Faina Muktepavela

STRUCTURE AND MECHANICAL PROPERTIES OF AL-B COMPOSITE POWDER

Abstract Al-B composite powder has been obtained by crushing pieces of composite material presenting industrial waste. Structural peculiarities and microhardness of separate powder particles (d∼1 mm) have been investigated. Original design of high precision microhardness tester made it possible to detect the properties of powder both in near-surface layer and below it. The powder represents a new structurally non-homogenous material with the increased microhardness (1.5 GPa) which grows up to 4 GPa in near-surface layers. Stable oxide compounds are formed on internal surfaces and defects of the aluminium alloy. Powder compacts were obtained. Adhesion on Al–B and Al–Al interfaces at various temperatures and pressures were investigated. The applications of the powder compacts were considered.

Structure Evolution and Diffusion During Interphase Boundary Sliding in Binary Eutectics Based on Sn

Mechanical behaviour of interphase boundaries (IB) and microstructure in the binary eutectics (Al–Sn, Zn–Sn, Pb–Sn, Cd–Sn) heavily deformed by different schemes and regimes have been investigated. Experiments were carried out on the atomically clean surfaces of alloys and on the bimetallic joints with clean interfaces used as a macromodel of deformed IB. It has been shown that for the eutectics with high IB energy (Al–Sn, Zn–Sn) the interphase boundary sliding (IBS) occurs by means of the dislocation gliding, followed by a remarkable strengthening and accompanied by the formation of narrow stable IB cracks with sharp angles. For eutectics Pb–Sn and Cd–Sn with low IB energy, the IBS occurs as viscous flow and is accompanied by a correlated diffusion along IB. The softening of IB was observed. Intensity of development of the diffusion-controlled accommodation processes on IB depends on the extent of preliminary deformation and values of IB energy.

Microhardness and adhesion measurements of reactively sputtered TiN/AlN multilayer coatings deposited as function of mass-flow of nitrogen

Abstract Multilayer coatings of (Ti, Al)N x have been deposited by reactive sputtering from Ti and Al targets in a side-by-side configuration on WC and stainless steel substrates. The rotation of the substrate holder varied from 2 to 14 r.p.m. corresponding to a bilayer thickness of 0.8–8 nm. The acoustic emission scratch technique for adhesion measurements was used for studying coating performance, and critical load values for the coatings on WC substrate up to 150 N were obtained. The Vickers microhardness in the load range 0.003–2 N was measured, and in order to obtain true hardness values, an optimal range of indentation depth and coating thickness was determined. Depending on the nitrogen flow rate and bilayer thickness, hardness values of 18–23 GPa were obtained at the film surface.

Interface Diffusion Controlled Sintering of Atomically Clean Surfaces of Metals

Diffusion mass transport on the free surfaces under annealing at 0.4 –0.6 Tm and the effect of the surface diffusion on the adhesion and sintering of metals and mi crocrystalline eutectic alloys have been investigated. Atomically clean surfaces of metals (Pb, S n, In, etc.) and Pb–Sn, Al–Sn alloys, were obtained by the method of controllable internal rupture. Pronounced surface diffusion was observed on free surfaces for all metals investigated. The effect of interface energy and grain boundary grooving on sintering is considered. It has been shown that the contr ibution of the surface and grain boundary diffusion to the formation of contact becomes significant, when not only kinetic but also definite structural and energetic conditions at the interfac e are met. Application of the compression load during annealing resulted in the temperature and time ependent increase in the adhesion strength due to creep and stress-promoted mass transport at the inter fac .

The Role of Diffusion Accommodation and Phase Boundary Wetting in the Deformation Behaviour of Ultrafine Grained Sn-Pb Eutectic

Mechanical properties, microstructure of the Sn–38wt. %Pb eutectic and the development of deformation - induced diffusion processes on interphase boundaries (IB) were investigated. Experiments were carried out both in deformed and annealed states of eutectic using micro- and nanoindentation, SEM, AFM and optical microscopy techniques. It was found that the deformation of the annealed alloy is localized at the Pb/Sn interphase boundaries and occurs by grain boundary sliding (GBS) accompanied by sintering micropore processes under the action of the capillary forces on the Pb/Sn IB. During severe plastic deformation of Sn-Pb eutectic phase transition in the Sn grain boundary occurs. This deformation-induced process takes place due to the wetting of tin with Pb. These diffusion accommodation processes (sintering and wetting) are facilitated by the low values of the Pb/Sn interphase energy (0.07 J/m2). Wetting is thermodynamically favourable because the condition γgb > 2 γib is satisfied and it is also kinetically allowed due to the relatively high homologous temperature (> 0.5•Tm). The obtained values of the nanohardness and elastic modulus evidence that the IBs in the Sn–Pb eutectic have to be considered as a separate quasi-phase with its own properties.

The Role of Interphase Boundaries in the Deformation Behaviour of Fine-Grained Sn-38wt.%Pb Eutectics

The Role of Interphase Boundaries in the Deformation Behaviour of Fine-Grained Sn-38wt.%Pb Eutectics The mechanical properties of binary Sn-38wt.%Pb eutectic alloys in the deformed and annealed states were investigated at room temperature using tensile, micro- and nano-indentation tests. The softening and high plasticity of a deformed Sn-Pb eutectic are explained as a result of grain boundary sliding (GBS) and fast diffusion-driven processes developing along the Sn-Pb interphase boundaries (IBs). From the results of micro- and nano-hardness measurements it follows that the Sn and Pb phases in the annealed eutectic are strengthened, and the relaxation processes occur mainly at the IB. Such IBs in the annealed Sn-Pb eutectic act as barriers to the motion of a dislocation ensemble when the size of the plastic zone is comparable with the grain size, lowering the hardness values due to the development of GBS when more grains are involved in the process of deformation. The nanohardness and elastic modulus values obtained evidence that an IB in the Sn-Pb eutectic is to be considered as a separate phase with its own mechanical properties. Starpfāžu Robežu Loma Smalkgraudainās Sn-38at.%Pb Eitektikas Plastiskā Deformācijā Sn-Pb eitektiskais sakausējums tiek plaši pielietots gan elektrotehnikā, gan arī aparātbūvē. Darbā veikti deformētas un atkvēlinātas binērās Sn-38wt.%Pb eitektikas mehānisko īpašību un struktūras pētījumi, izmantojot stiepes, mikro- un nanocietības metodes. Deformētas eitektikas augstais plastiskums un mīkstināšanās deformācijas procesā izskaidroti ar slīdēšanu un difūzijas kontrolētu relaksācijas procesu norisi pa starpfāžu robežām. Atkvēlinātā eitektikā Pb un Sn fāzes uzrāda relatīvi augstu stiprību, bet deformācijas procesi ir lokalizēti starpfāžu robežās. Nanocietības un Junga modula dati liecina par to, ka starpfāžu robežas var uzskatīt par trešo fāzi, kurai ir savas īpašibas, kas nosaka eitektikas plastiskumu.

Obtaining of nanostructured ZnO coatings using mechanoactivated oxidation

The concept to use nanostructured state of metal at the instant of destruction in air environment was used to obtain nanostructured Zn-ZnO coatings on glass and quartz by mechanical method. Subsequent annealing in the ambient atmosphere, annealing in vacuum and irradiation with 532-nm YAG:Nd laser were used to obtain completely oxidized, transparent ZnO coatings. The saturated with oxygen nanostructured coatings were transformed into nanostructured ZnO coatings after annealing above 773K or irradiation with laser (allowing to reach 673K) in ambient atmosphere. AFM and SEM images show that after annealing ZnO coatings have multi-shaped structure. The formation of ZnO need-like whiskers (d = 100nm, l = 2?m) was observed after laser irradiation. Obtained ZnO coatings have high microhardness (10--12GPa), strong adhesion with substrates and show green and blue luminescence at room temperature. The oxidation process is mechanoactivated due to the facilitated oxygen diffusion along deformation defects: vacancies, dislocation, microcracks, and developed network of grain boundaries.

Mechanical Properties of Deformed Interfaces in Bimetallic Joints

Bimetallic joints with clean interfaces, obtained by a specia l cold welding method, were used as a model of phase boundaries for investigation of their strengt h properties, deformation behaviour, and fracture mode. Pairs of very soluble and insoluble metals, as well as pairs forming chemical compounds and eutectics, were chosen for investigation. It ha s been shown that the strength of interfaces under shear test and the development of pla stic deformation and relaxation processes on the interfaces depend on the nature of metals, adherence, type of chemical interaction and extent of preliminary deformation. Introduction In modern technologies for production of composites, superplastic and nanost ructured materials, using active plastic deformation at relatively low temperatu res, the strength characteristics of the resulting phase boundaries comprise an important problem [1-3]. However, i n stigations of the boundary properties and accommodation processes in the bulk of the fine-gr ai d material are hindered by the experimental difficulties. Investigations of bimet allic joints can be employed to determine interface properties. The objective of the present wor k is to investigate the mechanical properties of interfaces in bimetallic joints obtained under conditions of severe plastic deformations at room temperature by a special cold welding method. The pairs of metals selected for investigation offered different types of physical and chemical interactions in the equilibri m state. Experimental Bimetallic joints with clean interfaces were obtained by a s pecial cold welding method [4]. Cold welding was carried out by two-side indentation of flat punches wi th a welding area of 23x3 mm. A hard foil was located between the samples to be welded and this sandwich was subjected to indentation until a crack in the foil arose and the newly formed cle an surfaces of the metals to be welded were brought into contact. During indentation of the sandwich, the e dges of the crack moved apart and oxides as well as other contaminants were removed f r m the contact zone together with the foil. The hard foil provides clean contact surfaces and makes for a strong bonding over the crack area. This area increases with increasing indentation depth of the punch and at optimal conditions approaches the area of the punch face. To obtain the interfac es of metals with highly different mechanical properties, the softer metal is locate d between sheet specimens of a harder metal and separated from both sides by a hard foil. Secondary I on Mass Spectroscopy (SIMS) method was used to determine the cleanliness of the interfaces. Th strength properties of the bimetallic joints were determined by shear tests. Fractographic and structural investigations were carried out by using optical and electron microscopes. Results and Discussion The results of measurements are summarized in Table 1. In the ca se of similar metals, the interface strength exceeded the sample’s bulk strength and rupture along the ori ginal contact interface was never observed. The data indicate that the difference in solubility had no significant influence on the joint strength at 293K. In case of dissimilar metals, which form no chemical compounds or eutectics, the rupture of most of joints took place in the softer met al indicating strong adhesion for the pairs of metals with a good (Ni/Cu) or limited solubility as well as for insoluble pairs of metals (Ni/Ag, Al/Cd, Fe/Pb and Al/Pb). Solid State Phenomena Online: 2003-06-20 ISSN: 1662-9779, Vol. 94, pp 79-84 doi:10.4028/www.scientific.net/SSP.94.79

Hardening of Steel Perforated Tape by Nd:YAG Laser

One of the directions of application of the perforated metal material is their use as cutting elements in the production of processing tools. In this case it is necessary to carry out hardening of cutting surfaces to increase their hardness. One of the methods of hardening metals could be laser treatment. Therefore, the present work is a study of the effect of Nd:YAG laser radiation on the microstructure and hardness of fragments formed from steel perforated tape. Different laser scan speeds (doses) were used in the experiments. The results have shown that the increase the microhardness of 30-40% after the laser treatment of steel perforated tape in the surface layer in a depth range up to 1 μm take place. The studies of microstructure of fragments formed from steel perforated tape have shown the reduction of the structure size and the presence of a thin oxide compounds, which is consistent with the results on nanoindentation. Hardening of the metal by laser radiation is carried out without surface melting which eliminates the change of macroroughness and the need for subsequent machining process.

Surface Development of (As2S3)1–x (AgI)x Thin Films for Gas Sensor Applications

Thin (As2S3)100−x(AgI)x (x = 0–40) films were deposited by thermal vacuum evaporation from the respective bulk glasses; their structure and morphology before and after illumination with light have been studied by scanning electron microscopy (SEM). As-deposited films show fractional evaporation and surface inhomogeneities but after illumination they become uniform on the surface and in the depth as revealed by SEM top-view and cross-section images. Mechanical parameters like stress and microhardness of as-prepared and illuminated films were also investigated. The results from the stress measurements show variation in both the sign and the magnitude of the values with increasing AgI content and with time. Pure As2S3 layers possess a low tensile stress. The addition of AgI initially reduces the tensile stress and turns it to compressive for higher AgI concentrations. The exposure to light does not affect significantly the magnitude of the stress. The microhardness of the thin films decreases when the content of AgI increases. Furthermore, the microhardness in the surface region of the films is higher than in depth; it increases after the exposure to light.