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This research shows different hard Ti-based coatings deposited over steel substrates using the physical vapor deposition (PVD) method. The graded coating of the three produced Ti, TiN and TiCN were assessed using phase composition analysis and spectroscopy study. The microstructure characterization was studied by X-ray Photoelectron spectroscopy (XPS), Scanning Electron Microscopy (SEM), and transmission electron microscopy (TEM). The results show that integrating Ti interlayer with subsequent TiN/TICN layers can be considered a suitable way to yield hard Ti-based coating with enhanced mechanical and tribological behavior due to nitride and carbonitride phases formed from the breakdown of carbon and nitrogen atoms. The elastic modulus and hardness of all layers were identified by nanoindentation and utilized to achieve yield strength. Later, the curvature of the unloading step and elastic properties are used for finding flow behavior parameters in terms of work hardening factors (n and K). The attained findings extracted from the load–displacement curve of both nanoindentation and nano scratch were analyzed to examine the microscopic performance of all three Ti, TiN, and TiCN coatings. Scratch mechanisms analysis in all coatings shows that the main failures in samples are caused by tensile stress stemming from Hertzian cracks. However, as the force increases, the coating surface undergoes an incremental deformation, and failure mode varies to interfacial spallation.

Monolithic metal-organic frameworks (MOFs) represent a promising solution for the industrial implementation of this emerging class of multifunctional materials, due to their structural stability. When compared to MOF powders, monoliths exhibit other intriguing properties like hierarchical porosity, that significantly improves volumetric adsorption capacity. The mechanical characterization of MOF monoliths plays a pivotal role in their industrial expansion, but so far, several key aspects remain unclear. In particular, the fracture behavior of MOF monoliths has not been explored. In this work, we studied the initiation and propagation of cracks in four prototypical MOF monoliths, namely ZIF-8, HKUST-1, MIL-68 and MOF-808. We observed that shear faults inside the contact area represent the main failure mechanism of MOF monoliths and are the source of radial cracks. MIL-68 and MOF-808 showed a remarkably high resistance to cracking, which can be ascribed to their consolidated nanostructure.

KDP single crystals are widely used in inertial confinement fusion and high power lasers due to the wide transmission band, high laser damage threshold, large nonlinear optical coefficient, etc. However, surface and subsurface damages are easily induced into the KDP crystal components during the machining process due to its high brittleness and distinct anisotropy. These damages will reduce the service accuracy and life of KDP crystal components. It is of great significance to study the brittle-to-ductile transition of KDP crystals to achieve high efficiency and precision machining of crystal components. In this work, a theoretical model of brittle-to-ductile transition load during the nanoindentation and nanoscratch processes of KDP crystals was established based on the energy conservation law and dislocation theory. This model took the anisotropy of KDP crystals into account. Nanoindentation and nanoscratch experiments by using different indenters were performed to verify the theoretical model of brittle-to-ductile transition load. The experimental results of the brittle-to-ductile transition load agreed well with the theoretical results, which indicated that the model was reliable. Both experimental and theoretical results showed that the critical load of brittle-to-ductile transition during the nanoindentation and nanoscratch processes increased as the half cone angle increased. In addition, the critical load of brittle-to-ductile transition load of the scratch was lower than that of the indentation under the same condition. The results also demonstrated that KDP crystals had distinct anisotropy during the nanoindentation and nanoscratch process. Brittle fracture was most likely to occur along [100] orientation during the scratch process. Under the same scratching condition, [110] orientation was prone to achieving ductile machining with high surface quality compared with other orientations.

Objectives: The aim of this study was to investigate the wear behavior of Dentinogenesis imperfecta type II (DGI-II) dentin and elucidate the correlation between its tribological properties and components., Methods: The mid-coronal dentin of normal and DGI-II teeth were divided into two groups: perpendicular and parallel to the dentin tubules. The microstructure of dentin was detected using atomic force microscopy (AFM). The wear behavior of dentin was evaluated by nanoscratch tests and scanning electron microscopy (SEM). Meanwhile, changes in molecular groups and chemical composition were analyzed by Raman and Energy-Dispersive X-ray (EDX) tests, respectively. Nanohardness was also evaluated., Results: AFM images of DGI-II dentin illustrated a decrease in the number of tubules and the tubule diameter. Nanoscratch test showed a higher friction coefficient and a greater depth-of-scratch in DGI-II dentin. The wear resistance of DGI-II dentin was reduced independent of tubule orientation. EDX results indicated that DGI-II dentin mineral content decreased and Raman spectra results showed DGI-II dentin had a decreased collagen matrix structure stability coupled with hypomineralization. Furthermore, a significant reduction in nanohardness and elastic modulus of DGI-II dentin was observed. Regression analysis revealed a close correlation between dentin components and inferior wear resistance., Conclusions: All results indicated the wear behavior of DGI-II dentin was significantly deteriorated, presumably caused by the disorder in microstructures and the reduction of chemical composition., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Ag-doped Cr/DLC coatings were deposited on medical grade 316 LVM stainless steel using DC magnetron sputtering. Morphological study of the coating indicated the formation of island of Ag clusters owing to the inability of Ag to form carbides, which is also corroborated from the XRD analysis. The composite coating showcased elastic nature suggestive from the p-h curve obtained from the nanoindentation test. However, the coating possesses 33% ductility, which is an important virtue for stress relieving attributed to Ag in the carbon matrix. The coating registered improved adhesion due to Cr 3 C 2 carbide formation in the interlayer. The composite coating was subjected to lubricated sliding in physiological fluid against carbon fiber reinforced PEEK (CFRPEEK) friction pair to realize a closer scenario to hip implant articulation. A lubricious film of Ag with scattered particles of PEEK was formed in the sliding interface resulting in a long run-in process during sliding. The composite coating suffered mild wear on the Ag-doped DLC top layer with few gullies of wear scar deep into the interlayer due to graphitization of carbon in the film. A statistically significant difference was observed in the hardness, H 3 /E 2 , elastic work, and plastic work; however, there was no statistically significant difference in H/E attribute between the unworn and worn surface. What is more, Raman spectra of the worn (I D /I G  = 1.9 ± 0.2) and unworn surface (I D /I G  = 2.1 ± 0.1) were indicative of no significant loss in the structural integrity of the composite coating., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

This research uses quasi-static nanoindentation and nanoscratching to quantify human tooth deformation as a function of enamel rod and dentin tubule orientations at the nanoscale. Nanoindentation tests were performed on enamel and dentin to determine elastic modulus, hardness, and observe fracture. Additionally, nanoscratch tests were performed to determine pileup geometry and parameters such as recovery, scratch hardness, and scratch roughness. In enamel, it was found that nanofiber orientation gives rise to unique microcrack propagation and nanofiber behavior that affect these properties. For dentin, densification and organic content affect these properties., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Chitosan (CS) is a biomaterial that offers many sophisticated and innovative applications in the biomedical field owing to its excellent characteristics of biodegradability, biocompatibility and non-toxicity. However, very low mechanical properties of chitosan polymer impose restriction on its further development. Cross-linking and nanoparticle reinforcement are the two possible methods to improve the mechanical properties of chitosan films. In this research, these two methods are adopted individually by using tripolyphosphate as cross-linker and nano-hydroxyapatite as particle reinforcement. The nanomechanical characterizations under static loading conditions are performed on these modified chitosan films. It is observed that nanoparticle reinforcement provided necessary mechanical properties such as ductility and modulus. The mechanisms involved in improvement of mechanical properties due to particle reinforcement are studied by molecular dynamics (MD). Further, improvement in mechanical properties due to combination of particle reinforcement and cross-linking agent with chitosan is investigated. The stress relaxation behavior for all these types of films is characterized under dynamic loading conditions using dynamic mechanical analysis (nanoDMA) experiment. A viscoelastic solid like response is observed for all types of film with modulus relaxing by 3-6% of its initial value. A suitable generalized Maxwell model is fitted with the obtained viscoelastic response of these films. The response to nano-scratch behavior is also studied for particle reinforced composite films., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

In this study, HA is superplastically embedded into Titanium substrate and the sample is subsequently deformed superplastically until 70% deformation degree. The former process is termed as superplastic embedment (SPE) while the later as superplastic deformation (SPD). After the SPE, HA is successfully embedded into the substrate, forming a layer with a thickness of about 249 nm. After the SPD the embedded HA layer thickness decreases to 111 nm. The SPD sample is then immersed in simulated body fluid (SBF) to evaluate its biological properties. A newly grown apatite is formed as a result of the immersion and the HA layer thickness increases with immersion time. The cohesion and adhesion strength within the HA coating and coating-substrate interface of the SPD samples before and after immersion in the SBF is evaluated through the nanoscratch test technique. The results indicate that the HA layer after SPD is still strong even though after being exposed in SBF environment for quite some time. The study suggests that the superplastically embedded HA nanolayer is still intact mechanically and functioning appropriately as biological activity base even after the SPD process., (Copyright © 2014 Elsevier B.V. All rights reserved.)