The aim of the present paper is to investigate the mechanical properties (hardness and tensile strength) of dental Co-Cr alloys fabricated via casting and selective laser melting (SLM). Two groups of metallic specimens (four-part dental bridges and standard tensile test specimens) made of Co–Cr dental alloys were produced by lost-wax casting and SLM processes. Vickers hardness distribution along the depth of the dental bridges as well as the Rockwell hardness and tensile strength of the samples were studied out. The hardness of Co–Cr dental alloys are dependent on the manufacturing technique employed. It was established that the average Vickers hardness of the samples, produced by SLM, was higher than that of the cast samples 382 HV and 335 HV respectively. The nearly even hardness distribution in the bridges, produced by SLM, and fluctuations of the hardness values along the depth of the cast bridges were observed. The Rockwell measurements confirmed the higher hardness of the SLM samples – 39 HRC in comparison with that of the cast ones – 33 HRC. The tensile strength is in good agreement with the hardness values. Due to the unique microstructure, the yield strength and tensile strength for the SLM samples were higher than those of the as-cast alloy.
Materials Science. Non-Equilibrium Phase Transformations.
Vol. 2 (2016), Issue 3
Table of Contents
Are investigated mechanisms and kinetics of structural transformations polymeric substrates and of disperse particles fillers and modifiers exposed defocused laser radiation with energy in the range of 1.5 to 6 J. Installed effect of hardening the thermoplastic matrices (polyolefins, polyamides, of polyesters) when exposed to short laser pulses on a film sample thicknesses of 50-200 microns. The methods of structural analysis (IR spectroscopy, X-ray diffraction, DTA) showed, that the predominant mechanism of manifestation hardening effect is the formation of nano-sized structures in the film sample volume due to leakage of recrystallization processes. When exposed to laser radiation to disperse and fibrous particles of silicates, graphite, schungite, carbon fibers is implementing a complex effect of increasing the dispersion and the formation of advanced morphology of the surface layer with an increase in the proportion of nano-sized fragments whisker and lamellar habitus. When laser irradiation of fibers fragments formed developed morphology of the surface layer, due to the occurrence of thermal degradation processes that lead to the appearance of cracks and of globular indentations. Spectroscopy method of thermally stimulated currents (TSC – spectroscopy) established the effect of changing the energy state of the surface layers of substrates and particulate modifiers, which are characterized by extreme values of magnitude TSC – currents in the temperature range 193-523 K. The combined effect of energy and morphological factors provides the effect of increasing the activity of modifying components subjected to the laser processing. Changing the energy state of the surface layer of the polymer substrate has a beneficial bactericidal effect, increases the effectiveness of antiseptic treatment of medical devices used in medical practice. Are presented examples of the practical use of the established laws when creating polymer composites for metal-polymer systems for various applications.
There were studied mechanisms interfacial interactions in composite systems based on dispersed particles of polymer materials (polyolefins, polyamides, fluorcontaining polymers) and modifiers of various composition and structure in the combination process in the units with intense mechanical action. There were established the effects of formation of products of mechanochemical interaction of active centers of modifiers particles and radical fragments of macromolecules degradation. The obtained results allow changing the technological paradigm of the creation of high-strength and highly filled engineering nanocomposites based on high-molecular matrix.
NEW MATERIALS FOR IMPLANTS OF THE HUMAN HIP JOINT AND TECHNOLOGY OF THEIR MACHINING WITH THE ACHIEVEMENT OF HIGH PRECISION AND QUALITY OF SPHERICAL SURFACESpg(s) 12-16
In view of the fact that the endo-prosthesis heads of human hip-joint are operated in extreme conditions, in respect of load, the selection of corresponding material and also increase of precision and quality of machining of spherical surfaces is rather topical task.
In the submitted work are reviewed the problems connected with definition of the influence degree of orientation of the sapphire crystal on its workability during diamond grinding with a butt of the ring and elaboration of the perspective, original scheme of formation of the incomplete spherical surface, particularly, of the sapphire head of endo-prosthesis of the human hip-joint.
ON A PHYSICO-MATHEMATICAL MODEL FOR CONTROLLED FORMATION OF PERIODIC NANOSTRUCTURES AT SOLID SURFACES IRRADIATED BY FEMTOSECOND LASER PULSESpg(s) 17-20
In this paper, we propose a physico- mathematical 3D model to study some of the basic features of the interaction of radiation with solid materials (metals, semiconductors , insulators) under the action of femtosecond laser pulses. The constructed model is a parametric model that, in particular, takes into account the dependence of the physical and chemical characteristics of the periodic nano-surface structures controlled laser irradiation parameters the polarization, angle of incidence, the energy density, wavelength, etc. The developed model is meant for the excitation of periodic nano-surface structures by electric waves which are in the process of irradiation and periodically amplified and attenuated, i.e. it holds periodic interference.
A study was made of the macro-scale plastic flow non-homogeneities, which occur in metals in the form of Luders bands or Portevin-Le Chatelier effect. The motion kinetics was investigated for the mobile fronts of Luders bands observed for the yield plateau as well as localized plasticity fronts traveling in the course of serrated plastic flow behavior (Portevin-Le Chatelier effect). It is shown that the propagation of the above two kinds of band fronts can be regarded as macro-scale auto-wave processes of switching and excitation, respectively, which frequently occur in active media of different kinds.
Тhe electronic devices are everywhere in our life and for their proper performance it is very important to have them protected from Electromagnetic Interference (EMI). Sources of EMI could be some components of the device, nearby conductors, other devices, high voltage lines, atmosphere static discharges, etc. One of the main methods for protection from external EMI is by shielding the whole device and for this purpose are used various materials. In this paper are presented two types of materials used for EMI shielding – polyester silk with electrolysis metal coating and nitrile butadiene based compounds (NBR) containing as a filler natural magnetite. For both materials is investigated the EMI absorption for electromagnetic waves in the band (8-12 GHz) and at 2380 MHz.
Bronzes type BrZhNA 12-7-1 (12% Fe, 7% Ni, 1% Al) form dendritic structure that consists of a maraging martensitic steel 03N15Yu1 mesh, which arms matrix given bronze with content Cu – base, 5-6% Ni and 1% Al. Dendrites can be strengthen by dispersion hardening. Mass transfer phenomena during crystallization and heat treatment in these bronzes were investigated. This bronze has elevated mechanical and technological properties, low friction coefficient and high wear resistance level during sliding friction.
INCREASING WEAR RESISTANCE OF MACHINES DETAILS FROM CARBON AND Cr – Mn – N STEELS OF THE COMPLEX BORIDE COATINGSpg(s) 31-34
The results of studies wear resistance of boron coatings alloyed with Сu, V, Nb, Cr or Ti under dry friction – slip in the air, and it was determined that the best coatings are the boride layers alloyed with copper. Alloying with copper inereases wear resistance of boride layers in 3 times. When alloying of boride layers with niobium wear resistance increases in 2,8 times, with titanium – in 2,4 times, with chromium and vanadium – in 1,5 times. Wear resistance of boride coatings alloyed with copper under dry friction – slip 14 times higher than wear resistance of bronze of Cu – Al – Mn system and wear resistance increases when applying boride layers alloyed with copper.