First−principles study of the effects of 4d transition metal solute segregation on the properties of the yttrium twin boundary101¯1

Abstract

Transition metals play a crucial role in tuning grain boundary (GB) properties. In this work, first−principles calculations were performed to investigate the segregation behavior of 4d transition metal solute atoms near the $\left(10\overline{1}1\right)$ twin boundary in the hcp rare−earth metal yttrium. The calculated segregation energies indicate that the boundary interface is the most favorable segregation site for all studied elements. The overall segregation tendency follows the order: Ru > Tc > Rh > Pd > Mo > Ag > Nb > Cd > Zr. Regarding grain boundary strengthening, Pd, Ag, and Cd exhibit positive strengthening energies at their most favorable segregation sites, indicating their tendency to embrittle the boundary strength. The remaining six elements enhance GB cohesion to varying degrees, with the strengthening capability decreasing in the order: Tc > Mo > Nb > Ru > Zr > Rh. When considering both strengthening effects and GB stabilization, Rh and Ru show the most promising overall performance. Furthermore, first−principles tensile tests were conducted to simulate the dynamic stretching behavior of grain boundaries segregated with Ru and Rh, and the resulting strengthening effect was consistent with the predictions of the Rice−Wang model. The strengthening energy was further decomposed into mechanical and chemical contributions, revealing that the enhancement in GB strength is predominantly governed by chemical effects, whereas mechanical contributions tend to embrittle the boundary. Charge density difference analyses reveal significant charge redistribution between solute and host atoms, leading to shortened interatomic distances near the segregation sites and consequently enhanced bonding strength. These findings provide valuable theoretical insights into GB engineering strategies for Y − based alloys.