Key Engineering Materials Vols. 592-593

Abstract: Alloys of Cu-Pt [1] are of interest for research, since the phase transitions "order - disorder" at different concentrations of components form several types of superstructures. In the alloy Cu₃Pt the ordering L1₂ superstructure formed on the basis of fcc lattice. In the ordering of the fcc lattice of the disordered solid solution the equiatomic composition transformed into the L1₁ superstructure with an rhombohedral crystal lattice (a state with an L1₁, whose angles α, β, and γ are other than π/2). A CuPt₃ in an ordered state has an L1₃ superstructure (a state with an L1₃, whose angles α, β, and γ are other than π/2). A possible existence of an ordered phase containing 20 at.% Pt was reported in the literature [2], which corresponds to the composition of Cu₄Pt (type of superstructure was not defined). In other sources, an occurrence of an ordered compound, Cu₇Pt, was predicted, containing 12.5 at.% Pt [3]. Computer experiments performed on the Monte Carlo method, showed that the alloys of the Cu - Pt different composition components undergo phase transformations "disorder - order" from the FCC to the structures of different symmetry [4,11]. This paper presents the results of a study of the structural transformations in the alloys Cu₃Pt, CuPt, CuPt₃ (superstructure L1₂, L1₁, L1₃), containing shear antiphase boundaries (APB) in the planes {111}.

Abstract: Metallic nanoparticles and nanocrystalline bulk materials are recently extremely popular. It is because of their properties and wide field of possible applications.In this work, silver nanoparticles were prepared by selective dissolving of the aluminium matrix from rapidly solidified (RS) AlAg30 (wt. %) alloy in the sodium hydroxide solution. This alloy was prepared by melt-spinning technique. The influence of production parameters such as sodium hydroxide concentration, dissolving temperature and using of ultrasound bath on the phase composition, morphology and size of the nanoparticles was studied.Phase compositions of the initial alloy and prepared nanoparticles were investigated by X-ray phase analysis. Furthermore, the nanoparticles were studied by means of transmission (TEM) electron microscope. Nanoparticle size was determined by image analysis of TEM micrographs and these results were also compared to the size of nanoparticles determined from diffraction patterns using Scherrer calculator.It was found that concentration of sodium hydroxide has significant effect on phase composition of the product and the dissolving temperature influences the particle size.

Abstract: In the paper a new surface refining technology which uses nano-particles to improve the soda – lime – silica glass surfaces is presented. The SEM-EDS (Energy Dispersive X-ray Spectrometry) analysis was carried out to determine modification of the glass surface. A very thin modification layer was observed on the glass surface. The surface modification leads to an improvement of physical and chemical properties of the investigated glass.

Abstract: We use quantum-mechanical calculations to study single-crystalline elastic properties of (Ca,Mg)CO₃ crystals with concentrations ranging from calcite CaCO₃ to magnesite MgCO₃. By analyzing results for a dense set of distributions of Ca and Mg atoms within 30-atom supercells, our theoretical study shows that those atomic configurations, that minimize the total energy for a given concentration, are characterized by elastic constants that either increase with the Mg content or remain nearly constants. Employing these ab initio calculated single-crystalline elastic parameters, the polycrystalline elastic properties of (Ca,Mg)CO₃ aggregates are determined using a mean-field self-consistent homogenization method. The computed integral elastic moduli (bulk and shear) show a significant stiffening impact of Mg atoms on calcite crystals. Our analysis also demonstrates that it is not advantageous to use a granular two-phase composite of stoichiometric calcite and magnesite instead of substituting individual Ca and Mg atoms. Such two-phase aggregates are not significantly thermodynamically favorable and do not offer any strong additional stiffening effect.

Abstract: Porous magnesium materials appear to be promising candidates for scaffold production. In this work we prepared porous magnesium samples by powder metallurgy using ammonium bicarbonate as space-holder particles. We focused on the influence of the magnesium powder size and shape on product characteristics. Samples prepared using magnesium chips showed significantly worse flexural properties than samples with similar porosities prepared from an equi-axed magnesium powder. Therefore, we can conclude that spherical particles are more suitable for the preparation of porous objects by powder metallurgy.

Abstract: In this work, the effect of the laser shock-wave treatment on the surface morphology and regularities in failure of nanotitanium is investigated. Based on the data of fractodiagnostics it is established that the shock-wave treatment changes the mechanism of failure from the brittle chipping to the mixed ductile-brittle one by the shear + separation scheme.

Abstract: Our aim was to use stereology to quantify the volume fraction of osteocyte lacunes, volume fraction of large blood vessels, numerical density of osteocyte lacunes, volume of osteocyte lacunae and bone surface in series of micro-CT images representing samples of spongy and compact bone of human tibia. The spongy bone had a smaller volume fraction of osteocyte lacunes, a greater numerical density of bone lacunes, a smaller volume of the lacunes within the same bone volume and a greater bone surface density when compared to the compact bone. Stereology provided us with data on hierarchical organization of bone structural heterogeneity with reasonable time costs.

Abstract: Since the temporomandibular joint (TMJ) disc material exhibits a non-homogenous and viscoelastic structure, the compressive properties in five different regions of eleven porcine TMJ discs were investigated over a wide range of loading frequencies. The results obtained suggest that the dynamic viscoelastic compressive modulus is region-specific and depends on the loading frequency, thus having important implications for the transmission of load in the TMJ. The dynamic storage and loss moduli increase with frequency, the highest values being attained at the posterior region, followed by the central and anterior regions. Loss tangent, tan δ, ranged from 0.20 to 0.35, which means that the disc is primarily elastic in nature and has a small but not negligible viscosity.

Abstract: The paper is concerned with the study of the elastic properties of dental enamel and its destruction by a microindentation technique. A series of experiments were performed to find differences in the mechanical properties of healthy and diseased dental enamel. It has been found that the times of dental enamel destruction in healthy and carious areas under a constant force are different. The effect of an infiltrated photopolymer on the hardness and elastic modulus of dental enamel was investigated by microindentation testing. A comparative analysis of the features of healthy, damaged by caries and treated by photopolymer enamel was carried out.

Abstract: The paper is concerned with the investigation of dental caries treatment by the modern method based on the application of special composite material that can diffuse into the damaged zone, harden by light and prevent tooth decay. Carious disease was modeled as a diffusion process of acid penetration from the oral cavity into the tooth enamel with further dissolution of dental hard tissues in the subsurface layer of enamel. The model of dental caries was mathematically formulated. The solution was obtained by a numerical method using MATLAB. It is shown that the proposed model adequately describes the properties of the examined dental system.