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• Fracture toughness of an AlTiN coating was characterized by nanomechanical measurements. • Microcantilever bending resulted in lower toughness compared to nanoindentation. • The test method and the coating microstructure influence the measurement results. • Fracture toughness of AlTiN is higher when compared to the literature data on TiN. Metal nitride coatings are increasingly used in MEMS applications. The brittle nature of these coatings makes fracture one of the main failure mechanisms during operation. Therefore, quantifying the fracture toughness of nitride coatings in a reliable fashion is important to understand the failure behavior and to optimize device performance and reliability. This study investigated the fracture toughness of AlTiN coatings produced by cathodic arc evaporation, a widely used technique in the industry. Nanoindentation and microcantilever bending-based measurements indicated a fracture toughness of 6.6 and 4.8 MPa·m1/2, respectively. The lower toughness results of microcantilever bending were attributed to the columnar growth of the coating, which promoted crack propagation perpendicular to the film surface. The results provide useful data toward a better understanding of the fracture of hard coatings and give insight into the advantages and disadvantages of different measurement methods. [ABSTRACT FROM AUTHOR]

Abstract The fracture toughness of nanostructured materials depends on anisotropic physical properties of individual microstructural features, their texture and/or topology. In this work, intentionally sculptured grain boundaries of low cohesive energy were used to form "weak" and "tough" crack propagation directions within a nanocrystalline TiN film, allowing to correlate the directional arrangement of grains and anisotropy of fracture toughness. By using a selective micromechanical testing approach, two different cracking directions were probed in a scanning electron microscope by loading microcantilever beam specimens prepared parallel and perpendicular to the stacked direction of the alternately tilted columnar grains. The fracture toughness along the sculptured grain boundaries was ~30% higher due to effective multiple crack deflection at the kink planes, which was not observed along weak cleavage planes in the stacked direction. The results indicate the fundamental importance of microstructural design in the synthesis of tough nanostructured ceramics, whose anisotropic mechanical properties can be controlled effectively by incorporating dedicated microstructural features of well-defined topology, orientation and density. Graphical abstract Unlabelled Image Highlights • Weakly bonded grain boundaries designed in a zig-zag pattern were used to enhance fracture toughness of a brittle TiN ceramic. • The toughening effect originates from a multiple crack deflection at the tilted grain boundaries. • The observed fracture anisotropy was identified in directional arrangement of columnar grains within the material volume. • It resulted in a difference of 30% between weak and tough planes inherently formed in two in-plane directions. [ABSTRACT FROM AUTHOR]

• Modified procedure for the J -integral testing on micro-scale cantilever beam specimens. • Old procedure delivers wrong J -values for smaller crack lengths. • Numerical case study to determine the plastic eta-factor, η pl. • Fitting procedure for the determination of correct η pl -values. The current paper presents a modified procedure for the J -integral testing on micro-scale cantilever beam specimens. For such tests, a non-dimensional factor is required that relates the plastic part of the area below the load vs. load-point displacement curve to J. This parameter is called the "plastic eta-factor", η pl. Up to now, a constant value of η pl ≈ 2 has been used, which is also valid for deeply notched single-edge bend specimens. A comprehensive numerical case study is performed to determine η pl for cantilever beam specimens as a function of the relative crack length a / W , the relative cantilever length L / W , the relative base distance d / W , and the load, i.e. the degree of plasticity in the specimen. It is shown that η pl ≈ 2 is applicable only, if the crack length is large, a / W ⩾ 0.5. For smaller a / W -ratios, which are commonly used in the fracture mechanics testing of nano- and micrometer sized materials, η pl can become much smaller and also dependent on the d / W -ratio. A fitting procedure is presented that enables the determination of the correct value of η pl , and modifications of the J -integral testing procedure for cantilever beam specimens are proposed. Finally, a numerical validation of the procedure is presented. [ABSTRACT FROM AUTHOR]

Superlattice structures enable the simultaneous enhancement in hardness (H) and fracture toughness (K IC) of ceramic-like coatings. While a deeper understanding of this effect has been gained for fcc-structured transition metal nitrides (TMN), hardly any knowledge is available for hexagonal diborides (TMB 2). Here we show that superlattices can—similarly to nitrides—increase the hardness and toughness of diboride films. For this purpose, we deposited TiB 2 /WB 2 and TiB 2 /ZrB 2 superlattices with different bilayer periods (Λ) by non-reactive sputtering. Nanoindentation and in-situ microcantilever bending tests yield a distinct H peak for the TiB 2 /WB 2 system (45.5 ± 1.3 GPa for Λ = 6 nm) but no increase in K IC related to a difference in shear moduli (112 GPa). Contrary, the TiB 2 /ZrB 2 system shows no peak in H, but for K IC with 3.70 ± 0.26 MPa∙m1/2 at Λ = 4 nm originating from differences in lattice spacing (0.14 Å), hence causing coherent stresses retarding crack growth. [Display omitted] [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]

Superlattice films are generally known for their exceptional high hardness compared to their monolithic constituents. Recently, we have shown that CrN/TiN superlattice films exhibit a peak in fracture toughness for a bilayer period of 6.0 nm, similar to the former reported peak in hardness. We propose that a dominating factor for obtaining such favourable material properties is the interface constitution between the individual layers. To proof this notion, we have intentionally modified the interface sharpness by post-deposition vacuum annealing of the samples at different temperatures. This promotes interdiffusion of Ti or Cr into its adjacent layers and gradually changes the interfaces to interphases (because TiN and CrN form a solid solution). In order to obtain reliable K IC fracture toughness values as a function of the annealing temperature, in-situ micromechanical cantilever bending tests on ex-situ vacuum annealed freestanding films were performed. High temperature loads take also place during machining processes like dry cutting or high-speed cutting, and are thus of high practical relevance. [ABSTRACT FROM AUTHOR]

Coherently grown nanolayered TiN/CrN thin films exhibit a superlattice effect in fracture toughness, similar to the reported effect in indentation hardness. We found –by employing in - situ micromechanical cantilever bending tests on free-standing TiN/CrN superlattice films– that the fracture toughness increases with decreasing bilayer period ( Λ ), reaching a maximum at Λ ~ 6 nm. For ultrathin layers ( Λ ~ 2 nm), the fracture toughness drops to the lowest value due to intermixing and loss of superlattice structure. Both, fracture toughness and hardness peak for similar bilayer periods of TiN/CrN superlattices. [ABSTRACT FROM AUTHOR]

The search for simultaneously strong and tough materials requires the development of novel design strategies and synthesis routes. In this work, it is demonstrated that a nanoscale variation in material mechanical property distributions can serve as a universal concept for improvement of fracture behavior of nanostructured brittle thin films. Mechanical tests performed on microcantilever beam specimens of multilayered TiN/SiO x thin films show that the fracture toughness of this hierarchical, microstructurally and mechanically heterogeneous material can be enhanced up to 60% with respect to either of its single-layered constituents, which is attributed to a large difference in their elastic modulus. Similarly, micro-bending tests of multilayered CrN/Cr thin films reveal an increase in fracture toughness of 40% with respect to CrN and Cr single layers. In this case, the enhancement of fracture toughness is attributed to the difference in strength of both constituents. These results indicate that the fracture toughness enhancement in brittle nanostructured films is conditioned by simultaneously occurring microstructural heterogeneity and a difference in the intrinsic mechanical properties of the material constituents, which ensure an effective increase of energy dissipation through the alternation of the crack path and crack deflection at the interfaces. [ABSTRACT FROM AUTHOR]

The stiffness and fracture toughness of a thermally grown oxide (TGO) on a MCrAlY coating were measured by the microcantilever bending technique. TGO cantilevers were prepared by a focused ion beam and bent in-situ by a nanoindenter in a scanning electron microscope. The Young's modulus and fracture toughness of the TGO were determined to be 352 GPa and 4.4 MPa·m1/2, respectively. The measurement results were compared with mechanical properties of the TGOs and bulk α-Al 2 O 3 ceramics reported in the literature to develop a mechanistic understanding of the microstructural features governing the stiffness and fracture toughness of the TGO. • Mechanical properties of a TGO have been measured by micro-beam bending. • Basal texture reduces the stiffness of the TGO. • The TGO has higher fracture toughness than bulk α-Al 2 O 3 ceramics. [ABSTRACT FROM AUTHOR]

The main goal of this work is to obtain a reliable value of the fracture toughness of single grains of tungsten carbide (WC). It is attempted by testing microcantilever and micropillar samples shaped out, by means of focused ion beam milling, of individual WC particles embedded within a WC-Co cemented carbide grade. Experimental testing included the use of a nanoindenter for inducing microcantilever bending and micropillar splitting, as well as sampling WC grains with basal and prismatic orientations. Experimental results are compared with those previously assessed through implementation of the indentation microfracture technique. Bending of notched microcantilevers yielded more consistent results than those measured out of micropillar splitting tests. In this regard, the average value of fracture toughness for single WC grains, within the two-phase interpenetrated network existing in cemented carbides, is found to be 5.6 ± 0.8 MPa·m1/2. Such a relatively high value – coherent with local plastic features evidenced in nanoindentation imprints - is in satisfactory agreement with results indirectly estimated from other macromechanical tests. • Fracture toughness of single WC grains is measured by micromechanical methods. • Microcantilevers produce the most consistent results. • Fracture toughness of WC grains of cemented carbides, is found to be 5.6 MPa·m1/2. [ABSTRACT FROM AUTHOR]