Crystalline Imperfections: Key Topics in Materials Science and Engineering

Crystalline Imperfections: Key Topics in Materials Science and Engineering deals with the practical aspects of compositional and structural imperfections, how they are controlled, and how they influence material properties and behaviors. The book is organized into two sections, the first of which is a tutorial on compositional impurities and different types of crystal lattice defects. The section that follows, the focal point of the book, furthers the learning process by guiding readers through a series of real-world problems and their respective solutions. The content of this book and its presentation format are particularly well suited for early-career engineers who would like to sharpen their understanding of physical metallurgy and its application in design and manufacturing.

Crystal Structure Defects and Imperfections

Alloying, heat treating, and work hardening are widely used to control material properties, and though they take different approaches, they all focus on imperfections of one type or other. This chapter provides readers with essential background on these material imperfections and their relevance in design and manufacturing. It begins with a review of compositional impurities, the physical arrangement of atoms in solid solution, and the factors that determine maximum solubility. It then describes different types of structural imperfections, including point, line, and planar defects, and how they respond to applied stresses and strains. The chapter makes extensive use of graphics to illustrate crystal lattice structures and related concepts such as vacancies and interstitial sites, ion migration, volume expansion, antisite defects, edge and screw dislocations, slip planes, twinning planes, and dislocation passage through precipitates. It also points out important structure-property correlations.

Structural Imperfections of the Hydroxyapatite Surface Layer to Engineer Its Electrical Potential

The Doctoral Thesis aims to identify the influence of hydroxyapatite (Hap) defects (such as OH-group, H-, O-vacancies, H-interstitials, and their combination) on the electrical potential of HAp’s surface which influences biocompatibility and control cell adhesion. HAp contains various structural imperfections (defects) and has a non-stoichiometric composition. The structural imperfections induce the heterogeneity of the surface electrical potential. However, the role of the defects OH-group, H-, O-vacancies, H-interstitials, and their combination in the formation of HAp surface polarization and their influence on HAp surface charge, energy band structure and electron work function has not yet been investigated. In this Thesis, for the first time the theoretical and experimental approaches were used to investigate the influence of structural imperfections (OH-, H-, O-vacancies, H-interstitials, and hydrogen atoms filling unsaturated hydrogen bonds) on HAp electrical properties. The computer simulations of HAp structures analyse the properties of these effects. Semiempirical methods of molecular mechanics and quantum mechanics, as well as methods of density functional theory were employed. The experimental studies of the HAp surface electrical properties were carried out by photoluminescence (PL) emission, synchrotron excitation spectroscopy, threshold photoelectron (PE) emission spectroscopy. The influence of annealing, hydrogenation, microwave, gamma irradiation and their combination on HAp defects was investigated experimentally for the first time. The obtained results are in accordance with computational data. The achieved results will help to improve technologies to engineer the surface charge of Hap.

Aluminium Alloy Foam Modelling and Prediction of Elastic Properties Using X-ray Microcomputed Tomography

X-ray microcomputed tomography has been gaining relevance in the field of cellular materials to characterize materials and analyse their microstructure. So, here, it was used together with finite element modelling to develop numerical models to estimate the effective properties (Young’s modulus) of aluminium alloy foams and evaluate the effects of processing on the results. A manual global thresholding technique using the mass as a quality indicator was used. The models were reconstructed (Marching Cubes 33), then simplified and analysed in terms of mass and shape maintenance (Hausdorff distance algorithm) and face quality. Two simplification procedures were evaluated, with and without small structural imperfections, to evaluate the impact of the procedures on the results. Results demonstrate that the developed procedures are good at minimizing changes in mass and shape of the geometries while providing good face quality, i.e., face aspect ratio. The models are also shown to be able to predict the effective properties of metallic foams in accordance with the findings of other researchers. In addition, the process of obtaining the models and the presence of small structural imperfections were shown to have a great impact on the results.

Global optimization of an encapsulated Si/SiO$$_2$$ L3 cavity with a 43 million quality factor

We optimize a silica-encapsulated silicon L3 photonic crystal cavity for ultra-high quality factor by means of a global optimization strategy, where the closest holes surrounding the cavity are varied to minimize out-of-plane losses. We find an optimal value of $$Q_c=4.33\times 10^7$$ Q c = 4.33 × 10 7 , which is predicted to be in the 2 million regime in presence of structural imperfections compatible with state-of-the-art silicon fabrication tolerances.

Influence of imperfections in the buckling resistance of steel beam-columns under fire

This paper presents an investigation on the influence of structural imperfections on the ultimate load capacity of steel welded beam-columns with class 4 cross-section under elevated temperatures. This is done by considering different amplitudes for the global and local (plate) imperfections, and different residual stresses distributions available in the literature. To this purpose, a geometrically and materially non-linear finite element model using Abaqus software has been used to determine the buckling resistance of a steel welded beam-column at elevated temperatures, using the material properties of EN1993-1-2. The imperfection sensitivity of beam-columns is reported: the influences of the amplitudes of the geometric imperfection and the patterns of the residual stress on the load capacity are compared.

Global optimization of an encapsulated Si/SiO2 L3 cavity with a 43 million quality factor

We optimize a silica-encapsulated silicon L3 photonic crystal cavity for ultra-high quality factor by means of a global optimization strategy, where the closest holes surrounding the cavity are varied to minimize out-of-plane losses. We find an optimal value of Qc = 4.33 × 107 , which is predicted to be in the 2 million regime in presence of structural imperfections compatible with state-of-the-art silicon fabrication tolerances.