The Influence of the Grain Size Effect on the Mechanical Properties of Metallic Tungsten during Nanoindentation

Tungsten plays a critical role in semiconductor electrical interconnects, and a thorough understanding of its mechanical properties is essential for optimizing its processing and performance. However, few studies have explored the effect of grain refinement on the mechanical behavior of tungsten. The work indicates a phenomenological transition around ~7.3 nm within the tested grain-size range that governs the nanoindentation response of tungsten. To establish this, we performed molecular dynamics (MD) simulations of nanoindentation for different grain sizes and analyzed surface pile-up, elastic recovery, atomic displacement, loading force, hardness, stress/strain behavior, dislocation density, and dislocation evolution. When the average grain size is smaller than ~7.3 nm, an increase in grain size leads to a higher elastic recovery ratio in the depth direction, increased loading force and hardness, and elevated local von Mises stress near the indenter, accompanied by greater shear strain. However, the number of surface pileup atoms and the associated pile-up area decrease. The distribution and magnitude of dislocation density are strongly influenced by grain size. These findings demonstrate that grain refinement can effectively improve the mechanical performance of tungsten, offering further insights for the nanoscale processing of this material.