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Duplex stainless steels are a group of widely used stainless steels, because of their attractive combination of strength and corrosion resistance. However, these steels embrittle because of a phase separation phenomenon in the ferrite phase when exposed to temperatures within the miscibility gap. This manuscript investigates the phase separation in two commercial stainless steels, the duplex stainless steel (DSS) 22Cr-5Ni (2205 or UNS S32205), and the super-duplex stainless steel (SDSS) 25Cr-7Ni (2507 or UNS S32750), and its subsequent effect on mechanical property evolution. Long-term isothermal aging heat treatments were carried out at industrially relevant temperatures between 250 °C and 350 °C for up to 48,000 hours, and quantitative measurements of the amplitude and wavelength of the phase separated nanostructure were obtained using Small-Angle Neutron Scattering (SANS). These quantifications were used as input parameters in hardness models to predict the hardness evolution. It is concluded that the quantitative information from SANS combined with these hardness models enables the prediction of hardness evolution in DSS at low temperatures, which in turn correlates with the embrittlement of the DSS.

In an industrial Ruhrstahl–Heraeus (RH) degasser, gas bubbles can expand rapidly due to heating by the melt as well as to the significant pressure drop when they rise in the melt. A suitable model for the bubble expansion is, therefore, essential for the accurate numerical prediction of argon–melt hydrodynamics in an RH degasser. This study focuses on the evaluation and comparison of different bubble expansion models available in the literature based on a coupled computational fluid dynamics–population balance model. The simulation results show that compared with the measured results, the modified Szekely–Martins model demonstrates the suitability for treating the bubble expansion behavior and thereby simulating the argon–melt hydrodynamics in an industrial RH degasser. The flow field and bubble expansion, breakup, and coalescence phenomena are then investigated.

The design of high performance structural materials is always pursuing combinations of excellent yet often mutually exclusive properties such as mechanical strength, ductility and thermal stability. Although crystal-glass composite alloys provide better ductility compared to fully amorphous alloys, their thermal stability is poor, due to heterogeneous nucleation at the crystal-glass interface. Here we present a new strategy to develop thermally stable, ultrastrong and deformable crystal-glass nanocomposites through a thermodynamically guided alloy design approach, which mimics the mutual stabilization principle known from symbiotic ecosystems. We realized this in form of a model Cr-Co-Ni (crystalline)/Ti-Zr-Nb-Hf-Cr-Co-Ni (amorphous) laminate composite alloy. The symbiotic alloy has an ultrahigh compressive yield strength of 3.6 GPa and large homogeneous deformation of ∼15% strain at ambient temperature, values which surpass those of conventional metallic glasses and nanolaminate alloys. Furthermore, the alloy exhibits ∼200 K higher crystallization temperature (TX > 973 K) compared to that of the original TiZrNbHf-based amorphous phase. The elemental partitioning among adjacent amorphous and crystalline phases leads to their mutual thermodynamic and mechanical stabilization, opening up a new symbiotic approach for stable, strong and ductile materials.

The ability to use common computational thermodynamic and kinetic tools to study the microstructure evolution in Inconel 625 (IN625) manufactured using the additive manufacturing (AM) technique of laser powder-bed fusion is evaluated. Solidification simulations indicate that laser melting and re-melting during printing produce highly segregated interdendritic regions. Precipitation simulations for different degrees of segregation show that the larger the segregation, i.e., the richer the interdendritic regions are in Nb and Mo, the faster the δ-phase (Ni3Nb) precipitation. This is in accordance with the accelerated δ precipitation observed experimentally during post-build heat treatments of AM IN625 compared to wrought IN625. The δ-phase may be undesirable since it can lead to detrimental effects on the mechanical properties. The results are presented in the form of a TTT diagram and agreement between the simulated diagram and the experimental TTT diagram demonstrate how these computational tools can be used to guide and optimize post-build treatments of AM materials.

A number of non-equimolar refractory high entropy alloys (RF HEAs) from the Al–Ti–Mo–Nb–V system are synthesized, with the selected compositions aimed to balance the conflicting requirements of the low-temperature ductility and high-temperature corrosion protection. Based on the thermodynamic modeling and experimental results, all the obtained alloys are characterized by the single-phase B2 structure with V acting as the main phase stabilizer. The microstructure and mechanical properties appear to be controlled mainly by the Al content, which is especially visible on the example of hardness, with a maximum value of 545 HV for Al20Ti5Mo25Nb25V25 composition. For the selected Al20Ti5Mo25Nb25V25 and Al10Ti30Mo20Nb20V20 alloys, the measured stress–strain curves indicate the highly coveted, ductile room temperature behavior, with the values of ultimate strain measured under compression mode being 9.17 and 9.00 pct, respectively, and compressive fracture strain of 13.38 and 13.25 pct, respectively. The obtained results suggest that it is possible to include Al as a vital component of refractory HEAs without compromising their low-temperature ductility. The next intended step will be the characterization of the high-temperature corrosion behavior in order to investigate the potential selective oxidation capabilities of such materials.

The dynamic recrystallization (DRX) behaviors and their transformation process during hot deformation with various Zener–Hollomon (Z) values were investigated in nuclear grade 316H stainless steel, and the factors influencing DRX transformation, especially adiabatic heating, were evaluated in depth. During hot deformation, with the increase of the Z value, the degree of flow softening (DFS) showed a tendency to decrease first and then increase gradually. The analysis of the microstructure revealed that at low Z value (not exceeding 3.9 × 1019 s–1) deformation conditions, DRX was massively activated and the recrystallization mechanism had a transition from continuous DRX (CDRX) to discontinuous DRX (DDRX) with the increasing Z values, leading to the transition of homogeneous grains to heterogeneous grains. Furthermore, with the reactivation of DRX at high Z value deformation conditions, the discontinuous DRX becomes the primary recrystallization mode. Adiabatic heating plays an important role in facilitating the reactivation of DRX and flow softening during hot deformation with low temperature or high strain rate (high Z values, above 6.1 × 1021 s–1).

A multi-component multi-phase-field model was conducted to simulate the solidification process of Fe-Mn-C-Al high-Mn steel with different solidification modes, especially that with the peritectic phase transition. The evolution of the microstructure and solute distribution during the solidification process was analyzed. In addition, the influence of the C content, cooling rate, and thermal undercooling was discussed. The results reveal that the area of interfaces and solute distribution influence the evolution of phase fractions. The amount of initial ferrite phase, the solute distribution formed by the initial ferrite phase, and the nucleation position of austenite phase are key factors affecting the microstructure morphology and microsegregation. The microstructure and microsegregation have an interactive effect. Increasing C content changes the solidification mode, leading to different microstructure and microsegregation. For all the steel with different C contents, the cooling rate and undercooling do not influence the phase transition sequence, while they affect the microstructure and microsegregation. The cooling rate and thermal undercooling have more influence on the solidification process of hypo-peritectic high-Mn steel than hyper-peritectic steel. The present study contributes to providing significant reference for the process control of the microstructure morphology and microsegregation of peritectic high-Mn steel.

Plasma arc additive manufacturing (PAM) is receiving an increasing attention because of its efficiency of dimensional size and cost, as compared to other additive manufacturing (AM) techniques. Despite the capacity of building medium to large-scale components by PAM, the heat-transfer behavior could be significantly influenced by component size (or build height) during processing. Understanding this build size effect on heat transfer is critical to predict the microstructure and mechanical properties and optimize the processing parameters. In the present work, the site-specific evolutions of the temperature and residual stresses along the build height were investigated under varying energy densities during PAM processing. A finite element method (FEM) was used to discretize and solve the thermomechanical partial differential equations (expressing the conservation of energy and momentum) governing the plasma arc additive manufacturing process. We studied the transient temperature and subsequent thermally induced residual-stress fields in PAM 304 stainless steel components with different deposition heights. Our study provides general insight into the residual-stress development in wire-based additively manufactured engineering materials.

The vortex at the Ta/Fe explosively welded interface is featured by the intermediate zone being fully bounded by Ta matrix, which differs from the vortex structures observed in the most bimetallic interfaces. In this work, advanced characterizations and numerical simulations were integrated to establish a detailed evolution model of the special vortex, and the associated governing mechanisms were identified. It was also inferred that the mesoscale cavity and microcracks within the vortex resulted from the geometric hole and extrusion movement that generated during the vortex evolution, respectively. Furthermore, a diversity of metallurgical structure was revealed at the Ta/Fe interface, which did support the deformation path of the interface material observed in the simulations. The insights gathered here benefit an in-depth comprehension of impact welding.

The effect of Cu addition on crystal structure, compressive properties and shape-memory effect of Ni50Mn25Ga25−x Cu x alloys was studied. With increasing Cu content, the type of crystal structure evolves following a sequence: L21 → 10M → 2M → 2M+γ. Addition of Cu significantly improves room temperature ductility. In polycrystalline Ni50Mn25Ga17Cu8 alloy, a full recoverable strain equal to 7 pct was achieved. High martensitic transformation temperature and large shape-memory effect makes this material potential candidate in high-temperature shape-memory applications.

Two approaches can be taken when designing properties of the native oxide layers formed on Ti-based biomedical materials: (i) changing the chemical composition of the substrate by adding biocompatible, valve alloying elements, and (ii) changing the microstructure of the substrate—especially its level of defectiveness—through large plastic deformation. However, especially in the aggressive fluoridated oral environment, it is still unknown what factor is more effective in terms of enhancing oxide layer protectiveness against biocorrosion: (i) the presence of valve alloying elements, or (ii) a high number of structural defects. To gain knowledge about the separate influence of both of these factors, surface properties were examined for commercially pure Ti and Ti–Nb–Ta–Zr alloy in microcrystalline state as well as after multiple-pass cold rolling, a process that can be readily scaled up to the industrial level. This study showed that while valve-alloying elements and structural defects individually have a beneficial effect on Ti oxide layer properties in fluoridated medium, they not have to act in a synergistic manner. These findings have to be taken into account when designing future Ti-based dental materials together with analyzing their mechanical performance with respect to mechanical strength and elastic properties.

Coatings have been used for a significant number of years in the Direct Reduction industry, and the ISO Cluster Index plays an important role in this context since it allows a better predictability of pellet performance in the industrial process. The present work developed a series of tests and characterization in order to better understand which materials, methods, and characteristics would be most relevant to decrease the clustering index. It was noticed that coating on green pellets is worse as compared to the conventional application method which coats the pellets after the hardening process in the pelletizing furnace. In an evaluation of predictive parameters, it was observed that the adhesion index and the sum of SiO2, Al2O3, CaO, and MgO content influence the clustering index response variable. Consequently, it was observed that the adhesion index is proportional to the microporosity and mesoporosity of the coating materials. Bauxite was the material that showed the best performance. Its differentials were the high content of Al2O3 combined with its high microporosity/mesoporosity, i.e., pores with diameter up to 50 nm.

New results about the influence of a small iron borided layer (~ 36 µm) obtained by the powder-pack boriding process (PPBP) and diffusion annealing post-process (DAP) were evaluated. Dry sliding wear tests on PPBP, PPBP + DAP and untreated AISI 1018 steel were performed under the pin-on-disc configuration, and balls of Al2O3 and WC were used as a counterpart at different sliding distances. Also, the contact pressures of the layer/substrate system were evaluated using the finite element model with the aid of the ABAQUS software. The results showed that the Al2O3 ball presented the major coupling (ball-disc), and the PPBP + DAP reduces the specific wear rate around ~ 304 times related to the untreated AISI 1018 steel to 500 m under severe sliding conditions.

A key-factor for the industrial implementation of beam-based additive manufacturing technologies is the development of novel Al alloys characterized by enhanced hot-tearing resistance. Indeed, most of the standard Al alloys are susceptible to solidification cracking and can hardly be used to produce structural parts by laser-based additive manufacturing processes. In this study, we investigate the strategies to design high-strength Al alloys for Laser Powder Bed Fusion. The addition of Zr to the chemical composition of an Al–Mg–Si alloy (EN AW 6182) was carried out by following two different routes to promote the formation of equiaxed grains which are able to suppress hot cracking and enhance processability of the material. The first route is based on mechanical mixing of ZrH2 particles and gas-atomized Al alloy powder and on the in-situ reaction of the hydride to form Al3Zr nucleants. The second route relies on the use of pre-alloyed gas-atomized powders that feature Zr among the alloy elements. The specimens produced using pre-alloyed powder showed the best mechanical performance. After direct aging from the as-built condition, the alloy showed yield strength and ultimate tensile strength of 354 and 363 MPa, respectively, and elongation at fracture of 9.0 pct. The achieved properties are comparable to those of wrought 6182 alloy processed by conventional routes.

This paper demonstrates how an analytical and experimental method can be used to rapidly define the additive manufacturing settings for a new alloy where the process parameters were previously unknown. A nickel-based superalloy, Haynes 282, was chosen for the analysis. An experimental matrix of focused processing parameters was predicted with a dimensionless number and 100 samples were printed using the Laser Powder Bed Fusion technique. High-throughput measurements validated the predicted process conditions needed to achieve desired density and hardness. The whole process was completed in 16 hours. The new technique was confirmed with analytical processing maps adopted by the metal additive manufacturing community. With the predicted set of process parameters, a low-throughput analyses of conventional microstructural characterizations and tensile testing were used to test the predictions. The resultant as-fabricated microstructures have refined length scales of both microsegregation and secondary phase distributions. The mechanical properties were comparable within the predicted processing window and exhibited high strength and high ductility.

The present study is the first attempt to join ultrafine-grained materials by electron beam welding. The aim of the study was to check the feasibility and effectiveness of this type of welding for thermally unstable materials. The results obtained are of high interest, while the welding did cause a decline in mechanical properties, the results were comparable to those obtained using solid-state welding, but with a significant advantage of narrower fusion- and heat-affected zones.

This work studies the solidification processes and microstructures of Zr55Cu30Al10Ni5 (at. pct) and Cu64Zr36 (at. pct) amorphous alloy sheets fabricated by twin-roll strip casting. A largely excessive volume was frozen in the alloy during the twin-roll strip-casting process, resulting in many soft regions and the inhomogeneity of the microstructure in the amorphous alloy sheet. The results provide insights into the solidification process of amorphous alloys and guidelines for adjusting their microstructure.

In this paper, a modulated permanent helical magnetic field is imposed to improve segregation during directional solidification in a binary Sn–3.5 wt pct Pb alloy. The magnetic force created by this magnetic field significantly interferes with heat, mass and momentum transfer of molten metal during solidification. Our experimental results show that this magnetic field, with an appropriate modulation frequency, can not only promote columnar-to-equiaxed transition (CET) but also significantly reduce solute segregation otherwise caused by conventional helical magnetic fields. Our analysis demonstrates the advantages of this approach over natural convection and conventional electromagnetically forced convection.

Environment-assisted fracture (EAF) behavior of Inconel718 (IN718) specimens made from virgin and recycled powder by laser powder bed fusion (L-PBF) process was investigated. To this, in situ slow strain rate tests (SSRTs) and fatigue crack propagation (FCP) tests were conducted in air and 3.5 pct NaCl/60 °C/Ecorr + 0.1 VSCE. Powder recycling up to 6 times did not affect the EAF sensitivity of L-PBF IN718 specimens in chloride-bearing environment, despite the marginal decrease in electrochemical resistance. Detailed fractographic and micrographic analyses were performed to identify the effect of powder recycling on static and dynamic EAF behaviors of L-PBF IN718 specimens.

Understanding diffusion-induced isothermal solidification time during transient liquid phase bonding is vital in producing intermetallic-free robust joints. The isothermal solidification completion time is overestimated by the existing analytical models, even by the closest one to the real bonding conditions, known as the moving interface model. It was found that the boride formation in the diffusion affected zone of Ni-based superalloy upon using B-containing filler metals is one of the reasons behind the inability of the moving interface model to predict the isothermal solidification completion time accurately, which has received scant attention in the literature. Moreover, simplified assumptions in deriving the moving interface model such as constant interfacial solute concentration, which is only valid for binary systems, along with the independency of diffusion coefficient to concentration introduce errors when estimating the isothermal solidification time using the moving interface model. The significant discrepancy between the predicted and experimentally obtained isothermal solidification times reinforces the idea that the existing moving interface analytical model needs to be modified.

The present study has investigated the influence of sulfur content in synthetic FeMn and SiMn from 0 to 1.00 wt pct on interfacial properties between these ferroalloys and slags. The effect of experimental parameters such as temperature and holding time was evaluated. Interfacial interaction between ferroalloys and slags was characterized by interfacial tension and apparent contact angle between metal and slag, measured based on the Young–Laplace equation and an inverse modelling approach developed in OpenFOAM. The results show that sulfur has a significant influence on both interfacial tension and apparent contact angle, decreasing both values and promoting the formation of a metal-slag mixture. Despite the fact that sulfur was added only to the ferroalloys, most of sulfur is distributed into slag after reactions with the metal phase. Increasing the maximum experimental temperature in the sessile drop furnace also resulted in a decrease of both interfacial properties, resulting in higher mass transfer rates and intensive reactions between metal and slag. The effect of holding time demonstrated that after reaching equilibrium in FeMn-slag and SiMn-slag systems (both with and without sulfur), interfacial tension and apparent contact angle remain constant.

The activation energy of creep rupture is determined based on a new tensile creep rupture model and then applied to rationalize the creep rupture data measured over a wide range of stresses and temperatures, which enabled the predictions of 100,000 hours and 200,000 hours creep rupture strengths to be made at different temperatures in the range of 650 °C to 875 °C for alloy Inconel 740/740H. The reliability of such long-term predictions is also analyzed.

Synergetic strengthening by designing of gradient nanostructures is a novel method to enhance strength in metals and alloys. Herein, we realize synergetic strengthening in strain-softening Zn alloy with gradient nanostructures. The results show that synergetic strengthening accounts for at least 25.5 pct of the yield strength of the strain-softening Zn alloy. The synergetic strengthening is induced by the microstructural gradient and the resultant strength gradient regardless of specific hardening or softening of the refined microstructures.

Fluorspar (CaF2) is commonly used to control the fluidity of slag in ladle-refining of steel. However, because it is desirable to reduce CaF2 consumption because of its environmental impacts, the industrial waste material such as white mud (WM) was investigated as a potential substitute for fluorspar. Steel sample (Fe-0.3C-0.9Mn-0.3Si-0.03Al-0.05S, mass pct) was melted in a high-frequency induction furnace, followed by additions of ladle slag (CaO-Al2O3-SiO2-5MgO-xCaF2, CaO/Al2O3=3, x = 0 to 10 mass pct) and fluxing agent (WM) at 1823 K (1550 °C). The desulfurization experiments were carried out by reducing CaF2 content in the ladle slag and increasing the addition of WM. Ladle slag with added WM showed an overall mass transfer coefficient of sulfur (k O) equivalent to or higher than that of conventional 10 mass pct CaF2-containing ladle slag. In a slag melting experiment based on DIN 51730 standard, the melting rate of mixed slag increased with the amount of WM added, which is considered to have a positive effect on the initial desulfurization rate. In addition, adding WM provided sulfide capacity of the slag equivalent to that of CaF2-containing slag. Consequently, the use of WM yielded slag having $$k_{{\text{O}}}$$ k O equivalent to or higher than that of conventional ladle slag with 10 pct CaF2, and thus, WM shows promise as a partial replacement for fluorspar.

This paper addresses the use of alloying additions to titanium alloys for additive manufacturing (AM) with the specific objective of producing equiaxed microstructures. The additions are among those that increase freezing ranges such that significant solutal undercooling results when combined with the rapid cooling rates associated with AM, and so be effective in inducing a columnar-to-equiaxed transition (CET). Firstly, computational thermodynamics has been used to provide a simple graphical means of predicting these additions; this method has been used to explore additions of Ni and Fe to the alloy Ti–6Al–4V (Ti64). Secondly, an experimental means of determining the minimum concentration of these alloying elements required to effect the CET has been developed involving gradient builds. Thirdly, it has been found that additions of Fe to Ti64 cause the alloy to change from an α/β Ti alloy to being a metastable β-Ti alloy, whereas additions of Ni do not produce the same result. This change in type of Ti alloy results in a marked difference in the development of microstructures of these compositionally modified alloys using heat treatments. Finally, hardness measurements have been used to provide a preliminary assessment of the mechanical response of these modified alloys.

An ultra-low carbon bainitic steel is developed through nanoprecipitation of high-density Mn/Fe-rich intermetallic B2-NiAl. A high yield strength of ~ 1.3 GPa and a good total elongation of ~ 13 pct are attained via minimal lattice misfit nanoprecipitation. Atom probe tomography and high-resolution transmission electron microscope were applied to characterize nanoscale precipitates. An increment of 544 MPa in yield strength is achieved after an aging process, predominantly attributed to the order strengthening mechanism.

This work is motivated by the industrial process of air (or dry) atomization of slag, where a high-speed jet of air impinges onto a free-falling stream of molten slag and disintegrates it into small droplets. The droplets solidify to form slag powder particles which may be used in applications such as sand blasting, roof shingles, and asphalt. Since different applications require slag powders with different ranges of particle size, controlling the particle size is of essence. A mathematical model is presented for the atomization process, which relates the Sauter Mean Diameter (SMD or $${D}_{32}$$ ) of molten slag droplets to the atomizer design and operating parameters. The model solves a set of non-linear governing equations, including conservation of mass, momentum, and energy, in the integral form using an iterative method. This universal model can be applied to any combination of gas-liquid, and thus the model is validated with existing experimental results for air atomization of a water stream. A strong agreement exists between the calculated and experimentally measured values of $${D}_{32}$$ . It is also found that at a constant air flowrate, the liquid flowrate affects the $${D}_{32}$$ of droplets and the opening angle of the spray; the former is the main output parameter, and the latter is an intermediate parameter.

This work concurrently investigates the microstructure evolution and stress state during continuous cooling of 1045 steel gear parts. A finite element algorithm was developed by two-way coupling of microstructural and thermal fields. Thermal coefficients were correlated to microstructural evolution, and a phase transformation kinetics model was considered to be both temperature and time dependent. Magee's rule was chosen for martensitic transformation modeling to incorporate the effect of stress state on microstructural field. The dilation curves for the benchmark sample show that martensite starting temperature increases when the stress state is considered in microstructure modeling. To determine the validity of the presented model, a cylindrical specimen was quenched in water and oil media, and their predicted microstructures were compared with experimental results. A reasonable harmony between simulated and experimental results was observed. The simulation was then performed for internal gear parts quenched in oil and water media. The simultaneous monitoring of microstructure and stress evolution during continuous cooling of an internal gear part was conducted. It was shown that simultaneous and separate transformations occurring between the tooth and root region have a determining role in the sign of stress for internal gear parts. Lastly, based on monitoring of different phase transformation scenarios occurring during water and oil quenching, a hybrid quenching was proposed to increase martensite volume fraction at the tooth region of an oil-quenched sample without altering the microstructure at root region.

Electron microscopy revealed continuous and discontinuous precipitation of κ-Co3AlC0.5 in a Co-10Al-3Cu-1C (at. pct) alloy during aging at 500 °C, 850 °C, and 900 °C. The kinetics of the discontinuous reaction at 500 °C are sluggish. Increasing the temperature increases the kinetics significantly, due to the exponential increase in the Al grain boundary diffusivity. However, the kinetics at 900 °C are slower than those at 850 °C, due to a significant decrease in the driving force.

To solve the problem of application of the reduction process in the continuous casting of round blooms, double-roll, three-roll and four-roll staggered extrusion schemes were proposed, and three series of three-dimensional thermal-mechanical coupling models were established to analyze the advantages and disadvantages of each reduction scheme. It was found that the double-roll scheme transfers the reduction deformation to the center of the round bloom and closes the internal porosity more efficiently. For each squeeze, the double-roll extrusion scheme can easily cause lateral deformation, which may improve the equivalent strain value to the inside of the round bloom more efficiently, and there is a concentration phenomenon in the center after several sets of reductions. The three-roll scheme and the four-roll scheme have difficulty causing lateral extension, and the reduction is basically consumed by the harder shell deformation, which causes much more longitudinal stretching deformation of the round bloom. With an increase in the solid fraction (fs), the round bloom will accept a larger reduction under the limit of the initiation of internal cracks. At positions with the same fs, the tensile strain of the crack risk area caused by the double-roll scheme is larger than that of others, which means that the limitation of the maximum reduction amount of the double-roll scheme is stricter than that of the other two schemes.

The goal of this work is to accurately measure the viscosity of an industrial secondary copper smelting slag. Established literature commonly performed such measurements in non-inert labware, such as alumina. Despite the fact that the dissolution of alumina into the slag was addressed as a source for errors, a comprehensive analysis of how this interaction affects the measurement reliability is hitherto lacking. Furthermore, the type of dissolution (direct or indirect) will influence the interaction kinetics. This work aims to verify a possible relation between the dissolution and viscosity measurement reliability. For this purpose, the infiltration depth during and time stability of four different slag ( $${\text{{PbO}-{SiO}}}_{2}{\text {{-CaO}-{Al}}}_{2}{\text {{O}}_{3}}{\text {{-ZnO}-{Fe}}}_{2}{\text {O}}_{3}$$ ) viscosity measurements were analyzed. Both in-situ viscosity measurements and post mortem SEM images of the interface were therefore analyzed. It was observed that a multiphase interfacial layer was formed upon alumina dissolution. This layer consisted of a spinel intermediate layer and an enclosed interfacial slag. EDX measurements confirmed the difference between the latter layer’s composition and the bulk slag. Samples with a high interfacial slag viscosity yielded a dense spinel layer. As a result, alumina dissolved indirectly and more reliable viscosity measurements were obtained that were more stable over time. While samples with a low interfacial slag viscosity yielded a discontinuous spinel layer and therefore alumina could dissolve fast into the bulk slag, resulting in more unreliable viscosity measurements that varied over time.

In prior works, a novel method for continuously obtaining Al-Zr master alloys from oxide raw materials by electrolysis of a low-melting electrolyte based on the KF-NaF-AlF3-ZrO2 system at 800 °C to 820 °C was proposed. In the present work, the method for preparing the Al-Zr master alloy proceeded in an enlarged 100 A electrolyzer and the obtained master alloy was applied for grain refinement and improvement of its aluminum alloy properties. The modifying ability of the master alloy was studied, drawing on the example of the Al-Si-Fe alloy. Different amounts of the Al-Zr master alloy with a content of 10 wt pct zirconium were added to the Al-Si-Fe alloy at 900 °C. The effect of the zirconium content in the aluminum alloy and its cooling rate on its structure and properties was revealed. It was found that the addition of zirconium to the alloy refined the grain by 4 to 5 times without changing its shape or structure. A study of the joint effect of alloying and rate cooling indicated that a grain size reduction of up to 5 mkm can be achieved by these procedures.

Adjusting pitch ratio in green anode formulation is becoming difficult due to the increasing raw material variability. The optimal quantity of pitch yielding the best anode properties for a given aggregate, known as the optimal pitch demand (ODP), changes more frequently and is unknown a priori. Exceeding the OPD increases the risk of generating post-baking anode-sticking events. Previously, the potential of a principal component analysis (PCA)-based monitoring scheme for detecting the onset of these undesirable events was assessed by using a set of five green anode resistivity measurements collected from over 120,000 anodes produced over a two-year period. The squared prediction error (SPE) was shown to be sensitive to abnormal events such as anode sticking. The objective of this paper is to further validate the soft sensor by studying the SPE dynamic behavior during a post-baking sticking event when changes in the anode paste formulation were introduced as part of normal operation. Descriptive and statistical analyses demonstrate that the SPE metric reacts significantly to changes in the recipe. The provided example illustrates how the SPE metric used together with pitch ratio data could help advised the operators of manufacturing conditions posing a higher risk of generating post-baking sticking problems.

The wettability of liquid slag from the CaO-SiO2-MgO-Al2O3 system on a solid Al2O3 substrate at 1773 K has been investigated using the sessile drop experimental technique. The liquid slag compositions were chosen to represent blast furnace hearth slags and test the effects of changing the Al2O3 (5.2-18.9 pct) and V ratio (0.41-1.17) of the slag on its wettability on solid Al2O3. All slag compositions tested were wetting with respect to solid Al2O3, and the contact angle (θ) changed with time, rapidly decreasing in ~10–15 seconds from an initial value between 40 and 80 deg to a plateau value of ~18 to 19 deg at extended times. There was no obvious effect of changing the initial Al2O3 content of slag on the wetting behavior, but increasing the initial V ratio of the slag lowered θ. Similarly, there was no obvious effect of changing the initial Al2O3 content of the slag on spreading rate but the slags with the higher V ratio had a faster spreading rate. The apparent of adhesion (W) of the slags on the solid Al2O3 was also evaluated and found to increase for increasing Al2O3 content of the slag and increasing the V ratio of the slag. This higher W indicates a stronger bond between the slag and solid Al2O3 substrate. Using electro-optical techniques to characterize the slag-substrate interface, it was established that the slag had penetrated and reacted with the solid Al2O3 and formed a layer. As a result of this penetration/reaction, new phases formed. The specific phases that formed were dependent on the initial slag composition. In the changing initial Al2O3 slags at a relatively constant V ratio of 1.1 to 1.2, calcium aluminates, CA2 and CA6, were found. At the lower V ratios (0.41 and 0.60) but constant Al2O3, compositions consistent with spinel, feldspar and melilite were found.

Titanium suboxides with the general formula TinO2n−1 (n > 1.0), also referred to as Magneli phases, have been the subject of numerous studies due to their unique properties. Titanium low oxygen suboxides located at n = 1 (TiO) or below (Ti6O, Ti3O and Ti2O) are no less important; however, there is a lack of research on the synthesis of such materials. Therefore, in this article, the combustion process in a TiO2-KClO4-kAl-Flux exothermic system for 0.5 ≤ k ≤ 4.0 (k is moles of Al) is investigated experimentally and thermodynamically to synthesize TinO2n−1 ingots in the 0.5 to 1.0 range of n. The synthesis temperatures and equilibrium reaction phases are calculated with and without a KClO4 booster and several fluxes (CaF2, NaF, CaO and Na3AlF6), which are used to melt the reaction product and achieve the self-separation of the TinO2n−1 ingot from the Al2O3-containing slag. The formation TiO, Ti2O, Ti3O and Ti6O phases is confirmed via XRD analysis and the effectiveness of fluxes is highlighted.

This study of the laser powder bed fusion (LPBF) of γ′-strengthened Ni superalloy CM247LC focuses on the development of a melt pool temperature model to predict crack density within the alloy. This study also analyzes spatter and elemental evaporation, which might cause defects and inhomogeneities, at different melt pool temperatures. The melt pool temperature model provides more accurate predictions than the widely used energy density model. Spatter particles were collected and characterized to study their sizes and chemical compositions, compared with the virgin powder, recycled powder, and as-built samples, to probe the impact of their entrapment into the melt pool. This study also investigated Al evaporation, revealing that its extent does not correlate with the laser energy density and is believed to be rather limited by comparing the chemistry of the virgin powder and the build. Last, the impact of LPBF process parameters on the formation of these inhomogeneities, and accordingly crack formation, was studied using finite element analysis by estimating the maximum melt pool temperature and correlating it with the formation of the microstructural inhomogeneities. The morphology of the various cracking modes was associated with the process parameters.

The effect of axial static magnetic field (ASMF) on inclusion removal during the magnetically controlled electroslag remelting M2 high-speed-steel was investigated. The results showed that the application of ASMF can significantly increase the inclusion removal efficiency, especially for the inclusions larger than 20 μm. The reason for the accelerated removal of inclusions was attributed to the alternating Lorentz force and the magnetically controlled spin-vibration induced in the liquid melt film after the application of ASMF.

The effect of slag composition under M’O (monoxide, M = Fe,Mg) saturation and fully liquid conditions on dephosphorization and slag foamability was evaluated in an electric arc furnace (EAF) steelmaking plant operation by considering thermodynamics and phase equilibria. It was confirmed that M’O saturation slag is more favorable for higher dephosphorization than fully liquid slag due to its high activity of CaO as a thermodynamic driving force. As a quantitative measure of slag foamability, the foaming index was clearly dependent on the temperature and slag composition. Moreover, foam stability was evaluated by applying the predominance stability diagram based on phase equilibria. Consequently, it can be suggested that an efficient direction for dephosphorization and slag foaming during the EAF process is to generate high CaO activity as well as small amounts of M’O monoxide and dicalcium silicate (Ca2SiO4) compounds.

In high-temperature experiments, the widely used molybdenum products may contaminate molten slags, affecting the properties of samples and thus the experimental accuracies. However, this impact has received little attention. Therefore, we have first undertaken detailed studies on the structure and viscosity of MoO3-containing molten slags, with a special focus on the characteristics of Mo, Si, and Al using molecular dynamic simulation and experimental measurements. It was found that the Mo ions in the molten slags were mainly hexavalent and in a four-fold coordinated state (MoO4), with the ability to polymerize Si-related frameworks and weaken bonds of the Al complexes. The decreasing degree of polymerization for the whole melt networks occurred because the introduced MoO4 tetrahedra existed as isolated islands that provided additional non-bridging oxygens. As a reflection of the microscopic structure, viscosities of molten slags at high temperatures gradually decreased, and viscous flow activation energy decreased from 218.47 to 167.79 kJ mol−1 as MoO3 content increased from 0 to 5.7 pct. Furthermore, a universal approach to correct systematic error caused by Mo products in property tests was proposed. It was suggested to control the MoO3 content within 0.55 wt pct when the allowable viscosity error did not exceed 5 pct.

Laser welding is currently a versatile and reliable assembly technique. To save weight in aerostructures and propulsion units and to reduce thermal distortions and the heat-affected zones in these assemblies, autogenous laser welding seems promising. This experimental work addresses dissimilar autogenous laser welding of thin alloy sheets using a Yb:YAG source and a particular optical fibre setting. Hastelloy X and Haynes 188 are the two base metals studied for this assembly. An experimental design allows us to determine the weldability domain. The macro- and microstructure and mechanical properties of the weld seams are investigated. EBSD and EDS analysis revealed microstructural and chemical heterogeneities in the high-power welded seam, but XRD results demonstrated a homogeneous depletion of the carbide density in its fusion zone. Despite such microstructural features, the mechanical properties of obtained assemblies were found to be satisfactory and slightly greater than those of the weaker Hastelloy X.

Nanophase separation sintering (NPSS) facilitates low temperature, pressureless sintering through the formation of solid phase necks driven by phase separation. Systems that have been shown to exhibit this phenomenon are W–Cr, Cr–Ni and to a lesser degree Ti–Mg. Initial information on the average rate-limiting sintering kinetics in these systems was obtained using traditional master sintering curve analysis, but it is very clear that multiple processes occur during NPSS, and these should each have their own characteristic kinetics. Here we analyze these three systems in greater kinetic detail using densification rates in a Kissinger-style analysis derived explicitly for densification data. For the W–Cr and Cr–Ni systems two critical temperatures were identified: one at low temperatures for the formation of the secondary phase necks, and a second one at high temperatures corresponding to the onset of rapid densification. The activation energies of these processes are different, and reflective of bulk solute diffusion and interdiffusion, respectively. Combined with microstructural observations, these data show that the onset of rapid densification at high temperatures is facilitated by the presence of the second-phase necks, and occurs at the point where the system can fully interdiffuse, rehomogenizing those necks. These observations help explain why the Ti–Mg system does not densify well, because it does not exhibit redissolution at high temperatures. These results help clarify the conditions needed to achieve NPSS and may support design of new alloys for NPSS behavior.

This study investigated the dissolution of Al2O3 particles in CaO–Al2O3–SiO2 slag by the single hot thermocouple technique (SHTT) in the temperature range between 1550 °C and 1650 °C. The Al2O3 content in slags with basicity (CaO/SiO2 ratio) fixed at 1 varied from 5 to 35 pct. The evolution of the particle radius over time was obtained by image analysis. In the results of our experiments, the dissolution rate of the Al2O3 particles was increased with increasing Al2O3 activity in the slag. The rotation of the particle was observed during the dissolution experiment. We used a kinetic model that considered the fluid flow to understand the dissolution phenomenon. We calculated the diffusion coefficient of Al2O3 from 10−13 to 10−10 m2/s and in a similar manner as in a previous study. The activation energy of Al2O3 was 323 kJ/mole at 5 wt pct Al2O3, 343 kJ/mole at 20 wt pct Al2O3, and to 486 kJ/mole at 35 wt pct Al2O3.

We revealed that hydrogen (H) in pure Fe promotes grain refinement during plastic deformation, which is caused by the increase in dislocation density by the shielding effect and the presence of vacancy-H clusters. The promotion effect of H was dependent on the temperature and the strain rate, which is considered to result from a change in the number density of vacancy-H clusters and the magnitude of shielding effect by H.

Oxygen–lime powder bottom blowing converters have significant advantages in metallurgical performance, and have drawn more attention in recent studies. The key for oxygen–lime powder bottom blowing converter applications is to solve the problem of the furnace life. Erosion wear of the bottom injecting lance induced by a high velocity gas–solid jet inside the lance is an important factor for the furnace life but has rarely been studied. To reveal the gas–solid jet flow and erosion wear characteristics in the bottom injecting lance, a computational fluid dynamic model coupled with a discrete phase erosion model was established in the present work. The geometric dimension and boundary conditions of the lance were consistent with a commercial bottom injecting lance applied on a 120 ton converter. The simulated results were validated via a jet measurement experiment and an industrial experiment. The results show that the pressure loss in the lance of the gas–solid jet is much higher than that of pure gas jet, and the gas velocity at the lance outlet decreases after powder addition. Mixing powder into the gas has an obvious influence on the pressure variation curve and the velocity variation curve of the gas in the lance. The effect of the lance structure on jet flow and erosion wear was discussed in detail. On the premise that the total length of the lance remains constant, prolonging the shrink pipe length is helpful for reducing the pressure loss in lance. Simultaneously, the value of the maximum erosion wear and the area of the high wear rate region can be significantly reduced by prolonging the shrink pipe, which is vitally important for protecting the lance from being worn out by powder particles. The results of this work provide meaningful explorations and references for the design of converter bottom injecting lance.

The present study was carried out to understand the correlation between viscosity and sulfide capacity of aluminosilicate slag from the viewpoint of ionic structure of the slag. Viscosity and sulfide capacity are significantly influenced by the behavior of ions in the slag. Viscosity of slag is determined by the interaction between ions and size of viscous flow unit. The sulfide capacity increases with increase in NBO/T with respect to the basicity and with increase in interactions between cations and sulfide anions. The relationship between viscosity and sulfide capacity is inversely proportional when CaO/SiO2 ratio is up to 1.3. Viscosity and sulfide capacity show a correlation in the compositional range such that viscosity is dominantly influenced by NBO/T than ionic interaction because the relationship was mediated by NBO/T. In the slag system with and without FeO, the relationship between the two properties shows different intercept values. This result indicates that the relationship is affected by the type of cation that comprises a slag system. In this respect, the effect of ionic structure on sulfide capacity, viscosity, and their relationship is discussed in detail.

Under the joint action of electromagnetic swirling flow in the nozzle (EMSFN) and mold electromagnetic stirring, Liquid level fluctuation in the mold is investigated to find the optimal combination parameters for the occurrence time of the minimum macrosegregation degree in continuous casting of round billet. When the current intensity of EMSFN device is 450 A, the optimal carbon range 0.045 pct appears, after the fluctuation reaches the minimum with the current intensity at 400 A.

MnS inclusions are the primary non-metallic inclusions in U75V high-carbon heavy rail steel and can be detrimental to the mechanical properties of this material. With the aim of identifying means of controlling the amount and morphology of these inclusions, the present work examined the precipitation thermodynamics and growth kinetics of MnS during the solidification of molten steel using the FactSage 7.0 software package with various modeling calculations. The results indicated that the equilibrium partition coefficients of both Mn (kMn) and S (kS) decreased monotonically with increases in the solid fraction, and the kMn and kS values ranged from 0.6557 to 0.6941 and from 0.0141 to 0.019, respectively. This work also demonstrated that MnS precipitates in the two-phase region during the late stage of solidification to a solid fraction of 0.9263, while increasing the solute concentrations generates earlier precipitation. The Mn and S concentrations were shown to increase rapidly prior to MnS precipitation, after which the Mn concentration continued to increase while the S concentration decreased. Increasing the cooling rate and decreasing the S concentration tended to reduce the size of MnS inclusions but decreasing the Mn concentration had the opposite effect. The sizes of MnS inclusions were calculated using a coupling model and determined to be in the range of 4.4–12.4 μm, in good agreement with values obtained from scanning electronic microscopy observations of a steel billet. Observations of MnS inclusions before and after the rolling process indicated that the deformation ability (defined as the ratio of the length (after the rolling process) to the diameter (before the rolling process) of inclusions) of MnS was in the range of 11.89 to 54.88. This work provides an improved understanding of the precipitation and growth of MnS inclusions in U75V high-carbon heavy rail steel.

Wire-based friction stir processing is introduced as a solid-state surface alloying strategy for surface alloying of AZ31 magnesium alloy with aluminum, as a key alloying element in magnesium alloys. This technique enables the formation of a defect-free, grain refined and alloyed surface with the increased volume fraction of Mg-Al second phase, and thus, enhanced surface hardness. This simple technique provides a solid-state surface alloying pathway to improve the surface properties of the metallic materials.

Strong and tough materials are desired for lightweight, energy efficient applications such as electric cars and aerospace applications. Recently, heterostructures are found to produce unprecedented strength and ductility that are considered impossible based on the materials science in our textbooks. Such superior mechanical properties are enabled by a new scientific principle: hetero-deformation-induced (HDI) strengthening and work hardening. Heterostructured (HS) materials consist of heterogeneous zones with dramatic difference (> 100 pct) in flow stresses. The inter-zone interaction produces back stress in the soft zones and forward stress in the hard zones, which collectively produces the HDI stress. HS materials possess a significant synergistic effect where the integrated property exceeds the prediction by the rule of mixtures. Importantly, HS materials can be produced by current industrial facilities at large scale and low cost. The new materials sciences and promising applications are driving the fast development of the HS materials as an emerging field. There are many fundamental issues that need to be probed so as to effectively design HS materials for superior properties. To solve these issues, it requires collaborative efforts by the communities of experimental materials science and computational material science and mechanics.