Void formation in nanocrystalline Cu film during uniaxial relaxation test

• Published in: Acta materialia 2008-10, Vol.56 (17), p.4921-4931
• Main Authors: Inoue, Junya, Fujii, Yosuke, Koseki, Toshihiko
• Format: Article
• Language: English
• Subjects: Applied sciences; Cavitation; Copper; Cross-disciplinary physics: materials science; rheology; Deformation; Density; Ductility; Exact sciences and technology; Grain size; Materials science; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Methods of deposition of films and coatings; film growth and epitaxy; Nanocrystalline Cu; Nanocrystals; Physics; Strain; Thin film; Thin films; Voids
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2008.06.008

Void formation in nanocrystalline Cu thin films with a grain size of 100 nm during uniaxial tensile relaxation experiments is quantitatively studied. Cu thin films with a two-dimensional fiber structure were deposited on heat-resistant polyimide substrates and subject to various subcritical uniform uniaxial tensile strains at an elevated temperature (∼0.3 T m), to observe void formations in nanocrystalline metals with a reduced amount of dislocation-based deformation. Microstructural observations were carried out at several stages of deformation, and the evolutions of void formation in subcritical strain levels are quantitatively discussed. A void formation model is proposed for approximating the nucleation and growth rate of voids. The resulting model shows a reasonable agreement with the observed number density and area fraction of voids for various strain levels and grain sizes. On the basis of the results, the stress and grain size dependences of the void formation process are further discussed.