The paper presents the impact of exceeding the railway rails lifespan which usually causes a railway structural failure, thus an accident. The research highlights the rails’s high degradation, especially on the running area, consisting in 60-70% weight loss by advanced wear of the rail, followed by fatigue fracture caused by alternating cyclic stresses that initiates the crack and also by tensile stresses resulting in the crack growth. The chemical composition, structural and mechanical properties were analyzed in order to establish the causes that led to the railway rails rupture.

The introduction of carbon nanotubes (CNTs) onto glass fibre (GF) to create a hierarchical structure of epoxy laminated composites has attracted considerable interest due to their merits in improving performance and multifunctionality. Field emission scanning electron microscopy (FESEM) was used to analyze the woven hybrid GF-CNT. The results demonstrated that CNT was successfully deposited on the woven GF surface. Woven hybrid GF-CNT epoxy laminated composites were then prepared and compared with woven GF epoxy laminated composites in terms of their tensile properties. The results indicated that the tensile strength and tensile modulus of the woven hybrid GF-CNT epoxy laminated composites were improved by up to 9% and 8%, respectively compared to the woven hybrid GF epoxy laminated composites.

Geopolymer is synthesized by polycondensation of SiO4 and AlO4 aluminosilicate complexes, tetrahedral frames linked with shared sialate oxygen. This paper studies the effect of the solids-to-fluids (S/L) and Na2SiO3/NaOH proportions on the preparing of metakaolin inorganic membrane geopolymer. By consolidating a mixture of metakaolin with sodium hydroxide, sodium silicate and foaming agent, the geopolymer membrane was made in required shape about 1 cm and cured at 80°C for 24 hours. After the curing process, the properties of the samples were tested on days 7. Sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) solution were utilized as an alkaline activator with a NaOH fixation fixed at 10 M. The geopolymer inorganic membrane tests were set up with various S/L proportions (0.8, 1.0, 1.2 and 1.4) and Na2SiO3/NaOH proportions (0.5, 1.0, 1.5, 2.0 and 2.5). Aluminium (Al) powder as a foaming agent was used to create bubbles in porous structure and provide details on the development of membrane geopolymers. This metakaolin membrane, based on the geopolymer, was synthesized by a suspension that depends on the fast cementing mechanism of high-temperature slurries. Porous geopolymeric circles provided a homogeneous composition and quantitative distribution of pores. The water absorption, density, impact toughness testing and microstructure analyses were studied. However, considering the promising results, an adjustment in the mix design of the metakaolin inorganic membrane geopolymer mixtures could increase their mechanical properties without negatively affecting the mechanical properties and porosity, making these sustainable materials a suitable alternative to traditional porous cement concrete.

The most common means to analyze redox gradients in sediments is by push/pulling electrochemical probes through sediment’ strata while repeating measurements. Yet, as electrodes move up and down they disrupt the texture of the sediment layers thus biasing subsequent measurements. This makes it difficult to obtain reproducible measurements or to study the evolution of electrochemical gradients. One solution for solving this problem is to eliminate actuators and electrode movements altogether, while instead deploying probes with numerous electrodes positioned at various depths in the sediment. This mode of operation requires electrode switching. We discuss an electrode-switching solution for multi-electrode probes, based on Complementary Metal-Oxide-Semiconductor (CMOS) multiplexors. In this solution, electrodes can be individually activated in any order, sequence or time frame through digital software commands. We discuss constraints of CMOS-based multilayer electrochemical probes during cyclic voltammetry.

This work presents the development of a safer processing route for hard metals. Traditional processing of fine particles under organic solvents presents significant explosion risks. The milling under dichloromethane (DCM) reduces the risks associated with fire hazards. After milling and drying, the samples have been sintered in an industrial sintering furnace under a vacuum at 1380°C. The materials’ characterisation has been done by X-ray diffraction, scanning electron microscopy, particle size analysis, optical microscopy, and by magnetic measurements. The present work results reveal the powders’ appropriate properties after milling and drying and the desired biphasic (Co-WC) phases obtained after sintering, thus proving the feasibility of such a route, therefore the diminishing of specific fire hazards.

The aim of this paper was to study the corrosion behavior of Nickel – Base – Dental Alloys in Ringer biological fluid. The Nickel base alloys are widely used for medical purposes, especially for prosthetic works in the field of dentistry. The applied electrochemical methods used for corrosion investigations are Open Circuit Potential, Linear Polarization during time of immersion in order to calculate the polarization resistance and corrosion rate. Potentiodynamic Polarization diagrams was performed to appreciate the passive domain. Ni-Cr Ugirex alloy show a better corrosion resistance in Ringer solution which will be reflected in a longer life of the dental structures made with this alloy as compared to the Ni-Cr Ducinox alloy, which will result in dental structures with a shorter lifespan.
The electrochemical studies has shown that the alloy have a corrosion behavior similar to a passivating alloy, displaying an extensive passivity area due to formation of an oxide film.

In this paper there are presented some results obtained by open circuit potential and electrochemical impedance spectroscopy measurements from studies performed on the behavior of tribocorrosion on metallic implant biomaterials as: 304L stainless steel, Co/nano-CeO2 nanocomposite layer and Ti6Al4V untreated and oxidized alloy to form a nanoporous TiO2 film. The open circuit potential technique used in measuring the tribocorrosion process provide information on the active or passive behavior of the investigated metallic biomaterial in the biological fluid, before, during friction and after stopping the friction. Thus it clearly show a better behavior of Co/nano-CeO2 nanocomposite coatings as compared with 304L stainless steel to tribocorrosion degradation in Hank solution; as well the better behavior of nanoporous TiO2 film formed annodically on Ti6Al4V alloy surface as compared with untreated alloy to tribocorrosion degradation in artificial saliva Fusayama Meyer. The slight decrease in polarization resistance value resulted from electrochemical impedance spectroscopy measured during friction in the case of the Co/nano-CeO2 nanocomposite layer (four times smaller), compared to 304L stainless steel, whose polarization resistance decreased more than 1000 times during friction shows the higher sensitivity of stainless steel to degradation by tribocorrosion. The same behavior is observed when comparing the polarization resistance of untreated titanium alloy recorded during friction that is about 200 hundred times smaller, while the specific polarization resistance of the oxidized alloy with the nanoporous film of titanium oxide, decreases very little during friction, highlighting the beneficial effect of modifying the titanium alloy by anodic oxidation to increase its resistance to the degradation process by tribocorrosion.

In the domain of the equipment and apparatus construction, a permanent preoccupation worldwide is ensuring technical performances and high fiability in exploitation. The users’ requirement growth in this field led to producing materials with high characteristics such as iron-nickel alloys having a high nickel content with special magnetic, thermal, or elastic properties. The theoretical and experimental researches had the aim of obtaining cold rolled strip, thin (2.6 mm) and narrow (86 mm) from iron-nickel alloys with 41% Ni (low content of C: 0.02-0.04%; Fe: 58%; other elements: Mn, Si, Cu, Cr, Al: under 1%). Our own experiments aimed to establish an optimal cold rolling technology of hot rolled strips of iron-nickel alloys, in order to obtain cold rolled strips with superior mechanical and technological characteristics, strip profile according to current standards, including a finished product characterization.

The study investigated the primary structure of the new generation of superalloys based on Co-10Al-5Mo-2Nb and Co-20Ni- 10Al-5Mo-2Nb cobalt. Research on a group of cobalt-based materials was initiated in 2006 by J. Sato [1]. These materials may replace nickel-based superalloys in the future due to their excellent properties at elevated temperatures relative to nickel-based superalloys. The primary microstructure characterisation of the Co-10Al-5Mo-2Nb and Co-20Ni-10Al-5Mo-2Nb alloy are the basic subject of this article. The Co-10Al-5Mo-2Nb and Co-20Ni-10Al-5Mo-2Nb alloy are tungsten free alloys of a new type with the final microstructure based on the Co-based solid solution L12 phase of the Co3(Al,Mo,Nb) type as a strengthened structural element. The analysed alloys were investigated in an as-cast state after a vacuum casting process applied on graphite moulds. The primary microstructure of the alloys and the chemical constituent of dendritic and interdendritic areas were analysed using light, scanning electron and transmission microscopy. Currently, nickel-strengthened γ’ phase steels are still unrivalled in aerospace applications, however, cobalt based superalloys are a response to their existing limitations, which do not allow maintaining the current rate of development of aircraft engines.

Biodegradable materials represent a new class of biocompatible materials with applications in many medical cases where the support must be provided only for a certain period. In this article obtaining of ZnMgY alloy is presented along with some basic characteristic investigations like chemical composition (energy dispersive spectroscopy – EDS), microstructure (optical microscopy – OM and scanning and electron microscopy – SEM), immersion behavior in 10xDPBS (Dulbecco Phosphate Buffer Saline) solution (mass loss and surface degradation), electro-corrosion behavior (potentiostat with a three electrodes cell) and micro-hardness of the experimental alloy compared to cast Zn and ZnMg materials. The results present an improvement of micro-hardness of Zn by alloying with Mg and Y and a modification of corrosion resistance.

Nanostructured systems based on ZnO nanoparticles composite systems/polymer fibers have attracted a lot of attention in the last years because of their applications in multiple areas. Nanofibres based on polymers are used in many domains such as nanocatalysis, controlled release of medicines, environmental protection and so on. This work show the synthesis of cellulose acetate butyrate (CAB) nanofiber useful as substrates for growing ZnO nanocrystals and that ZnO is an unorganic metal oxide nanoparticle used to improve the piezoelectric properties of the polymer. The piezoelectric propertiesof ZnO-doped polymeric was investigated with atomic force microscopy and measurements were performed, in contact technique, in piezoelectric response mode (PFM).In order to analyze the structural and textural features, the obtained materials were characterized using advanced physical-chemical techniques such as X-ray diffraction (XRD), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM). The XRD patterns show the characteristic reflections of ZnO with a hexagonal type wurtzit structure and the broad peaks of the polymer. The SEM images reveal the presence of ZnO nanoparticles on top of the polymer nanofibres.In most ZnO-based nanocomposites their morphology is uncontrolled (agglomerated granules), but in ase of using cellulose acetobutyrate this becomes controlled by observing through flower-like structures SEM and AFM) The study of the functional properties of ZnO/polymer fiber composite systems showed that they have piezoelectric properties which give them the characteristics of smart material with possible sensor and actuator applications.Recent literature reports that the synthesis and characterization of ZnO-polymer nanocomposites are more flexible materials for various applications.

Setting time in geopolymers is known as the time taken for the transition phase of liquid to solid of the geopolymer system in which is represented in the initial setting and final setting. Setting time is significant specifically for application in the construction field. This study intends to determine the setting time of high calcium fly ash geopolymers and the properties of the geopolymers after setting (1-day age). This includes the determination of heat evolved throughout geopolymerization using Differential Scanning Calorimeter. After setting properties determination includes compressive strength and morphology analysis at 1-day age. High calcium fly ash was used as geopolymer precursor. Meanwhile, for mixing design, the alkali activator was a mixture of sodium silicate and sodium hydroxide (concentration varied from 6M-14M) with a ratio of 2.5 and a solid-to-liquid ratio of 2.5. From this study, it was found that high calcium fly ash geopolymer with 12M of NaOH has a reasonable setting time which is suitable for on-site application as well as an optimal heat evolved (–212 J/g) which leads to the highest compressive strength at 1-day age and no formation of microcracks observed on the morphology. Beyond 12M, too much heat evolved in the geopolymer system can cause micro-cracks formation thus lowering the compressive strength at 1-day age.

This paper presents a comparative study of the preparation and characterisation of Fe _38.5 Co _38.5 Nb ₇ P ₁₅Cu ₁ alloy produced by mechanical alloying (MA) and rapid quenching (RQ) method. In order to obtain the starting mixture (SS) in the present study, we opted for the replacement of elemental Nb and P powders with ferroalloy powders of niobium and phosphorus. Benzene was used as a control agent of the process (PCA) for wet MA. The samples obtained (powders and ribbons) were characterised by X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), X-ray microanalysis (EDX), magnetic measurements M(H) and thermomagnetic measurements M(T). After 40 h of wet MA, the alloy was partially amorphous, and the ribbons obtained by RQ do not show an amorphous state. Also, the magnetic measurements show the influence of the method used on the magnetic properties.

Research in additive manufacturing of tungsten carbide-cobalt has intensified over the last few years due to the increasing need for products designed using topology optimisation and multiscale structures (lattice). These products result in complex shapes and contain inner structures that are challenging to produce through conventional techniques, thus involving high costs. The present work addresses this problem using a two-step approach to 3D print parts with complex shapes and internal structures by employing indirect selective laser sintering (SLS) and tungsten carbide-cobalt sintering. The paper takes further our research in this field [1] to improve the part density by using high bulk density tungsten carbide-cobalt powders. Mechanically mixing tungsten carbide-cobalt with the sacrificial binder, polyamide 12, results in a homogenous powder successfully used by the selective laser sintering process to produce green parts. By further processing, the green parts through a complete sintering cycle, an average final part density of 11.72 g/cm3 representing more than 80% of the theoretical density is achieved.

Ballistic targets are multi-material assemblies that can be made of various materials, such as metal alloys, ceramics, and polymers. Their role is to provide collective or individual ballistic protection against high-speed dynamic penetrators or kinetic fragments. The paper presents the impact behavior with incendiary perforating bullets having 7.62 mm of ballistic packages made of combinations between Dyneema ultra-high-molecular-weight polyethylene and high entropy alloy from alloying system AlCoCrFeNi, by analyzing the dynamic phenomena (deformation, perforation) that take place at high speeds. The geometry evolution of the physical model subjected to numerical simulation allows a very good control over the discretization network and also allows the export for modeling to nonlinear transient phenomena. The results obtained by numerical simulation showed that the analyzed ballistic package does not allow sufficient protection for values of impact velocities over 500 m/sec.

Initial investigations on oxidation behaviour and phase transformations of equimolar AlCoCrCuNi high entropy alloy with and without 1 at.% silicon addition during 24-hr exposure to air atmosphere at 1273 K was carried out in this work. After determining the oxidation kinetics of the samples by means of thermogravimetric analysis, the morphology, chemical and phase compositions of the oxidized alloys were determined by means of scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction analysis. Additional cross-section studies were performed using transmission electron microscopy combined with energy dispersive X-ray spectroscopy and selected area electron diffraction. From all these investigations, it can be concluded that minor silicon addition improves the oxidation kinetics and hinders the formation of an additional FCC structure near the surface of the material.

Friction stir welding (FSW) currently contributes a significant joining process for welding aluminium, magnesium, and other metals in which no molten or liquid state were involved. It is well known that aluminium alloys are more effective, promising for different applications light weight, strength and low cost. This study aims to determine how such tools geometry and tool speed can be related to dissimilar material in the joining process. Specifically, it investigates whether the distribution of the weld zone particularly between tool pin profile to rotational speed. In this context, the influence of tool pin profile and tool rotational speed in relation to the mechanical properties and microstructure of friction stir welded. The aim of this study is also to test the hypothesis that better mixing between dissimilar metals at higher tool rotational speed along the weld path. Three different tool profiles were configured with AA5083 and AA7075. During welding, notable presence of various types of defects such as voids and wormholes in the weld region. The results of this work showed that the tool pin profile and weld parameter are significant in determining mechanical properties at different tool rotational speed. The highest tensile strength achieved was about 263 MPa and the defectfree joint was obtained by using the threaded tapered cylindrical pin tool at a rotational speed of 800 rpm. These findings indicate that different tool profiles influence differently on the formation of defects at welds. On this basis, the tool geometry should be considered when designing experimental friction stir welded joint.

The S304H steel is used in the construction of pressure components of boilers with supercritical operating parameters. The paper presents the results of the research on the microstructure after ageing for 20,000 hours at 650 and 700°C. The microstructure examination was performed using scanning and transmission electron microscopy. The precipitates were identifies using transmission electron microscopy. The influence of ageing time on microstructure changes and the precipitation process of the tested steel is described. The presented research results are an element of material characteristics of the new generation of steel, which are used in the design work of pressure devices of steam boilers and in diagnostic work during operation.

In this case ceramic layers from Metco ZrO2 and Al2O3 powders mixture (25/75; 50/50 and 75/25) were obtained through atmospheric plasma spraying (APS) after five passes on low carbon steel substrate. The sample surfaces mechanically grinded (160-2400) before and after ceramic layer deposition. Powder’s mixtures and the surface of ceramic thin layers were analyzed through: scanning electron microscopy (SEM). In order to understand the effect of surface wettability of the ceramic layers, before and after grinding the surface, three different liquids were used. Experimental results confirm the modification of the steel substrate surface characteristic from hydrophilic to hydrophobic when the ceramic layer was deposited. Surface free energy of hydration increases for all the samples with zirconia percentage addition before polishing process.

AlCrFeCuCoNi high entropy particles were alloyed on Ti-6Al-4V surface using Plasma transferred arc (PTA) process. PTA alloyed surfaces were investigated for their phase formation, microhardness improvement and wear behaviour. The various wear mechanism and their corresponding surface roughness were studied. The results revealed that the dual phase of BCC and FCC microstructure along with some intermetallic compounds were grown in the alloyed region through the PTA technique and good metallurgical bonding of the alloyed region with the base material were achieved. The PTA alloyed region exhibited a hardness of 718 HV0.2 which is 2.2 times higher than the hardness of base material. The PTA alloyed samples showed higher wear resistance due to the solid solution strengthening as the HEA has high entropy of mixing that leads to the reduction of free energy of the alloyed region. It exhibited better interconnection of the coated material and superior metallurgical bonding to the base material. Frictional heat produced during the wear test has promoted the formation of FeO, Cr2O3, CuO, NiO and Al2O3 oxide film on the PTA alloyed sample. These oxide films act as a barrier between two mating surfaces and improve the tribo performance of the PTA alloyed sample.

In the past decades, Mg alloys have been studied intensively as potential orthopedic applications. The present research work, the FEA of the obtained contact stresses in the case of the load applied on Mg-0.5Ca-xMn alloys has been investigated. It has been used the NCB Curved Femur Shaft Plate type as a model in order to establish the necessary modeling parameters. The objective of the present work was to highlight the strain values at the contact point on the surface of the Mg-0.5Ca-xMn alloys. The results showed that the highest stresses observed near the gaps of the plate and in the screws. It means that all mechanical loads are sustained by the plate and screws, and the patient’s femur can be recovered.

Plates of AZ91 magnesium alloy were butt-welded using a CO2 laser. The non-equilibrium solidification of the laser-melted metal caused fragmentation of the weld microstructure as well as the supersaturation of a solid solution of aluminium in magnesium, which enabled the T5 ageing of the weld. The weld proved to be a mechanically stable part of the joint; all the tensile-tested specimens, both as-welded and post-weld T5 aged, fractured outside it. During the ageing of the supersaturated joint, which involved heat treating it to the T6 condition, the weld was the region where discontinuous precipitation was observed and this was the location of fracture in the tensile specimens. Thus, the strength properties of welded, supersaturated and aged AZ91 were much worse than when the non-welded material was T6 tempered.

Effect of annealing treatment on deep drawing behavior of hot-rolled Q235 carbon steel/410/304 stainless steel three-layer composite plate was investigated. Deep drawability of the unannealed composite plates exhibits a sharp difference for various contact surfaces with the die. The limit drawing ratio (LDR) of the composite plate with the carbon steel contacting the die is 1.75, while it is 1.83 with the stainless steel contacting the die due to the different mechanical responses to the tensile stress at the corner of the die. After annealing at 900°C for 2 h, however, the deep drawabilities of the composite plates both for various contact surfaces with the die are significantly improved and becomes almost identical, which are attributed to the stress relief, the enhanced ductility and the improved interface bonding strength of the hot-rolled component plates during annealing.

The effects of hydrogen absorption and manganese substitution on structural, electronic, optical, and thermoelectric properties of silicon-carbon nanotubes (SiCNT) are studied using the density functional theory and the GGA approximation. An examination of the PDOS curves and the electronic band structure showed that the Mn substitution leads to an increase in magnetic anisotropy and the occurrence of semi-metallic behavior and that the hydrogen absorption shifts the band gap toward the lower energies. A study of these nanostructures’ thermoelectric behavior reveals that the H absorption leads to a significant escalation in the figure of merit of the SiCNT to about 1.6 in the room temperature range. The effects of the H absorption on this nanotube’s optical properties, including the dielectric functions and its absorption spectra, are also investigated.