Influence of Composition on Nanoindentation Response of Ni-Zr Alloy Thin Films
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METALLIC films with sub-micrometer thicknesses are well known to exhibit non-trivial size-effects not only with regard to electrical, optical, and magnetic properties,[1–7] but with respect to the mechanical behavior as well.[8–13] Various processing techniques, like electrodeposition,[14] magnetron sputtering,[15] electron beam evaporation,[16] etc., have been used to synthesize metallic thin films with different microstructures and grain sizes. In particular, magnetron sputtering is one of the most widely adopted techniques for fabricating thin films by employing high-purity targets in an inert atmosphere.[15] In the fabrication of metallic films, it offers the advantage of controlling the composition of an alloy with significant precision. Several earlier studies have suggested that the microstructure of the deposited metallic film is sensitive to the variation in composition.[17,18] As a matter of fact, this technique allows the formation of crystalline, or amorphous structures, or the
BIBHU PRASAD SAHU, AMLAN DUTTA and RAHUL MITRA are with the Department of Metallurgical and Materials Engineering, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal 721302, India. Contact e-mail: [email protected] Manuscript submitted July 3, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
composite of both, by tuning various processing parameters, like negative bias voltage,[19] target power,[20] inert gas pressure,[21] etc. Even for the simple binary alloys, extensive studies have been reported,[22–25] where the deposited thin film microstructure is found to be strongly dependent on the composition, thus providing control over the properties of the metallic films. The composition-microstructure relationship in metallic thin films suggests a link between their compositions and mechanical properties. Mechanical behavior of a metallic film is often investigated using nanoindentation, which is typically used to explore the deformation mechanism at small length-scale. In this context, a rigorously studied aspect is the effect of loading strain rate (LSR), which determines the strain rate sensitivity of the film. The strain rate sensitivity is a fundamental quantity, which provides crucial information about the underlying deformation mechanism by characterizing the plastic flow characteristics of a material. Several studies have reported negative values of strain rate sensitivities in the thin films of metallic glasses,[26–30] and the nanocrystalline films typically exhibit reduced strain rate sensitivity with alloying.[30,31] Another important information extracted from the nanoindentation test is the creep behavior observed during the dwelling period, which offers valuable insight into the slow activities governing the time-dependent deformation processes.
The composition of a metallic thin film is known to be a crucial factor influencing its creep behavior. Kaur et al.[32] have shown that the addition of W to NiTi thin films control the grain size, thereby affecting their creep behaviors. Similarly, Ma et al.[33] have demons
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