Analysis of the formed track in solid state materials using atomic force microscopy

The track formation in solid state materials, from the theoretical point of view, is still under study. One way to understand the track formation mechanisms and radiation damage of the charged particles in some materials such as polymers, glasses and minerals, is to analyse the surface topography effects. In this work, the track formation analysis in polycarbonate material is presented using an atomic force microscope (AFM) to characterise the evolution of the track on the material surface and beyond a thin layer of the surface material. The AFM is very useful to obtain valuable information at the level of the atomic structure of the materials and of the nuclear tracks, due to its high resolution and very easy operation involving also a simple sample preparation. The results show the development of the formed track by means of induced surface effects after being exposed to ionising radiation and chemical etching.     

Experimental evidence and physical models of fatigue crack initiation

Results of the study of the early fatigue damage in a number of model and structural crystalline materials using modern experimental techniques are presented. The dislocation structure of the persistent slip bands and the evolution of the surface relief resulting in the formation of persistent slip markings during cyclic loading are documented. The dislocation mechanisms leading to production of point defects in cyclic loading are described and point defect production and annihilation rates are derived. The kinetics of point defect migration is characterized. The physically based models of the surface relief formation describing the formation of extrusions and intrusions are presented. The models are confronted with experimental evidence. It is concluded that intrusions representing sharp surface crack-like defects play the principal role in the initiation of fatigue cracks.     

Experiments on Photographic Sensitivity

The methods used for preparing thin sheets of silver chloride, silve r bromide, binary and ternary mixed crystals of silver halides, and mixed crystals of silver bromide with silver sulphide and other metallic bromides are described in detail. The results of expriments on the chemical sensitization of these materials are presented. The conclusion has been reached that, as far as the formation and development of the latent image is concerned, there is no significant increase in the sensitivity of the mixed crystals compared with that of strained crystals of pure silver bromide. Experiments with antifogging agents, antiplumming agents, development accelerators and dye sensitizers and supersensitizers are briefly described , The causes of low intensity reciprocity failure in the formation of the surface and internal latent images in the thin sheets are discussed in detail and methods which may be used to diminish low intensity failure in the formation of the surface latent image are outlined.     

Influence of Vibroshock Interaction Between a Cutting Tool and the Processed Billet on the Conditions of Formation of Its Roughness in Mechanical Sawing of Brittle and Hard Materials

A modernized unit of the ShP-2 sawing machine for vibroshock sawing of hard and brittle materials in three modes of vibrodrive operation has been described. The mechanism for forming the roughness of the sawn surface is presented. The data that allow judgment on the effect of the vibroshock mode of processing brittle materials on the parameters characterizing initial roughness of the sawn surface are obtained from results of the experiments. Based on these data, formation of the topography of the processed parts of billets made from a hard material is analyzed. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 3, pp. 171–176, May–June, 2005.     

Duality in Metal Cutting: Impact to the Surface Layer Residual Stress

This paper concerns the residual stress formation during the processes of rigid kinematics mechanical surface treatment. Taking conventional turning as example, we examine the features of the deformation zone, which cause the principal residual stress deviation from speed and feed directions and their in-depth rotation governing in-plane shear residual stress formation. Three stress components of the plane residual stress state are presented as functionally combined. The existence of materials providing residual stress distribution by principally different ways is theoretically predicted. The formation of the residual stress states of different types is confirmed by experimental results. A hypothesis based on the simple shear cutting deformation approach is advanced to explain the revealed relationships.     

表面纳米化对金属材料耐磨性的影响

材料的磨损起源于表面,金属材料的摩擦磨损性能与表面结构密切相关。利用表面纳米化(Surface nanocrystallization)技术可以在金属材料的表面制备出一定厚度的纳米结构表层,从而大大提高金属的耐磨性。结合国内外学者的研究报道,综述了表面纳米化在金属耐磨性方面的影响,讨论了表面纳米化方法与机理以及表面纳米化影响耐磨性的因素,简述了应用表面纳米化技术改善各种金属材料耐磨性的研究和实用成果,最后进行了总结和展望。     

Dislocation-assisted crack propagation in zinc

The basal cleavage surface energy of pre-deformed zinc crystals has been shown to be a factor of twenty times smaller than the thermodynamic value. A theoretical model is presented which rationalizes this energy reduction based on the formation of sessile dislocations which exert a net force on the precursor crack. The model analyzes uniaxial tension as well as fatigue predeformation with results which have serious implications regarding the “in-service” reliability of materials.     

Antimicrobial and anticorrosive efficacy of inorganic nanoporous surfaces

The relationship between microbe populations that are active on engineered-product surfaces and their relationship to surface corrosion or human health is increasingly being recognized by the materials engineering community as a critically important study-direction. Microbial contamination from biofilms and germ colonies leads to costs that are reported to be extremely high every year in infection control, epidemics, corrosion loss and energy/infrastructure materials loss throughout the world. Nanostructured surfaces, particularly those that are hard-surface nanoporous (pore radii between 2 and 1000 nm), are an emerging class of surfaces that have recently been recognized as important for the prevention of microbial colony growth and biofilm formation. Such nanostructured/nanoporous surfaces, whether made with deposited nanoparticles (welded nanoparticles), or formed by ion-assisted growth on a surface have been found to display biocidal activity with varying efficacy that depends on both the microbe and the nanosurface features. The rate of mortality from common pathogens that are resident in ubiquitous bio-films when attached to common engineering surfaces made of steels, titanium and zirconium appears to be increasing. In this short review, we look at methods of manufacture of durable (i.e., highly scratch resistant) nanostructuring on commonly used engineering surfaces. The microstructures, energy dispersive X-ray analysis, X-ray photo-electron spectroscopy and other types of characterization of a few such surfaces are presented. Simple tests are required by the surface engineering community for understanding the efficacy of a surface for antimicrobial action. These are reviewed. The surface drying rate and the dynamics of the droplet spread have been proposed in the literature as quick methods that correlate well with the residual antimicrobial activity efficacy even after some surface abrasion of the nanostructured surface. A categorization of a surface against short-term antimicrobial action and long-term action is proposed in this review article. Test periods that span time-frames greater than 5 years have demonstrated a high efficacy of the nanoporous nanostructures for preventing bio-film formation. New comparative results for diamond- and graphite-containing surfaces are presented. A brief discussion on a recently developed plasma application technique for creating durable nanoporous surfaces is presented. Although considerable information is now available regarding tunable surface nanofeatures for antimicroabial efficacy, there is a need for more research activity, particularly directed toward the low cost manufacture and rapid characterization of durable (wear and chemical resistant) surfaces that display permanent antimicrobial behavior.     

Hard “skiving” turning

The results of the comprehensive studies of a highly efficient method of finishing, the so-called hard “skiving” turning, are discussed. Special features of the oblique cutting with a tool equipped with cBN-based polycrystalline superhard materials are shown, the regularities of the surface roughness formation and surface layer hardening in machining are considered.     

金属材料表面自身纳米化研究进展

近年来采用表面自身纳米化技术时纯金属、低碳钢及其他合金进行表面改性已得到广泛而深入的研究.相对于其他金属材料的表面改性技术,表面自身纳米化具有特定的技术优势.简要综述了金属材料表面自身纳米化技术的组织结构特征、组织演变机理、力学性能、元素扩散行为、腐蚀性能等.层错能的不同导致了不同表面纳米化形成机制,表面纳米晶的形成能有效改善原子的扩散行为,提高金属的硬度、强度、耐摩擦和疲劳性能.     

Femtosecond Laser Technology for Solid-State Material Processing: Creation of Functional Surfaces and Selective Modification of Nanoscale Layers

Information on the rapidly increasing use of modification of solid-state materials surfaces by femtosecond laser pulses at moderate intensities (around 0.1–10 TW/cm²) is presented as applied to creation of functional surfaces with tailored thermophysical, hydrodynamic, and mechanical properties and in application to selective modification and removal of nanoscale (1–100 nm) layers of bulk and thin-film multilayer materials. The problems in obtaining functional surfaces with the externally controllable wetting behavior of superhydrophobic surfaces showing a self-cleaning effect and superhydrophilic surfaces with a controlled Leidenfrost temperature, critical heat flux, and heat transfer coefficient are considered for heat-transfer enhancement during the evaporation and boiling of the working fluid. Data on the hardening of the surface layer of structural materials and the synthesis of diamond-like films are given. The methods for the precision selective removal of nanoscale films and surface modification with the formation of subnanoscale structures are considered.     

Deactivation of Materials and Articles in the Presence of Silver(II)

Radiochemistry - Experimental results are presented to substantiate conditions and modes of the process of deactivation of materials and articles to remove the surface α-, and...     

Characterization of real surfaces of vitreous silica by ellipsometry

It is shown that ellipsometry can be successfully used to characterize the contaminant surface film as well as the damaged surface layers on optically transparent materials. The results of ellipsometric measurements on vitreous silica specimens subjected to various surface treatments such as mechanical polishing, chemical etching and sputter-cleaning are presented and discussed.     

Surface effects on the mechanical properties of nanoporous materials

Using the theory of surface elasticity, we investigate the mechanical properties of nanoporous materials. The classical theory of porous materials is modified to account for surface effects, which become increasingly important as the characteristic sizes of microstructures shrink to nanometers. First, a refined Timoshenko beam model is presented to predict the effective elastic modulus of nanoporous materials. Then the surface effects on the elastic microstructural buckling behavior of nanoporous materials are examined. In particular, nanoporous gold is taken as an example to illustrate the application of the proposed model. The results reveal that both the elastic modulus and the critical buckling behavior of nanoporous materials exhibit a distinct dependence on the characteristic sizes of microstructures, e.g. the average ligament width.     

Optical,surface and magnetic properties of the Ti-doped GaN nanosheets on glass and PET substrates by thermionic vacuum arc (TVA) method

Room-temperature ferromagnetism of GaN and doped GaN materials has been reported in nanostructured form. Especially, nanoparticles show ferromagnetic properties at room temperature. In this paper, Ti-doped effects on GaN were deposited on glass and Polyethylene terephthalate (PET) substrates by thermionic vacuum arc and their room temperature magnetic properties are presented for the first time. The structure of the Ti-doped GaN was crystallized in a novel form, nano honeycomb formation. Optical and surface properties of the nano honeycombs and honeycomb nanosheets were determined. GaN and TiN phases were detected in X-ray diffraction patterns. Field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) device were used for imaging of the crystal structure. According to FESEM images, hexagonal crystal formations were detected for all samples. Crystal formations are very good oriented on PET substrates materials according to glass samples. The band gap value of the sample is changed by crystallization dimension. It was found that increasing crystallizations and decreasing crystal dimensions were increased the band gap of the Ti-doped GaN approximately 50?meV. Fourier transform infrared spectra and a vibrating sample magnetometer results were presented. These results confirm the Ti doped GaN honeycomb nanosheets and nano honeycombs show the room temperature ferromagnetic properties.     

Ursachen,Ermittlung und Bewertung von Randschichtveränderungen durch Kugelstrahlen

Origin, determination and assessment of near surface microstructural alterations due to shot peening processes In practice, the improvements of the properties of metallic components achievable by shot peening processes are a result of near surface plastic deformations. In comparison with the unpeened condition, they can cause dimensional changes, alterations of the surface topography, near surface materials strength, the macro and micro residual stress state, the near surface microstructure, the porosity and the texture. After describing the elementary processes occurring during shot peening, the influence of important process parameters on the surface materials state is considered. Subsequently, recent results concerning the thermal relaxation of shot peening residual stresses are presented and discussed.     

A mechanism for crystal twinning in the growth of diamond by chemical vapour deposition

A model for the formation of crystal twins in chemical vapour deposited diamond materials is presented. The twinning mechanism originates from the formation of a hydrogen-terminated four carbon atom cluster on a local {111} surface morphology, which also serves as a nucleus to the next layer of growth. Subsequent growth proceeds by reaction at the step edges with one and two carbon atom-containing species. The model also provides an explanation for the high defect concentration observed in 111 growth sectors, the formation of penetration and contact twins, and the dramatic enhancement in polycrystalline diamond growth rates and morphology changes when small amounts of nitrogen are added to the plasma-assisted growth environments.     

Shaping Colloidal Rutile into Thermally Stable and Porous Mesoscopic Titania Balls

High crystallinity and controlled porosity are advantageous for many applications such as energy conversion and power generation. Despite many efforts in the last decades, the direct synthesis of organic–inorganic composite materials with crystalline transition metal oxides is still a major challenge. In general, molecules serve as inorganic precursors and heat treatment is required to convert as‐synthesized amorphous composites to stable crystalline materials. Herein, an alternative approach to the direct synthesis of crystalline polymer–metal oxide composites by using a spherical polyelectrolyte brush as the template system is presented. Pre‐synthesized electrostatically stabilized rutile nanocrystals that carry a positive surface charge are used as inorganic precursors. In this approach, the strong Coulomb interactions between anionic polyelectrolyte brush chains and cationic crystalline rutile colloids, whose surfaces are not capped and therefore reactive, are the key factors for the organic–inorganic crystalline composite formation. Stepwise calcination first under argon and followed with a second calcination in air lead to the complete removal of the polymer template without collapse and porous rutile balls are obtained. The results suggest that any colloids that carry a surface charge might serve as inorganic precursors when charged templates are used. It is expected that this hierarchical route for structuring oxides at the mesoscale is generally applicable.     

MACHINABILITY OF SOME FIBER-REINFORCED THERMOSET AND THERMOPLASTICS IN DRILLING

Polymer-based composite materials are the major candidates for substitution for conventional materials in industry. Drilling is most frequently employed among machining processes for composite materials due to the need for structural integration. In this paper, some aspects of both experimental observation and machinability are presented for thermoset-based and thermoplastic-based composites with high and low fiber loading. The experimental observation discusses chip characteristics and specific cutting energy to reveal the mechanism of material removal. These materials fracture due to the brittle reinforcement, hence the sensitivity of defects in bulk volume is demonstrated. The level of fiber loading and the deformation behavior of matrix polymer determine the extent of plasticity in chip formation and the chip length. The discussions of machinability include drilling force, surface roughness and edge integrity affected by cutting conditions (feed rate and cutting speed), drill geometry and lay-up system. An optimal domain of cutting parameters is suggested for secured machinability.