controlling grain growth and results in much finer equiaxed grains. A very high growth activation energy of 511 kJ /mol was obtained, double that of NiCoCr MEA (251 kJ/mol). This work shows that the grain growth kinetics of the NiCoCr based MEA during traditional thermomechanical processing can be tuned by adjusting carbide precipitates and selecting appropriate solute elements.