Metallic biodegradable materials have higher strength and modulus of elasticity compared to polymers, as well as higher toughness than ceramics and bioactive glasses, which makes them preferred candidates for use as replacements for hard tissues in biomedicine. An attractive choice for such replacements are magnesium-based alloys, which, in addition to the aforementioned advantages, also meet the requirements of biodegradability and biocompatibility. As an example, biodegradable magnesium stents can be mentioned. Studies in the development of corrosion-resistant Mg-based bioresorbable alloys suggest that by appropriate microalloying with elements such as Li, Mn or Ag and subsequent thermomechanical processing, the desired combination of mechanical and chemical properties can be achieved. The presented work is focused on the development and characterization of Mg-Li alloys prepared by hot extrusion. The effect of different Li content (0.2, 0.4, 0.6, 0.8, 1.4 wt.%) and thermomechanical processing on the microstructure, texture, and mechanical properties was studied.
The corrosion coupons of 800H alloy with TIG weld filled with Nicrofer were exposed to impure helium in the High-Temperature Furnace (HTF) at 760 °C for 372, 1000 and 1500 hours. Impurities CH4, CO, H2 and H2O were chosen to simulate conditions in a High-Temperature Gas Reactor system (HTGR). The specimen surface, corrosion layer thickness and composition were evaluated by Scanning Electron Microscope (SEM) with Energy Dispersive Spectroscopy (EDS). Specimens were covered with a uniform protective oxide layer up to 3 µm thick, growing with exposure time. The layer contained mainly Cr, O2 and a minor amount of Mn. Localized deep oxidation was found after 1500 hours in between of weld and base material.
The output of these measurements is the evaluation of the properties of the tested materials and the assessment of their resistance to corrosion effects. 800H alloy and Nicrofer alloy were found to degrade similarly in an oxidizing environment. This combination of base material and weld metal appears to be suitable for use at high temperatures.
As a result of the development and needs of modern technologies, we still receive and we improve new materials. In the automotive industry, composites are increasingly used - often with a matrix of aluminum alloys, e.g. aluminum - silicon, called silumins, and nanomaterials, i.e. materials with reduced grain sizes, thanks to which it is possible to obtain much better physical and mechanical properties, including increased hardness and strength. Currently, on an industrial scale, elements operating in conditions of high frictional loads are manufactured, for example: brake discs and pads and in sliding combinations piston - sleeve. An example of such a combination are pistons and cylinder liners used in car engines. In this case, the cooperating parts are separated by a lubricating film, which is engine oil. Another example is air compressors. It is important to use the right materials and coatings to ensure proper performance of mating parts. Pistons used in compressors should therefore be light, have high mechanical strength, dissipate heat well and have low thermal expansion. A very important feature is also a low coefficient of friction and resistance to operational wear, which is why cast aluminum alloys with additives such as silicon or magnesium are used for the production of pistons. The subject of the research are cast pistons used in air compressors. The aim of the work was to characterize the wear of pistons made of aluminum-silicon alloys and to demonstrate the differences in material characteristics for various aluminum-silicon alloys. Several types of pistons were selected for the tests - pistons made of aluminum-silicon alloy AK12 and AK7. The scope of work included observations of pistons using light microscopy and scanning electron microscopy with X-ray microanalysis of chemical composition (EDS). Then, hardness measurements were carried out using the Vickers method.
The article concerns the experimental determination of a suitable method of heat treatment of the shank of a hip arthroplasty, that is, an artificial replacement of the femoral head with neck, to obtain the mechanical properties required by ISO 5382-3. The hip replacement shank is manufactured from Ti-6Al-4V titanium alloy. As the requirements of ISO 5382-3 for the mechanical properties of the hip replacement stem were not met after the hardening process, in this case quenching in water and subsequent tempering, repeated standardisation annealing was experimented, the first 900 °C/air, the second 900 °C/air, and the third 880 °C/air. Normalisation annealing of the hip stem was performed in a Realistic 2 continuous oven. Austenitisation was carried out in the gas part of this furnace consisting of four sections, the first two sections being heating sections and the following two sections being working sections. The furnace sections were set to 780-880-900 °C and the total time was set to 120 minutes. The cooling was carried out in still air without the use of fans. After each alternative normalisation annealing of the hip replacement shank, a circular cross-sectional test bar was made, and then the mechanical properties of the material were evaluated by tensile testing. The tests carried out show that after the first standardisation annealing the mechanical properties of the material may not be satisfactory, and it is therefore advisable to repeat the standardisation annealing. In the present case of a suitable heat treatment method for the shank of a hip arthroplasty, the requirements of ISO 5382-3 for its mechanical properties after the third standardisation annealing were met.
Manganese-based alloys with the composition Mn2FeZ, Z = Si, Al, have been widely investigated in recent years due to their potential applications in spintronics. Mn2FeSi alloy already prepared in the form of ingot, powder or ribbon exhibits a cubic full-Heusler (L21) or inverse-Heusler (XA) structure or combination of both. Contrary, the Mn2FeAl alloy has so far only been prepared in the form of an ingot and owns a primitive cubic (β-Mn type) structure. This paper is devoted to the new quaternary Mn2FeSi0.5Al0.5 alloy synthesized from pure Mn, Fe, Si, and Al powders by mechanical alloying. The ball milling of elemental powders for 168 h at ball to powder ratio 10:1 was followed by the annealing at 1173 K for 6 h in the argon protective atmosphere. The scanning electron microscopy (SEM) completed by the energy dispersive X-ray (EDX) spectroscopy revealed homogeneous distribution of elements and composition of 49.3 at.% Mn, 25.6 at.% Fe, 12.3 at.% Si and 12.8 at.% Al close to the nominal one. The presence of minor oxidation phases was also observed in the particle structure of the powder. The X-ray diffraction (XRD) analysis confirmed the origin of β-Mn type structure with the lattice parameter of 0.6279 nm being slightly lower than that of Mn2FeAl ingot (0.6339 nm). Room temperature magnetization curve consisted of paramagnetic contribution at higher magnetic fields and ferro-/ferrimagnetic contribution at lower magnetic fields. The Curie temperature was estimated from the thermomagnetic curve to about 370 K. The detected magnetic properties of the alloy powder do not correspond to the known magnetic characteristics of Mn2FeSi and Mn2FeAl systems, which are paramagnetic at room temperature and have negative Curie temperatures. An improvement in the magnetic properties could probably be achieved by extending the annealing time of the powder.
The aim of this work is to design and define technological procedures enabling the use of titanium scrap in the form of chips or piece material as input raw materials for the production of spherical powders suitable for powder metallurgy or additive technologies. It was used a plasma metallurgy in the horizontal and vertical furnaces under a high purity atmosphere of argon (5N8). The results of chemical analyses of titanium material before and after melting will be presented as well as results of phase composition using of a light microscope, scanning electron microscope and EDX analysis. ACKNOWLEDGEMENTS: This work was solved in the frame the project of the Technological Agency of the Czech Republic Nr. FW06010136 „Applied research and development of the use of titanium scrap as a primary charge in the production of products with higher added value“.
Studies on the influence of the addition of refractory metals on the structure and properties of light metal alloys have not been widely discussed in scientific reports so far. Currently, metals such as Re or W were commonly used as modifying additives for heavy metal alloys for appli-cation in high-temperature processes, such as sintering or metal casting. It has been shown that such modification can result in the improvement of mechanical properties, i.a. hardness, tensile strength, and fracture toughness, of the obtained materials.
In this work, the attempt for the addition of refractory metals (Re and W) for the assessment of their impact on tensile strength, Young's modulus, or hardness of light metal alloys (Al and Ti) is presented. Al and Ti powders subjected to ball milling with Re and W will be used for the manufacturing of sinters by the spark plasma sintering SPS technique. Apart from examining the effect of the addition of Re and W on mechanical properties, the corrosion resistance of the obtained sinters will also be assessed. The concept of the developed idea primarily con-cerns the manufacturing of unconventional composite powder materials for the production of sintered elements for applications in automotive, aviation, or military industries. The following project, as part of the Implementation Doctorate Program, contributes to the expansion of both theoretical and practical knowledge about refractory and light metals composite materials as well as SPS technology. Acknowledgments: This work was financially supported by the Polish Ministry of Education and Science as part of the Implementation Doctorate Program (Grant no RJO15/SDW/006-07).
The turbulent manufacturing market, and in particular the metallurgical industry, determines continuous improvement in the level of production efficiency and product quality. The aim of the study was to create a universal model enabling an assessment to be made of the impact of the modernity of aluminium casting machining technology on the quality of the final product and occupational safety in the company under study. The research methodology included the determination of the degree of modernity of machines, identification of the impact of the degree of modernity of machines on the quality and safety of the process, as well as the analysis of relations that occur between critical nonconformities and technological factors and accidents and near misses. The method presented in the study[ can be useful for the effective management of casting treatment technology in manufacturing companies, in order to select an appropriate development strategy and ensure safe working conditions.
The current automotive industry requires weight savings in the components used in the production of vehicles. At the same time, however, the demand for safety, high strength and fatigue life is increasing. The aim of this study is to create a comprehensive methodology that will help designers and material engineers in choosing the appropriate technical solution and material for a highly stressed axle element. Specifically, the possibility of replacing the front axle weight produced from ductile iron with a high-strength aluminum alloy EN AW-7075 in T6 condition is addressed. As part of the solution concept, a 3D model was created and, using the finite element method (FEM), a simulation of the response of the mass to the load corresponding to traffic on the road was carried out. Furthermore, the technological procedure for testing automotive components using a multi-axis dynamic testing facility was established, where the DIC (digital image correlation) method was used to evaluate load states and deformations. The basic limit states of vehicle operation, braking and cornering were tested. The work also deals with material factors that influence the choice of a suitable alloy, and verification of the degree of safety of the structural and material solution. The measurement results from both methods were compared with the contractual yield strength and fatigue strength. The results of FEM simulations and measurements using DIC positively verified the possibility of changing the material of the block, from ductile cast iron to EN AWE-7075 strength aluminum alloy in T6 condition. The described methodology can therefore be used in the design, construction and implementation of car prototype chassis.
In the present work, dissimilar tungsten inert gas (TIG) welding of AA6061-T6 to AA5086-H32 has been conducted using pulsed and alternative welding current. Microstructure examination revealed that the extent of the HAZ in pulsed weld joint is narrower than the one obtained by alternative current. EDS analysis showed that, regardless the welding process, both alloys contained Fe-rich intermetallic precipitates (IMPs) in BM and HAZ. Besides, only β-phase is detected in 6061 while Al3Mg2 was found in 5086 alloy. The electrochemical behaviour of each zone of the weldments is evaluated in ASTM G69 media according to two setups where the open circuit potential is affected, a second setup is used to check the results. The results showed that the polarization curves of BM and HAZ of both alloys overlap each other and the entire curves exhibit a cathodic plateau with constant current density while the lowest resistance polarization was obtained in WM of both assemblies. AFM and SEM micrographs of the exposed surface suggest that all specimens suffer from localized corrosion and the IMPs act as nucleation sites for corrosion.
The first half of the 20Th century, was accompanied with a big interest to the phase transition sequences in gold alloys. Where, theses phase transition sequences have a huge impact on the physical properties of the alloys. The knowledge of such precise temperatures and sequences is of high importance according to the gold alloys industrial use [1-3]. This communication will be concerned with an illustrated comparison of the phase transitions happening from 25°C to 700°C upon heating and cooling using two different starting phases of AuCu alloy. Therefore, a thorough characterization techniques, possible till now, have been used which are the in-situ XRD accompanied with the mechanical spectroscopy. A very interesting shift in the phase transition temperatures accompanied with the appearance of a new phase around 160°C only for one case of the two studied cases. These results can even open the door for a new industrial and thermodynamic studies.
The aim of this work was to study the influence of thermal treatment of the NiTi alloy on its microstructure, fracture features, and phase composition. NiTi sheets with a thickness of 2 mm and a chemical composition of 56.31 Ni and 43.69 Ti (wt. %) were used for the experiment. The samples were subjected to solution treatment at 850 °C for 1 hour and subsequent aging at 450 °C for 1 hour, or only aging at the same temperature and time for the as-received state of the material. All steps were finished by water quenching. Experiments were carried out for four states of the samples, namely the as-received state, after solution treatment, solution treatment and aging, and only aging. The study of the microstructure was carried out using a transmission electron microscope. The samples were broken in a tensile test at a strain rate of 6.67·10-5 s-1 and then the fracture surfaces were examined using a scanning electron microscope. The experiment was supplemented with a phase analysis using XRD spectroscopy.
Nowadays, the use of waste materials from various technologies is increasingly discussed, not only in terms of environmental impact, but especially in terms of reducing primary raw materials wherever appropriate. One such use appears to be the reuse of material by recycling and subsequent processing of selected multimetallic high temperature materials (in this case, for example, tungsten-based alloys/composites). It is this reuse of waste as a substitute for original, relatively expensive raw materials supplied by external suppliers and the application of selected recycling technologies that will serve as a suitable alternative compared to the use of original raw materials. Selected high-temperature composite materials are, for example, part of transport containers (together with steel elements) or radiation shielding elements. These materials have specific material properties (e.g. high material density) that can be clearly exploited in the design and construction of energy components. These material properties, as well as the recycling technology of multimetallic materials will be discussed in this presentation. Furthermore, the use of such prepared and manufactured components in a defined energy system, which is part of alternative energy sources, will be described.
Biodegradable alloys are a popular area of focus for potential medical applications, with numerous systems being researched to balance mechanical-physical properties with biocompatibility. Magnesium alloys have obtained popularity due to their low densities and excellent mechanical properties. However, the corrosion resistance of magnesium alloys has hindered their widespread use. In recent times, magnesium alloys containing zinc and iron have received extensive attention due to their suitable degradation rate. The present contribution examines the effect of ytterbium (Yb) addition on the mechanical and corrosion properties of the Mg66Zn30Ca4 alloy, which has gained significant recognition due to its remarkable mechanical properties and strong biocompatibility. The Mg66-xZn30Ca4Ybx (x = 0, 2, 4, 6) rods were prepared by a rapid solidification process. The mechanical and corrosion properties were compared with the initial alloy. Our research indicates that the addition of Yb can significantly improve the mechanical and corrosion properties of the Mg-Zn-Ca alloys, making them appropriate for various engineering applications that demand high strength and good corrosion resistance.
In the production of molybdenum compounds, JSC "Almalyk MMC" (Republic of Uzbekistan), for a long time used the method of nitric acid opening of raw material, replaced by the scheme of ammonia, then soda leaching of the cinder of the industrial product of molybdenum after oxidative roasting. In view of the improvement of technologies and equipment, there is an interest in environmentally friendly hydro-oxidative methods for their processing based on a strong oxidizer. Molybdenum disulfide in the composition of molybdenite concentrate is subject to surface passivation under the oxidizing conditions of processing the cinder of an industrial molybdenum product. The use of a strong oxidizing agent, nitric acid, makes it possible to overcome it in the hydrometallurgical process of oxidative leaching. The purpose of the study: to study the kinetics of the reaction of oxidative leaching of molybdenite concentrate of industrial production of molybdenum in nitric acid solutions, with the regeneration of nitric acid in them. Used samples of molybdenite concentrate, composition, %: 38.0 Mo; 2.5 Cu; 13.8 Fe; 0.7Re; 0.009p; 0.025Sb; 0.05 WO3; 25.2S; 10.8 SiO2; 0.42H2O; in solution, %: HNO3-0-25, H2SO4-5, O2. Kinetics of reagent oxidation of a sulfide mineral in nitric acid solutions, in the temperature range of 24-70 °C, at atmospheric pressure. was studied by the rotating disk method with control of the mass of the disk and the concentration of Cu(II), Fe(III), Mo(VI), Re(VII) ions in solutions. kinetic measurements were performed on powder samples of Mo disulfide concentrate pressed into discs 10 mm in diameter. Elemental analysis of sample samples was performed spectrometrically (ICP-Agilent 7500 IСP MS), methods of potentiometry, pH-metry, atomic absorption and optical emission (ICP), IR-, UV-spectrometry, X-ray phase and X-ray fluorescence analysis, scanning electron microscopy were used. . The parameters of the kinetic equation of the leaching process are obtained, the order of the reaction in terms of the concentration of the oxidizing agent, the activation energy of the process of solid-phase diffusion of molybdenum (VI) ions from the crystal lattice of the mineral into the liquid phase of the solution are calculated. Thermal analysis was carried out by dilatography, microscopy of samples was carried out on scanning electron microscopes: SEM-EDS EVO-MA (Carl Zeiss Instrum); spectral analysis - on a Nicolet iS50 FT-IR spectrophotometer (Thermo Scientific, USA), phase analysis - on an XRD Empyrean X-ray diffractometer (PANalytical).
One of the types of technogenic metal-containing raw materials of Almalyk MMC JSC (Uzbekistan) is waste processing of molybdenite concentrate of previous years, based on nitric acid opening of sulfide concentrate: cakes stored in the tailings of the plant, allowing to some extent to increase the output of the plant's main products. In their composition, %: 4.1 Mo; 2.0 Fe, 3.87 S, 78.98 SiO2, 5.26 CaO, others 4.79 (including Au 20-25 g/t). Purpose: development of technology for the extraction of Mo. Au, other components from molybdenum cakes by electrooxidation in hydrochloric acid medium. Interest in the method is caused by the modernization of hydrometallurgical technologies, due to the increase in environmental requirements for them, and also due to the emergence of new hydrometallurgical equipment. We used a two-chamber electrolysis plant for Mo-cake leaching, with a membrane, a direct current source, 20 A, generating active chlorine: hypochlorite ions at the anode. Mo(VI), Аu(III), Cu(II) ions were analyzed by photocolorimetric and spectrometric methods (ICP - Agilent 7500 IСP MS). The concentration of NaClO was determined according to the State Standard 18190-72, free chlorine was determined by titration with methyl orange. The behaviour of gold in Mo-cake in contact with hypochlorite ions is considered. The oxidation of Mo cakes in a hydrochloric acid medium by hypochlorite ions generated anode at the anode has been studied, the parameters of their electrooxidation have been calculated, and the leaching products have been studied. The method of electrooxidation, in the presence of HCl, on the basis of 3-factor planning of the experiment, regression equations were obtained. Checking their adequacy, according to the Fisher criterion, by comparing the calculated and experimental data on the degree of extraction of these metals, showed the adequacy of the proposed process models. A technology for the electrooxidation of molybdenum cake has been developed, which is an alternative to the existing scheme of oxidative roasting of molybdenite concentrate, followed by soda leaching of molybdenum from the cinder, with cyanide processing of cake for gold. It has been established that the electrooxidation of Mo-cakes makes it possible to process them efficiently, with through extraction of gold up to 90 %, molybdenum - up to 72.6 %.
Carbon dioxide is one of the possible working media for future advanced technologies in energy and industry. Its use is possible in the supercritical state as a cooling medium in the nuclear power industry, as an extraction solvent, in the combustion of fossil fuels, in concentrating solar systems, or in CCS processes. An important factor for these technologies will be the durability and compatibility of the construction materials in CO2 and flue gas environments at high temperatures. This work describes the exposure of nickel alloys 738, 625, and MoNiCr, 800H alloys in a moisture-free model flue gas environment of 6%O2, 13%CO2, 81%N2 at 600°C and the condition of the surface layers of the exposed samples. The material samples were exposed in a high-temperature furnace for 500 h with a heating rate to the desired temperature of 1°C/min and the same cooling rate to minimize the effect of temperature changes in the formed surface layers. After exposure, the surface composition of the samples was studied by XPS, and then the composition of the surface layers in the cross-section of the exposed samples was determined by EDS analysis on an electron scanning microscope. According to analyses, a very thin layer of oxides was formed on the surface of the materials. A more pronounced inhomogeneous layer was detected (up to a thickness of units of µm) on the surface of the Inconel 738 material, and a local surface layer related to sample preparation by polishing was found on the MoNiCr material. According to the exposure results, the nickel alloy samples are suitable for the model flue gas environment, and their suitability will be verified at 900 °C in further experiments. ACKNOWLEDGEMENTS: This project TK01030089 was co-financed with the state support of the Technology Agency of the Czech Republic within the Théta Programme.
The organ cabinet represents a specific corrosion environment with a high concentration of organic compounds that are released into the environment during the degradation of wood, glues and varnishes used in the production of the organ cabinet. Moreover, most of the metals from which organ pipes are made (lead, lead-tin alloy, zinc) are highly sensitive to organic substances. In this study, the effect of relative humidity (54%, 75% and 100%) and concentration of organic compounds (formaldehyde, formic acid, acetic acid and propionic acid) on the corrosion of metals (lead, lead-tin alloy, tin and zinc) from which organ pipes are usually made was monitored. Corrosion rates were determined using gravimetric data and the composition of corrosion products was analysed by XRD.
It is known that Cu and Ag have very similar properties: both are ductile metals with better electrical and thermal conductivity than other metals. As to their drawbacks, Cu is characterized by poor oxidation resistance and Ag is an expensive material. However, there is a special type of material (denoted as “core-shell”) that combines the advantages and eliminates the disadvantages of these two metals. The Cu-Ag core-shell consists of spherical Cu core coated by a thin layer of Ag [1,2]. In the present study, the Cu-Ag core-shell powder was used to produce the model metastable metal matrix composite (m-MMCs) by Spark Plasma Sintering (SPS) method. The parameters of SPS were the following: pressure 50 MPa, gradual heating to 700 °C at a speed of 100 °C/min and 5-minute hold at this temperature. The microstructure of the default powder as well as compacted material and fracture surfaces were observed with light microscope (LM) and scanning electron microscope (SEM equipped by EDS). In terms of mechanical properties investigation, tensile tests at laboratory temperature with different strain rates (10-2, 10-3, 10-4 mm/s) were done. It was found that powder Cu-Ag is a suitable material to produce m-MMCs by SPS with satisfactory structure and improved properties compared to either Cu or Ag.
REFERENCES: [1] Yang, G. et al. (2021). Towards understanding the facile synthesis of well-covered Cu-Ag core-shell nanoparticles from a complexing model. Journal of Alloys and Compounds, 874, 159900.; [2] Titkov, A. I. et al. (2019). Synthesis of ˜10 nm size Cu/Ag core-shell nanoparticles stabilized by an ethoxylated carboxylic acid for conductive ink. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 577, 500-508.
Aluminium alloys are widely used as a structural material due to their high strength-to-weight ratio, which is the result of the alloying and heat treatment. The AA7075 alloy belongs to the group of aluminium alloys with the highest mechanical properties. Usually, it is used in aerospace, mechanical engineering, sport and leisure equipment.
We processed the AA7075 alloy by selective laser melting (SLM) to exploit the remarkable properties for additive manufacturing. During the process, the metal powder is preheated, melted and rapidly cooled in sequence. After the process metal powder is re-used. Because of this, the SLM technique requires a protective atmosphere where the oxygen concentration is kept to a minimum (usually from 10-20 ppm). To achieve this, the working chamber is constantly flooded with argon. However, oxidation always occurs to some extent, and can cause problems in the final product. In this investigation the oxidation kinetics of AA7075 alloy were investigated in different oxygen-argon mixtures in the temperature range from 100-620 °C. The results in this study are important for understanding alloy’s behaviour in high temperature oxidation conditions. Therefore, they are crucial for our further studies of processing Al-Zn-Mg-Cu alloys with selective laser melting technique.