Molybdenum segregation at grain boundaries in a nanograined Ni-Mo alloy: Implications for yielding behavior and plastic deformation modes

• Sites within amorphous GBs were categorized into tensile and compressive stress ones. • Mo atoms predominantly occupy tensile stress sites within amorphous GBs. • GB atomic volume declines while atomic compressive stress increases with Mo segregation. • Dislocation emission from GBs is inhibited by Mo segregation. • Nanograin boundary relaxation is induced by Mo segregation. Solute segregation at grain boundaries (GBs) significantly modifies GB characteristics and influences the macroscopic properties of nanograined polycrystals. This study demonstrates a substantial impact of Mo segregation at GBs on the GB characteristics, yielding behavior, and plastic deformation modes in a nanograined Ni-Mo alloy. Atomic segregation simulations reveal that Mo atoms primarily occupy tensile stress sites at amorphous GBs without substantially altering site volume. However, Mo atoms at tensile stress sites compress atomic volumes at compressive stress sites, thereby increasing compressive stress. Consequently, overall GB atomic volume decreases while GB atomic compressive stress increases. Tensile deformation simulations indicate that dislocation emission from GBs is inhibited as the fraction of Mo atoms at GBs increases. The decreased GB energy and atomic volume, along with increased atomic compressive stress, are indicative of the inhibition of dislocation emission due to Mo segregation. When the excess Mo concentration reaches 2.9 at.%, nanograin boundary relaxation is induced, mitigating nanograin coarsening and softening.