Microstructure evolution and the deformation mechanism in nanocrystalline superior-deformed tantalum

Abstract

The temperature-controlled relationship between the mechanical properties and deformation mechanism of tantalum (Ta) enables the extension of its application potential in various areas of life, including energy and electronics industries. In this work, the microstructure and deformation behavior of nanocrystalline superior-deformed Ta have been investigated in a wide temperature range. The structural analysis revealed that the high-performance Ta consists of several different substructures, with an average size of about 20 nm. The tensile behavior of nanocrystalline Ta (NC-Ta) was analysed and simulated at various temperatures from 100 K to 1500 K by the molecular dynamics (MD) method. It is shown that with increasing average grain size, the elastic modulus of NC-Ta linearly increases, and the impact factor reaches a value close to 1.8. The critical grain size, as obtained from the Hall–Petch relationship, was found to be about 8.2 nm. For larger grains, the flow stress follows the Hall–Petch relationship, and the thermal behavior of twin bands determines the deformation process. On the other hand, when grains are smaller than the critical size, the relationship between the flow stress and structure transforms into the inverse Hall–Petch relationship, and the deformation mechanism is controlled by grain rotation, boundary sliding or atomic migration. The results of numerical simulations revealed that temperature significantly affects the critical grain size for the plastic deformation of NC-Ta. In addition, it is demonstrated that both the elastic modulus and dislocation density decrease with increasing temperature. These findings provide guidance for the design of polycrystalline tantalum materials with tailored mechanical properties for specific industrial applications such as heat exchangers and condensers in aerospace, bone substitutes in biomedicine, and surface acoustic wave filters or capacitors in electronics.