Grain Refinement via Changing the Shuffling Motion of the Grain Boundary by Traces of Ce and Lu in Gold Alloys

Adding traces of an alloying element into gold bonding wires to improve mechanical performance is an important strategy for meeting the requirements of chip miniaturization. The mechanism of traces of elements to strengthen gold bonding wires is unclear. Using microstructure characterization, we find that traces of Ce have a more obvious effect on strengthening gold wires via grain refinement than Lu does. Atomic simulation based on stochastic surface walking and density functional theory calculation show that Ce significantly segregates at the grain boundary (GB), increases the energy barrier of shuffling motion, and prevents GB migration inducing a typical solute drag effect, but the segregation of Lu at GB is weak, which well accounts for the better grain refinement effects of Ce. Our results not only are fundamental for developing high-strength gold bonding wires but also provide new knowledge on GB shuffling motion and the nature of the solute drag effect.