In-situ TEM mechanical testing of nanocrystalline zirconium thin films

Mechanical behavior of nanocrystalline zirconium thin films was investigated in-situ inside a transmission electron microscope (TEM). The yield stress measured for specimens with <10 nm grain size was around 450-500 MPa compared to the bulk value of 250-300 MPa. Similar grain size effects are seen on fracture stress and strain of about 0.9 GPa and 1.5-2% respectively. Using in-situ TEM, we demonstrate control of grain size in the specimens using electro-migration stress and temperature. The experimental results suggest that the critical grain size for inverse Hall-Petch type relationship in nanocrystalline hexagonal close packed metals could be around 15 nm.