Metals, Volume 11, Issue 4 (April 2021) – 148 articles

This article is dedicated to quantitatively and systematically revealing the changes of mechanical properties and bake hardening properties of AA6014 alloy during six-month natural aging in detail. Three directions (0, 45, and 90° relative to the rolling direction) of the aluminum alloy sheets and 16 time points within six months were selected to conduct experiments. The change trend of six mechanical properties (0.2% offset yield strength, ultimate tensile strength, plastic extension at maximum force, elongation after fracture, and strain hardening exponent) were obtained by a large number of micro-hardness measurements and tensile tests. The results show that elongations along the three directions are basically the same and do not drop significantly with the progress of natural aging but fluctuate within a certain range. The trends of the n value during natural aging before and after bake hardening are opposite and bake hardening leads to ~0.07 decrease of the n value. The PLC phenomenon disappears after 90 days of natural aging, and the yield strengths along the three directions also stabilize; thus, it can be inferred that the cluster changes tend to stabilize after 90 days natural aging. The large and systematic dataset are clearly and intuitively presented, which can not only be used to provide data reference for industrial production of automobile manufacturers but also be used to reveal the microscopic mechanism of the natural aging process. Full article

In this study, the deposition of martensitic stainless-steel (Metco 42C) powder on 42CrMo4 structural steel by direct laser deposition (DLD) was investigated. Clads were produced by varying the laser power, scanning speed, feed rate, and preheating. The effect of these processing variables on the microstructure and microhardness of the clads was analyzed, as well as their soundness, yield (measured by dilution), and geometric characteristics (height, width, and depth). The complex interaction of the evaluated processing variables forced the application of complex parameters to systematize their effect on the clads. A genetic optimization algorithm was performed to determine the processing conditions warranting high-quality clads, that is, sound clads, metallurgically bonded to the substrate with required deposition yield. Full article

To solve the challenge of welding aluminum alloys, a unified adjustment model for Gaussian pulse welding is established. This model can achieve improved welding performance by adjusting the base current of the weak pulse group within a specific range of average welding current inputs. The flat overlaying welding is carried out on the base material: 6061 aluminum alloys with thicknesses of 2 mm, 3 mm, and 5 mm. A stable welding process, indicated by reduced spatter, is produced, with a soft arc sound and good repeatability in the waveforms of the real-time current and voltage. The weld has a shiny surface and regular fish scale ripples. Metallographic analysis shows that the fusion line is clear, and there are no visible defects, while the weld zone has fine dendritic structures. The tensile test results indicate that fractures occur in the heat-affected zone, and that the tensile strength reaches about 68% of that of the base metal. Full article

This article deals with material research of selected types of quartz and quartzites in order to determine the priority of their use in the production of ferrosilicon and pure silicon, respectively. The highest quality quartzes and quartzites are commonly used in metallurgy, but not all types of these silicon raw materials are suitable for the production of ferrosilicon and pure silicon, despite their similar chemical composition. Behavior differences can be observed in the process conditions of heating and carbothermic production of ferrosilicon and silicon. These differences depend, in particular, on the nature and content of impurities, and the granularity (lumpiness) and microstructure of individual grains. The research focused primarily on determining the physicochemical and metallurgical properties of silicon raw materials. An integral part of the research was also the creation of a new methodology for determining the reducibility of quartzes (or quartzites), which could be used for real industrial processes and should be very reliable. The results of the laboratory experiments and evaluation of the physicochemical and metallurgical properties of the individual quartzes (or quartzites) are presented in the discussion. Based on comparison of the tested samples’ properties, their priority of use was determined. This research revealed the highest quality in quartzite from Sweden (Dalbo deposit) and Ukraine (Ovruč deposit) and quartz from Slovakia (Švedlár deposit). The use of these raw materials in industrial conditions is expected to result in the achievement of better production parameters, such as higher yield and product quality and lower electricity consumption. Full article

This paper presents the chemical and phase composition, microstructure, and selected properties both at room temperature and at the temperature corresponding to the expected operating conditions of three successive generations of TiAl-based alloys (Ti-47Al-2W-0.5Si, Ti-45Al-8Nb-0.5(B,C), and Ti-45Al-5Nb-2Cr-1Mo-0.5(B,C)-0.2Si) melted in a vacuum induction furnace with high-density isostatic pressed graphite crucibles. The obtained results of mechanical and physical properties of the produced alloys were compared to the properties of reference alloys with similar chemical composition and melted in a cold copper crucible furnace. The effect of increased carbon content in the produced alloys due to the degradation of the graphite crucible during melting is higher strength properties, lower plastic properties, higher coefficient of thermal expansion, and improved creep resistance. It was shown that the proposed technology could be successfully used in the production of different generation TiAl-based intermetallic alloys. Full article

Spatially resolved elastic strains in the bulk interior of a laminated Ti-Al metal composite were studied during in situ tensile loading at strains up to 1.66% by a synchrotron-based micro-diffraction technique, namely differential aperture X-ray microscopy (DAXM). For both Al and Ti grains, deviatoric elastic strains were estimated based on polychromatic X-ray microbeam diffraction, while lattice strains along the normal direction of the tensile sample were directly measured using monochromatic X-ray microbeam diffraction. The estimated deviatoric strains show large spatial variations, and the mean values are consistent with the external loading conditions, i.e., increasing tensile strain along the tensile direction and increasing compressive strain along the sample normal with increasing loading. The directly measured lattice strains also show large spatial variations, although the magnitude of this variation is smaller than that for the estimated deviatoric strain. The directly measured lattice strains in Ti grains are largely consistent with the external loading, whereas those in Al grains are in contradiction with the external loading. The causes of the experimental results are discussed and related to both the laminated microstructure of the composite material and the limitations of the techniques. Full article

The effects of carbon contents on the mechanical properties and deformation behavior of medium Mn steels, 6Mn steels with 0.06C, 0.15C, and 0.3C, were investigated in this study. With the increase of the carbon content, not only the ultimate tensile stress, but also the total elongation, was increased (from 22.44% to 40.23%). The enhancement of carbon content promoted the diffusion of C and Mn atoms from ferrite to austenite and led to an increase of C and Mn concentrations in austenite, which increased both the volume fraction (from 15.5 vol% to 39.7 vol%) and the stability of austenite; therefore, the transformation-induced plasticity (TRIP) effect was intensified and larger amount of austenite transform in a greater strain range, which could continuously provide work hardening for the steels, thus preventing necking and improving the ductility of the material. Full article

Cobalt is the most used metal binder in hard metals since its extraordinary wetting, adhesion and mechanical properties. Nevertheless, it has been recognized genotoxic and cancerogenic with higher toxicity in combination with WC. To substitute Co with an alternative binder, the interaction between the binder and WC must be taken into account. In this work, IN625 is considered as a binder alternative due to its desirable combination of high-temperature strength and corrosion/oxidation resistance. A characterization of the interaction between WC and IN625 was carried out by means of Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDXS) and X-Ray Diffraction (XRD). Depending on the sintering temperatures, different phases were evidenced at the WC–IN625 superalloy interface. From 1250 °C to 1300 °C, where solid-state sintering takes place, (Cr,Mo)₂₃C₆, W₂C and (Cr,W) solid solutions were detected. At a sintering temperature of 1350 °C, IN625 melts and the formation of additional phases, such as an intermetallic Ni₄W phase and (Mo,W) and (Mo,Nb) solid solutions, were observed. The precipitation of NbC and (Mo,Cr)₂₃C₆ carbides in IN625 was also detected. Full article

In this study, the efficacy of an innovative ultra-fast sintering technique called electro-sinter-forging (ESF) was evaluated in the densification of Fe-Cr-C steel. Although ESF proved to be effective in densifying several different metallic materials and composites, it has not yet been applied to powder metallurgy Fe-Cr-C steels. Pre-alloyed Astaloy CrM powders have been ad-mixed with either graphite or graphene and then processed by ESF. By properly tuning the process parameters, final densities higher than 99% were obtained. Mechanical properties such as hardness and transverse rupture strength (TRS) were tested on samples produced by employing different process parameters and then submitted to different post-treatments (machining, heat treatment). A final transverse rupture strength up to 1340 ± 147 MPa was achieved after heat treatment, corresponding to a hardness of 852 ± 41 HV. The experimental characterization highlighted that porosity is the main factor affecting the samples’ mechanical resistance, correlating linearly with the transverse rupture strength. Conversely, it is not possible to establish a similar interdependency between hardness and mechanical resistance, since porosity has a higher effect on the final properties. Full article

Gas bubbles are of major importance in most metallurgical processes. They promote chemical reactions, homogenize the melt, or float inclusions. Thus, their dynamics are of crucial interest for the optimization of metallurgical processes. In this work, the state of knowledge of bubble dynamics at the bubble scale in liquid metals is reviewed. Measurement methods, with emphasis on liquid metals, are presented, and difficulties and shortcomings are analyzed. The bubble formation mechanism at nozzles and purging plugs is discussed. The uncertainty regarding the prediction of the bubble size distribution in real processes is demonstrated using the example of the steel casting ladle. Finally, the state of knowledge on bubble deformation and interfacial forces is summarized and the scalability of existing correlations to liquid metals is critically discussed. It is shown that the dynamics of bubbles, especially in liquid metals, are far from understood. While the drag force can be predicted reasonably well, there are large uncertainties regarding the bubble size distribution, deformation, and lift force. In particular, the influence of contaminants, which cannot yet be quantified in real processes, complicates the discussion and the comparability of experimental measurements. Further open questions are discussed and possible solutions are proposed. Full article

Modern forming processes often allow today the efficient production of complex parts. In order to increase the sustainability of forming processes it would be favorable if the forming of workpieces becomes possible using production waste. At the Chair of Forming and Machining Technology of the Paderborn University (LUF) research is presently conducted with the overall goal to produce workpieces directly from secondary aluminum (e.g., powder and chips). Therefore, friction-based forming processes like friction spinning (or cognate processes) are used due to their high efficiency. As a pre-step, the production of semi-finished parts was the subject of accorded research work at the LUF. Therefore, a friction-based hot extrusion process was used for the full recycling or rework of aluminum chips into profiles. Investigations of the recycled semi-finished products show that they are comparable to conventionally produced semi-finished products in terms of dimensional stability and shape accuracy. An analysis of the mechanical properties of hardness and tensile strength shows that a final product with good and homogeneously distributed properties can be produced. Furthermore, significant correlations to the friction spinning process could be found that are useful for the above-mentioned direct part production from secondary aluminum. Full article

Two submerged entry nozzles (SENs) used for casting 1300 tons and 260 tons of Al-killed steel were dissected. Several parameters including block rate, nozzle clog angle, port width, and port height of the clogged nozzle were introduced to describe the geometry of clogs in the SENs based on the dissection; furthermore, a geometry model was established to describe the characteristics of the nozzle clogging of the SENs. A large-eddy simulation (LES) coupled with the volume of fraction (VOF) method was adopted to simulate the steel–slag interface’s interaction behavior. The vortex visualization and rotation magnitude were characterized by the Liutex method. Quantitatively, the influence of nozzle clogging resulted in block rates of 0% to 45.9% on the flow and vortex distribution in the mold, and the characteristics of the steel–slag interface fluctuation were well verified in the industrial experiment. Full article

Mill scale (MS) is a iron-rich waste generated in the wire drawing process with high iron content and is still mainly disposed in landfills. The scientific community has been studied its use in other applications such as pigments, concretes, among others. This work aims to study a new added-value application for MS—the development of coloured ceramic pastes. For this purpose, the influence of the added amount (0, 1, 3, 5 and 10 wt.%), the pre-treatment (milling + sieving at 212 μ$\mathsf{\mu }$m), the maximum firing temperature (from 1043 to 1165 ${}^{°}$C) and the type of furnace (laboratory/industrial) were analysed on the sample’s characteristics. A dark grey stoneware product was obtained through the incorporation of 10 wt.% of MS and leaching tests conducted at pilot scale with cups confirmed its immobilization in the ceramic matrix. Furthermore, it was proved that the firing temperature can be reduced by about 100 ${}^{°}$C without affecting the specimen’s characteristics. This reduction leads to a considerable decrease in the energy consumption upon firing, inducing economic and environmental advantages. Therefore, this work provides a new added-value application for MS and contributes to the reduction of virgin raw materials consumption and development of more sustainable stoneware products. Full article

Friction press joining (FPJ) is an innovative joining process for bonding plastic components and metal sheets without additives in an overlap configuration. This paper focuses on the resulting bond strength. Tensile tests showed that the direct bonds produced by FPJ have either an equivalent or a higher bond strength compared to adhesive bonds. For the material combination of HD-PE and EN AW-6082-T6, an equivalent bond strength was achieved. In contrast, for the material combinations PA6-GF30 with EN AW-6082-T6 and PPS-CF with EN AW-2024-T3, higher tensile shear strengths were achieved via the FPJ technology. In addition to the technical considerations, this paper presents an evaluation of the technological maturity of FPJ. It was found that the basics of the technology are already well developed, and prototypes for showing the applicability have already been manufactured. The last part of this paper deals with the classification of FPJ into the standard for manufacturing processes, according to DIN 8593. The authors suggest a categorization into Activation bonding (item 4.8.1.3). These investigations show the high technical potential of FPJ for joining plastic components with metals. Full article

Nitinol is a group of nearly equiatomic alloys composed of nickel and titanium, which was developed in the 1970s. Its properties, such as superelasticity and Shape Memory Effect, have enabled its use, especially for biomedical purposes. Due to the fact that Nitinol exhibits good corrosion resistance in a chloride environment, an unusual combination of strength and ductility, a high tendency for self-passivation, high fatigue strength, low Young’s modulus and excellent biocompatibility, its use is still increasing. In this research, Atomic Layer Deposition (ALD) experiments were performed on a continuous vertical cast (CVC) NiTi rod (made in-house) and on commercial Nitinol as the control material, which was already in the rolled state. The ALD deposition of the TiO₂ layer was accomplished in a Beneq TFS 200 system at 250 °C. The pulsing times for TiCl₄ and H₂O were 250 ms and 180 ms, followed by appropriate purge cycles with nitrogen (3 s after the TiCl₄ and 2 s after the H₂O pulses). After 1100 repeated cycles of ALD depositing, the average thickness of the TiO₂ layer for the CVC NiTi rod was 52.2 nm and for the commercial Nitinol, it was 51.7 nm, which was confirmed by X-ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscope (SEM) using Energy-dispersive X-ray (EDX) spectroscopy. The behaviour of the CVC NiTi and commercial Nitinol with and without the TiO₂ layer was investigated in a simulated body fluid at body temperature (37 °C) to explain their corrosion resistance. Potentiodynamic polarisation measurements showed that the lowest corrosion current density (0.16 μA/cm²) and the wider passive region were achieved by the commercial NiTi with TiO₂. Electrochemical Impedance Spectroscopy measurements revealed that the CVC NiTi rod and the commercial Nitinol have, for the first 48 h of immersion, only resistance through the oxide layer, as a consequence of the thin and compact layer. On the other hand, the TiO₂/CVC NiTi rod and TiO₂/commercial Nitinol had resistances through the oxide and porous layers the entire immersion time since the TiO₂ layer was formatted on the surfaces. Full article

The phase composition of nanobainitic steel 0.56–0.60%C, 1.68–1.95%Mn, 1.58–1.80%Si, 1.30–1.47%Cr, 0.57–0.75%Mo is described in this paper. The phase composition is controlled in order to obtain diversified mechanical properties for specific applications, such as armor plates. The effect of temperature and time of isothermal heat treatment on both the microstructure and the mechanical properties of the steel were determined. Dilatometric studies, as well as measurements of volume fraction and size distribution of retained austenite were carried out. Analysis of the kinetics of isothermal transformation in the temperature range of 200–225 °C for times of up to 144 h were also carried out, and the parameters of the production process of the steel were determined. A microstructure consisting of nanolathy carbideless bainite and blocky and lathy retained austenite, providing tensile strength of at least 2000 MPa, yield strength of at least 1300 MPa, and total elongation of at least 10% has been found. Full article

Due to the synergistic effect that occurs between CNTs and alumina, CNT/alumina hybrid-filled epoxy nanocomposites show significant enhancements in tensile properties, flexural properties, and thermal conductivity. This study is an extension of previously reported investigations into CNT/alumina epoxy nanocomposites. A series of epoxy composites with different CNT/alumina loadings were investigated with regard to their thermal-degradation kinetics and lifetime prediction. The thermal-degradation parameters were acquired via thermogravimetric analysis (TGA) in a nitrogen atmosphere. The degradation activation energy was determined using the Flynn–Wall–Ozawa (F-W-O) method for the chosen apparent activation energy. The Ea showed significant differences at α > 0.6, which indicate the role played by the CNT/alumina hybrid filler loading in the degradation behavior. From the calculations, the lifetime prediction at 5% mass loss decreased with an increase in the temperature service of nitrogen. The increase in the CNT/alumina hybrid loading revealed its contribution towards thermal degradation and stability. On average, a higher Ea was attributed to greater loadings of the CNT/alumina hybrid in the composites. Full article

Friction stir processing (FSP), a severe plastic deformation process, was applied on pure Cu to obtain a stir zone with a very fine grain size. Yet, when FSP is used, the stir zone is as wide as the diameter of the shoulder at the upper surface of the weld and markedly narrower near its opposite surface. This property, as well as the differences between the advancing side and the retreating side, makes it impossible to obtain a uniform cross-section as far as the microstructure and mechanical properties are concerned. For these reasons, a new approach is proposed in which the material was processed on both sides, thus yielding a wider, rectangular and more homogenous stir zone from which all the specimens were machined out. Processing the material from both sides eliminated any microstructural difference between the upper and the lower side, at least within the gauge length’s cross-section of the creep specimens. Although grain refinement was detected, the mechanical properties of the friction-stir-processed (FSP’ed) material are inferior relative to those of the parent material. The TEM study reported in the current paper revealed the existence of nanosized grains in the FSP’ed material due to dynamic recrystallization (DRX) occurring during the processing stage. Because both X-ray inspection and fractography showed that the FSP’ed material was free of defects, the material may not comply with the Hall–Petch relation due to lower dislocation density caused by XRD occurring during FSP. The inverse Hall–Petch effect may also be considered as an assistive mechanism in mechanical property deterioration. Full article

This paper aims to investigate the diffusion bonding of Ti6Al4V to Al₂O₃. The potential of the use of reactive nanolayered thin films will also be investigated. For this purpose, Ni/Ti multilayer thin films with a 50 nm modulation period were deposited by magnetron sputtering onto the base materials. Diffusion bonding experiments were performed at 800 °C, under 50 MPa and a dwell time of 60 min, with and without interlayers. Microstructural characterization of the interface was conducted through scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS). The joints experiments without interlayer were unsuccessful. The interface is characterized by the presence of a crack close to the Al₂O₃ base material. The results revealed that the Ni/Ti reactive multilayers improved the diffusion bonding process, allowing for sound joints to be obtained at 800 °C for 60 min. The interface produced is characterized by a thin thickness and is mainly composed of NiTi and NiTi₂ reaction layers. Mechanical characterization of the joint was assessed by hardness and reduced Young’s modulus distribution maps that enhance the different phases composing the interface. The hardness maps showed that the interface exhibits a hardness distribution similar to the Al₂O₃, which can be advantageous to the mechanical behavior of the joints. Full article

Particles in molten steel, including argon-gas bubbles, slag droplets, and non-metallic inclusions, are removed into the surface-slag layer or captured by the solidifying steel-shell during continuous steel casting. Captured particles often become serious defects in the final steel product, so understanding particle-capture mechanisms is important for steel quality. Slab casters often have a straight mold and upper-strand prior to a curved lower-strand. The present work investigates particle capture in such a caster using computational modeling with a standard k-ε model for molten-steel flow, a discrete phase model for inclusion transport, and an advanced capture criterion for inclusion entrapment and engulfment into the steel shell. A new postprocessing methodology is presented and applied to predict inclusion-capture rates in commercial cast product. The locations and size distributions of particles captured into the shell, and actual capture rates are quantified. The model predictions are validated with ultrasonic-test plant measurements of the locations of large particles captured in a steel slab. The results reveal how large-inclusion capture accumulates in the beginning of the curved strand, leading to a capture band in the slab inside radius. Finally, the capture fractions and locations due to all capture mechanisms are compared for different inclusion sizes, and the implications are discussed. Full article

In this work, we examined the irregular resistive switching behaviors of a complementary metal–oxide–semiconductor (CMOS)-compatible Cu/Al₂O₃/Si resistor device. X-ray photoelectron spectroscopy (XPS) analysis confirmed the chemical and material compositions of a Al₂O₃ thin film layer and Si substrate. Bipolar resistive switching occurred in a more stable manner than the unipolar resistive switching in the device did. Five cells were verified over 50 endurance cycles in terms of bipolar resistive switching, and a good retention was confirmed for 10,000 s in the high-resistance state (HRS) and the low-resistance state (LRS). Both high reset current (~10 mA) and low reset current (<100 μA) coexisted in the bipolar resistive switching. We investigated nonideal resistive switching behaviors such as negative-set and current overshoot, which could lead to resistive switching failure. Full article

This article introduces the microstructural and mechanical properties of low and medium-carbon advanced martensitic steels (AMSs) subjected to heat-treatment, hot- and warm- working, and/or case-hardening processes. The AMSs developed for sheet and wire rod products have a tensile strength higher than 1.5 GPa, good cold-formability, superior toughness and fatigue strength, and delayed fracture strength due to a mixture of martensite and retained austenite, compared with the conventional martensitic steels. In addition, the hot- and warm-stamping and forging contribute to enhance the mechanical properties of the AMSs due to grain refining and the improvement of retained austenite characteristics. The case-hardening process (fine particle peening and vacuum carburization) is effective to further increase the fatigue strength. Full article

As a major gangue mineral in sulfide ores, talc is difficult to separate from chalcopyrite in the flotation process due to its natural floatability, which affects the subsequent smelting process. In this study, the effects of calcium ions and calcium lignosulfonate (CLS) as a combination depressant for talc were systematically investigated along with the fundamental mechanisms. The results of our flotation tests showed the talc floating can be effectively depressed via the combination depressant effect of calcium ions and CLS over the pH range of 6–12. Measurements of the adsorption capacity, zeta potential, and Fourier transform infrared (FTIR) showed an enhancement of the adsorption capacity and adsorption strength of CLS on the talc surface after calcium ions were added. This result indicates that calcium ions adsorbed onto the talc, neutralized the negative charge on the surface of talc, generated the binding site with CLS, and formed the [talc-Ca²⁺/Ca(OH)⁺-CLS] system by strong adsorption. Further, the coverage rate of CLS on talc was significantly improved after the addition of calcium ions, as shown in the AFM imaging. Full article

Evaluation of thermal conductivity of composite materials is extremely important to control material performance and stability in thermal applications as well as to study transport phenomena. In this paper, numerical simulation of effective thermal conductivity of Al-Sn miscibility gap alloys is validated with experimental results. Lattice Monte-Carlo (LMC) method is applied to two-phase and three-phase materials, allowing to estimate effective thermal conductivity from micrographs and individual phase properties. Numerical results are compared with literature data for cast Al-Sn alloys for the two-phase model and with a specifically produced powder metallurgy Al-10vol%Sn, tested using laser flash analysis, for a three-phase simulation. A good agreement between numerical and experimental data was observed. Moreover, LMC simulations confirmed the effect of phase morphology as well as actual phase composition on thermal conductivity of composite materials. Full article

Iron-based shape memory alloys (SMAs) have been widely studied during the last years, producing new formulations with potential applications in civil engineering. In the present paper, the microstructure and the thermomechanical behavior of the Fe-28Mn-6Si-5Cr memory alloy has been investigated. At room temperature, the presence of ε-martensite and γ-austenite was confirmed using optical and electron microscopy techniques. The martensitic transformation temperatures (A_s, A_f, M_s, and M_f) were determined by differential scanning calorimetry, together with an X-ray diffraction technique. The use of these techniques also confirmed that this transformation is not totally reversible, depending on the strain degree and the number of thermal cycles. From the kinetics study of the ε → γ transformation, the isoconversion curves (transformation degree versus time) were built, which provided the information required to optimize the thermal activation cycle. Tensile tests were performed to characterize the mechanical properties of the studied alloy. These kinds of tests were also performed to assess the shape memory effect, getting a recovery stress of 140 MPa, after a 7.6% pre-strain and a thermal activation up to 160 °C. Full article

High-entropy alloys (HEAs) have been around since 2004. The breakthroughs in this field led to several potential applications of these alloys as refractory, structural, functional, and biomedical materials. In this work, a short overview on the concept of high-entropy alloys is provided, as well as the theoretical design approach. The special focus of this review concerns one novel class of these alloys: biomedical high-entropy alloys. Here, a literature review on the potential high-entropy alloys for biomedical applications is presented. The characteristics that are required for these alloys to be used in biomedical-oriented applications, namely their mechanical and biocompatibility properties, are discussed and compared to commercially available Ti6Al4V. Different processing routes are also discussed. Full article

Within the implementation of the Industry 4.0 paradigm in the steel sector, robots can play a relevant role in improving health and safety conditions at the workplace, by overtaking cumbersome, repetitive and risky operations. However, the implementation of robotics solutions in this particular sector is hampered by harsh operating conditions and by particular features of many procedures, which require a combination of force and sensitivity. Human–robot cooperation is a viable solution to overcome existing barriers, by synergistically combining human and robot abilities in the sense of a human-centered Industry 5.0. In this sense, robotics solution should be designed in a way to integrate and meet the end-users’ demands in a common development process for successfully implementation and widely acceptance. The paper presents the outcomes of the field evaluation of a robotic workstation, which was designed for a complex maintenance operation that is daily performed in the steel shop. The system derives from a co-creation process, where workers were involved since the beginning in the design process, according to the paradigm of social innovation combining technological and social development. Therefore, the evaluation aimed at assessing both system reliability and end-users’ satisfaction. The results show that the human-centered robotic workstations are successful in reducing cumbersome operations and improving workers’ health and safety conditions, and that this fact is clearly perceived by system users and developers. Full article

Springback is a common defect caused by elastic recovery in the plastic forming process, which can cause the formed workpiece to deviate from the target shape. The purpose of this paper is to grasp the influence law of process parameters on springback deviation so as to optimize process parameters to reduce springback. Taking the Y-profile as the research object, the influence of process parameters such as horizontal bending radius, vertical bending radius, transition zone length, radius of roller dies, and wall thickness of the profile on springback deviation is discussed by numerical simulation. Additionally, the validity of the numerical simulation is verified through experiments. The springback law obtained by numerical simulation is applied to practical production, and the large-scale production of the Y-profile is realized. Full article

The effect of high-temperature thermomechanical treatment on the structural transformations and mechanical properties of metastable austenitic steel of the AISI 321 type is investigated. The features of the grain and defect microstructure of steel were studied by scanning electron microscopy with electron back-scatter diffraction (SEM EBSD) and transmission electron microscopy (TEM). It is shown that in the initial state after solution treatment the average grain size is 18 μm. A high (≈50%) fraction of twin boundaries (annealing twins) was found. In the course of hot (with heating up to 1100 °C) plastic deformation by rolling to moderate strain (e = 1.6, where e is true strain) the grain structure undergoes fragmentation, which gives rise to grain refining (the average grain size is 8 μm). Partial recovery and recrystallization also occur. The fraction of low-angle misorientation boundaries increases up to ≈46%, and that of twin boundaries decreases to ≈25%, compared to the initial state. The yield strength after this treatment reaches up to 477 MPa with elongation-to-failure of 26%. The combination of plastic deformation with heating up to 1100 °C (e = 0.8) and subsequent deformation with heating up to 600 °C (e = 0.7) reduces the average grain size to 1.4 μm and forms submicrocrystalline fragments. The fraction of low-angle misorientation boundaries is ≈60%, and that of twin boundaries is ≈3%. The structural states formed after this treatment provide an increase in the strength properties of steel (yield strength reaches up to 677 MPa) with ductility values of 12%. The mechanisms of plastic deformation and strengthening of metastable austenitic steel under the above high-temperature thermomechanical treatments are discussed. Full article

The feasibility for friction stir welding (FSW) surface-treated AA2099-T83 aluminium extrusions with AA2060-T8E30 aluminium sheets in the overlap configuration and using a sealant at the interface was investigated in this work. New Cr-free surface treatments such as thin film sulphuric acid anodising (TFSAA) and sol–gel were applied to the parent materials, and a sealant was applied before applying the FSW process. FSW welds were produced using several combinations of surface treatments and sealant application with no significant influence on FSW process stability and performance. The metallographic examination of the welds showed that a good protection of the crevice was achieved with some sealant accumulation at the edges of the overlapping region. The microstructural analysis showed no sealant remnants but the presence of some oxide remnants in the stir zone (SZ) of the welds, especially in the TFSAA treated parent material cases. However, these remnants did not show any significant effect in the static pull-out strength of the joints and failures at the most stressed zone of the AA2099-T83 extrusions outside the FSW weld region were consistently obtained. Full article