Metals

Ti-Co binary intermetallic compounds have attracted lots of attention due to their excellent toughness and interesting anomalous ductility. However, systematic theoretical calculations of alloy properties of different Ti-Co compounds have not been properly investigated yet. In this work, first-principles calculations were performed to study the phase stability, mechanical properties bonding characteristic and slip properties of five Ti-Co binary compounds. The negative enthalpy of formation and cohesive energy showed that all the Ti-Co binary compounds were thermodynamically stable, and TiCo is the most mechanically stable one. According to the elastic stability criterion, these compounds are also mechanically stable. In addition, the mechanical anisotropy of Ti-Co compounds was analyzed by the anisotropy index and the three-dimensional surface of Young’s modulus, where Ti₂Co shows the strongest anisotropy, and TiCo₂(h) has weakest anisotropy. The phonon calculations of these compounds also show that all five Ti-Co compounds are thermodynamically stable. The density of states (DOS) and differential charge density distributions were analyzed to identify the chemical bonding characteristics of the Ti-Co binary compounds, which exhibit metal and covalent-like bonding and different magnetic properties. Finally, the plastic deformation mechanism of Ti-Co compounds was understood by calculating the generalized stacking fault energy (GSFE) of different slip systems. The anomalous ductility of TiCo and TiCo3 mainly arises from the complex slip system and the lower slip energy barrier of the compounds. Full article

The jarosite family of minerals are part of the alunite supergroup with the general formula AB₃(TO₄)₂(OH)₆. Jarosite family minerals are known to incorporate silver (Ag), but the extent to which this occurs, and at what temperature range, is not well constrained. To address this knowledge gap, jarosite compounds with the A site filled with K, Na, Ag and H₃O were synthesised at 22 °C, 97 °C and 140 °C to simulate low-, moderate- and high-temperature environments, respectively. The compounds were characterised by XRD, SEM, chemical analysis and Raman spectroscopy. All of the synthesised compounds took up Ag. In general, higher temperatures of synthesis increased alkali and Ag occupancy of the A site of the products. Silver contents increased with the increasing concentration of Ag in the starting solutions at all temperatures. The order of preference for occupancy of the A site in the synthesised solids is K > Na > H₃O > Ag at all temperatures, which is consistent with the reported order of ΔGf of −3309 kJ/mol, −3270 kJ/mol, −3247 kJ/mol and −2948 kJ/mol for jarosite, natrojarosite, hydroniumjarosite and argentojarosite, respectively. The results of this study show that Ag can be incorporated in jarosite and natrojarosite at low-to-high temperatures, and therefore, jarosite family minerals can be important stores of Ag in in natural and engineered environments. Full article

In order to study the effects of rare earth La–Ce alloying treatment on the characteristics of inclusions in non-oriented silicon steels, industrial experiments were conducted studying the composition, morphology, size and quantity of inclusions in W350 non-oriented silicon steel during the RH (Ruhrstahl-Hereaeus) refining process and tundish process, after rare earth treatment. The products were analyzed by means of ICP-MS (inductively coupled plasma mass spectrometry), SEM/EDS (scanning electron microscope-energy dispersive spectrometry), and ASPEX (automated SEM/EDS inclusion analysis). The research results showed that the types of inclusions in experimental steel changed significantly after rare earth treatment. The types of inclusions after RE (rare earth) treatment are typically rare earth composite inclusions that are mainly composed of (La, Ce)Al₂O₃, and conventional inclusions. The addition of rare earth promotes the agglomeration of inclusions; the morphologies of the inclusions are mostly blocky, and some are distributed in long strips. After rare earth treatment during the RH refining process, the number of inclusions with sizes of 1.0~3.5 μm in the experimental steel is increased, and the average size of the inclusions is 2.66 μm. In addition, the number of inclusions larger than 4 μm in the specimens increases due to the collision and growth of inclusions caused by the RH circulation. After rare earth treatment during the tundish process, the number of micro inclusions with sizes of 1.0~2.5 μm in the specimen steels decreases, while the number of inclusions larger than 5 μm increases. The size distribution of micro inclusions in hot-rolled sheets after rare earth treatment was studied using TEM (transmission electron microscopy). In the specimens without rare earth, the content of micro inclusions (≤1 μm) is 51,458.2/mm² and the average size is 0.388 μm. In the specimens with rare earth added, the content of micro inclusions (≤1 μm) is 24,230.2/mm² and the average size is 0.427 μm. Compared to sheet produced by the original process, the iron loss of the 0.35 mm finished experimental sheet is reduced by 0.068 W/kg, and the magnetic induction is increased by 0.007 T. The iron loss of the 0.50 mm finished experimental sheet is reduced by 0.008 W/kg, and the magnetic induction is increased by 0.004 T. After rare earth treatment, the average size of micro inclusions increases and the magnetic properties are obviously improved. Full article

A novel dual-phase PHSS consisting of lath martensite plus allotriomorphic δ ferrite (ALF) with nanoprecipitates was characterized by high-resolution field emission transmission electron microscopy for quenched, solid-solution-treated, and aged stainless steel. The effects of aging at various durations prior to H₂O or liquid N₂ quenching were investigated. Cu-rich nanoprecipitates evolve from body-centered cubic clusters to 9R Cu under quenching to 3R Cu and subsequently to face-centered cubic ε-Cu at various aging durations. Maximum hardness was observed after aging at 600 °C for 1 h. However, after this aging, both reversed austenite and Cu-rich nanoprecipitates coexisted in the martensite matrix. The segregation and diffusion of austenite-stabilizing elements promoted the nucleation of reversed austenite. Full article

Laser cutting is a thermal cutting process based on material melting that results in characteristic features of the cut edge. The dross in particular is a crucial quality-determining feature which occurs especially when processing higher sheet thicknesses. The influence of the dross geometry on the fatigue behavior of AISI 304 was investigated in this work. Using iterative experimental design, samples with different dross geometries were produced by varying laser cutting parameters. Four characteristic dross geometries were identified and used to classify manufacturing parameters: dross-free, small droplets, large droplets and very coarse dross. Fatigue tests were performed up to 10⁷ load cycles and revealed a dependence of the fatigue behavior on the dross geometries due to their different notch effects. It was found that the dross dominated the fatigue strength only above a certain dross height. At low dross heights, the surface relief of the cut edge dominated fatigue strength. The different cut edge properties (surface relief and dross) depend on the process parameters during laser cutting. Gas pressure and feed rate in particular showed a significant influence. The findings of this work provide information about the fatigue behavior’s dependence on dross geometry, which can be transferred to higher sheet thicknesses or complex sample geometries. Full article

A Monte-Carlo-assisted phase field model for the simulation of grain growth in metals and alloys is presented. The simulation time in this model is connected to real time through an experimental data-based kinetic model. Site selection probability is introduced to simulate grain structure evolution under non-isothermal conditions. The grain evolutions with temporal and spatial distributions of temperature during the welding process are comprehensively reproduced. The average size and topological texture of the generated grains in the fusion zone and heat-affected zone are examined. The computed results are compared to experimental data for laser-welding two alloys: Fe–6.5 wt.%Si and low-carbon steel. The applications of real-time–temperature based phase field simulation to material processing indicate significant promise for understanding grain structures during the welding process or additive manufacturing processes. Full article

Closed-cell A356 aluminum alloy foams refined and modified were successfully fabricated by using barite and calcium carbonate as thickening and foaming agents, respectively. A melt treatment consisting of adding master alloys of Al-5Ti-1B and Al-10Sr for refining the dendritic microstructure and modifying the primary eutectic silicon, respectively, were included in the foaming process. The microstructure and mechanical properties of the foams manufactured were analyzed and compared with foams produced without the refining and modifying treatments. The secondary dendritic arm spacing (SDAS) was determined by optical measurements. Lower SDAS values were obtained in foam regions closer to the mold walls due to the high solidification rate imposed during the cooling step and a decrease in the SDAS values for the foams produced with the addition of the Al-5Ti-1B master alloy was evident. Additionally, the addition of the Al-10Sr master alloy caused the formation of solid solution dendrites and a fine irregular fibrous form of silicon. Foams produced with the melt treatment exhibit a good combination of structure and mechanical properties. Therefore, the melt route established is a feasible way to improve foam performance where the lowest SDAS and the highest mechanical properties were obtained for the closed-cell foams produced. Full article

This work addresses the lack of focus on verification and comparison of existing fatigue damage accumulation and life prediction models on the basis of large and well-documented experiment datasets. Sixty-four constant amplitude, 54 two-level block loading, and 27 three-level block loading valid experiments were performed in order to generate an open-access, high-quality dataset that can be used as a benchmark for existing models. In the future, more experiments of various specimen geometries and loading conditions will be added. The obtained dataset was used for a study comparing five (non)linear fatigue damage and life prediction models. It is shown how the performance of several (non)linear damage models is strongly dependent on the considered material dataset and loading sequence. Therefore, it is important to verify models with a broad set of independent datasets, as many existing models show significant bias to certain datasets. Full article

In this paper, based on MSC Simufact.Forming v16.0 simulation software, the process parameters in the multi-pass spinning production of deep cylinders with a large diameter–thickness ratio are optimized, and the ten-pass spinning process of a deep cylinder with a diameter of 500 mm, thickness of 2 mm and depth of 700 mm is realized. By controlling the four process parameters of mandrel speed, feed rate, spinning wheel fillet radius and spinning wheel angle of attack, the influence of the four process parameters on the spinning force and the wall thickness deviation of the formed workpiece is studied. The results show that the radial spinning force and tangential spinning force are at their minimum when the mandrel speed, feed rate, spinning wheel fillet radius and spinning wheel angle of attack are 500 rpm, 1 mm/rev, 6 mm and 35°, respectively. At these setup conditions, the spinning efficiency is the highest and the workpiece is not prone to defects. The wall thickness deviation of the workpiece will decrease with the increase in the mandrel speed; with the increase in the feed rate, the radius of the round corner and spinning wheel angle of attack, the wall thickness deviation increases first and then decreases. Full article

Magnesium alloys have broad applications, including medical implants and the aerospace sector owing to their great density and high strength-to-weight ratio. Dry cutting is a frequent technique for machining this material. However, it always leads to an excessive rise in temperature due to the absence of cooling at the cutting zone, which affects the machined surface integrity and chip morphology. In this study, chip morphology and surface integrity of the AZ31 magnesium alloy were investigated in the turning process using an internal cooling method called submerged convective cooling (SCC) to overcome the absence of cooling in dry cutting. This method can exploit the advantage of the high specific heat capacity of water as a cooling fluid without any reaction between water and magnesium to create a cooling element in the cutting zone. The chip morphologies and surface integrity were analyzed experimentally with varying cutting speeds under SCC and dry cutting. The experimental results revealed that SCC and dry cutting produced saw-tooth or serrated chip formation. The chips produced in dry cutting were continuous, while SCC was short and discontinuous as a result of a severe crack on the back surface of the chip. It was discovered that the grain refinement layer on the machined samples was thinner under SCC turning. SCC machining increased the microhardness of the AZ31 magnesium alloy by 60.5% from 55 HV to 88.3 HV, while dry turning exhibited a 49% increase in microhardness. The result revealed that surface roughness improved by 10.8%, 9.4% and 4.7% for cutting speeds (V) of 120, 180, and 240 m/min, respectively, under the SCC internal cooling. Based on the result obtained, SCC cutting outperformed dry cutting in terms of chip breakability, grain refinement, microhardness, and surface roughness. Full article

Graphene-reinforced aluminium composites have been widely studied due to their excellent mechanical properties. However, only a few studies have reported their dynamic compression properties. The purpose of this study is to investigate the quasi-static and dynamic compression properties of graphene-reinforced aluminium composites. The addition of graphene improved the compressive stress resistance and energy absorption capacity of the aluminium matrix. An aluminium-0.5 wt.% graphene composite exhibited good compressive properties due to the different interfacial wave impedance generated by the additional grain boundaries or Aluminium-Graphene interfaces. Full article

The U.S. Department of Energy’s (DOE) Sunshot 2030 initiative has a goal of reducing the cost of concentrating solar power (CSP) to 5 cents per kWh for baseload power plants. One of the potential pathways to this goal includes a reduction in the cost of the supercritical CO₂ (sCO2) power block to 0.9 cents per kWh. Recuperators—high and low temperatures, used in the sCO2 power cycle, contribute to >50% of the cost of the power cycle. This work studies the feasibility towards a ≥10% cost reduction for High Temperature Recuperators (HTR) used in the sCO2 power cycle. One way to address the cost reduction is by leveraging low-cost additive manufacturing, specifically, Binder Jet Additive Manufacturing (BJAM) to 3D print HTRs at scale. This study focuses on the development of a BJAM process towards 3D printing HTR cores using Stainless Steel alloy 316L (SS316L). To evaluate the suitability of the BJ process towards the HTR, high level specifications of the application are translated to materials capability requirements. Subsequently, at-temperature materials testing is conducted on as-printed and sintered additively manufactured coupons. Data from the coupons are compared against cast and wrought SS316L data obtained from the literature. Results show that the tensile properties from the BJ process compare well against cast properties. Furthermore, a baseline analysis of creep testing data is established for the BJ process, and insights are drawn from the results towards future improvements of the process. Full article

The use of lead as a primary coolant is one of the most attractive options for next-generation lead-cooled fast reactor systems (LFR). Despite many favourable features, liquid Pb is a harsh environment that induces many problems on metallic components. Therefore, candidate materials for LFR must be qualified, and the solutions to improve their properties must be found. This paper’s objective is to present the results obtained from the tensile tests of AISI 316L steel in liquid lead at 400 °C, 450 °C, and 500 °C, and the short-term corrosion tests performed on coated and uncoated AISI 316L steel at 550 °C. The coating was made of Al₂O₃ with a CrNiAlY interlayer using the electron beam-physical vapor deposition (EB-PVD) technique. Both the mechanical and corrosion tests were performed in stagnant lead saturated with oxygen. After testing, the specimens were characterised by several analyses, including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), optical microscopy (OM), scratching test, and Vickers micro-hardness test. The tensile test results highlight the ductile behaviour of the material, and in the case of the corrosion tests, the coatings prove to be effective in protecting the substrate from the harsh environment. Full article

Gallium alloys are ideal base carriers for temperature-sensitive ferrofluids, which can be used for energy convection, soft robotics, microchannels, magnetorheological devices, etc. In this study, gallium was mixed with different substances (In, Sn, Zn, Ge, and Al) to obtain a low melting point, reduce the wetness and adhesion of its alloys, and realize low viscosity. The melting point, contact angle on certain solid plates, viscosity, and viscoelasticity of the gallium alloys were measured, and some useful gallium alloys were obtained. The experimental results showed that Ga₈₀In₁₀Sn₁₀ had lower wettability at a larger contact angle of 148.6° on the Teflon plate. Here, (Ga₈₀In₁₀Sn₁₀)₉₇Zn₃ with a melting point of 8.2 °C, lower than the melting point of Galinstan, was developed. It had a viscosity about three times that of water at room temperature and an elastic response from 0.1 to 100 Hz at a 1% strain amplitude for the viscoelasticity. It was expected that a kind of temperature-sensitive magnetic fluid with a gallium-based liquid alloy as the base carrier liquid would be prepared in the future with Teflon as the container to achieve energy conversion under the drive of the magnetic field. Full article

The effect of rare-earth Ce on the evolution behaviour of inclusions in heavy rail steel was studied. The addition of Ce can significantly reduce the number and size of class A, B, D, and Ds inclusions in the heavy rail steel smelting process. According to the statistical analysis of the size of inclusions in steel, the number and size of A and B inclusions in steel tend to decrease significantly, while D and Ds inclusions disappear. Ce splits the aluminium inclusion into several small-sized inclusions and improves the morphology of the large-size aluminium inclusion, thereby making aggregation and growth difficult while facilitating easy floating and removal. Because the addition of Ce reduces the concentration of S element in steel, MnS inclusions are difficult to grow. The decrease in the number and size of core inclusions required for MnS growth leads to a corresponding decrease in the number and size of MnS inclusions. Meanwhile, the S element also easily gathers on the surface of CaO–MgO–Al₂O₃–SiO₂–CeO inclusions, forming composite inclusions that are more easily removed, thus reducing the quantity and size of MnS inclusions. Full article

In this paper, aluminum coatings were prepared on a steel substrate by thermal spraying, and the corrosion morphology and corrosion resistance of the coating were investigated by salt spray and immersion tests. The results showed that after three months of salt spray tests, the coating still exhibited a surface morphology without significant damage and had good damage tolerance. Further effective protection of the substrate can be achieved by spraying the coating surface with paint. After three months of immersion test, the corrosion rate of samples with thicker coatings was located between 0.002 mm/y and 0.005 mm/y, and only a small amount of corrosion products was observed on the coating surface. The coated samples after salt spray and immersion tests maintained sufficient adhesion (17.07 MPa and 19.25 MPa), and the surface aluminum coating was highly reliable for protection of the steel substrate. In general, the reliability of the coating can be further improved by painting the surface of the thicker Al coating. This provides more ideas for the protection of transmission and transformation equipment. Full article

Mn–Co alloys were electroplated on AISI 430 stainless steel using an electrodeposition technique with the aim to reduce oxidation and chromium volatilization. The electroplating parameters were designed to improve the coating quality. The increased current density with decreased MnSO₄ content resulted in a denser coating layer. A sample coated with 0.10 M CoSO₄ and 0.50 MnSO₄ at 350 mA cm⁻² showed the best oxidation resistance after being oxidized at 800 °C for 90 h. The X-ray diffraction (XRD) result revealed that the oxide growth on the surface of the coated samples mainly formed oxides of MnCo₂O₄, MnCr₂O₄, and Cr₂O₃. The chromium volatilization was evaluated by exposing the coated samples to humidified synthetic air at 800 °C for 96 h. The mass flux of Cr volatilization was on the order of 10⁻¹¹ g cm⁻² s⁻¹. Furthermore, different heat treatments in O₂ and CO₂ atmospheres were compared. Annealing in CO₂ at 800 °C for 4 h helped increase the Mn–Co coating density. The relationship between the porosity and its failure behavior was also discussed. Full article

In this work, a method concerning thermal consolidation is proposed to simulate the traditional powder metallurgy process and accomplish the composition screening of powder metallurgy Ni-based superalloys U720Li and RR1000 with rare metal scandium, and superalloys with zero scandium addition, medium scandium addition and high scandium addition are selected. Then effects of scandium on the microstructure and mechanical properties of superalloys are further investigated through fast hot pressed sintering. The results indicate that scandium doping can effectively refine the grain through modifying the size and volume fraction of primary γ’ precipitates at the grain boundary. Meanwhile, scandium can promote the growth and precipitation of secondary γ’ precipitates to some extent. Due to the comprehensive effects of γ’ precipitate modification and grain boundary strengthening, as-sintered U720Li with 0.043 wt.% scandium presents an excellent combination of tensile strength and ductility at ambient and elevated temperature while as-sintered RR1000 with 0.064 wt.% scandium has a good performance at elevated temperature. Full article