Materials Science Forum Vol. 1121

Abstract: Measurements over fractured surfaces of samples obtained from impact Charpy tests and four-point double-notch bend tests, carried out at-60°C and-196°C were performed in the present work. This in order to quantify cleavage facets misorientation for the resistance of cleavage fracture propagation. The material used for the analyses was a ferritic Grade A ship plate steel. The grains misorientation angle was quantified by measuring the orientation of single cleavage facets with respect to its neighbors, of a number of cleavage facets, and the misorientation angle was measured. The misorientation angle of cleavage facets was analyze in four groups: all facets, small-small, small-large and large-large facets in order to identify how this classification can affect the misorientation angle of cleavage facets. The results showed that high misorientation angles between neighboring grains, can act as barriers for cleavage propagation, and offer more resistance for brittle fracture propagation or may arrest potential microcracks of critical size in the ductile-brittle transition of ferritic steels. Therefore, the analysis revealed arrest of microcracks when the fracture path found high misoriented grains in the lower shelf of a Grade A ship plate steel. The effect of the misorientation of the ferrite grains in terms of the cleavage facets misorientation on fracture propagation was also discussed in the present work. Keywords: Cleavage fracture, Misorientation angle, Charpy tests, Four-point double-notch bend tests, Cleavage facets.

Abstract: A mechanical work piece created industrially frequently contains more than one machining process. Furthermore, it is a common activity of programmers, who make this selection every time a milling and drilling operation is conducted. Tool wear and borehole quality are two essential challenges for high precision drilling procedures, with Al 356 alloy being employed in experimental planning. Drilling specifications will be assessed in this work to get optimal parameters in minimizing the influence of drilling damage on alloy using a swarm-based optimization model. The drilling parameters are optimized using the Bacterial Foraging Optimization (BFO) method, which includes three control factors: depth, feed rate, and spindle speed. Each parameter is designed in three levels, with multiple performance characteristics such as thrust force, surface roughness, and delamination factor. This investigation was carried out in order to obtain the proper optimization. The feed rate, next to the spindle speed, was discovered to be the essential element inducing lamination in drilling, with this phenomenon occurring in each diameter of the drill bit. The results reveal that the feed rate and drill type are the most important parameters influencing the drilling process, and that employing this strategy can successfully improve drilling process outcomes.

Abstract: Steel hydrogen embrittlement (HE), a complex and multifaceted issue, can lead to sudden and catastrophic failure, without significant plastic deformation, making it a critical concern in the industrial sector. The present investigation focuses on the evaluation of HE effects regarding microstructure, mechanical properties degradation and type of fracture of AISI 1010 low-carbon steel, after accelerated hydrogen cathodic charging. Hydrogen was diffused electrolytically in 0.2 Μ H₂SO₄ solution, containing 3g/L of NH₄SCN, using a cathodic current density of 10 and 20 mA/cm², for 6 and 18 h. Mechanical properties were investigated through slow-rate tensile tests, as well as Charpy V-notch (CVN) impact tests, to determine the value of fracture toughness, both in uncharged and electrochemically pre-charged specimens. Vickers microhardness tests were conducted on the cross-sections of the hydrogen charged samples to evaluate embrittlement susceptibility, due to the presence of dissolved hydrogen. The microstructure modification was carried out through light optical (LOM) and scanning electron microscopy (SEM), in conjunction with an energy-dispersive X-ray detector (EDS). Slow scan X-ray diffraction (SSXRD) was also conducted for crystal structure analysis. The microstructure analysis showed the presence of large amounts of secondary cracks and cavities into the steel matrix, due to hydrogen diffusion and its accumulation at various sites. Hydrogen charging caused a significant gradual elongation decrease of the parent material, from 25% to 6.73%, in case of embrittlement at 20 mA/cm² for 18h. Accordingly, after 18 h of exposure, the impact energy decrement was determined at 31.5%, at a current density of 10 mA/cm², whereas the corresponding reduction at 20 mA/cm² reached 68%.

Abstract: Superduplex stainless steels have great mechanical and corrosion properties. However, its chemical composition makes it prone to intermetallic phase precipitation during thermal processing. Sigma (σ), chi (χ), and chromium nitrides (Cr₂N) remove Cr and Mo from the matrix, reducing the corrosion and mechanical resistance. Understanding the effects of thermal processing on the secondary phase’s precipitation and depletion of the material’s performance is crucial to its applications. Thus, this work aims to analyze the behavior of the corrosion performance of the UNS S32750 after thermal treatment at 800°C, for 60, 180, 300, and 420 minutes, in comparison to the as-received material. Optical emission spectrometry, X-ray diffraction, and SEM with backscattered electrons (BSE) were used to evaluate the material. The corrosion performance was evaluated with the cyclic potentiodynamic polarization technique. The main results and conclusions obtained in the study were a decomposition of the ferrite phase into the χ and σ phases, with the formation of the χ phase being predominant in shorter times, while for longer aging times σ formed in greater quantities. It was also possible to verify a more aggressive corrosion trend for aged samples in the regions adjacent to the formation of the χ and σ phases. It was also possible to observe that the losses generated in corrosion resistance were greater for aging times longer than 60 minutes. The aging treatment significantly reduced the material’s corrosion resistance in conjunction with the formation of precipitates.

Abstract: In the present study the notched fatigue behavior of two multi-phase medium entropy alloys (MEAs) AlCrFe₂Ni₂ and AlCrFe₂Ni₂Mo_0.1 was characterized by three-point-bending (3-PB), along with a super-duplex steel 1.4517 as a reference material. An analytical approach for characterizing the fatigue notch factor (k_f), based on grain size analysis in combination with finite element modelling (FEM) was used, relating the theory of critical distances (TCD) to the grain size of the material. To validate the approach, for the reference steel, the fatigue notch factor was also determined experimentally by comparing the fatigue behavior of notched and smooth specimens, resulting in an experimentally determined fatigue notch factor (k_f) ~ 1.07. The numerically and analytically estimated notch effects increase with decreasing average grain size and vary between ~ 1.07 for the coarse-grained reference material – in very good agreement with the experimental results – and ~ 1.35 for the much more fine-grained AlCrFe₂Ni₂Mo_0.1 medium entropy alloy. Note that these values are significantly lower than the stress concentration factor (k_t) ~ 1.58, associated with the notch geometry. Fatigue endurance limits were measured at a fatigue stress ratio R ~ 0.1 (unidirectional stress), but were converted to fatigue amplitudes at R = -1 (σ_{a, R-1}, fully reversed stress), to be able to make due comparisons with available literature data, by using the elliptical relationship. The resulting fatigue endurance limit amplitudes for specimens surviving at least 2E+06 cycles for a minimum of three tested samples and including notch effects are σ_{a, R-1} ~ 508 MPa for the AlCrFe₂Ni₂ alloy, σ_{a, R-1} ~ 540 MPa for the AlCrFe₂Ni₂Mo_0.1 alloy modification and σ_{a, R-1} ~ 400 MPa for the reference super-duplex steel, putting the analyzed MEAs into a very competitive position compared to Cobalt containing multi-phase high or medium entropy alloys as well as commercially available steels.

Abstract: The study of water treatment technologies has been growing due to mounting concerns regarding dye contamination. Adsorption-based technologies that use porous materials have been proven useful in water decontamination. However, porous silica xerogels have not been extensively explored as adsorbents for the methyl orange (MO) dye. In this study, the MO-adsorptive behavior of silica xerogels was investigated. Two silica xerogels were synthesized using tetraethyl orthosilicate, and one was modified with cetyltrimethylammonium bromide (CTAB). The adsorptive capacities of the unmodified silica xerogel (SiO₂-UN) and the CTAB-modified silica xerogel (SiO₂-CTAB) were compared. Results showed a better fit to the Langmuir isotherm model, with maximum adsorbed amounts of 1.52 mg g^-1 and 25.5 mg g^-1 for SiO₂-UN and SiO₂-CTAB, respectively. The higher value for SiO₂-CTAB is mainly attributed to the electrostatic interactions between MO and the ammonium groups present in the modified xerogel. A study of the porosities of both xerogels, using N₂ adsorption and desorption isotherms, indicated the samples were mesoporous. These findings suggest that SiO₂-CTAB exhibits favorable MO adsorption and could be employed in future wastewater treatment processes.

Abstract: At present, adding solid waste in plant substrate to replace part of planting soil has become a new direction in the field of ecological slope protection substrate research. In this paper, 16 groups of indoor orthogonal experiments were carried out with fly ash and sludge as the components of vegetation substrate and tall fescue as the planting object to explore the influence of ecological slope protection substrate on vegetation growth. Based on the range analysis method, the three functions of substrate planting performance, mechanical properties and substrate properties were used as references, and the entropy weight method (EWM) was used to assign weights to the proportion of each index in the total score, and the ratio was optimized. The results show that the optimal substrate ratio is 10% sludge content, 30% fly ash, 4% cement, 6% fiber, 50% planting soil (the ratio of loess and peat soil is 1:3). Fly ash has a great influence on the height of plants and vegetation coverage, and has a significant effect on the internal friction angle and fertility of the substrate. Sludge mainly affects the growth height of plants and the pH value and fertility of the substrate. The importance of factors affecting the growth of plants from large to small is: fly ash, the ratio of loess and peat soil, sludge, rice husk, cement.

Abstract: The monooxidation of methane into methanol was carried out on biomimetic heterogeneous catalyst – iron pentafluorotetraphenylporphyrin on Al₂O₃ (ImtOH), at atmospheric pressure and temperatures of 200-350°C, which resulted in liquid one-carbon compounds CH₃OH (19.2%), CH₂O (1.55%), CH₃OCH₃ (8.2%) with high selectivity and are widely used in the chemical industry. In order to establish the routes of these products formation and the mechanism for the methane conversion into them, the investigation of the methanol conversion reaction was carried out, as an intermediate compound of the methane oxidation, under identical conditions on the same catalyst.The result was only dimethyl ether with 100% selectivity. This proved that in this reaction system, methanol obtained from the methane monooxidation is converted only into dimethyl ether, and formaldehyde, in parallel with methanol, is formed from methane. The mechanisms of the elementary stages of the formation of methanol, formaldehyde and dimethyl ether on the surface of the bioimitator through the formation of an active complex (ImtOOH) are presented, in which the unity of the mechanisms of redox and acid-base catalysis traced within the framework of the principle of the bond redistribution chain (BRC), similar to enzymatic reactions.

Abstract: In Algeria, polyethylene (PE) pipes are commonly installed for the distribution of potable water and natural gas in urban and rural areas. They are used for economic reasons, in addition to perfect maintenance, compared to metal pipes. The experiences of these tube installations have shown technical advantages in operational safety aspects and structures lifespan with very interesting mechanical properties. The connection between the polyethylene pipes is done through couplings, which are considered expensive during their replacement due to frequent use, especially in the agricultural field. The main objective of the present experiment is to elicit the main parameters of friction stir welding on polyethylene pipes (butt welding) using a milling machine, especially the rotational speed of the clamped pipe sections called the rotational welding speed, which replaced the welding speed, with the highlighting of the clamping device to form a butt joint. In the present work, the process using the conventional tool is presented with the design and provision of a pipe assembly device intended for this research in order to weld these pipes together during the FSW process. The rotary device used in this experiment is mounted on a milling machine and rotates the tube sections attached to the rotating arms of the support. The spindle can rotate freely 360 ̊ with the tool's rotating speed of 1100 rpm. Two sections of high-density polyethylene pipes with an outer diameter of 125 mm, which are intended for natural gas distribution, were successfully welded to achieve the conventional friction stir welding (C-FSW) reliability of polyethylene pipes. This study makes it possible to highlight the parameters and the method, on which it is recommended to improve welded joints, in the context of research that will always be ongoing.