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~6nm. For ultrathin layers (Λ~2nm), 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.
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Hard coatings used to protect engineering components from external loads and harsh environments should ideally be strong and tough. Here we study the fracture toughness, K
, of Ti
Al
N upon annealing ...by employing micro-fracture experiments on freestanding films. We found that K
increases by about 11% when annealing the samples at 900 °C, because the decomposition of the supersaturated matrix leads to the formation of nanometer-sized domains, precipitation of hexagonal-structured B4 AlN (with their significantly larger specific volume), formation of stacking faults, and nano-twins. In contrast, for TiN, where no decomposition processes and formation of nanometer-sized domains can be initiated by an annealing treatment, the fracture toughness K
remains roughly constant when annealed above the film deposition temperature. As the increase in K
found for Ti
Al
N upon annealing is within statistical errors, we carried out complementary cube corner nanoindentation experiments, which clearly show reduced (or even impeded) crack formation for annealed Ti
Al
N as compared with their as-deposited counterpart. The ability of Ti
Al
N to maintain and even increase the fracture toughness up to high temperatures in combination with the concomitant age hardening effects and excellent oxidation resistance contributes to the success of this type of coatings.
In the Cu–Cr system, the formation of supersaturated solid solutions can be obtained by severe plastic deformation. Energy-dispersive synchrotron diffraction measurements on as-deformed Cu–Cr samples ...as a function of the applied strain during deformation confirm the formation of supersaturated solid solutions in this usually immiscible system. Due to evaluation of the diffraction data by a newly developed energy-dispersive Rietveld program, lattice parameter and microstructural parameters such as domain size and microstrain are determined for as-deformed as well as annealed samples. The obtained information is used to deepen the understanding of the microstructural evolution and the formation of supersaturated solid solutions during severe plastic deformation. Complimentary transmission electron microscopy investigations are furthermore performed to characterize the evolving microstructure in detail. After annealing at elevated temperatures, the formed solid solutions decompose. Compared to the as-deformed state, an enhanced hardness combined with a high thermal stability is observed. Possible mechanisms for the enhanced hardness are discussed.
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•High entropy nitride coatings were deposited by reactive DC magnetron sputtering.•Silicon addition leads to decreased indentation modulus.•30% higher elastic deformability with Si, ...leading to increased damage tolerance.
We present micromechanical experiments of DC magnetron sputtered high-entropy nitride thin films, single-phase (Al,Ta,Ti,V,Zr)N with nearly equimolar metal-fractions, and of their Si-alloyed variant. The (Al,Ta,Ti,V,Zr)N coating exhibits a hardness of ∼30 GPa and a fracture toughness of 2.4 MPa√m. Alloying this high-entropy nitride with ∼5 at% Si does not influence the hardness and fracture toughness but lowers significantly the elastic response. Consequently, the elastic strain to failure increases by more than 30% leading to a significantly improved damage tolerance for the Si alloyed (Al,Ta,Ti,V,Zr)N.
•Study provided first estimate of dietary exposure to mycotoxins in Lebanese adults.•Exposure to DON exceeds the toxicological reference value (TRV).•The excessive consumers’ exposure to OTA ...approaches the TRV.•Exposure to AFB1 and AFM1 exceed that reported by several countries.•Findings place Lebanon among countries highly exposed to mycotoxins through the diet.
Exposure to mycotoxins may be associated with carcinogenic, immunosuppressant and estrogenic effects. In the Middle-East, studies investigating food contamination and dietary exposure to mycotoxins are particularly scarce. This study aims at evaluating the dietary exposure of an adult Lebanese urban population to four mycotoxins (AFB1, AFM1, OTA, DON) classified as priority food contaminants by the WHO. Dietary exposure assessment was performed by means of the total diet study approach. Average and excessive consumer exposure estimates (p95) were calculated and compared with appropriate toxicological reference values (TRVs). Average dietary exposure levels to OTA and DON represented 29.9% and 156.8% of the respective TRVs, with the p95 exposure estimates approaching or exceeding the TRVs for these mycotoxins (95.1% and 355.8%, respectively). Based on the mean dietary exposure level to AFB1, cancer risk was estimated at 0.0527–0.0545cases/100,000persons/year, while mean exposure to AFM1 was associated with a population risk of 0.0018–0.0027cases/100,000persons/year. The study’s findings place Lebanon among countries that are highly exposed to mycotoxins through the diet and call for larger-scale studies aiming at providing a comprehensive assessment of the dietary exposure of the Lebanese population to mycotoxins as well as to other food contaminants.
The thermal expansion coefficient of nanocrystalline materials and its dependence on grain size was investigated in two different model systems, soft metallic Cr and hard ceramic CrN thin ...nanocrystalline films, both composed of grains having a cubic structure and sizes ranging between 10 and 30
nm. The dominant contribution to the enhancement of thermal expansion in nanocrystalline materials with respect to their coarse-grained counterparts was identified in the interfacial area containing weakly bonded atoms. Based on the experimental results a model is proposed which aids in understanding the thermal expansion of nanocrystalline solids and of the origin and development of thermal stress in thin nanocrystalline films. This model was experimentally validated by the correlation between the thermal expansion coefficient and the material grain size, which was controllably varied by the film deposition process, coating architecture and thermal treatment. The number of atoms in grain boundaries and their bonding character were, in addition, found to be crucial for the development of intrinsic stress. Its increase with increasing volume fraction of grain boundaries is attributed to the enhanced diffusional flux of weakly bonded surface adatoms into this area and enhanced defect generation due to the higher sensitivity of grain boundary atoms to displacement by incident particles.
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 6.0nm, 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 KIC 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.
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•The effect of annealing on hardness and KIC of CrN/TiN superlattices was studied.•Due to recovery effects the hardness steadily decreases with increasing Ta.•The fracture toughness dependence does not entirely follow this trend.•For larger bilayer periods (18nm) KIC increases with increasing Ta.•A mechanism addressing this behaviour is proposed.
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 KIC, 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 KIC. 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.
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•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.
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 Al2O311¯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.
In recent years, 3D printing has undergone a transformational journey – from prototyping technology, limited to laboratories, to a production method used in industry – becoming a powerful tool for ...creating functional objects. Despite this progress, 3D printing faces ongoing challenges related to defect detection and print quality control. We present an innovative, non-contact, fast and cheap microwave sensor for detecting defects in printed components, related to both mechanical errors and conductivity inhomogeneities. We discuss in detail the methodology of the microwave surface mapping technique and the results obtained for several samples printed with popular filaments. Tests show the ability to detect faults with millimetre precision. The simple design of the entire quality control module allows for easy integration with various types of 3D printers, from popular ones used by hobbyists to professional, highly specialised ones.
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