Materials Science. Non-Equilibrium Phase Transformations. Vol. 5 (2019), Issue 1

Green chemistry: carbon-bearing minerals as a source of nanocarbons

pg(s) 3-7

Natural abundant, cheap and widely used raw materials like calcite, magnesite and dolomite contain elemental carbon up to several wt percent. Such rocks have been chemically processed here using combustion synthesis route to yield novel nanocarbons including two-dimensional graphene-like structures. The fast and efficient reduction of powdered minerals with strong reducer (Mg) produces, after chemical wet purification, carbon nanomaterial which was analyzed using different techniques like XRD and SEM. This ‘combustion’ process was followed on-line to evaluate reaction duration (usually within 1 sec).

Increase in strength properties of low-carbon steels due to structural transformations at deformation by rotary swaging

pg(s) 8-10

Mechanical properties of low-carbon St.20 and 07G2MFB steels after rotary swaging (RS) were studied. It was established that an increase in strain ratio and decrease in temperature increase strength but decrease plasticity. The ultimate tensile strength of 867-927 MPa was obtained in both steels after deformation at temperature of 400 °C with a true strain ratio of 2.3 at good ductility of 15-17%.

Features of structure formation and mechanical behavior of metallic materials under conditions of application of gradient deformations

pg(s) 11-12

The study of technological methods of plastic structure formation is an urgent task. Taking into account that structure formation depends on many factors and, first of all, on the deformed state, studies of the deformed state and structural studies involving TEM were carried out in the work. It is known that reliable data of the structural state allows predicting the mechanical and operational properties of the obtained semi-finished products and products. In this regard, the analysis of the effect of the processing route (C, Bc) on the structural changes after high-cycle active bending was carried out. A numerical simulation of the active bending process was also carried out, and the accumulated strain values were determined for 8 processing cycles. Established patterns of structure formation, depending on the level of accumulated deformation and processing route.

The influence of heat treatment on properties of steel for cementation

pg(s) 13-15

During the injection molding procedure of plastics, the gear pumps in their work are exposed to the effect of elevated pressure and temperature. On one of these pump there has been frequent downtime due to breakage of the driven gear. Gears which were installed as standard spare parts had stood out in operation for three months. On a sample of a broken gear were perfomed laboratory examinations (metallographic examinations, hardness control on cross-section and surface of the fracture was examined). Conclusion was that it was high quench hardening of a steel of which a part is made, the most likely cause of the fracture of a standard gear. In order to extend the useful life, two test gear are made from steel for cementation 20MnCr5. By applying the appropriate parameters of thermal chemical treatment useful life of the gear is significantly extended, after which the test gears have worked for nine months from the moment of installation.

Corrosion stability in salt medium of stainless steel and carbon steel, using different oxide sol gel coatings

pg(s) 16-18

Three types of oxide sol gel coatings: TiO2, CeO2 and TiO2/CeO2 composite were deposited by sol gel method on stainless steel and carbon steel. The morphology was examined by means of Scanning electron microscopy (SEM). X-ray diffraction analyses (XRD) were applied to investigate the phase composition. The corrosion resistances of the coatings were studied by evaluation of the weight loss in NaCl medium for 1200 hours. The surface of the TiO2 samples were relatively dense with a few surface nanocrystals and after tests does not shown any signs of corrosion. Тhe composite TiO2/CeO2 samples possess deep cracks which evidently favor the attacks in corrosion medium. Ceria and titania coatings deposited on stainless steel have zero weight loss in corrosive medium. The TiO2 coatings could also effective protect carbon steel, while the TiO2/CeO2 and CeO2 coatings exhibited lower corrosion resistance.

Comparative tribological properties of AZ91D magnesium alloy after strengthening by SiC powder and after severe plastic deformation

pg(s) 19-22

The paper presents the results of studies of tribological properties of the contact of the tool steel composition Fe-18W-4Cr-1,2V with the magnesium alloy AZ91D strengthened by submicron powder filling out of SiC and severe plastic deformation (SPD), namely equalchannel angular pressing (ECAP). It is stated that introduction of SiC powder filling to the magnesium alloy the friction coefficient on the moving frictional contact increases, the wear rate reduces. These tribotecnical characteristics are influenced by the size and volume of the particles of powder filling, normal loading force and slip rate. SPD of the initial material results in reduction of the adhesion constituent of the friction coefficient.

Influence of the synthesis method on the crystalline structure, phase composition and properties of TiCrFeNiCuC equiatomic alloys

pg(s) 23-25

Equiatomic alloys TiCrFeNiCuC were made by two methods of powder metallurgy – vacuum sintering and hot forging followed by annealing. In the process of sintering the TiCrFeNiCuC blanks, the influence of entropy of mixing resulted in the formation of solid substitution solutions mainly on the basis of the FCC lattice, and also formed titanium carbide (TiC0.74). In samples obtained by hot forging and subsequent annealing, two carbides TiC and Cr3C2 were found, and titanium carbide being formed with lower carbon content (TiC0.58). In addition, the forged samples showed significantly higher values of the defect of the crystalline structure, which leads to increase in their hardness.

Surface treatments and coatings application on the aluminum products

pg(s) 26-27

The aim of this work is to present the influence of anodic surface treatment parameters on thickness and structure of an anodic layer formed on aluminum products.
The materials used in this study are the aluminum products from Alumil Company in Albania. The analyses of samples were performed using Optical Microscopy (Leica DMI 5000 M) for characterization of macrostructure of anodizing layer and Vickers micro-hardness (HMV-2 tester) of non-anodized aluminum products and anodized aluminum products. Aluminum product of the series A6060 are taken in Alumil Company in Albania. Comparing the results in this research (analyses) we have concluded the characteristics of anodizing layer in the aluminum product, which have improved and increase their surface and product performance.

Evaluation of mechanical properties of ductile cast iron and inverse regression

pg(s) 28-31

The evaluation of ductile cast iron is common foundry practice. For the correct non-destructive evaluation (NDE) of mechanical properties (ultimate tensile strength; relative lengthening; Brinell’s hardness; elasticity modulus) by means ultrasonic testing and inverse regression analysis are used.

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