Context <p>In the present work, the investigation of polycrystalline nanomaterials has been extended to a specific nanoalloy of copper and tantalum having a 9:1 atomic concentration. The study aims to analyze the influence of temperature and average grain size (AGS) on the mechanical behavior of the polycrystalline Cu-Ta nanoalloy. The results indicate that the critical grain size of polycrystalline 9Cu-Ta is smaller than that of pure Cu. The critical grain size of polycrystalline Cu (6.86&#xa0;nm) is reduced to 3.89&#xa0;nm with the addition of approximately 10% Ta atoms. This reduction is attributed to the combined effects of dislocation slip and subgrain strengthening mechanisms. Furthermore, the investigation highlights the variation of mechanical properties with increasing temperature and the influence of temperature on the critical grain size. The analysis also reveals the existence of distinct plastic deformation mechanisms corresponding to the critical grain size in the polycrystalline Cu-Ta nanoalloy.</p> Methods <p>Molecular dynamic simulation has been carried out under a fixed strain rate of 1.0 × 10¹⁰&#xa0;s⁻¹ for specifically analyzing the effect of temperature and average grain size (AGS) of the polycrystalline nanoalloy using embedded atom method potential (EAM). The polycrystalline structures with different grain sizes were generated using the Voronoi construction method. Simulations were carried out to evaluate the effect of temperature and grain size on the deformation behavior. The obtained data were analyzed to determine the critical grain size, variation in mechanical properties, and the associated deformation mechanisms of the polycrystalline 9Cu-Ta alloy.</p>