Nanoindentation study of polycrystal Nb

Grain boundary hardening and slip transmission across grain boundary are two important aspects in deformation of materials. Using depth-sensing indentation, a pop-in phenomenon induced by grain boundaries has been observed in polycrystalline niobium. This phenomenon is about a sudden displacement jump observed near a grain boundary segment at a larger force than the initial elasto-plastic pop-in, which is observed not to be affected by grain boundary. The experimental results show that this pop-in effect has a close relationship with misorientations of the grain boundary. Further studies found that no evident change of grain boundary hardness was observed even though there existed grain boundary pop-in.