On the Influence of Residual Stress on Nano-Mechanical Characterization of Thin Coatings
In the present paper, the effect of residual stress on the mechanical behavior of thin hard coatings has been investigated by a new methodology based on the combined use of focused ion beam (FIB) micro-machining techniques and nanoindentation testing. Surface elastic residual stress
were determined by nanoindentation testing on Focused Ion Beam (FIB) milled micro-pillars. The average residual stress present in a 3.8 μm CAE-PVD TiN coating on WC-Co substrate was calculated by the comparison of two different sets of load-depth curves, the first one obtained at
centre of stress relieved pillars, the second one on the undisturbed (residually stressed) surface. Results for stress measurement were in good agreement with the estimate obtained by XRD (sin2
ψ method) analysis on the same sample, adopting the same elastic constants.
In addition, nanoindentation on stress relieved pillars also allowed to perform a more accurate evaluation of elastic modulus and hardness of the coating. The effect of residual stress on crack propagation modes was quantitatively analyzed by high-load nanoindentation and application of energy
methods for fracture toughness evaluation. It is found that compressive residual stress plays a relevant role in determining the fracture behavior and failure modes of the coating. Finally, Microstructural observations of the deformation mechanisms of the TiN coating were performed by TEM
analysis on the cross section of the indentation, obtained by FIB lamella thinning. Results showed that plastic deformation at the nanoscale essentially occurs by formation of shear bands inside the columnar grains, independently of residual stress. A transition between intra-granular shear
deformation and columnar grain sliding is also observed as a function of the applied load.
Keywords: FOCUSED ION BEAM; NANOINDENTATION; RESIDUAL STRESS; THIN COATING; TOUGHNESS
Document Type: Research Article
Publication date: 01 October 2011
- Journal for Nanoscience and Nanotechnology (JNN) is an international and multidisciplinary peer-reviewed journal with a wide-ranging coverage, consolidating research activities in all areas of nanoscience and nanotechnology into a single and unique reference source. JNN is the first cross-disciplinary journal to publish original full research articles, rapid communications of important new scientific and technological findings, timely state-of-the-art reviews with author's photo and short biography, and current research news encompassing the fundamental and applied research in all disciplines of science, engineering and medicine.
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