The Role of Chemical Composition for the Ductility and Microstructure of Thin NiAl Films

Abstract

ABSTRACTIn this work, NiAl films deposited by magnetron co-sputtering onto silicon substrates with compositions between 45.0 and 51.5 at-% Al and a thickness of 1.2 μm were studied. The films exhibited grain sizes comparable to the film thickness. Furthermore, the films were found to have fiber textures with the strongest component being (110) for the very Ni-rich and (111) for the stoichiometric and Al-rich films. The residual stresses in the Ni-rich and stoichiometric films after annealing were found to be independent of composition, while the Al-rich films showed a significant decrease in film stress. This stress drop can be related to severe cracking in the Al-rich films, which has not been observed in the stoichiometric and Ni-rich films, indicating that the fracture toughness depends on composition. Based on a simple estimate, the fracture toughness of these Al-rich films was determined to be in the range of 1 to 2 MPa m-1/2, which is somewhat smaller than commonly reported bulk values for polycrystalline NiAl.