International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

Choosing a profession has always been difficult for most of young people. When choosing a profession, most of them follow the dream of a future good realization.
The aim of the article is to outline their main motivating incentives in choosing the military profession as their professional perspective. In clarifying this objective, the main task was to outline the basic material and non-material incentives associated with the military profession.

The geopolymers are novel class of inorganic polymer materials consist of chains, sheets or networks made of covalently bonded mineral molecules. The main precursors of the geopolymers are reactive alumosilicate material and hardener solution. Various suitable raw materials are located in Bulgaria. The present paper shows successful examples of geopolymers based on Bulgarian raw materials – fly ash, metakaolin, natural zeolite and iron-rich waste from copper industry. The properties and structure of the prepared geopolymers greatly depend on the composition and type of the raw material, as well as concentration and type of the activator solution. The results show the potential of geopolymers based on Bulgarian raw materials as building materials.

Analysis of the structural state and phase composition of surface metal layers after combined treatment of steel which includes preliminary surface plastic deformation of the workpiece, electrospark doping with use of rotating disk electrode 2 mm thick, made of WCCo hard alloy and subsequent surface ball smooth rolling, has been performed. It was shown that the use of combined treatment provides a gradient-layered structure with low surface roughness. Phase composition of the obtained layer consist of ferritic α-Fe phase and a number of carbide phases formed during the interaction of the electrode material with steel: F3W3C, WC and W2C semi-carbide. Wear resistance of the material after treatment exceeds similar properties of the original carbon steel up to 4 times.

The work is devoted to the study of evolution of flaws in aluminium alloys of Al-Zn-Mg-Cu, Al-Cu-Mg-Мn alloying systems and to the determination of their connection with structural factors of the material such as the size and composition of intermetallic phases conditioned by heat treatment tempers, and also to the study of the effect of big number of physical factors on the long-term behaviour of structural elements of aluminium alloys, and to the determination of the rate of formation of corrosion damages in structural elements of the aircraft wing

This study reports the milling time optimization of the Al-7 wt.% Si alloys by using planetary ball mill, the incorporation of 2 wt.% LaB6, NbB2, VB and TiB2 particles into Al-7 wt.% Si matrix and the fabrication of composites using cold pressing and pressureless sintering. Mechanical alloying (MA) time carried out for 4, 8, 12, 16 and 20 h was optimized via crystallite size and phase determinations and microstructural investigations. 12 h was chosen as optimum MA time. Then, different particulate reinforcements were added to Al-7 wt.% Si matrix to constitute boride reinforced composites. All composite powder batches were also milled for 12 h, then compacted and
sintered at 570°C for 5 h. Microstructural, physical and mechanical (hardness and wear volume loss) properties of these composites were performed. Hardness values of 120.8 ± 11.37 and 121.77 ± 19.02 were obtained for the LaB6 and TiB2 reinforced composites, respectively.

The effect of the low-frequency vibration processing on the residual elastic stresses in the Ti-6Al-4V alloy manufactured by 3D printing (Selective laser melting) was investigated. The studied sample was manufactured horizontally in respect to the building platform. Different vibration oscillations modes (vertical, horizontal, and elliptical) were chosen for study. The oscillations were done with frequency of 16 Hz, and a processing time was 20 minutes. Studies shown that 3D printed sample had a high level of residual elastic stresses, which were changed after vibration treatment. The optimal parameters of vibration processing, which provide a minimum level of residual elastic stresses in 3D printed Ti-6Al-4V alloy are discussed.

The application of the selective laser melting (SLM) method requires knowledge of not only the properties of the material after manufacturing, but also after mechanical loading. The aim of this work is to investigate the strain-rate dependence and microstructure of Ti6Al4V samples manufactured by SLM method with different angles to the building platform. SLM Ti-6Al-4V samples were manufactured using the EOSINT M280 (EOS GmbH) at angles of 0°, 30°, 45°, 90° to the building platform. A medicine Ti6Al4V (ASTM grade 23) powder was used for the study. Tensile tests were performed with an Instron test machine using two strain rates 0.5 mm/min and 2 mm/min at room temperature. It was found the strain-rate dependence in the studied samples. The features of the mechanisms of hardening and softening in an investigated SLM Ti-6Al-V alloy are discussed.

Cu-based shape memory alloys are increasingly used instead of nitinol alloys, due to their low price, good shape memory effect and superelasticity. In this work, Cu-Al-Mn alloys with different content of aluminium were investigated. Alloys were melted in the electric-arc furnace and casted in the cylindrical moulds as well as continuous casted. Microstructure of prepared samples was followed by scanning electron microscopy and phase transformations were determined by DSC analysis.

The potential of using the ultrafine dispersion powder material obtained by the ECA pressing from a copper powder have considered for the production of fast-acting fuse links. The dependences of the density and microhardness along the length of the sample under different deformation conditions obtained. A deformation zone of constant density is determined and recommended for using in the production of fuse links. The dependence of the electrical resistance along the sample cross-section and across the deformation axis has determined. The fuse links calculation procedure has proposed.

An aim of a research was to determine the reasons of fracture of aluminium alloy components used for spinning of chemical fibres and to improve spinning process by selecting material with better performance.

Effects of additions of 0.0039, 0.01, 0.019 and 0.029 wt.% Sb on austenite transformation and the metallic matrix structure in the wall thicknesses of 3, 12, 25, 38, 50, 75 and 100 mm of ductile iron casting containing 2.11 wt.% Si and a low amount of Cu, Sn and Mn were analyzed in this paper. In the examined ductile iron casting without the addition of Sb, the share of pearlite in the metal matrix was decreased and the share of ferrite was increased with increasing wall thickness. The share of pearlite was low. Additions of Sb were increased the share of pearlite in all the walls. Increase of Sb content resulted in increasing the share of pearlite. Almost the same high share of pearlite in the wall thicknesses of 12, 25, 38, 50, 75 and 100 mm was obtained by addition of 0.029 wt. % Sb (varied from 96.00 to 97.61 %). The additions of 0.01, 0.019 and 0.029 wt.% Sb were resulted in a fully pearlitic metallic matrix in the wall thickness of 3 mm. Iron carbides were found in the wall thickness of 3 mm when Sb was added.

Because of the combination of high specific strength and excellent corrosion resistance in many media, titanium and titanium alloys are used in aerospace engineering, chemical industry, mechanical engineering etc.
The present work introduces results that demonstrate the effect of the thermal cycle on mechanical properties of Grade 1 Titanium welds, produced by hollow cathode arc discharge in vacuum. Dimensions of the welds were established. The mechanical properties of the welds – hardness and tensile strength – were determined. The influence of the thermal cycle on welds structure was investigated.