Search

Detailed structural and chemical analyses reveal that Ti-Si-N coatings prepared with high nitrogen partial pressure and temperature are composed of nm-sized (nearly equiaxed) TiN crystallites encapsulated by ~1.0 nm thin Si-rich tissue phase. This nanocomposite structure allows for superior hardness (37.6 ± 1.5 GPa) and fracture toughness (4.5 ± 0.6 MPa√m). Contrary, deposition at lower nitrogen partial pressure and temperature does not allow for such a clear Si segregation during film growth, leading to nm-sized solid solution Ti 1-x Si x N crystallites. Although having the same Si content of 8.5 at.%, their hardness (32.1 ± 0.9 GPa) as well as fracture toughness (3.0 ± 0.2 MPa√m) is significantly lower. Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract: An experimental study with total 504 specimens has been carried out to investigate the fracture and physical properties of the carbon anode materials. The specimens were sampled from anodes produced with machined stub holes. From normal-and Weibull analysis the fracture toughness and the tensile strength showed a clear temperature dependency and orthotropic behavior. It has been found that both the fracture toughness and tensile strength increases with the temperature and are larger for the specimens directed in the horizontal direction than in the vertical direction. The variation in the tensile strength within an anode decreased with the temperature but the variation in the fracture strain increased. The tensile strain appears to be only dependent on the temperature and insensitive to the routine anode properties of the anode material. A multivariate linear regression analyses of the fracture toughness and tensile strength has been conducted and a typical correlation of R 2 =0.5 (R is the Coefficient of Determination) to the measured routine anode properties was found. The thermal expansion coefficient is also larger in the vertical anode direction which makes the crack initiation more sensitive to temperatures. The orthotropic studies also showed that the air permeability has a tendency to be larger in the horizontal direction in the upper part of the anode which can induce unnecessary burning from the anode sides. The influence of the processing parameters in the paste plant and baking furnace has not been presented in this paper. [Copyright &y& Elsevier]

TiN/AlN superlattice coatings combine the superlattice effect and the outstanding properties of AlN in its non-equilibrium face-centred cubic (NaCl-type, rs) structure. In comparison with their non-layered counterparts, the superlattice films exhibit superior and strongly bilayer-period-dependent mechanical properties. Here we analyse the structure and mechanical properties of superlattices with AlN layer thicknesses of 0.9, 1.2, and 1.5 nm and different TiN layer thicknesses. We found that the maximum AlN layer thickness, up to which AlN can be fully stabilized in its metastable rs structure, depends on the substrate material and is at least 1.5 nm for coatings on MgO (100) and 0.9 nm for the coatings grown on Si (100) or Al 2 O 3 1 1 ¯ 02. Our data also show that with increasing thickness of the template layer, the crystallization of AlN in the stable wurtzite structure is favoured. TiN/AlN superlattice coatings on MgO (100) exhibit the highest hardness values, peaking at 37.0 ± 0.5 GPa for AlN layer thicknesses of 0.9 nm and a bilayer period of 2.5 nm. Films with ultra-small bilayer periods exhibit high hardness combined with low values of elastic modulus suggesting a high elastic-strain-to-failure for these coatings. The highest toughness was found for superlattice films grown on MgO (100), scaling inversely with the bilayer period. • Growth on MgO (100) maximizes the thickness of the cubic AlN layer. • Thicker template layers promote crystallization of phases in their stable structure. • TiN/AlN superlattices grown on MgO (100) exhibit superior mechanical properties. • Fracture behaviour indicates deformation-induced phase transformation. [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]

In contrast to earlier work, where we focused on the evolution of fracture toughness upon annealing of free-standing Ti-Al-N films using cantilever bending experiments, here we study the practically more relevant case of thin Ti-Al-N films firmly attached to a stiff substrate. We found - experimentally and by continuum mechanics modelling using the Transformation Field Analysis - that the formation of even tiny fractions of hcp (ZnS-wurtzite type) AlN during decomposition of supersaturated fcc (NaCl-type) Ti-Al-N gives rise to high in-plane compressive stresses in both the matrix and the precipitates. These eigenstresses impede the formation and propagation of cracks as evidenced by cube corner nanoindentation experiments – the measured fracture toughness (K IC ) increases from the as-deposited value of ∼4.4 MPa√m to ∼8.0 MPa√m when annealed at 900 °C. The (apparent) toughening effects combine with less pronounced inherent toughening and concomitant age hardening effects to enhanced damage tolerance of annealed Ti-Al-N. [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]