The paper presents study results of laser alloying of CT90 tool steel with an applied pre-coat of boron, molybdenum or a mixture of these elements. Pre-coats were applied on steel substrates in the ...form of a paste. The aim of the study was to investigate the microstructure, chemical and phase composition, microhardness and corrosion resistance of these newly-formed coatings. The laser alloying process was carried out using a diode laser with a nominal power of 3 kW. In this study a laser beam power of 900 W and a scanning speed of 48 mm/s were used. As a result of the laser beam action, the presence of three areas was observed in cross-sections of specimens: a remelted zone, a heat affected zone and the substrate. The properties of coatings enriched with both molybdenum and boron were better than those of the steel substrate, but only the use of a Mo-B mixture resulted in a significant improvement in microhardness and corrosion resistance.
In this paper, the influence of bentonite (BNT) on rheological properties, linear shrinkage, hardness, and structure of polyethylene wax (PE-wax) used in the lost-wax casting process are studied. ...Experiments were conducted with PE-wax with different contents of bentonite (from 0.1 to 5 wt.%). The structural changes of modified polyethylene wax were evaluated using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The addition of bentonite in a concentration range between 0 and 0.8 wt.% into PE-wax caused a decrease of the linear shrinkage and the hardness of PE-wax/BNT blends. Modified polyethylene wax containing greater than 1 wt.% of the filler showed an increase in viscosity. The DSC-based investigations confirmed good miscibility and a uniform structure of PE-wax with BNT. Moreover, an increase in melting temperature onset and its enthalpy observed for filler PE-wax material showed an influence of bentonite on the crystalline structure of the polymeric matrix. SEM observations of the fractured surfaces confirmed the homogeneous structure of blends with contents up to 0.8 wt.% BNT. In the case of higher filler concentrations, the presence of more numerous and large clusters of filler in the polymer matrix was observed due to the increase in the viscosity of the PE-wax/BNT melt composition during mixing. The PE-wax blend with 0.4 wt.% BNT gives better results of reduced linear shrinkage and lower hardness than unmodified material. Lastly, a new developed material (PE-wax/0.4 BNT) was subjected to technological tests, consisting of the preparation of the mold and manufacture of a high-quality aluminum cast, using the lost-wax method.
The paper presents the results of the microstructure investigation, phase and chemical composition, microhardness as well as corrosion and wear resistance tests of B-Si coatings produced on C45 ...steel. In this study, boron and silicon were added to the surface of steel using the laser alloying process. The main purpose of the study was to check whether the use of silicon, boron or a mixture of these chemical elements would improve the mechanical properties of the surface. Boron and silicon, as well as its mixture, were prepared in various proportions and subsequently were applied on steel substrate in the form of pre-coat (paste) of 80 µm thick. All pre-coats were processed by a laser beam and the obtained microstructures were analyzed and compared. Laser alloying processes were carried out using device equipped with a CO2 laser. After laser alloying, the microstructure consisted of a melted zone, heat affected zone and unchanged steel substrate. The newly created B-Si coatings were characterized by properties better than the case of boron and silicon coatings, with particularly high microhardness in the range from 1430 HV to 1870 HV, as well as high corrosion and wear resistance.
The paper presents the results of microstructure, mechanical and tribological tests of copper matrix sinters with the addition of nano-TiO2 and copper-decorated multi-walled carbon nanotubes. A ...powder metallurgy was used for the production of composite materials. The aim of the work was to determine the properties and wear mechanism of the produced sinters with single additives and to investigate the synergistic interaction of titanium dioxide and carbon nanotubes. Wear tests were carried out using the pin-on-disc method at room temperature and 600 °C. Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Raman Microscopy, Thermogravimetric Analysis (TGA), Dilatometry (DIL), X-Ray Diffraction (XRD), and profilometer were used for the research. Moreover, the stiffness and hardness of the sinters were examined. The main wear mechanisms of the friction pairs tested at room temperature and 600 °C were adhesive, abrasive, and oxidation wear. Furthermore, at the test temperature of 600 °C, the formation of a tribofilm was observed on the surface of the friction pairs, which reduced friction wear. The introduced additions to the copper matrix increased its hardness, stiffness, work of axial deformation, and wear resistance. Moreover, additions decreased the relative value of the thermal expansion coefficient of the sintered copper. The friction pair no. 2 (Cu + 1 wt % MWCNTs – Inconel®625) was characterized by the lowest coefficient of friction at room temperature and 600 °C, of approximately 0.62 and 0.56, respectively. The sintered composite material of Cu – 10 wt% nano TiO2 – 1 wt%. MWCNTs was characterized by the highest mechanical properties and the lowest wear.
•The influence of MWCNTs decorated with copper and nano-TiO2 on the mechanical and tribological properties was determined.•Stiffness modulus, axial deformation work, and tribological behavior of Cu-TiO2-MWCNTs composite materials were studied.•The improved wear resistance resulted from the formation of tribofilm on the worn surface at 600 °C.
4,5-Dicyanoimidazole and 2-aminothiazole are azoles that have previously been implicated in prebiotic nucleotide synthesis. The former compound is a byproduct of adenine synthesis, and the latter ...compound has been shown to be capable of separating C2 and C3 sugars via crystallization as their aminals. We now report that the elusive intermediate cyanoacetylene can be captured by 4,5-dicyanoimidazole and accumulated as the crystalline compound N-cyanovinyl-4,5-dicyanoimidazole, thus providing a solution to the problem of concentration of atmospherically formed cyanoacetylene. Importantly, this intermediate is a competent cyanoacetylene surrogate, reacting with ribo-aminooxazoline in formamide to give ribo-anhydrocytidine an intermediate in the divergent synthesis of purine and pyrimidine nucleotides. We also report a prebiotically plausible synthesis of 2-aminothiazole and examine the mechanism of its formation. The utilization of each of these azoles enhances the prebiotic synthesis of ribonucleotides, while their syntheses comport with the cyanosulfidic scenario we have previously described.
The paper presents the study results of the diffusion boronized layer and their laser modification. Diffusion boronized processes were carried out on Vanadis-6 steel at 900°C for 5h. Boronized layers ...were characterized by dual-phase microstructure consisting of iron borides having a microhardness in the range from 1800 to 1400 HV. The laser heat treatment was carried out using CO2 laser after diffusion boronizing process. The research goals of this paper was analysis of microstructure, microhardness as well as phase and chemical composition of boronized layers after laser modification. Microstructure of boronized layer after laser modification consisted of remelted zone, heat affected zone and substrate. Remelted zone was characterized by microstructure consisted of boron-martensite eutectic. In this zone, the phases of borides and carbides were detected. Boronized layers after laser modification were characterized by the mild gradient of microhardness from surface to the substrate.
•After laser remelting of boronized layers microstructure composed of three areas.•Boron content after laser remelting is dependent on the LHT parameters.•Microhardness after laser remelting had a mild transition from surface to substrate.
The paper presents the results of microstructure observations, microhardness measurements and wear resistance tests of B–Ni complex layers. Boronickelizing is a three-step process of layer production ...on metallic substrate. Nickel modified boronized layers were called ‘boronickelized’. Nickel plating was applied first and, as a result, nickel coatings with a varying thickness were obtained. Diffusion boronizing was carried out as a second step. Boronickelized layer was formed following the merger of galvanic and diffusion processes. In the third step the galvanic-diffusion boronickelized layer was obtained by remelting it with a CO2 laser beam. Galvanic-diffusion boronickelized layer had a dual-zone microstructure. The first zone was continuous and nickel-enriched, and characterized by reduced microhardness, whereas the second zone was characterized by needle-shaped microstructure, with microhardness similar to Fe2B iron borides. After laser modification steel specimens with the boronickelized layer consisted of remelted zone (MZ), heat affected zone (HAZ), and substrate. It was found that increasing the thickness of nickel coating leads to decreasing the microhardness of the remelted zone. Increasing thickness of nickel coating causes the reduction of wear resistance of boronickelized layer modified by laser beam. The application of a nickel coating thicker than 20µm causes incomplete remelting of needle-shaped microstructure of boronickelized layer.
•Nickel modified boronized layers have dual-zone structure.•After laser modification B–Ni complex layer consisted of three different zones.•New layers resulted in smooth microhardness gradient between surface and substrate.•Laser modification of B–Ni complex layers increased wear resistance.
We have synthesized alkyl(cyclohexyl)dimethylammonium bromides, formates and acetates, 2-methoxyacetates, 2-(2-methoxyethoxy)acetates, 2-2-(2-methoxyethoxy)ethoxyacetates, and 2-ethoxyacetates and ...assessed their ability to dissolve cellulose. Their physicochemical properties and microbiological activity were determined. Alkyl(cyclohexyl)dimethylammonium cation dimensions of alkyl groups are essential for cellulose solubility and are generally limited to butyl, hexyl, and octyl as effective substituents. In parallel, the alkyl group determines activity of the entire molecule against microbes. The molecule's biological activity against microbes begins when a length of the alkyl substituent begins to block cellulose solubility. We present the computational model of the solubility mechanism, composed of an ensemble of two cellobiose units and (cyclohexyl)hexyldimethylammonium acetate.
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