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Abstract: This paper theoretically proposed a series of formulae for a novel tensile testing method to extract the residual stress in the surface film on metallic substrates. Finite element calculations were conducted to verify the accuracy and reliability of the proposed formulae. From the tensile stress–strain curves of metallic substrates with and without a surface film, one can evaluate the residual stress in the film using these formulae. A tarnish film on a brass substrate formed after immersion in Mattsson’s solution was tested to demonstrate these methods, and the obtained residual stress showed a low difference below 6.8%. [Copyright &y& Elsevier]

Abstract: In this study we focus on the fracture behavior of two types silicon-thin film glass-silicon (Si-Glass-Si) triple stacks specimens with a sharp corner. We determine the notch stress intensity factor K n for both specimens using a combination of the Williams eigenfunction expansion method, Stroh’s sextic formalism, finite element analysis, and the path-independent H-integral. Empirical solutions of dimensionless stress intensity factors are proposed for two typical specimens, and the dependence of geometry is analyzed. Furthermore, the effect of glass thickness on stress intensity is explored for anodic-bonded Si-Glass-Si triple stacks. We discuss the feasibility of using a critical value of K n to correlate the failure results for both specimens with various bond area and glass thickness. [Copyright &y& Elsevier]

Nanocrystalline materials such as thin films, and in particular, multilayers with a periodicity in the nanometer range, i.e. superlattice films, possess properties that cannot be found in their coarse-grained bulk counterparts. Mechanical characterization of such structures is therefore of high interest, but also very challenging, due to the small length scales involved and has therefore most often been performed ex-situ using electron microscopy. In this work, however, we report on the first in-situ micromechanical analysis of a CrN-AlN superlattice thin film cross-section. The sample was deposited using reactive magnetron sputtering and sublayer thicknesses were chosen so as to stabilize AlN in its cubic crystal structure. Using a synchrotron X-ray nanoprobe, maps of internal stresses and morphological changes were tracked by means of wide-angle X-ray diffraction and simultaneous small-angle X-ray scattering, while the sample was loaded to various degrees with a wedged diamond tip. The results reveal a high compressive strength of about 13 GPa, while through-thickness cracks form, following tensile stresses >1.4 GPa and thereby provide a relaxation mechanism. Layer rotation up to several degrees and significant layer compression up to 7% were also found, but along with the internal stress response, their nature is mostly elastic, meaning that in the post-loading state only a fraction of the effects observed under load remains. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Through superlattice (SL) architectures, the hardness as well as the fracture toughness of ceramic thin films can be enhanced. The hardness-related SL effect is reasonably well understood, however, the mechanisms driving the toughness-enhancing effect are still partially unexplored. To isolate the effect of the lattice mismatch from the elastic moduli mismatch on the toughness-related properties, we designed TiN/Cr 0.37 Al 0.63 N superlattices, in which the involved layers have effectively identical elastic moduli, but sizeably different lattice parameters. Micromechanical bending tests show an enhanced fracture toughness K IC of the SLs (2.5±0.1 MPa√m) compared with monolithic TiN (2.0±0.1 MPa√m) and Cr 0.37 Al 0.63 N (1.3±0.1 MPa√m) with only a weak bilayer period (Λ) dependence. Superimposing an analytical model based on continuum mechanics on the experimental data, we demonstrate that, at low Λ, the nanolayers within the SL exhibit strong coherency strains, as misfit dislocation formation is energetically unfavourable. With increasing layer thicknesses, misfit dislocations start to form in the two layer materials – first in Cr 0.37 Al 0.63 N and slightly Λ-shifted in TiN. The associated evolution of coherency strains in the TiN and Cr 0.37 Al 0.63 N layers causes the observed bilayer-period-dependent toughness enhancement beyond the constituent materials. Supporting structural, morphological, chemical, and mechanical analyses are provided by X-ray diffraction, electron microscopy techniques, and nanoindentation. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Ti-Si-N nanocomposite thin films usually consist of a few nm sized crystals embedded in an amorphous matrix. Here we study the influence of the Si content in Ti-Si-N films – prepared by reactive magnetron sputtering using Ti targets alloyed with intermetallic TiSi 2 (to obtain Si contents of 0, 10, 15, 20, 25 at.% in the targets) – on fracture toughness ( K IC ) and hardness. Single cantilever bending experiments show that Ti-Si-N exhibits K IC values of up to 3.0 ± 0.2 MPa√m, which are significantly higher than those for TiN with 1.9 ± 0.2 MPa√m. Complementary nanoindentation experiments reveal also a higher hardness for Ti-Si-N with 34 ± 1 GPa as compared to 26 ± 1 GPa for TiN. The film structure is carefully studied by X-ray diffraction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. [ABSTRACT FROM AUTHOR]

Abstract: Two CrN(001) films with different thickness were grown on MgO(001) substrates using unbalanced d.c. magnetron sputtering. The morphology and interfacial structure of the films are characterized by using conventional transmission electron microscopy, weak-beam dark-field microscopy and spherical aberration (CS )-corrected high-resolution transmission electron microscopy. The microscopy studies revealed the well-known cube-on-cube orientation relationship. While an interface dislocation network with edge dislocations was identified, only part of the lattice mismatch is relaxed. The misfit dislocation structure and growth defects are analyzed and discussed based on the weak-beam dark-field and high-resolution transmission electron microscopy results. [Copyright &y& Elsevier]

We provide an experimental and theoretical description of the high temperature fracture behaviour of TiN thin films. For this, we employ molecular dynamics and density functional theory, to show that the surface energies drop insignificantly between 0 and 1000 K. We utilise these results to predict a slight decrease of the fracture toughness over the aforementioned temperature range. For the experimental perspective, we use unbalanced DC reactive magnetron sputtering to synthesise a TiN film, on which we perform in situ high temperature microcantilever bending tests. Upon increasing the testing temperature from room temperature to 773 K our results present a slight, irreversible decrease of K IC , once the deposition temperature of the film (~653 K) is exceeded. Based on our theoretical groundwork, as well as complementary data produced by X-ray diffraction, nanoindentation, transmission electron microscopy, and wafer curvature measurements, we identify growth defect recovery as the main reason behind the decrease of K IC. We observe no change in the deformation and/or fracture mechanism of TiN across the experimentally investigated temperature range. Using an analytical model based on continuum mechanics, we estimate the influence of macro residual stresses on the temperature-dependent fracture toughness of TiN attached to a Si (100) wafer. Unlabelled Image • Temperature-dependent molecular dynamics calculations of the (100), (110), and (111) surface energies of TiN. • In situ microcantilever bending tests performed at ambient, and elevated temperatures. • Growth defect recovery identified as a decreasing factor for the fracture toughness of TiN thin flims. • Analytical continuum mechanics model consulted to estimate the temperature-dependent apparent fracture toughness of TiN attached to a Si substrate. [ABSTRACT FROM AUTHOR]