Al Steel Research Articles

Nanoscale precipitation, mechanical properties, and deformation behavior of NiAl-strengthened high-strength steels: Effects of Ni and Al contents and ratios

Effects of Ni and Al contents and ratios on the continuous and discontinuous precipitation, mechanical properties, and deformation behavior of NiAl-strengthened steels were systematically studied through a combination of 3D atom probe tomography (APT), transmission electron microscopy (TEM), mechanical tests, and first-principles calculations. Microstructural analyses reveal that increasing the Ni and Al contents results in grain refinement and an increase in chemical potential gradient, both of which promote the discontinuous precipitation. The NiAl-strengthened steels with different Ni and Al contents and ratios exhibit high tensile strengths of 1000–1500 MPa but significantly different ductilities and fracture behaviors. TEM analyses indicate that fine-sized precipitates are sheared by moving dislocations, which leads to the formation of intersecting slip bands, thereby enhancing the work hardening capability. In contrast, coarse-sized discontinuous precipitates are bypassed by dislocations, resulting in a low rate of dislocation storage and hence low work hardening rate. In addition, increasing the Ni/Al ratio changes the fracture mode from brittle cleavage to ductile failure and improves the ductility of the Fe–Ni–Al steels. Microstructural analyses indicate that the ductilizing mechanisms are related to the increased bulk to shear modulus ratio (B/G) and the refined grain structure.

Research on the Microstructure and Properties of Al Alloy/Steel CMT Welding-Brazing Joints with Al–Si Flux-Cored Welding Wires

Al alloy/steel composite structures combine the advantage of a lightweight Al alloy and high-strength steel and are widely used in new energy vehicles, solar photovoltaic, and other fields. The main problems with the connection of an Al alloy and steel are poor weld formation and difficulty in controlling the thickness of the intermetallic compounds (IMCs) at the interface of the Al alloy and steel, which deteriorates the mechanical properties and corrosion resistance of the Al alloy/steel joints. Therefore, experiments on Al alloy/steel CMT (cold metal transfer, CMT) welding brazing were conducted by using AlSi5 and AlSi12 flux-cored welding wires as filler metals. The macro morphology, microstructure composition, tensile strength, and corrosion resistance of the Al alloy/steel joints were then analyzed. The mechanism of the Noclock flux on the wettability and spreadability of the Al–Si welding wire to a low-carbon steel surface was discussed and the formation behavior of the IMCs at the interface layer of the Al alloy/steel joints was clarified. The results showed that the NH4F and NH4AlF4 of the Noclock flux induced and accelerated the removal of oxide films on the surface of the Al alloy and Al–Si welding wire at a high temperature. It promoted the wettability and spreadability of the Al–Si welding wire, which resulted in the improvement of the Al alloy/steel joint formation. Under the CMT arc heat source, the Al–Si welding wire melted, and then a chemical metallurgical reaction occurred among the Al, Si, and Fe elements. The τ5-Al7.2Fe1.8Si phase formed preferentially near the Al alloy fusion zone while the θ-Fe (Al, Si)3 phase formed near the steel side. Actually, the interface reaction layer was composed of a double-layer compound including the τ5-Al7.2Fe1.8Si phase and θ-Fe (Al, Si)3 phase. Additionally, the IMC thickness of the Al alloy/steel joint with the AlSi12 flux-cored welding wire was 3.01 μm, which was less than that with the AlSi5 flux-cored welding wire, so its tensile strength was less but its corrosion resistance was superior. The main reason for the corrosion resistance of Al alloy/steel joints was the presence of a large amount of Al2O3, FeO, and Fe2O3 in the passive film.

Fe-14Ni-14Cr-2.5Al steel showing excellent corrosion-resistance in flowing LBE at 550 °C and high temperature strength

We investigated the corrosion behavior, microstructural evolutions, and mechanical properties in an alumina forming austenitic (AFA) Fe-14Ni-14Cr-2.5Al steel after exposure in the flowing lead-bismuth eutectic (LBE) at 550 °C for 4008 h and aging in air for 5000 h. The results showed that the AFA steel exhibited not only excellent corrosion-resistance in the flowing LBE but also a strong stability of austenite and high yield strength (589 MPa) at 550 °C. The excellent corrosion-resistance was ascribed to the rapid formation of a thin Al2O3 scale. For the first time, the precipitation of γ'-Ni3Al phase was observed in the AFA steel after long-term aging at 550 °C.

(Digital Presentation) Understanding the Electrochemical Stability of Potential Current Collectors in Zinc Sulfate Electrolyte for Rechargeable Aqueous Zinc Ion Battery Application

The need for clean and sustainable energy sources has witnessed a sudden upsurge in recent years owing to rising environmental degradation and climate disruption brought on by an overdependence on fossil fuels [1-3]. Electrochemical energy conversion technology is a crucial complement to the storage and on-demand utilization of renewable energy resources [4-6]. Rechargeable aqueous zinc ion batteries (AZIBs) have gained a significant research upsurge in recent times owing to their attractive potential for large-scale energy storage applications. In addition to low cost and naturally abundant raw materials, AZIBs technology offers competitive electrochemical performance and compatibility with water-based electrolyte systems, thereby eliminating the safety concerns associated with prevalent lithium-based battery technology. Moreover, multivalent AZIBs offer the opportunity to attain high energy and power density by permitting multiple electron transfers during reversible electrochemical operations [7]. In the context of AZIBs, significant research efforts are being actively pursued to develop high energy density cathode materials and to address the issue of Zn dendrite formation [8]. However, the selection of stable and low-cost current collectors is equally important as it serves as a bridge between the battery components and the external circuit, thereby influencing the battery capacity and its rate capability [9-10]. In this work, we have analyzed the electrochemical behavior of potential current collectors that are used globally in battery applications, namely Ni, Al, carbon paper, Cu mesh, graphite, and stainless steel in near-neutral aqueous ZnSO4 electrolyte (pH value = 5-6). The electrochemical stability of different current collectors has been investigated using linear sweep voltammetry and chronoamperometry techniques for their application as anode and cathode collectors. Scanning electron microscopy analysis has also been performed to understand the sign of corrosion post-electrochemical study. With stability up to 2.3 V w.r.t. Zn/Zn2+, Ni has proved to be the most corrosion-resistant current collector among the tested collectors on the cathode side. Although Zn itself is sufficiently stable at the anode side than any other current collector under the ZnSO4 electrolyte environment, Ni has shown considerable stability. Nonetheless, understanding the electrochemical stability of current collectors for AZIBs is a vital step in their design and future practical applications.

Nano-scale characterization of intermetallic compounds in dissimilar aluminum-steel resistance element welded joints

To achieve the goal of lightweight vehicle and energy-saving, the joining of dissimilar materials, specifically aluminum (Al) alloy and steel, is gaining increasing attention in car body structure. In the present study, 6061 Al alloy and DP780 steel sheet were joined using the resistance element welding (REW) technique with a flat Q235 rivet. The intermetallic compounds (IMCs) in the welded joints were thoroughly analyzed using various characterization techniques such as scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), electron backscatter diffraction (EBSD), focused ion beam (FIB), high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). The results showed that the IMC in the REWed joints consists of a tongue-shaped Fe2Al5 towards the steel side and a finger-shaped Fe4Al13 towards the Al side. Dislocations were observed at the grain boundaries of Fe2Al5 grains for the first time. Nanotwins and stacking faults inside the Fe4Al13 grains were observed indicating that the formation of planar defects was mainly by rapid cooling. The (100) twining was considered to be the main twining type during the solid/liquid interfacial reaction in dissimilar REW welding between Al alloys and steel.

Effect of Al content on the agglomeration behavior of inclusions in high Al steel

The product quality problem of high Al steel is closely related to the agglomeration behavior of inclusions. The present study firstly established the stability diagram of inclusion in the Fe–Al–O–N system, thereby evaluating the formation behavior and control condition of various inclusions can be obtained. Based on that, laboratory-scale experiments with different Al contents were designed to obtain the inclusion evolution process. Furthermore, the calculated agglomeration forces were used to explain the difference of evolution of various inclusions. The cavity bridge force increases with the increase of diameter of inclusions and decrease of distance between inclusions, and the van deer Waals force decreases with the increase of diameter and distance. Due to the cavity bridge force is larger than van deer Waals force, the inclusions firstly approached each other by van deer Waals force and then agglomerated by cavity bridge force. In addition, the cavity bridge force of Al2O3 is larger than that of AlN at the same condition because of the larger contact angle. However, the increase of Al content makes this phenomenon converse. When the Al content is > 3 wt. %, the cavity bridge force of AlN is larger than that of Al2O3. When the Al content is > 7 wt. %, the cavity bridge force of Al2O3 disappears. The study can provide theoretical support for inclusion control in high Al steel.

Corrosion resistance of Aluminium steel in 1N Sodium Hydroxide solution by an aqueous extract of Thespesia populnea plant leaves

Corrosion resistance effect of aluminium steel in 1N sodium hydroxide by an aqueous extract of Thespesia populnea plant leaves has been investigated by mass loss method. It is observed that as the concentration of the inhibitor increases, the inhibition efficiency increases. The mechanistic aspects of corrosion resistance have been studied by potentiodynamic polarization technique and electrochemical impedance spectroscopy. A maximum inhibition efficiency of 78.70% is achieved by this inhibitor system. Potentiodynamic polarization technique reveals that the inhibitor system functions as a mixed type of inhibitor, controlling anodic and cathodic reactions. It is noted that in the presence of inhibitor, linear polarization resistance value increases and corrosion current decreases. Electrochemical impedance studies reveal that a protective film is formed on the Al steel surface, since in the presence of inhibitor system, the charge transfer resistance value increases and double layer capacitance value decreases. This is due to adsorption of the molecules of the active ingredients of the extract on the Al steel surface. The inhibition efficiency increases due to adsorption of hetero atoms present in TP plant leaves extract on the Al steel surface. The maximum inhibition efficiency and the lower corrosion rate are obtained at high concentration 1200 ppm for TP plant leaves extract. By further increase in inhibitor concentration above 1200 ppm, the inhibition efficiency and corrosion rate almost remained constant. So, the 1200 ppm concentration is fixed as the maximum inhibition for the investigative aqueous extract of plant leaves as corrosion inhibitor. This concentration corresponds to the attainment of a saturation value in surface coverage of Al steel. The protective film formed over the Al steel surface has been characterized by Fourier Transform infra-red spectroscopy. The surface morphology of the protective film of carbon steel immersed in sodium hydroxide in the absence and presence of inhibitor has been studied by Scanning electron microscopy. The outcome of the study can be used in pickling industry wherein sodium hydroxide is used to remove the rust on the Al steel surface.

Decomposition of γ-Fe in 0.4C–1.8Si-2.8Mn-0.5Al steel during a continuous cooling process: A comparative study using in-situ HT-LSCM, DSC and dilatometry

Continuous cooling transformation (CCT) diagrams represent roadmaps for producing all heat-treatable steels. CCT curves provide valuable information on the solid-state phase transformation sequence, depending on the defined cooling strategies, the alloying concept of the steel and previous processing steps. The experimental characterization of CCT diagrams is usually done on a laboratory scale applying thermal analysis of dilatometry. In current research studies, however, also other in-situ methods such as high-temperature laser scanning confocal microscopy (HT-LSCM) or differential scanning calorimetry (DSC) are frequently used to investigate phase transformations during thermal cycling. In the present study, HT-LSCM observations and DSC analysis are critically compared with dilatometry results by investigating the CCT diagram of a 0.4%C-1.8%Si-2.8%Mn-0.5%Al (in mass pct.) advanced steel grade. Furthermore, classical examinations by optical microscopy and hardness measurements were performed to support the analysis. In general, very good consistencies between all experimental techniques were identified in determining the transformation start temperature for pearlite, bainite and martensite. The optical microscopy confirmed the observed phase transformations and the results correlated with the measured hardness response. Based on the results, coupling of HT-LSCM and DSC is considered as a valuable novel approach to plot CCT diagrams in future research.

Effect of CaO/Al2O3 Ratio on Physical Properties of Lime-Alumina-Based Mould Powders

High-aluminium steels contain a significant amount of aluminium. The reaction between Al in the liquid steel and SiO2 in lime-silica-based mould powders during the continuous casting process of high Al steel causes chemical compositional changes in the mould powders, subsequently affecting the surface quality of slabs. In order to solve the aforementioned problem, lime-alumina-based mould powders have been developed, which can lead to an increase in the surface quality of cast slabs by inhibiting steel/slag interaction. However, the mould slag tends to crystallise easily, which leads to a deterioration of the mould lubrication. In view of this aspect, it is important to develop and optimize lime-alumina-based mould powders to meet the requirements of continuous casting of high-aluminium steels. In this study, the changes in crystallinity, viscosity and melting temperature of lime-alumina-based mould powders with the effects of increasing the CaO/Al2O3 ratio have been observed through STA (Simultaneous Thermal Analysis), HSM (Hot Stage Microscopy), XRD (X-ray Diffraction), IPT (Inclined Plate Test) and rotational viscometer. The crystallisation behaviour of these mould powders was evaluated by generating CCT (continuous cooling transformation) diagrams. Additionally, the changes in steel chemistry have also been analysed using XRF (X-ray fluorescence) and ICP (Inductively Coupled Plasma Mass Spectrometer). The results of these analyses demonstrated that crystallinity of lime-alumina-based mould powder is increased while the initial crystallisation temperature and viscosity are decreased by CaO/Al2O3 additions. However, the degree of steel/slag interaction decreases with an increase in Al2O3 content.

Microstructure and Dynamic Mechanical Behavior of Thermomechanically Rolled 3Mn–Al and 5Mn–Al Sheet Steels

The comparison of the dynamic mechanical behavior and microstructure of two medium manganese sheet steels (3Mn–Al and 5Mn–Al) alloyed with aluminum is aimed. Mechanical properties under dynamic tensile loads are determined by means of rotary hammer dynamic tests at strain rates of 250 and 1000 s−1and analyzed together with the results of static tensile test. It is found that the results are significantly affected by the variations in Mn content in the range from 3 to 5 wt%. In both steels, the tensile strength increases with increasing strain rate, but the variation in the strain rate range has a moderate effect on mechanical behavior. The highest ultimate tensile strength of 1475 MPa is measured in the 5Mn–Al steel, whereas the 3Mn–Al steel is characterized by better total elongation due to a larger fraction of retained austenite and more pronounced transformation‐induced plasticity effect. The results show that the mechanical properties of 3Mn steel are more strain rate sensitive than those of 5Mn steel. The microstructural features are characterized qualitatively and quantitatively by X‐ray diffraction, scanning electron microscopy, and electron back‐scattered diffraction techniques.

Estimation of Changes in Content and Characteristics of Mold Flux during Continuous Casting

Estimation of changes in the composition and physical properties of mold flux during continuous casting was investigated for control of slab surface quality. In this study, 0.7 mass% Al steel and normal Al-killed steel were cast with three kinds of mold flux having Al2O3 contents of 1.3 to 6.0 mass% and different basicities. The results can be summarized as follows:(1) The Al2O3 content of these mold fluxes increased to 30 mass% during continuous casting. The composition change of the mold flux can be reproduced by the Equilibrium Effective Reaction Zone Model (EERZM) by fitting parameters, referring to the casting results.(2) The analysis by EERZM revealed that the viscosity of the mold flux and the throughput of the molten steel affect the rate of increase of the Al2O3 content in the mold flux.(3) The change of the physical properties of the mold flux was estimated based on the changes in the flux composition. The change of the crystallization temperature and main crystal can be estimated by FactSage.(4) Mold flux viscosity can be estimated by revising the modified Iida’s equation, which considers the effect of Al2O3 as an amphoteric oxide.

Unbalanced thermal field assisted thermo-compensated resistance brazing welding 6061 aluminum alloy to 304 stainless steel

The reliable Al/steel resultant welded joint with a large contact area was of great significance in electrolysis cells to produce aluminum. Herein, a large-area 6061 aluminum alloy/304 stainless steel dissimilar welds were successfully obtained by unbalanced thermal field assisted thermo-compensated resistance brazing welding(abbreviated as UTC-TC-RBW). In the present study, the heating distribution conditions of the joint were adjusted based on the introduction of the auxiliary welding current, forming an unbalanced temperature field. The whole welding temperature field of the joint was improved significantly with the increase of the auxiliary current, which promoted the interdiffusion of Al and Fe elements at the interface. Hence, the connection area between Al alloy and steel was increased gradually. The final interface between Al alloy and steel was changed to the Al(s.s) diffusion layer and Fe2Al5 layer. XRD results proved the presence of these phase compositions. When the auxiliary current was 0.3 kA, the maximum thickness of the Al(s.s) diffusion layer and Fe2Al5 layer reached 5.25 μm and 0.86 μm. The final load of the obtained joint with the auxiliary current of 0.3 kA was the maximum and reached 1789.7N, which was approximately 3 times that of the joints without auxiliary current.

Microstructural Evolution and Mechanical Properties Co relation of Cold rolled Ferritic Lightweight Steel with Increasing Carbon

The structure-properties relationship of cold-rolled and annealed Fe-7wt.%Al lightweight steels for varying carbon contents is explored in this work.Unlike Fe-Mn-Al-C based steels, which experienced processing issues, the hot-worked plates of the present steel were successfully cold-rolled to 2mm thick sheets. Various phases present in the steel for different carbon contents as predicted using the ThermoCalc programme are in line with the experimental findings. The basic alloy with 0.01C contains only a ferrite phase, however, the alloys with higher carbon content have a significant quantity of κ-carbide precipitates. The addition of carbon to Fe-7wt.%Al steel has improved its tensile strength significantly (438 to 828MPa). Tensile elongation, on the other hand, has decreased dramatically (26 to 12 percent) with increasing carbon content The reduction in ductility with increasing carbon is mainly ascribed to the increasing κ-carbide precipitates volume fraction with higher hardness, but not due to the environmental embrittlement as observed in case of higher Al containing steels.

Properties of medium-manganese steel processed by laser powder bed fusion: The effect of microstructure in as-built and intercritically annealed state on energy absorption during tensile and impact tests

The presented research was aimed at applying laser powder bed fusion (LPBF) technology and TRIP (Transformation Induced Plasticity) steel with medium Mn content to produce thin-walled parts with enhanced crashworthiness. It was expected that the simultaneous use of the excellent combination of strength and ductility of the new type of medium-Mn steel and the advantages of LPBF technology would allow the development of an alternative to the conventional method of manufacturing the energy absorbing components. The energy absorption capability of LPBF-processed Fe-0.15C-7.5Mn-1.8Al steel was evaluated based on its deformation behavior under monotonic and impact loading. Tensile and Charpy V-notch specimens were fabricated by LPBF with layer thicknesses of 30 and 60 μm, using processing windows set established according to the criteria of low porosity (<0.3%) and good surface quality. Specimens were tested in as-built state and after intercritical annealing at a constant temperature (670 °C), but for different holding times and cooling rates to obtain a large fraction (30–50 vol%) of retained austenite capable of strain-induced martensitic transformation. Based on multiscale microstructure examinations (OM, SEM, EBSD, XRD, EDS) the relationships between the morphology of LPBF-specific microstructures before and after intercritical annealing, as well as between their behavior in tensile and impact test, were analyzed and discussed. For both layer thicknesses, the best combination of strength, elongation and impact toughness was obtained after annealing at 670 °C for 6 h followed by argon cooling. LPBF technology has been shown to be suitable for the fabrication of thin-walled energy-absorbing components from medium-manganese TRIP steel with the potential to reduce fabrication time by doubling the layer thickness compared to standard.

Influence of Structural Parameters - the Shape of Graphite and Matrix on Change of Ultrasonic Wave Propagation Rate and Value of Attenuation in Graphitic Cast Irons

Abstract Despite the tendency of the current industry, especially the automotive industry, it is to use modern, light and super-strong materials based on Al or HSLA steels, the application of classic materials such as cast iron still makes sense, especially concerning price and excellent castability. The article presents one of the possible ways of using the ultrasonic non-destructive method in quality control and simplification of the identification of the type of cast iron concerning the change of parameters of ultrasound propagation in materials. The main criteria for assessing the quality and determining the type of graphite cast iron were considered to be the rate of propagation of ultrasound - cL and the value of attenuation - α, which vary depending on the shape of the graphite and matrix. Graphitic cast irons with different graphite shapes (lamellar, vermicular, and globular shapes) and a matrix with different ferrite/perlite ratios were used as experimental material. Along with the ultrasonic tests, a metallographic analysis was also performed to quantify the microstructure of cast irons.

Influence of chemical composition and processing conditions on the microstructure and magnetic properties of low-carbon Si-Al-Sb electrical steel sheets

It has been recently reported that the magnetic behavior of electrical steels containing Si + Al, can be improved by an alternative processing route, which involves the intercritical annealing of the hot-rolled bands before cold-rolling. The effects of such processing route has not been investigated in steels containing Si-Al-Sb. It has been reported that Sb can enhance the magnetic behavior of these steels. The present work reports the microstructure and magnetic properties of Si-Al-Sb electrical steels processed by the alternative processing route. Results were compared with those of Si-Al electrical steel sheets processed both by the conventional and the alternative route. Microstructural characteristics of hot-rolled electrical steel samples were modified by an intercritical annealing conducted at 850 °C from 30 min to 720 min. After this, samples were cold rolled using thickness reductions of 80 % and 90 %, and annealed at 750 °C, 850 °C and 950 °C for 8 min. Characterization of the samples included: spark optical emission spectrometry, dilatometry, optical microscopy and scanning electron microscopy, while magnetic properties were determined in a silicon steel sheet iron loss tester. Results demonstrate that, Si-Al-Sb steels processed by the alternative route exhibit better performance (higher permeability, lower coercivity, lower core loss), than Si + Al steels processed either by the conventional or the alternative route.

Investigation of the relationship between the microstructural evolution mechanism and mechanical properties in hot rolled Fe-0.2C–6Mn–3Al steel

The objective of the present research is to investigate the influence of the microstructural evolution mechanism on mechanical properties during deformation. For this purpose, hot rolled Fe-0.22C-6.12Mn-3.08Al steel is subjected to intercritical annealing at 740 °C for 10 min. The annealed specimen contains a mixture of lath-like α-ferrite and reverted γ, whose volume fraction is approximately 38.7%. During deformation, once the critical stress caused by the severe dislocation pile-ups is reached, the strain/stress-induced phase transformation occurs. First, grain boundaries of γ/α serve as the preferential nucleation sites for fresh α′-martensite. Subsequently, fresh α′-martensite nucleates inside reverted γ. In the meantime, the interfacial α′-martensite grows continuously into the reverted γ interior. During deformation (prestrain at 0.0%, 5.1% and 7.8%), the misorientation (MO) in α-ferrite+α′-martensite continuously rises from 0.63° to 0.67°; nevertheless, the MO in reverted γ increases from 0.65° to 0.73° and then rapidly decreases to 0.69°. Hence, the phase transformation of reverted γ is accompanied by obvious stress softening; thus, effective work hardening occurs in the subsequent deformation region due to α-ferrite and fresh α′-martensite. This phenomenon greatly enhances the strength and delays necking, e.g., the annealed specimen possesses outstanding mechanical properties (992 MPa, 47.6% and 47.2 GPa × %). Once necking occurs, the residual reverted γ is rapidly consumed in the necking region. Hence, the hardness in the necking region (5.31 ± 0.20 GPa) is much higher than that in the uniform deformation region (4.53 ± 0.17 GPa) due to the abundant hard fresh α′-martensite.

The Effect of Fe/Al Ratio and Substrate Hardness on Microstructure and Deposition Behavior of Cold-Sprayed Fe/Al Coatings.

Fe/Al composite coatings with compositions of Fe-25 wt.% Al, Fe-50 wt.% Al and Fe-75 wt.% Al were deposited on pure Al and P91 steel plates by a cold spray, respectively. The microstructure of the cross-section of the fabricated coatings was characterized by SEM and EDX. The bonding strength between the coatings and substrates was measured and analyzed. The effects of the Fe/Al ratios and substrate hardness on the deposition behavior were investigated. It was interesting to find fragmented zones in all fabricated coatings, which were composed of large integrated Al particles and small fragmented Al particles. Meanwhile, the fraction of fragmented zones varied with the fraction of the actual Fe/Al ratio. An Fe/Al ratio of 50/50 appeared to be an optimized ratio for the higher bonding strength of coatings. The in situ hammer effect caused by larger and harder Fe particles played an important role in the cold spray process. The substrate with the higher hardness strengthened the in situ hammer effect and further improved the bonding strength.

Template-free scalable growth of vertically-aligned MoS2 nanowire array meta-structural films towards robust superlubricity.

Two-dimensional (2D) molybdenum disulfide exhibits a variety of intriguing behaviors depending on its orientation layers. Therefore, developing a template-free atomic layer orientation controllable growth approach is of great importance. Here, we demonstrate scalable, template-free, well-ordered vertically-oriented MoS2 nanowire arrays (VO-MoS2 NWAs) embedded in an Ag-MoS2 matrix, directly grown on various substrates (Si, Al, and stainless steel) via one-step sputtering. In the meta-structured film, vertically-standing few-layered MoS2 NWAs of almost micron length (∼720 nm) throughout the entire film bulk. While near the surface, MoS2 lamellae are oriented in parallel, which are beneficial for caging the bonds dangling from the basal planes. Owing to the unique T-type topological characteristics, chemically inert Ag@MoS2 nano-scrolls (NSCs) and nano-crystalline Ag (nc-Ag) nanoparticles (NPs) are in situ formed under the sliding shear force. Thus, incommensurate contact between (002) basal planes and nc-Ag NPs is observed. As a result, robust superlubricity (friction coefficient μ = 0.0039) under humid ambient conditions is reached. This study offers an unprecedented strategy for controlling the basal plane orientation of 2D transition metal dichalcogenides (TMDCs) via substrate independence, using a one-step solution-free easily scalable process without the need for a template, which promotes the potential applications of 2D TMDCs in solid superlubricity.

Effects of the microstructure on the fatigue fracture of friction stir lap welded Al-clad Al and Al-clad steel sheets

The microstructural characteristics and mechanical properties of friction stir lap welding (FSLW) of thin Al-clad Al (1.5 mm) and ultra-thin Al-clad mild steel (0.7 mm) sheets are experimentally investigated. Optical microscopic observation confirms that the FSLW joints are successfully fabricated without noticeable joining defects, such as cracks and hooks. The material flow is correlated with the silicon (Si) element distribution in the stir zone (SZ). The distribution of Si indicates that material flow is asymmetrical between the advancing side (AS) and the retreating side (RS) of the SZ. The tensile test result shows that all the FSLW joints fracture from the Al-clad Al side of the joints. During the fatigue tests, two different crack propagation modes (vertical crack in the Al-clad Al loading side; horizontal crack in the Al-clad mild steel loading side) are observed simultaneously due to the combined effect of the asymmetric geometry of the FSLW joint and the different loading configurations. The results of fatigue tests suggest that the asymmetric microstructure of the joint retards the propagation of a vertical crack in the Al-clad Al loading side for the RS-loaded FSLW joint. As a result, the fatigue life of the RS-loaded FSLW joint becomes clearly higher than that of the AS-loaded FSLW joint.