Nanocluster-induced creep inhibition for nanocrystalline materials: A theoretical model

Abstract

Nanocrystals have been well known for their high strength, but the comparatively poor creep properties have limited the application as engineering structural materials. Recently, it has been noticed that adding nanoclusters of alloying elements can effectively inhibit the creep behavior of nanocrystals. In order to fundamentally comprehend the creep inhibition mechanism, a theoretical model is proposed in this work that combines the crystal plasticity theory and viscoplastic self-consistent method. At the grain level, creep strain rate dominated by the grain boundary and grain interior is characterized, respectively. Nanoclusters result in the suppression of grain boundary creep from three aspects, including the influence on diffusion coefficient, dislocation glide area and movement resistance. For the grain interior, the average distance between dislocations is reduced by nanoclusters, thereby affecting the evolution of dislocation density. At the polycrystalline level, viscoplastic self-consistent method is applied to predict the creep behaviors of nanocluster-contained nanocrystals. To validate the developed creep model, experimental data of both nanocrystalline pure Cu and Cu–Ta alloys has been considered. A good agreement of the creep curves is achieved between the theoretical results and experimental data, which provides a basis for further analyzing the creep inhibition mechanisms from the perspective of microstructure evolution.