Decoupling the effects of temperature and stress on grain growth in nanocrystalline Ni films

Understanding the interplay among microstructure, stress and temperature in controlling microstructural stability remains challenging. Here, we use in situ transmission electron microscopy (TEM) annealing and micro-electromechanical-system (MEMS)-based tensile testing to track grain-scale evolution in 100 nm-thick nanocrystalline Ni films with three different initial textures. Thermal annealing at 700 °C causes conventional grain growth driven by surface and grain boundary energy minimization, producing annealing twins and a strong ⟨111⟩ out-of-plane texture. In contrast, stress-induced texture evolution is strongly influenced by the initial microstructure. Grain-resolved statistics from 4D-STEM orientation mapping of over 100,000 grains reveal that stress alters grain growth through two distinct mechanisms. At ambient temperatures, differential yielding drives the growth of larger grains, resulting in size-biased coarsening. At 100 °C, stress helps grain boundaries overcome kinetic barriers, allowing low–surface-energy orientations to grow in a manner similar to thermally driven coarsening. Consequently, the final texture reflects the dominant grain growth mechanism, determined by the relative magnitudes of applied stress and temperature.