Suppressing liquid Bi intergranular penetration in Cu by tailoring grain boundary mobility

The intergranular penetration of liquid metal involved in the grain boundary (GB) embrittlement phenomenon has been studied for decades. However, strategies with high adaptability to bulk workpieces that could effectively suppress the penetration of liquid metal along the GB network have rarely been proposed. Herein, we observed abnormally shallow penetration depth (<10 µm) of liquid Bi into severely deformed Cu disks after annealing at 600 °C for 60 min. By conducting scanning transmission electron microscopy and transmission Kikuchi diffraction characterization, we surmised that the dramatic suppression of the liquid Bi intergranular penetration was due to the continuous GB migration during annealing enabled by nanosized nitrogen-filled bubbles in the sub-surface layer of the Cu disk. This study sheds light on the microstructure design and possible methods for the suppression of intergranular penetration and GB embrittlement in polycrystals.