Materials Proceedings

: The properties of duplex stainless steels (DSSs) depend on the ferrite–austenite ratio and on the contents of secondary phases. Therefore, it is necessary to control the volume fractions, morphologies, and distribution patterns of all phases. The phases in the samples were identified using thermodynamic modeling and scanning electron microscopy. Investigated specimens were obtained after different heat treatments, such as solution annealing and quenching from 1050 to 1250 °C to obtain different amounts of ferrite and annealing at 850 °C to precipitate the σ-phase. Therefore, a metallographic technique for assessing the phases in DSSs based on selective etching and subsequent analysis according to ASTM E 1245 was developed. It was shown that the developed method of quantitative analysis based on selective etching and metallographic assessment according to ASTM E 1245 allows obtaining much more accurate results compared to the proposed ASTM E 562 method, which correlates well with the XRD quantitative phase analysis. Full article

This paper presents the results of the study of nickel-based coatings fabricated by cold gas spraying. In this study, compositions based on Ni, Ni–Cu, Ni–Zn, and Ni–Al₂O₃/TiC coatings applied to low-alloyed steel bases were investigated. The composition, type of powder (mechanical mix or mechanically alloying), and thickness varied to choose the optimal characteristics for recovery, repair procedures, and specific applications in the oil and gas industry media. The second phase was added to Ni-based coatings to increase corrosion and wear resistance. Pure nickel coatings were also studied as a benchmark. Corrosion resistance was studied by means of electrochemical testing and autoclave testing in simulated oilfield conditions. Hydroabrasive resistance was studied using a unique testing bench. Scanning electron microscopy mappings, microhardness testing, and adhesion testing were used to correlate the results of the tests with the structure, continuity, and porosity of the studied coatings. It was shown that applying mechanical alloying of the powder did not lead to an effective increase of corrosion and hydroabrasive resistance. All the studied coating specimens have a sufficiently high adhesion. Ni–Zn coating has the lowest corrosion resistance and high hydroabrasive resistance. Ni–Cu coatings have high corrosion and the lowest hydroabrasive resistance. Al₂O₃/TiC additives give ambiguous results in the studied properties. A thickness of 40–60 microns provides sufficient performance of the studied coatings. Thus, varying chemical composition and thickness of coatings allows for obtaining the optimal qualities of Ni-based coatings made by cold gas spraying for use in the oil and gas industry. Full article

In the present work, an attempt is made to use non-contact charcoal in the reduction of run-off mine goethite ore at heating temperatures above 570 °C. The reduction mechanism was adopted, following Levenspiel’s relations for the shrinking core model at different stages of reduction. The non-contact charcoal reduction approach is adopted to maximize the benefit of using CO/CO₂ gases from charcoal for reduction without the need for beneficiation and concentration. The rate-controlling steps for the reduction kinetics of average particle sizes 5, 10, 15, and 20 mm at 570, 700, 800, 900, and 1000 °C were studied after heat treatment of the ore-wood charcoal at a total reduction time of 40 min using activated carbon reactor. Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) analyses were done to investigate the spectrometric phase change and metallic components of the ore sample after reduction, respectively. The average percentage of the metallic iron content (56.6, 60.8, and 61.7%) and degree of metallization (91.62, 75.96, and 93.6%) are achieved from the SEM/EDX analysis of the reduced ore sample at reduction temperatures of 570, 800, and 1000 °C, respectively. The results indicate the tendency for high carbon deposit at the wustite stage of the reduction process at the lowest of temperature 570^oC and the residence time of at 10 min. This study demonstrates that diffusion through the ash layer is the controlling resistance of the overall reduction process. Full article

Smooth and notched mechanical components made of metals frequently experience repeated cyclic loads at different temperatures. Thus, low cycle fatigue (LCF) is considered the dominant failure mode for these components. Stainless steel (SS) is the most widely selected material by engineers owing to its outstanding mechanical and LCF and anti-corrosion properties. Moreover, a reliable estimation of the fatigue life is essential in order to preserve people’s safety in industries. In the present study, an evaluation of some of the commonly known low cycle fatigue life methodologies are performed for notched and un-notched samples made of 316L (N) SS at ambient and higher temperatures. For the notched samples, the elastic–plastic strains were firstly determined and then the fatigue lives were estimated for constant nominal strain amplitudes, varying from ±0.4% to ±0.8%. A comparison between the calculated fatigue lives and those obtained experimentally from the literature was made. Overall, some of the widely used fatigue life prediction methods for smooth specimens have resulted in unsafe estimations for applied strain amplitudes ranging from ±0.3% to ±1.0%, and those of the notched specimens were generally found to give strongly conservative predictions. To overcome this problem, attempts were made to suggest new parameters that can precisely assess the lifetimes of smooth samples, and a new equation was suggested for notched samples under both room and high temperatures. Full article

The rise of metal additive manufacturing technology has increased the demand for high-performance alloys such as metal matrix composites (MMCs). The metallurgical production of MMCs remains a challenge. The nano-powder of dielectric particles does not mix well into the liquid metal because of several reasons. On a macroscopic level, the powder is rejected by the molten metal through buoyancy and surface tension forces. On a microscopic level, the particles are held together by Van der Waals forces forming particle agglomerates. Our research strategy is to address these issues separately in two steps. We are investigating an electromagnetically assisted MMC casting method for the production of particle-strengthened, directionally solidified aluminum alloys. In the first step, nanoparticles are mixed into melt while it is in a semi-solid state by efficient permanent magnet stirrers. Then, the alloy is subjected to ultrasound treatment for fine particle dispersion. Semi-continuous casting of MMC is used to obtain material for additive manufacturing process. Material is cast in 6–20 mm rods by a direct chill casting method and can be made into wire with the application of wire-feed additive manufacturing. We investigate the possibility of improving Al alloy SiC composite material properties by applying electromagnetic interactions during solidification. Electric current and a moderate static magnetic field (0.1–0.5 T) creates melt convection in mushy zone. Such interaction enhances heat and mass transfer near the solidification interface and hinders the re-agglomeration of the added particles. Full article

The goal of this work was to study the effects of cyclic close die forging on the microstructure and mechanical properties of Ti–5Al–3Mo–1.5V alloy, which was produced in Vietnam. The factors considered include the deformation temperature (T_d), at 850 °C, 900 °C, and 950 °C, and the number of cycles performed while forging in closed die (n)— 3, 6, and 9 times. The responses measured were average grain diameter (d_tb) and tensile stress (σ_b). The results indicate that the smallest average grain size of 1 μm could be obtained at T_d = 900 °C, n = 9 times and the tensile stresses were enhanced. The experimental results we obtained also suggest that the microstructure of Ti–5Al–3Mo–1.5V alloy is accordant for superplastic deformation. The superplastic forming of this alloy can show maximum elongation of 1000% or more. Full article

In this study, the viscosity of CaO-Al₂O₃ based mould fluxes with the addition of B₂O₃ and the effects of increasing the lime/alumina ratio have been observed through IPT (Inclined Plate Test). Additionally, FactSage software, Riboud and Urbain models were used to calculate the viscosity of the mould fluxes. The experimental results show that the viscosity of the mould fluxes decreases dramatically with a change in the lime/alumina ratio from 1 to 1.5. They also show that with an increase in the lime/alumina ratio ranging from 1.5 to 2.5, the viscosity slightly decreases, then when the lime/alumina ratio is over 2.5, the viscosity becomes stable. However, the addition of B₂O₃ decreases the viscosity of the mould fluxes at a lime/alumina ratio of 1.2, 3.3 and 5.5. Full article

The chemical and physical routes are usually used to synthesize metal nanoparticles. However, the harmful effects on the environment and human health has turned scientists into finding greener methods. We have developed the novel green method for the synthesis of flower Pd nanoparticles based on the chitosan (CS) polymer. In this method, CS can work as a stabilizer, a shape-directing agent, and a size-controllable agent for the synthesis of these nanoparticles. This study provides pioneer evidence about the multifunctional roles of natural polymers in the preparation of metal nanoparticles. Deep and extensive studies should be conducted to explore the great benefits of natural polymers in the green synthesis of metal nanoparticles. Full article

This paper suggests parametric accelerated life testing (ALT) as a systematic reliability technique to generate the reliability quantitative (RQ) specification such as mission cycle for identifying design flaws in mechanical systems as exerting the accelerated load, defined as the reverse of stress ratio, R. Parametric ALT therefore is a procedure to improve the fatigue for mechanical products subjected to repetitive loading. It includes: (1) a system BX lifetime shaped on the parametric ALT plan; (2) a fatigue failure and design; (3) tailored ALTs with alternatives; and (4) an assessment of whether the design(s) of the product attains the targeted BX lifetime. A BX life ideas, a life-stress model, and a sample size formulation for parametric ALT are proposed. A reciprocating compressor in a domestic refrigerator is utilized to explain this methodology. The compressor was subjected to repetitive impact loading due to the pressure difference between condenser and evaporator, which results in the compressor field failure. To analyze and conduct parametric ALTs, as mass/energy balance was utilized on the vapor-compression refrigerating cycle, a simple pressure loading of the compressor in operating the refrigerator was investigated. At the first ALT, the compressor was locked due to the fractured suction reed valve made of Sandvik 20C carbon steel (1 C, 0.25 Si, 0.45 Mn). The dominant failure modes of the suction reed valve in the parametric ALTs were established to be very close to that of the fractured product from the marketplace. The root cause of the fatigue failure of the suction reed valve was an amount of overlap between the suction reed valve and the valve plate in combination of repeated pressure loading in the compressor. To supply sufficient mechanical strength, the design faults were altered by the trespan dimensions tumbling process, a ball peening and brushing process for the valve plate. At the second ALT, a compressor was locked due to the intrusion between the crankshaft and the thrust washer. The corrective action plan was to give heat treat the surface of crankshaft made of cast iron (0.45 C, 0.25 Si, 0.8 Mn, 0.03 P). After these alternations, there were no issues at the third ALT. The lifetime of the compressor was ensured to have B1 life 10 years. Full article

Their low density and high specific stiffness and impact energy/vibration absorption ability make Al-based metal foams promising materials in applications for which a light weight and energy/vibration absorption abilities are crucial. In view of these properties, Al-based foams can be extremely interesting as cores in cast components in order to improve their performances and simplify their whole technological process. However, both in the scientific literature and in technological application, this topic is still poorly explored. In the present work, Al-based metal foams (Cymat foams and Havel metal foams in the form of rectangular bars) are used in a gravity casting experiment of an Al-Si-Cu-Mg alloy (EN AB-46400). The foams were fully characterized before and after insertion in casting. Porosity, cell wall and external skin thickness, microstructure, infiltration degree, and the quality of the interface between the foam core and the dense cast shell, have been investigated by means of optical microscopy and scanning electron microscopy equipped with energy dispersive spectroscopy (SEM-EDS). The analyses evidenced that a continuous and thick external skin protect the foam from infiltration by molten metal, preserving the initial porosity and insert shape. A detailed analysis of the foam’s external skin highlights that the composition of this external skin is crucial for the obtaining of a good joining between the molten metal and the Al foam core. In fact, the presence of Mg oxides on the foam surface prevents bonding, and maintains a gap between the core and the shell. This point opens up the opportunity to design innovative surface modifications for this external skin as promising strategies for the optimization of cast components with a foam core. Full article

The mechanical properties of thixoextrusion components can be improved by controllable processing parameters such as the solid fraction of alloy, holding time, punch velocity, heat treatment and die temperature. In this study, the effects of thixoforming parameters on the microstructures and mechanical properties of thixoextrusion ADC12 alloy Aptomat Contact are studied. ADC12 has excellent castability with high fluidity and low shrinkage rate, so it is widely used in industry, especially in automotive and motorcycle engine part casting. It is a near eutectic alloy with high strength and low ductility (1%). The optimization parameters mechanical properties were investigated by changing the punch velocity, specimen temperature and holding time. The results also indicated optimal value at punch velocity (15 mm/s), specimen temperature (560 °C) and holding time (5 min) which was changed microstructure from eutectic dendrite to globular grain, increasing the ductility (3.3%) of this alloy during the semi-solid forming process while the remaining mechanical properties lead to an increase in the quality of finished parts. Full article

Currently, the commercial production of ferromagnetic cores involves staking thin sheets of soft magnetic material, alternating with dielectric material to reduce the eddy current losses. High silicon FeSi steels show excellent soft magnetic properties. Anyway, their workability decreases Si content increases thus imposing a technological limit in the production of thin sheets up to 3.5–4% Si. The additive manufacturing (AM) process based on laser powder bed fusion (L-PBF) offers the possibility to redesign the magnetic components, compared to conventional design, allowing to act on the chemical composition of magnetic materials and on the geometry of the components. In the case of FeSi alloys, the additive technology allows to overcome the limit of Si content opening new perspectives for the production of ferromagnetic cores with high magnetic performance. In this work the feasibility study on the production of FeSi magnetic steel components by L-PBF technology is reported. Two variants of FeSi steels, with Si content of 3.0 wt.% and 6.5 wt.%, were considered. The effect of process parameters on the densification of manufactured parts was investigated. The best operating window has been identified for both steel chemical compositions, in terms of laser scan speed and power. Full article

Hot stamping technology has shown a significant scientific yield in the last decade. The research activity in that field has spread across several disciplines such as materials science, mechanics, process engineering, instrumentation, physics, or part-tool design engineering. Some recent publications have gathered this richness in the format of scientific reviews. This work is aimed to draw a picture of this scientific production in bibliometric terms, which are complementary to the existing reviews. The literature is, in this case, approached from different angles: geographical, collaborative, disseminative, and keyword-based. The first one leads to mapping the share of each region worldwide in advance of the hot stamping technology in terms of scientific production volume. The second angle allows identifying the most productive networks that have been established between institutions and the most influential agents in the field. The third one ranks the most influential journals and events based on citation rates, which indicates where to publish in order to achieve the highest impact. Finally, the fourth approach targets to infer research trends from assessing the keywords employed in the published scientific literature. Altogether, the results show a scenario with Asia as the major player both in volume and networking success, CHS2 as the most relevant event, and exploring alternatives to the conventional AlSi coated 22MnB5 hot stamping as a subject rising of interest. Full article

During the last fifty years, the metal forming of aluminum alloys advanced significantly, leading to a more competitive market on which production rate and overall quality are kept as high as possible. Within the aluminum industries, extrusion plays an important role, since many industrial products with structural or even aesthetic functions are realized with this technology. Especially in the automotive industry, the use of aluminum alloys is growing very fast, since it permits a considerable weight loss and thus a reduction of the emission. Nevertheless, the stringent quality standards required don’t allow the use of extruded aluminum alloys produced for common building applications. An important parameter that can be used as an index of the quality of the extruded product is the emergent temperature: if the temperature at the exit of the press is kept constant within a certain limit, products with homogeneous properties and high-quality surface are obtained and the so called “isothermal extrusion” is achieved. As extrusion industries are spread all over the world with different levels of automation and control, a universal but simple on-line tool for determining the best process condition to achieve isothermal extrusion is of particular interest. The aim of this work is to implement this model, which allows evaluation of the thermal gradient which has to be imposed on the billet. Several experiments have been carried out on an industrial extrusion press, and the outer temperature was recorded and compared with the simulated one to demonstrate the model consistency. Full article

Red mud is a hazardous waste of alumina production. Currently, the total accumulated amount of red mud is over 4 billion tons. The promising method of red mud processing is a carbothermic reduction of iron at 1000–1400 °C into metallic form followed by magnetic separation. In this study, the mechanism of carbothermic solid-phase reduction of red mud was investigated. Based on the experimental data, the two-step mechanism of the first rapid stage of the process was proposed, which leads to almost full iron reduction. The estimated value of activation energy has indicated that solid-phase diffusion is a rate-controlling step for this stage. However, an almost full reduction is necessary, but insufficient factor for successful magnetic separation. The second crucial factor of the process is enlargement of iron grain size, which leads to gangue-grain release during grinding and increases efficiency of the magnetic separation. The prediction model of iron grain growth process during the carbothermic reduction process was suggested. The calculation of average size of iron grains formed during the reduction process that was performed according to the assumption of diffusion-controlled process showed their correlation with experimental data. Various methods were proposed to promote the process of iron grain growth during carbothermic reduction of red mud. Full article

Steel products made of ferritic steel can show some defects, such as jagged edges, following the hot rolling process. Aiming to identify the origin of this type of defect in order to help their reduction, an in-depth study has been carried out considering the hot rolling conditions of flat bars made of EN 1.4512 steel. A wide number of references to austenitic stainless steel can be found in literature: almost all the semi-empirical models describing the microstructural evolution during hot deformation refer to austenitic stainless steel. In this work, a comprehensive model for recrystallization and grain growth of the ferritic stainless steel grade EN 1.4512 is proposed, enriching the literature and works regarding ferritic stainless steels. Thermomechanical and metallurgical models have been implemented. The microstructural evolution and the damage of the material were calculated through the coupling of metallurgical and damage models. In the thermomechanical simulations of the roughing passes, three granulometry levels (PFGS) and three heating furnace temperatures were considered. The ferritic grain evolution metallurgical model was obtained by introducing apposite equations. The results highlight that the defect could be produced by process conditions that spark abnormal heating and consequently uncontrolled growth of the grains. The work-hardened grains undergo elongation during hot deformation without recrystallizing. Those grains “squeeze” the surrounding recrystallized grains towards the edges. Thus, on the edges occurs a series of cracks that macroscopically manifest themselves as jagged edges. Full article

The reduced activation martensitic steel EUROFER97 is recognized in Europe as the reference steel for structural applications in future nuclear fusion reactors. Usually, EUROFER97 steel plates are manufactured by hot rolling and successive heat treatments: (1) austenitization at 980 °C for 30 min, (2) air cooling, and (3) tempering at 760 °C for 90 min. Recently, thermo-mechanical treatments have been investigated by us with the scope to improve the mechanical properties, namely, to strengthen the steel without reducing its ductility. The experiments involve cold rolling with three reduction rates (30%, 40%, 50%) and, for each of them, heat treatments at different temperatures in the range from 550 °C to 750 °C. The mechanical and microstructural characterization of the samples after successive stages of the process is now underway and present work reports some preliminary results. The characteristics of the samples after cold rolling have been examined by means of hardness tests, metallography, and X-ray diffraction measurements, and work-hardening is discussed in terms of dislocation density. Full article

Additive manufacturing of an AISI 316L austenitic stainless steel was studied via an integrated thermomechanical and microstructural modelling approach. A finite element technique was employed to evaluate the temperature evolution due to successive material deposition. Heat transfer simulations provided the temperature field history, required to determine the microstructural evolution. Thermodynamic and kinetic simulations were employed to calculate temporal and spatial distribution of phases and alloying elements upon solidification and subsequent thermal cycling. The ensuing microstructural properties could be provided as an input for a mechanical finite element analysis to calculate, based on local mechanical properties, the residual stresses and distortions. Full article

The rapid evolution of materials and manufacturing processes, driven by global competition and new safety and environmental regulations has had an impact on automotive structures (Body In White; BIW) manufacturing. The need for lighter vehicles, with more equipment, that are safer and eco-friendly at the same time, relates to the entire life cycle of the car. Car and steelmakers agree that weight reduction is possible, and the solution involves the use of new advanced high-strength steels. Thinner and stronger materials lead to higher demands on stamping, the most used manufacturing in BIW parts. The use of advanced high-strength steels raises new challenges, especially concerning the lubrication between the die and the sheet. To study the lubrication conditions of the stamping process, a sheet metal forming a simulator was developed. The simulator consists of two cylinders that pull the strip of steel and a pin in between. The angle between the cylinders can be adjusted from 0 to 90 degrees, which allows analysis of the effect of the stamping angle. The pull force and velocity can be set and measured, and the peripheric pin velocity, the strain, and the strain velocity can be measured as well. In this work, the tribological properties of Dual-Phase 600 stainless steel using different processing conditions have been analyzed. To this end, a factorial experiments design with twelve parameters that compare the behavior of different angles and diameters was run. The results showed that the friction coefficient increases by increasing the bending angle and decreases with pin diameter. Full article