Materials and Technology

THE EFFECT OF CORROSION ON THE DYNAMIC BEHAVIOUR OF AISI 4140, AISI 4340, AND AISI 5140 STEELS EXPOSED TO 3.5 wt.% NaCl ENVIRONMENT

2024-12-05T12:40:04+01:00

Material loss due to corrosion can weaken the structural integrity of systems and potentially lead to failure if timely action is not taken. Such deterioration adversely affects the dynamic behavior of metals. This study deals with the post-corrosion changes in the dynamic behavior of AISI 4140, AISI 4340 and AISI 5140 metals after exposure to 3.5 wt.% NaCl for 1, 7, 15 and 30 days. Electrochemical impedance spectroscopy (EIS) and dynamic electrochemical impedance spectroscopy (Dynamic-EIS) were used to elucidate the corrosion mechanisms. Modal analysis and finite element method (FEM) were used to characterise dynamic behavior changes. In addition, scanning electron microscopy (SEM-EDS) was used to analyse changes in surface morphology after corrosion. The results show a decrease in the corrosion resistance of AISI 4140, AISI 4340 and AISI 5140 metals over time, although there is an improvement after 30 days. The electrochemical test results indicated that the metal with the highest corrosion resistance in a 3.5 wt.% NaCl environment was 4340, while the lowest was 5140. In particular, the natural frequency values showed a decreasing trend with increasing corrosion exposure time, accompanied by discernible changes in mode shapes.

INVESTIGATION OF THE FACTORS AFFECTING THE STRENGTH OF A METAL-RUBBER INTERFACE JOINED BY VULCANIZATION: A REVIEW

2024-12-05T12:33:29+01:00

Metal-rubber parts are used in many sectors because of their ability to combine the advantages of both rubber and metals. Thanks to the advances acquired as a result of the studies carried out by researchers and industries, the usage area of metal-rubber parts expands day by day. The focus of researchers in this field continues to be on achieving effective joints, improving their durability, and ensuring their preservation, as these composites find wide-ranging use. In particular, the positive effects of newly developed surface treatments and adhesive materials on bond strengths have been observed in recent years. Within the scope of this study, the metal-rubber bonding mechanism, vulcanization, bonding during/after vulcanization, some standards related to rubber, bond failures, and their causes are investigated. This review focuses on studies addressing the factors influencing the interfacial strength of metal-rubber bonds joined by vulcanization. Additionally, it provides information on studies and their findings up to date regarding the effects of vulcanization parameters, corrosive environments, components in the bonding process, and different substrates on the bond strength.

EFFECTS OF DIFFERENT LOADING DIRECTIONS ON THE ORGANIZATION AND PROPERTIES OF MAGNESIUM SINGLE CRYSTALS BASED ON MOLECULAR DYNAMICS

2024-12-05T12:33:29+01:00

Magnesium and its alloys are widely used as high-quality metal materials in various fields. In this study, the tensile properties of magnesium single crystals under different loading directions were investigated based on the molecular dynamics theory. By analyzing the changes in stress, potential energy, crystal structure, and dislocation lines, the following conclusions can be drawn: There are differences in strain values, dislocation line arrangement laws, and crystal structures of magnesium single crystals when dislocation lines are generated under different loading directions. However, the types of dislocation lines are generally the same, with 1/3 dislocations and dislocations with an unknown structure being dominant. Furthermore, the results indicate that the number of 1/3 dislocations is larger than that of dislocations with an unknown structure. These findings are of great significance for a deeper understanding of the deformation mechanism of magnesium single crystals.

EXPLORING CORROSION RESISTANCE AND MICROSTRUCTURE OF MANGANESE PHOSPHATE CONVERSION COATING ON 65Mn SPRING STEEL

2024-12-05T12:33:30+01:00

Manganese phosphate conversion coatings were prepared on 65Mn spring steel. The surface morphologies and compositions of the coatings were examined through scanning electron microscopy (SEM) and X-ray diffraction (XRD). The corrosion resistance of the coatings was investigated using a copper sulfate titration experiment, salt spray test and electrochemical corrosion test. The results showed that a uniform and dense coating was obtained when the acid ratio was 10, the phosphating temperature was 85 °C, and the phosphating time was 5 min. There was no obvious rust on the manganese phosphate coating surface after 48 h of salt spray. Ultimately, the growth mechanism and corrosion behavior of the manganese phosphate conversion coating are explained.

DEFECT CHARACTERIZATION OF METALLIC MATERIALS USING SELF-PARAMETERIZED DENSITY-BASED CLUSTERING AND COMPUTATIONAL INTELLIGENCE TECHNIQUES

2024-12-05T12:33:30+01:00

Rapid growth of manufacturing industries is propelled by transformative technologies such as machine intelligence, autonomous computing and non-destructive testing (NDT). During the manufacturing of wrought products, there is no guarantee that the final product is 100-% flawless. Thus, all final products are subjected to quality checking to identify and eliminate defective products. In industries, most of internal defects are identified using NDT techniques, which fail to precisely characterize the defects. In this paper a novel algorithm, called Self-Parameterized Density-Based Clustering (SPDBC), is proposed for defect characterization. The proposed clustering method uses spatial parameters to identify the size and position of defects by filtering out the noise and other data that correspond to the non-defect area. Using these filtered data, computational intelligence techniques are employed to predict the defect type. SPDBC achieved Jaccard indices of 97.02 % and 98.78 % for identifying the defect size and position, respectively. Gradient boosting regression trees (GBRT) achieved a maximum accuracy of 97.44 % in predicting the defect type. As a result, the proposed approach can assist NDT experts in various sectors to differentiate between problem severities faster and replace defective parts before any major breakdown occurs.

COMPOSITION DESIGN OF 316LN AUSTENITIC STAINLESS STEEL FOR LIQUID-HYDROGEN STORAGE BASED ON HIGH-FLUX PREPARATION

2024-12-05T12:33:31+01:00

Designing multi-element alloy compositions to achieve target performance was the first step in the development of modern materials, but the traditional trial-and-error experiment seriously restricted the development of new materials due to its low efficiency. In this investigation, the composition design of 316LN austenitic stainless steel for enhanced liquid-hydrogen storage using multi-crucible synchronous metallurgy in a high-flux experiment was proposed. Sixteen groups of as cast austenitic stainless steel samples with different compositions were smelted using high-flux material preparation. Then, through the observation of their microstructures, the chemical composition that best matched the target performance was finally selected. The results show that high-throughput experiments can greatly improve the efficiency of composition design optimization of new stainless steel products. At the same time, this investigation also analyzed the elemental composition of δ-ferrite and the method for effectively controlling the δ-ferrite content. In 316LN stainless steel, Cr and Mo were easily enriched in ferrite grains or grain boundaries, forming Cr and Mo enriched regions. This resulted in a gradient transition of Cr and Mo from the ferrite region to the austenite region, forming galvanic corrosion. In this study, the distribution of Cr, Mo and other elements in 316LN stainless steel was studied by means of a metallographic microscope, electron probe microanalysis, transmission electron microscope and scanning electron microscope. In addition, the relationship between the ferrite content and chemical composition was explored. Finally, it was determined that high-temperature, long-term sensitization treatment is an effective method for controlling the δ-ferrite content.

DEVELOPMENT OF REFRACTORY CONCRETE USING GLASS GRINDING WASTE SAND

2024-12-05T12:33:32+01:00

This study investigates the utilization of glass grinding waste sand as an alternative fine aggregate in the formation of refractory concrete. Experimental refractory-concrete samples were subjected to sintering at 1200 °C, followed by a comprehensive evaluation of their physical and mechanical properties. The parameters assessed included flexural strength, volume density, shrinkage/expansion behavior upon drying and firing, thermal shock resistance, and thermal conductivity, following Vietnamese standards. Additionally, the mineral composition was determined using X-ray diffraction, while the microstructural characteristics were analyzed via scanning electron microscopy. Experimental findings indicate that incorporating 5 wt.% of glass grinding waste sand enhances the degree of sintering in refractory concrete at elevated temperatures while maintaining its essential refractory properties. The XRD analysis revealed the presence of α-Al₂O₃ and γ-Al₂O₃ phases, contributing to the refractory concrete’s improved heat resistance and thermal shock resistance. The SEM analysis corroborated these findings by illustrating the microstructural modifications imparted by the glass grinding waste sand. Incorporating glass grinding waste sand at an optimal concentration of 5 w/% promotes sintering at high temperatures and preserves the critical refractory characteristics of concrete. This study underscores the potential of glass grinding waste sand as a viable alternative fine aggregate for refractory concrete, contributing to material sustainability and performance improvement.

EFFECT OF Y ON THE MECHANICAL PROPERTIES AND CORROSION RESISTANCE OF AS-EXTRUDED Mg-4Sn ALLOYS

2024-12-05T12:33:32+01:00

In this study, the effects of Y element on the microstructure, mechanical properties and corrosion resistance of an extruded T4 alloy at room temperature were studied by comparing the as-extruded Mg-4Sn (T4) and Mg-4Sn-1Y (TW41) alloys. The results showed that the second phase of the as-extruded T4 alloy is mainly the Mg₂Sn phase, while the ternary MgSnY and Mg₂Sn phases mainly precipitate after the addition of Y element. Incomplete dynamic recrystallization of the two alloys occurs during the extrusion process, and the addition of Y element can promote dynamic recrystallization and refinement of the grains in T4 alloy. At room temperature, TW41 alloy has higher strength compared to T4 alloy, with tensile and yield strengths of 228 MPa and 165 MPa, respectively, but the elongation and corrosion resistance are reduced. Grain refinement is believed to play the key role in improving the yield strength of TW41 alloy, while the deterioration of the corrosion resistance of TW41 alloy is mainly attributed to the increase in the grain boundary density caused by grain refinement, accelerating the dissolution of the alloy anode.

STUDY ON THE CORROSION RESISTANCE OF HOMOGENEOUS Mg-1Bi-0.5x (x=Nd,Ce,La) ALLOYS

2024-12-05T12:33:33+01:00

Mg alloys are widely used in the aerospace and automotive industries, as well as in electronic products due to their low density and high specific strength. However, the poor corrosion resistance of Mg alloys limits their applications. Rare earth elements have been shown to improve the corrosion resistance of alloys. In this study, Mg-1Bi-0.5x (x = Nd, Ce, La) alloys were prepared by alloying with Bi, Nd, Ce, and La. The microstructure and corrosion behavior of Mg-1Bi-0.5x (x = Nd, Ce, La) alloys were investigated using X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), hydrogen evolution tests, weight loss experiments, and electrochemical measurements. The results indicate that the Mg-1Bi-0.5Nd alloy exhibits higher corrosion potentials and lower corrosion current densities, indicating superior corrosion resistance. This improvement is attributed to the formation of a more stable and uniform film of corrosion products, which prevents further corrosion and enhances corrosion resistance.

YARN UNWINDING FROM PACKAGES

2024-12-05T12:41:24+01:00

Yarn unwinding from a package is important in many processes. In production the yarn is being withdrawn from cross-wound packages in warping and weft insertion. The quality of the yarn is numerically expressed mainly by the values of mechanical quantities. They depend on how the yarn is stressed. During unwinding of the yarn at high speed from a stationary package, the tension oscillates within some interval. It happens that, when the yarn is not strongly stressed and the tension is not high, the yarn breaks. This is why we think that a cross-wound package is not an ideal form of package and that such packages are not always made without flaws. We strive to achieve the fastest warping and weaving speeds as possible; therefore, our aim is to improve the theory of cross-wound package unwinding and to find the necessary modifications of the yarn-unwinding process. The goal of our contribution is to state the equations of motion that describe the unwinding yarn and to develop a mathematical model that would enable us to simulate the process of unwinding.

COMPARISON OF NITROGEN-DOPED PHOTOCATALYTIC SURFACES SYNTHESIZED BY PVD AND SOL-GEL METHODS

2024-12-05T12:33:34+01:00

The aim of this study was to produce photocatalytic TiO_2–xN_x coatings that can be active in visible light using different methods. Physical vapour deposition (PVD) and sol-gel methods were preferred for these coatings. Thin films were synthesized by dip coating on a glass substrate using the sol-gel method. In addition, thin glass film coatings were obtained by applying an arc for one minute to the glass films using the PVD method. Since the coating phase is important in terms of photoactivity, a phase analysis was performed using XRD. The obtained surfaces will be used in antibacterial applications. Therefore, the thickness of the coatings was determined with the X-Ray refraction method, and their optical band gap was measured. Based on these values, it was observed that nitrogen has a reducing effect on the optical band gap in titanium oxide-based coatings. The aim of nitrogen doping was to enhance photoactivity by adding an additional band between the valence band and conduction band of a photocatalytic surface. After these experiments using rhodamine-B and methylene blue solutions, specimens’ photocatalytic effects under fluorescent, sun and UV light were tested. It was determined that nitrogen’s decreasing effect on the optical band gap results in increased photoactivity with both PVD and sol-gel techniques. In addition, it was found that the coatings made with PVD exhibited a more controlled structure in a shorter time, while the production of sol-gel coatings was a much cheaper method, with low investment costs.

SMART PIEZO-ENABLED GLASS-FABRIC-REINFORCED COMPOSITE STRUCTURE: EXPERIMENTS AND FINITE-ELEMENT MODELING

2024-12-05T12:33:34+01:00

This paper deals with an experimental and finite-element investigation of smart polyvinylidene fluoride (PVDF) embedded with a glass-fabric-reinforced polymer (GFRP) beam structure under vibration. PVDFs are well known stretchy polymer that process the properties of both piezoelectric and pyroelectric materials. An LDT0-028K PVDF polymer film is proposed in the present paper. Glass-fiber-reinforced polymer is a lightweight composite material having a high specific strength and specific stiffness, due to which it has a wide range of applications in the field of smart composite structures. GFRP laminates and beam structures are fabricated in the present investigation through a vacuum-assisted resin-infusion process (VARIP). Mechanical characterization in accordance with ASTM standards were also carried out for the purpose of the estimation of uni-directional mechanical properties of GFRP, which are a pre-requisite for finite-element simulations. Both the experiments and the finite-element modelling were carried out for the smart piezo composite beam structure under forced vibration conditions. The finite-element computations were incorporated in the present study using ANSYS^® 16.0 Mechanical APDL. The results of the experimental and FEM investigations show a deviation of around 6.2 %, with the experimental values validating the FEM analysis. Based on the harmonic response of the smart piezo-composite beam, a micro-energy harvesting study was established with reference to the varying frequency and voltage.

THE EFFECT OF SILICON-CARBIDE ADDITIONS ON THE MECHANICAL AND THERMAL CONDUCTIVITY PROPERTIES OF FIBER-REINFORCED EPOXY COMPOSITES

2024-12-05T12:33:35+01:00

This study investigates the impact of adding silicon carbide (SiC) filler with various weight percentages on the mechanical and thermal properties of carbon- and glass-fiber-reinforced epoxy composites. Alterations in the filler content were analyzed to observe the composite material’s response to loading, assessing mechanical properties such as hardness, impact resistance, tensile strength, flexural strength and thermal conductivity. The investigation focuses on composite materials comprising carbon fibers and glass fibers to enhance the binder material (epoxy resin). Accordingly, four different groups of samples were prepared for experimentation. The first group consisted solely of epoxy resin, while the second group of samples contained epoxy resin reinforced with 15 w/% SiC. The third and fourth groups of samples included three layers of glass fibers, with and without 15 w/% SiC reinforcement, respectively. In the fifth and sixth groups of samples there were three layers: one upper layer of glass fibers, one layer of carbon fiber in the middle, and one layer of glass fiber at the bottom, with and without 15 w/% SiC reinforcement, respectively. The experimental findings revealed that the sixth group of samples exhibited lower heat conductivity (with an overall reduction of 10.9 % compared to samples from other groups), while demonstrating the highest tensile strength, hardness, flexural strength values and impact resistance (showing improvements of 20 %, 50 %, 19.5 %, and 11 % respectively, compared to samples from other groups).

THE EFFECT OF ALLOYING ADDITIVES AND PROCESS PARAMETERS ON THE SOLIDIFICATION CHARACTERISTICS OF THE ALUMINIUM ALLOY AlSi7Mg0.3

2024-12-05T12:33:35+01:00

We have investigated the aluminium alloy AlSi7Mg0.3, which is used in the production of castings. Melting was carried out in an electric resistance furnace. Casting was done into measuring cells with thermocouples for simple thermal analysis. Six samples that differed in terms of the additives used for grain refinement and inoculation, with two different holding times, were cast. An alloying material AlTi5B1 was used for grain refinement. The inoculation effect on the solidification was studied with the addition of the inoculant AlSr10. The temperature of the melt in the furnace was 750 °C and the melting time was one hour and ten minutes. Firstly, the samples were cast, the melt was cooled, solidification occurred and finally it was cooled down in the solid state. During the entire cooling process, the temperature as a function of time was measured and the cooling curves were obtained. After the casting, samples for metallographic inspection were prepared. The cooling curves show that in samples with a longer holding time, the additions of either the inoculant or the grain refinement agent, had a better effect. This is evident with a higher maximum liquidus temperature T_Lmax in sample Ti10 and lower maximum eutectic temperature T_E1max in sample Sr10 in comparison to the basis alloy. The same we can conclude from the microstructure analysis of the samples. The samples with inoculant and with a longer holding time, possessed a finer eutectic structure (α_Al+β_Si), than the samples with the shorter holding time. The same applies for the samples with grain-refinement additions. The estimated grain sizes were smaller in the sample with the longer holding time.

EFFECT OF NITROGEN ON THE THERMAL DEFORMATION BEHAVIOR OF MARTENSITIC STAINLESS BEARING STEEL

2024-12-05T12:33:36+01:00

The thermal deformation behaviors of martensitic stainless bearing steels (0.16N, 0N) in the temperature range 850–1150 °C, strain rate 0.01–10 s^–1, and deformation of 60 % were studied using a single-pass compression experiment. After adding 0.16 % nitrogen, the peak stress of the martensitic stainless bearing steel increased under all thermal forming conditions, and the average peak stress increased by about 33.724 MPa. The strain-rate sensitivity diagram, power dissipation diagram, instability factor diagram, and thermal processing diagram under different strains were constructed based on the stress-strain curve. The thermal deformation activation energy under different strains was constructed and combined with a metallographic structure analysis. The results show that under the same conditions, the occurrence of DRX in 0.16N bearing steel is less than that of 0N bearing steel, but the grains are finer than those of 0N bearing steel.

OPTIMIZATION OF Al-BASED AMORPHOUS COATINGS BY WARM SPRAYING BASED ON A NUMERICAL SIMULATION AND A RESPONSE-SURFACE METHODOLOGY

2024-12-05T12:33:36+01:00

Al-based fully amorphous coatings with low porosity were prepared using a warm-spraying technology by combining numerical simulations and a response-surface methodology (RSM). The influences of spraying parameters (reactant flow rate, oxygen/fuel (O/F) ratio, coolant flow rate, and spraying distance) on the particle temperature and velocity were investigated using numerical simulation methods. On this basis, the response-surface equations for temperature and the velocity of the particles were established using the Box-Behnken Design (BBD) methods. The RSM was used to analyze the influence of the interactions between the spraying parameters on the temperature and the velocity of the particles. The optimum spraying parameters (OSP) predicted by the response optimizer were 0.012047 kg/s for the reactant flow rate, 0.011034 kg/s for the coolant flow rate, 2.7 for the O/F ratio, and 142 mm for the spraying distance. According to the OSP, the Al-based fully amorphous coatings with a porosity of 0.08% were obtained by warm-spraying experiments. This work provides guidance for the production of Al-based fully amorphous coatings with low porosity using warm spraying.