In-situ Observation of Cross-Sectional Microstructural Changes and Stress Distributions in Fracturing TiN Thin Film during Nanoindentation

Abstract

Load-displacement curves measured during indentation experiments on thin films depend on non-homogeneous intrinsic film microstructure and residual stress gradients as well as on their changes during indenter penetration into the material. To date, microstructural changes and local stress concentrations resulting in plastic deformation and fracture were quantified exclusively using numerical models which suffer from poor knowledge of size dependent material properties and the unknown intrinsic gradients. Here, we report the first in-situ characterization of microstructural changes and multi-axial stress distributions in a wedge-indented 9 μm thick nanocrystalline TiN film volume performed using synchrotron cross-sectional X-ray nanodiffraction. During the indentation, needle-like TiN crystallites are tilted up to 15 degrees away from the indenter axis in the imprint area and strongly anisotropic diffraction peak broadening indicates strain variation within the X-ray nanoprobe caused by gradients of giant compressive stresses. The morphology of the multiaxial stress distributions with local concentrations up to −16.5 GPa correlate well with the observed fracture modes. The crack growth is influenced decisively by the film microstructure, especially by the micro- and nano-scopic interfaces. This novel experimental approach offers the capability to interpret indentation response and indenter imprint morphology of small graded nanostructured features.

In Situ X-ray Diffraction Analysis of Stresses during Deep Rolling of Steel

“…This approach is comparable to the analysis done by Zeilinger et al [10] for the determination of loading stress during the fracturing of thin films. The strain state was then recalculated with the X-ray elastic constants 1 2 S 2 = 5.81 × 10 −5 MPa −1 , which are connected to the elastic modulus E and the Poisson value ν, as given by Noyan for steel specimens [9], to determine the σ xx , σ yy , σ yz , and σ zz stress components as well as the hydrostatic σ h and equivalent (von Mises) stress σ eq , as used by Kuznetsov et al [11] for the description of burnishing processes using Equation (2).…”

Grain boundary strengthening in nanocrystalline zinc aluminate

“…Given the similarities of those cracks to the bottom median vent, one may hypothesize they are being formed during loading by grain shearing at the high stress regions, causing intergranular microcracking. Zeilinger et al 40 have shown that in ceramics, the subsurface underneath the indenter edge shows indeed a high stress gradient, which could be accommodated by grain boundary fracturing.…”

Investigations on micro-mechanical properties of polycrystalline Ti(C,N) and Zr(C,N) coatings

“…Nanoindentation is the standard and most frequent method used to characterize mechanical properties of thin film materials [30]. Accordingly, studies on deformation mechanisms of thin films variants of transition-metals carbides/nitrides (TMC/N) were mainly performed through micro/nano-indentation experiments combined with modeling [31][32][33][34][35][36]. Intergranular shear sliding is identified as a common and important failure mechanism in these studies.…”