Quantitative three-dimensional characterization of critical sizes of non-spherical TiO2 nanoparticles by using atomic force microscopy

Since both size and shape of nanoparticles are challenging to be quantitatively measured, traceable 3D measurements are nowadays an issue. 3D nanometrology plays a crucial role to reduce the uncertainty of measurements, improve traceable calibration of samples and implement new approaches, models, and methodologies in the study of the nanomaterials. AFM measurement of nanoparticles with unusual shape represent a non-trivial challenge due to the convolution with the finite size of the tip. In this work, geometric approaches for the determination of critical sizes of TiO2 anatase bipyramids and nanosheets are described. An uncertainty budget is estimated for each nanoparticle size with the aim of assessing the different sources of error to obtain a more reliable and consistent result. The combined standard uncertainties are respectively less than 5% and 10% of the dimensions of bipyramids and nanosheets. Due to the stability and monomodal distribution of their critical sizes, bipyramids and nanosheets are suitable to apply as candidate reference materials at the nanoscale. Moreover, quantitative measurements of shape and texture descriptors are discussed in order to understand the quality of the synthetized batch

Nanoindentation characterization of clay minerals and clay-based hybrid bio-geomaterials

Layered hydrous aluminosilicates are key constituent minerals in rocks, soils, and other parts of the Earth crust. Understanding mechanical properties of these aluminosilicates is crucial for seismic study, stability of parent rocks and geomaterials, and for geophysical subsurface exploration. Recently, growing prospects of clay based nanocomposites have renewed further interest in understanding the fundamental elastic and plastic properties of hydrous aluminosilicates. Their distinct, nanoscale layered crystal structure is known to result in anisotropic responses to loading, however, owing to their tiny sizes; it is a significant challenge to determine the anisotropic properties. There is a little data available in the literature on the elastic and plastic properties of clays and clay-based geomaterials. This Ph.D. research work has undertaken the novel approach to study mechanical properties of geomaterials using a pioneering nanomechanical testing method, nanoindentation, to probe the elastic and plastic properties at nano/micro scale. Genesis of these nanomechanical properties are analyzed in the light of microstructures, interatomic bonds, mineralogical and chemical composition. A nanoindentation study of muscovite mica revealed highly anisotropic behavior. Both elastic and plastic anisotropy exist for indentation normal and perpendicular to the basal plane. Nano-mechanical behavior of the well-ordered, nanocrytalline clay minerals is, mainly, governed by generation and storage of dislocations, formation and annihilation of kink bands and intermittent kink bands. Interpretations of indentation test based on continuum mechanics and gradient plasticity models, therefore, give satisfactory result. On the other hand, chemical, morphological, microstructural and structural characterization of a hybrid clay-lime-starch bio nanocomposite material revealed highly heterogeneous, amorphous and multi-phase matrix. Statistical analysis of the massive volume of data obtained using grid indentation technique revealed that this matrix is composed of five distinct mechanical phases. Thus, this study proposes that slow and weak pozzolanic reaction between clay and lime produces cementitious binder network consisting of C-S-H phase. Interaction of the biopolymer (sticky rice) with clay and C-S-H resulted in intercalated nanocomposites that have superior mechanical and barrier properties. Clay, sand, and silt particles act as active fillers in this composite, whereby forming a dense and compact mass, which renders durability and toughness to this hybrid composite

Investigation of the Surface Mechanical Properties of Single Crystal ZnO by Nanoindentation

Mechanical and Aerospace Engineerin

Modeling of friction-induced deformation and microstructures.

Frictional contact results in surface and subsurface damage that could influence the performance, aging, and reliability of moving mechanical assemblies. Changes in surface roughness, hardness, grain size and texture often occur during the initial run-in period, resulting in the evolution of subsurface layers with characteristic microstructural features that are different from those of the bulk. The objective of this LDRD funded research was to model friction-induced microstructures. In order to accomplish this objective, novel experimental techniques were developed to make friction measurements on single crystal surfaces along specific crystallographic surfaces. Focused ion beam techniques were used to prepare cross-sections of wear scars, and electron backscattered diffraction (EBSD) and TEM to understand the deformation, orientation changes, and recrystallization that are associated with sliding wear. The extent of subsurface deformation and the coefficient of friction were strongly dependent on the crystal orientation. These experimental observations and insights were used to develop and validate phenomenological models. A phenomenological model was developed to elucidate the relationships between deformation, microstructure formation, and friction during wear. The contact mechanics problem was described by well-known mathematical solutions for the stresses during sliding friction. Crystal plasticity theory was used to describe the evolution of dislocation content in the worn material, which in turn provided an estimate of the characteristic microstructural feature size as a function of the imposed strain. An analysis of grain boundary sliding in ultra-fine-grained material provided a mechanism for lubrication, and model predictions of the contribution of grain boundary sliding (relative to plastic deformation) to lubrication were in good qualitative agreement with experimental evidence. A nanomechanics-based approach has been developed for characterizing the mechanical response of wear surfaces. Coatings are often required to mitigate friction and wear. Amongst other factors, plastic deformation of the substrate determines the coating-substrate interface reliability. Finite element modeling has been applied to predict the plastic deformation for the specific case of diamond-like carbon (DLC) coated Ni alloy substrates

Técnicas de indentación aplicadas al estudio de propiedades mecánicas de recubrimientos cerámicos de nitruro de titanio

Este trabajo trata con el estudio de la respuesta mecánica de Nitruro de Titanio (TiN) a situaciones de contacto estático con indentadores Vickers y Rockwell C Se depositaron capas de TiN sobre aceros M2 y 304L a través del proceso de Arco-PAPVD. Para este propósito se utilizaron dos equipos: un reactor comercial de marca Balzers y uno experimental. Las probetas fueron sometidas a ensayos de indentación estática con cargas entre 5 mN y 1500 N, aplicadas por medio de un nanoindentador Fisher H 100V y equipos de indentación convencional equipados con indentadores Vickers y Rockwell C. Las indentaciones permitieron obtener la dureza y módulo de elasticidad de las capas y sustrato y su variación con el desplazamiento relativo del indentador (RID). La microestructura de estos sistemas, espesor de las capas, patrones de agrietamiento fueron obtenidos a través de microscopía electrónica de barrido (MEB), microscopía e fuerza atómica (MFA), difracción de rayos X (DRX) y ensayos Calo-test. En el caso de los sistemas recubiertos en el reactor experimenta, se tuvieron problemas con la medición de la dureza y módulo de elasticidad debido a la redondez de la punta del indentador y la hereogeneidad en la microestructura y espesor de las capas. Los valores de dureza y modulo de elasticidad medidos en las capas depositadas en el reactor Balzers, fueron de aproximadamente 25 GPa y 400 GPa. Las curvas (RID) mostraron una variación de estas propiedades y mostraron ser una herramienta importante para el desempeño de estas capas. Además las curvas (P-h^2), (P-h^1.5) y (P-h) permitieron correlacionar los patrones de agrietamiento generados durante los ensayos, con la capacidad de estos sistemas para sostener cargas y la posibilidad de agrietamiento. Los ensayos de indentación Rockwell C permitieron medir la adherencia de las capas al sustrato. Todos estos resultados indican que los sistemas M2-TiN se comportan mejor que los 304L-TiN, y estos a su vez que los depositados en el reactor experimental. También se demostró que algunos modelos estudiados para la medición de Kc, and Kc^INT de las capas e intercara respectivamente, no son adecuados para este propósito en los sistemas fabricados. Esto debido a la diferencia entre los patrones de agrietamiento en que los modelos se basan y los obtenidos.Abstract : This work was concerned with the study of the mechanical response of Titanium Nitride (TiN) films during Rockwell and Vickers static indentations. TiN films were deposited onto M2 and 304L steels through Arc-Plasma Assisted Physical Vapor Deposition (PAPVD) process. For this purpose two equipments were used: A commercial Balzers reactor and an experimental reactor. Specimens were subjected to static indentation with loads between 5 mN and 1500 N, applied in either a Fischer H100V nanoindenter or conventional hardness equipments with Vickers and Rockwell indenters. Indentations allowed obtaining the hardness and Young’s modulus of films and substrate, and their variation with the relative indenter displacement (RID). The microstructure of these systems, film thickness and crack patterns were assessed by scanning electron microscopy (SEM), atomic force microscopy (AFM), X ray diffraction (XDR) and Calo-test. In the case of coatings obtained in the experimental reactor, problems due to tip roundness, in-homogeneity in microstructure and films thickness avoided to measure hardness and elastic modulus of the films. The Measured hardness values of TiN films deposited in the Balzers reactor were about 25 GPa and Elastic modulus of 400 GPa. The (RID) plots showed a variation of these properties and became an important tool to evaluate the performance of these systems. Besides, (P-h2), (P-h1.5) and (P-h) plots allowed to relate the crack patterns generated during tests to both the capacity of these systems to sustain loads and cracking. Also Rockwell C indentations allowed to measure the adherence of these films to substrate. The results showed that the M2-TiN systems performed better than the 304L-TiN systems, while the behavior of the systems obtained in the experimental reactor was always worse. It was also demonstrated that some proposed models for the evaluation of Kc and KcINT of films and interface respectively, are not suitable in the systems studied in this investigation. This is due to the difference between the crack patterns assumed in the models and those actually observed in the specimens.Maestrí