Electron Backscatter Diffraction Research Articles

Microstructure Evolution and Cryogenic Impact Toughness Changes in Ce‐Containing Novel Cryogenic High‐Mn Austenitic Steel Weld Metals under Different Heat Inputs

The Ce‐containing novel cryogenic high‐Mn austenitic steel weld metals under different heat inputs are prepared by submerged‐arc welding to provide a satisfactory welding parameter scheme and further optimize its cryogenic impact toughness. The effect of heat input on microstructure, inclusion, and cryogenic impact toughness of weld metals are investigated via optical, scanning electron microscopy, electron backscatter diffraction, electronic probe microanalyzer, and cryogenic impact test. The results show that the dendrite arm spacing, segregation ratio of Mn, Si, and C elements and average effective grain size of the weld metals gradually increase, and the proportion of high‐angle grain boundaries decrease with the heat input increase from 11.91 to 20.24 kJ cm−1. The type of inclusions of weld metal with different heat inputs are all Ce2O3 and Ce2O2S. The number density of inclusions decreases monotonically from 5976 to 4912 mm−2, while the average size increases from 0.32 to 0.45 μm with the heat input increased. The increase in heat inputs consistently decreases the mean cryogenic impact toughness of weld metals from 123 to 102 J. The higher proportion of high‐angle grain boundaries and finer inclusions at lower heat input play the critical role in improving the cryogenic impact toughness.

Kyanite-muscovite-dumortierite vein mineralization mechanisms from advanced microstructural analysis using EBSD

Abstract Dumortierite, an aluminous borosilicate mineral, is relatively rare in Earth’s crust, but it is the second most abundant aluminous borosilicate after tourmaline. Boron is an element with many uses in modern societies worldwide, from health products to wind turbine blades for clean energy, but of limited availability and at future risk of supply. Only a limited number of studies have been published on dumortierite mineralization processes and the factors that control its abundance and distribution remain poorly understood. Here we present the first comprehensive electron backscatter diffraction (EBSD) study of dumortierite mineralization mechanisms in kyanite-muscovite-dumortierite veins occurring in the metapelites of the Amgaon Gneiss Supracrustals, in the Girola hill area, Sakoli region, Central India. Advanced microstructural and chemical analyses show that mixed-mode brittle-viscous deformation in kyanite, by fracturing and easy glide on (100) [001] slip system, facilitates fluid-rock interactions with reactive hydrothermal fluids rich in B, F, and K and containing Na, Ti, Mg, Fe and Pt. These interactions cause the dissolution of kyanite along fracture and cleavage surfaces and the precipitation of muscovite (F = 0.32 wt %) and topaz (F = 16.48 wt %). The motion of ripplocation defects in muscovite facilitates fluid migration along cleavage surfaces and crystallisation of dumortierite needles within these surfaces. Fluid flux removes silica in solution from the system, so reactions may continue. The observed mineral assemblage, the microstructural signature of kyanite and muscovite, the moderate fluorine content of topaz, and low fluorine content of muscovite, together suggest that dumortierite mineralization results from hydrothermal activity, possibly in a transitional magmatic-hydrothermal environment, likely at P > 2.5 kbar and 400°<T < 550°, that could be linked with granite intrusions in the area. Using EBSD we demonstrate that dumortierite mineralization is focussed along muscovite basal cleavage surfaces and dumortierite needle elongation is likely controlled by the fluid flux direction. These new results advance our understanding of dumortierite mineralization mechanisms and conditions and have important implications for our understanding of the distribution of this aluminous borosilicate mineral in muscovite-rich rocks.

Atomistic simulation of primary microstructure formation in metals during crystallization from the melt.

Additive manufacturing of metallic parts by Selective Laser Melting (SLM) implies high temperature gradients and small volume of the melt bath. These conditions make the process scales close to those available for state-of-the-art massively parallel atomistic simulations. In the paper, the microscopic mechanisms responsible for the formation of primary microstructure during molten metal solidification are investigated using classical molecular dynamics (CMD). The 316L austenitic stainless steel with face centred cubic lattice, which is widely used in industry including SLM applications was chosen as a material for the CMD simulations. It was shown that solidified material inherits substrate defects and catches new ones, which interact with the solidification front thus producing the primary microstructure. Peculiarities of solidification in different crystallographic directions and solidification front interaction with grain boundaries and newly produced defects (mostly twin boundaries) as well as their formation are under study. Resulting microstructures of virtual samples are compared with those of real samples produced by SLM and analysed by the electron backscatter diffraction (EBSD) method. The comparison shows similarities of EBSD and CMD sample patterns and evidences for the capability of the large-scale atomistic simulations to reproduce main features of the microstructures formed in the metallic SLM additive production.

Influence of Cold Drawing on Phase Transformation and Tensile Properties of FeCrMn Austenitic Stainless Steel 201

Manganese stabilizes the austenite and reduces the stacking fault energy in face‐centered cubic (FCC) structures, promoting the formation of hexagonal and cubic structures. This study investigates the phase transformation and mechanical behavior of extremely low‐carbon FeCrMn austenitic stainless AISI 201 steel subjected to cold drawing in three stages, ultimately reaching a true strain of 0.93. The objective is to examine the transformation from the parent FCC structure to hexagonal close‐packed and body‐centered cubic structures as a combination of transformation‐induced plasticity and twinning‐induced plasticity phenomena. X‐ray diffraction and electron backscatter diffraction analyses are utilized to investigate phase transformations under significant plastic deformation and the crystallographic orientation relationships between phases. Additionally, tensile and hardness tests are performed to assess the impact of plastic deformation on mechanical properties. Results indicate that a true strain of 50% is optimal for balancing strength and ductility in CrMnFe austenitic stainless steel. After applying a true strain of ε1 = 26.7%, yield strength (YS) increases by 192% and ultimate tensile strength (UTS) by 35%, while elongation reduces by 41%. With a further strain of ε2 = 57.5%, YS increases by 71% and UTS by 44%, but elongation drastically decreases by 94%. Applying the final strain of ε3 = 94.0%, YS and UTS only increase by 3% and 2%, respectively, while elongation further reduced by 40%. These findings suggest that a true strain of 50% shall be considered the maximum reduction for maintaining a balance between strength and ductility in CrMnFe austenitic stainless steel.

Magnetic Fabrics in Laminated Rocks of the Ilímaussaq Igneous Complex, Southern Greenland

ABSTRACT Nepheline syenites from the ∼1.2 Ga Ilímaussaq Complex of southern Greenland are examined to assess the utility of anisotropy of magnetic susceptibility (AMS) fabrics as proxies for silicate petrofabrics. Mineral lamination is a relatively common structural feature in cumulate rocks, including in the Ilímaussaq intrusion, but there is little consensus on the process (or processes) responsible for its formation. The Ilímaussaq AMS data are combined with rock magnetic experiments and electron backscatter diffraction (EBSD) measurements to characterize the magnetic mineralogy and compare the magnetic fabrics obtained to the silicate petrofabric. The data show that Na-amphibole (arfvedsonite) is most likely the dominant control on the AMS fabrics in the coarse-grained nepheline syenites (referred to as kakortokites), and that the AMS fabric is inverse relative to the observed silicate fabric. The EBSD data for a kakortokite sample suggests that the petrofabric is defined by arfvedsonite and is wholly planar, with evidence of only weak cross-lineation of c axes. The fine-grained nepheline syenites (lujavrites), two of which have a well-developed lamination carried by Na-pyroxene (aegirine), appear to have composite AMS fabrics that are considered to be a consequence of a mixed aegirine (normal) and arfvedsonite (inverse) response. The combined datasets shed light on the mechanisms of fabric acquisition in both lithologies. In the kakortokites, the AMS fabrics and silicate crystallographic preferred orientations, as well as the lack of observed microstructural evidence for subsolidus intra-crystal deformation, support models invoking gravitationally controlled crystal mats in the development of the macro-rhythmic layering of these rocks. In the lujavrites, the strong planar fabrics revealed by both the AMS and EBSD datasets, with some evidence of subsolidus deformation, point to fabric formation and perhaps even aegirine crystallization at the postcumulus stage. The combination of EBSD and AMS fabric datasets is a powerful means of deciphering the processes responsible for mineral alignment in igneous cumulates.

Short Crack Behavior of an Additively Manufactured Ti–6Al–4V Alloy Under Ultrasonic High Cycle Fatigue Testing

ABSTRACTThe high cycle fatigue (HCF) behaviors of an additively manufactured (AM) Ti–6Al–4V alloy with fully lamellar microstructures processed electron beam powder bed fusion (EB‐PBF) and wire‐fed electron beam directed energy deposition (Sciaky) routes were compared. Ultrasonic fatigue (USF) testing at the stress ratio of R = −1 was applied to monitor the growth of small cracks initiated at surface micronotches. Crack growth rates lower than 10−8 (m/cycle) at ΔK = 6 MPa·m1/2 were measured in samples processed by both methods. The finer α lath thickness (~1 μm) of the Sciaky samples resulted in a slower fatigue crack growth rate than the EB‐PBF samples with coarser laths. The interaction of cracks with the lamellar microstructures was characterized by electron backscatter diffraction. Crack propagation largely followed the lath interfaces in the Sciaky samples, whereas cracks cut across colonies in the EB‐PBF samples. Different fatigue fracture surface characteristics were observed for the EB‐PBF and Sciaky samples.

An in-situ investigation of microstructure neighborhood effects on hydrogen-induced dislocation activity

The interactions between hydrogen and crystallographic defects are the key to understanding hydrogen induced localized plasticity or damage mechanisms. However, unraveling such interactions based on the resulting mechanical effects alone can be challenging, due to the spectrum of various effects hydrogen can create in a given microstructure. Pre-deformation or post-mortem characterization of hydrogen segregation has similar limitations, as they can only provide snapshots of these complex processes with challenging spatial and temporal scales. To tackle this, we design in situ experiments that combine electron channeling contrast imaging (ECCI), electron backscattered diffraction (EBSD), and desorption spectroscopy, to investigate hydrogen defect interactions, under no external loading. We show that the inhomogeneous hydrogen distribution within microstructures can cause long-range (>200 nm) dislocation rearrangements. Interpretation of these results as manifestations of boundary-segregation induced stress suggests that microstructural characteristics on either side of the boundary should also play an important role. We provide quantitative assessments of these microstructure neighborhood effects and discuss additional contributions from hydrogen-induced changes in stacking fault energy and elastic modulus.

Effect of aging temperature on the microstructural evolution and mechanical properties of 18Ni (200) maraging steel

Herein, we used transmission electron microscopy (TEM), electron backscattering diffraction (EBSD), and X-ray diffractometry (XRD) to investigate the effects of different aging temperatures on reversed austenite and precipitates in 18Ni (200) maraging steel, as well as their evolving patterns of cryogenic toughness and strength. Aging at 510 °C was found to enhance cryogenic toughness at −196 °C and deliver peak strength, which is attributable to the significant aging-strengthening effect and the reversed austenite. Furthermore, this study investigated the factors that contribute to the formation and high stability of reversed austenite and quantitatively assessed the contributions of aging strengthening, dislocation strengthening, and grain-boundary strengthening to yield strength at various aging temperatures.

Microstructures, crystallography and growth patterns of serpulid tubeworms (Class Polychaeta)

Serpulid polychaetes are marine worms that secrete calcium carbonate tubes in which they live. Despite extensive previous research on their microstructures, there are no crystallographic data and their biomineralization process remains unclear. Here, the microstructures of the tubes of seven serpulid species were studied, including their chemical composition, mineralogy and crystallography, using X-ray diffraction, Raman and Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, focused ion beam, electron backscatter diffraction, and thermogravimetric analysis. Generally, serpulid tubes have a high amount of organic matter (~ 7.5 wt%), consisting of chitin and proteins, and the calcite is always present as medium to high magnesium calcite. Three main microstructures were identified: granular-prismatic and lamello-fibrillar calcite, and fibrous aragonite. They all displayed an axial texture, which is stronger in the lamello-fibrillar calcite, with the c-axis aligned with the elongation axis of the crystals. These findings demonstrate that only some instances of the granular-prismatic and the lamello-fibrillar calcite are biogenic (primary) microstructures. Conversely, other instances of the granular-prismatic calcite and the fibrous aragonite are a consequence of a recrystallization process (i.e. secondary). Replacement may occur on either primary or secondary calcitic microstructures (replaced by aragonite). Secondary microstructures retain remnants of the previously replaced microstructures, such as vestigial crystals or major growth increments. The high-Mg nature of the calcite favors recrystallization. The plywood arrangement of the lamello-fibrillar calcite is hypothesized to result from the ordering of a chitin fibrillar precursor into a cholesteric liquid crystal phase, with the calcite subsequently growing by oriented nucleation onto the organic fibrils.

Hot Uniaxial Pressing and Pressureless Sintering of AlCrCuFeMnNi Complex Concentrated Alloy—A Comparative Study

External pressure is often applied during sintering to obtain materials with improved properties. For complex concentrated alloys (CCAs), this processing step is commonly performed in vacuum. However, this can promote the evaporation of elements and increase the oxide content, thereby degrading the properties of the alloy. In this study, we compared the microstructures and properties of AlCrCuFeMnNi CCA samples obtained by hot uniaxial pressing sintering (HPS) and pressureless sintering (PLS) using a helium atmosphere purified by an oxygen getter system. The powders were prepared from mixtures of CrFeMn, AlNi and Cu and sintered by HPS at 900 °C for 1 h with an applied pressure of 30 MPa and by PLS at 1050 °C for 1 h. The samples were characterised using X-ray diffraction, scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, electron backscattering diffraction, density measurements and hardness tests. It was found that the oxygen getter system promoted oxygen partial pressure values at sintering temperatures similar to those of a mixture of 90% helium and 10% hydrogen. The HPS allowed us to obtain almost fully dense samples with a smaller average grain size and finer distribution of aluminium oxides than PLS. These differences increased the hardness of the samples sintered under pressure.

Changes in Microstructure and Mechanical Properties of Goryeo Dynasty Bronze Vessels with Manufacturing Process

Bronze vessels are manufactured using casting and forging techniques, and various microstructures can be observed depending on the manufacturing process. In this study, we confirmed mechanical properties and microstructural evolution in the manufacturing process by observing the microstructures and composition analysis of 18 bronze vessels in the Goryeo Dynasty excavated from historical sites. The results show that 13 of the bronze vessels were manufactured using a Cu-Sn alloy with a Sn content of 20 to 24 wt%. The α phase and β(M) phase were observed, indicating that hot forging and quenching treatment were performed after casting. 3 bronze vessels were produced from a Cu-Sn-Pb alloy, and considering that the α phase and α+δ phase were observed, it could be seen that the process was completed by slow cooling after casting. The correlation between the type of bronze vessel and the manufacturing process has not been confirmed, except of ewer. It was confirmed that various microstructures were created depending on the manufacturing process and that the mechanical properties also changed. Bronze vessels composed of the α phase and α+δ phase due to the casting process had lower Vickers hardness values compared to bronze vessels that showed the quenched β(M) or γ phase. Electron backscatter diffraction (EBSD) phase analysis and kernel average misorientation (KAM) were performed using six bronze vessels composed of α and β(M) phases. The results showed that the factors affecting hardness were the ratio of the β(M) phase and the KAM value. However, it could not be confirmed to what extent the ratio of the β(M) phase and KAM value affected the improvement in mechanical properties.

Study of microstructural evolution during operation of electrically connected components and analysis of failure mechanism

Abstract As a key current-carrying structure of high-voltage bushings, the reliability of electrical connection components is crucial to the safe and stable operation of power equipment. To obtain the microstructural evolution of electrical connection components with different deterioration states, CUD strap contactors were deteriorated in different ways, and electron backscatter diffraction (EBSD) technique was used to test the microstructure of strap contactors with different deterioration states. The results showed that compared to the unused contactors, the contact resistance of the contactors under the combined effect of friction and high temperature increased 203.12 times and was in a failed state. During the process from unused state to wear deterioration, high temperature deterioration, and then to eventual failure of the contactors, the average grain size gradually grows from 8.15 μm to 25 μm, the dislocation density gradually decreases from 2.38×1014 m-2 to 1.04×1014 m-2, and there are a significant proportion of the recrystallized organization. These changes are detrimental to the mechanical properties of the contactors. In addition, the distribution of grain boundaries in the contact area proves the occurrence of over-temperature phenomenon in this area, which will accelerate the deterioration of the contactors and eventually lead to the failure of the component. The relevant conclusions can provide a theoretical basis for the design of electrical connection structure of strap contacts as well as the study of deterioration mechanism.

Microstructure evolution and grain refinement mechanism of 316LN steel

Abstract The hot compression behavior of 316LN stainless steel for the supporting system in a magnet confinement fusion reactor was isothermally compressed at 1,050℃ and 0.1 s−1. Electron backscatter diffraction was used to study the microstructure and texture evolution during the deformation process. The results showed that the necklace structure is eventually formed by increasing compression strain due to dynamic recrystallization (DRX). The proportion of low-angle grain boundaries first increases and then decreases. The dominant DRX mechanism of 316LN is discontinuous DRX, which is characterized by the grain boundary bulging. Besides, twinning is found to be induced to accommodate the plastic strain, helping the development of DRX.

Unveiling the mechanical anisotropy and related deformation mechanisms of heterostructured Mg alloy laminate with unique texture feature

In this study, a well-bonded AZ31/ZK60/AZ31 sandwich-structured laminate was prepared using extrusion. Microstructural heterogeneities in grain size, precipitate phases, and texture were evident between the constituent layers. Tensile testing revealed significant mechanical anisotropy in the laminates along the extrusion direction (ED), transverse direction (TD), and 45° directions, with the 45° direction samples exhibiting the highest tensile ductility, while ED and TD samples showed similar high strength. In-situ electron backscatter diffraction and slip trace analysis indicated that the heterogeneities in grain size and precipitates had minimal influence on the mechanical anisotropy of the laminates. Instead, texture emerged as the primary influencing factor, as it affected the initiation difficulty of basal slip and extension twinning mechanisms in various directions, thereby influencing the deformation coordination between the successive layers and resulting in varied mechanical responses in different directions.

Weldability and microstructural characterisation of gas tungsten arc welded Al0.3CoCrFeNi high entropy alloy

ABSTRACT High entropy alloys (HEAs) have received significant interest from researchers due to their exciting set of properties such as an optimum combination of strength and ductility. The Al0.3CoCrFeNi alloy has shown promising properties for applications such as structural components in marine environments, cryogenic applications, and antiballistic armour. This study investigates the weldability of Al0.3CoCrFeNi using gas tungsten arc welding (GTAW). GTAW of Al0.3CoCrFeNi results in a higher tensile strength than that of BM. Microstructural investigations were carried out with X- ray diffraction (XRD), scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), accompanied by tensile and hardness testing. The BM and welded samples were found to have yield strengths of 255 MPa and 405 MPa, respectively. However, the welded sample has a lower ductility (20% elongation) than the BM (53% elongation). The high strength and lower ductility of the weld are mainly attributed to the evolution of the BCC/B2 phase and carbide phases in the microstructure of the welded sample. The precipitation of the BCC/B2 phase in the welded sample is a consequence of the lower free energy associated with the B2 phase at intermediate temperatures.

Microstructure evolution and hydrogen absorption characteristics of gradient-hydrogenated Ti-4.5Al-3V-2Mo-2Fe alloys

Ti-4.5Al-3V-2Mo-2Fe rolled material is a dual-phase titanium alloy with an average grain size of less than 3 μm; its optimal superplastic forming temperature of 760 °C is at least 50 °C lower than the temperature required for diffusion bonding, making it challenging to carry out superplastic forming/diffusion bonding within a process window. The promotion of hydrogen on the low-temperature diffusion bonding of the alloy was verified through thermohydrogen processing, and the absorption characteristics of hydrogen in the alloy at various temperatures, holding times, and pressures were investigated. Subsequently, a mathematical model for achieving standardized hydrogen content was developed. X-ray polycrystalline diffractometer (XRD) analysis was utilized to preliminarily explore phase differences in samples with varying levels of hydrogen content. Furthermore, scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron back scatter diffraction (EBSD) and time of flight secondary ion mass spectrometry (TOF-SIMS) were employed to analyze microstructure changes and hydrogen distribution in both the surface and core regions of the titanium alloy following hydrogenation, demonstrating its feasibility for surface hydrogenation treatment of titanium alloy sheets

Influence of post-weld rolling and artificial aging on microstructure and mechanical properties of friction stir welded 2195-T4 Al-Li alloy joints

Fiction stir welding (FSW) of a naturally aged (T4) 2195 Al-Li alloy was conducted to study the effect of post-weld artificial aging (AA) and rolling+artificial aging (R+AA) on microstructure and mechanical properties of the FSW joints. Grain features were analyzed by electron back scattered diffraction (EBSD) technology, and precipitates were characterized using transmission electron microscopy (TEM) along [011]Al and [001]Al zone axes. Mechanical properties of the joints were evaluated through micro-hardness and tensile testing. The results indicate that grain development, including grain orientation, grain boundary components and dislocation density, varies within different regions of the As-welded joints due to complicated thermal-mechanical history. The alloying elements mostly exist as Guinier-Preston zones in the base material (BM) with a few formations of δ'/β', and slightly precipitate into T1 in the heat affected zone (HAZ), form σ in the thermal-mechanical affected zone (TMAZ), as well as develop T1 and S' in the nugget zone (NZ) after FSW. The lowest hardness zone (LHZ) exhibits elevated precipitation levels, generating coarse T1 and grain boundary precipitates with evident σ and precipitate free zone. The overall precipitation level of the As-welded joints remains minor, resulting in a slight decrease in hardness at the LHZ. Post-weld AA promotes many T1 formations, enhancing the joint strength and hardness. As a result, the ultimate tensile strength (UTS) of the joints increases from 440 MPa to 506.5 MPa, while the elongation decreases from 13.5% to 3.4%. Furthermore, hardness profiles transform from a low-amplitude wave curve to a high-amplitude W-shaped curve, generating a significant LHZ due to the minimal precipitation of T1. Pre-rolling deformation can enhance dislocation density and low angle grain boundaries (LAGBs), promoting the nucleation of high-density, fine T1 during artificial aging, and especially improves precipitation ability of the LHZ, leading to an elevated hardness increment in the region after AA. Compared to the Joint-AA, both strength and elongation of the Joint-R+AA increase, obtaining 530.5 MPa and 3.9%, respectively.

A novel cobweb-like sub-grain structured Al-Cu-Mg alloy with high strength-plasticity synergy

Al-Cu-Mg alloys, as the most widely used lightweight structural materials, have been recognized as promising candidates in the transportation field for a low-carbon economy. However, the tensile strength and plasticity of alloys cannot be simultaneously improved to satisfy the requirements of continuously upgraded transportation vehicles. In this work, inspired by high-tensile strength and high plasticity of cobweb structure, a novel cobweb-like sub-grain structure was developed in Al-Cu-Mg alloys by a successive solution, high-strain-rate rolling (4.4 s-1), cryogenic treatment (–196°C) and aging process (SRCA). Notably, the tensile strength and plasticity of this alloy were superior to those reported in the current study. An ultrahigh Vickers hardness and tensile strength value of 206.2 Hv and 619.6 MPa, which were 39.8% and 31.8% higher than those of traditional T6 heat-treated Al-Cu-Mg alloys, were obtained after SRCA. Meanwhile, an increase in the elongation of this alloy from 4.31% to 8.23% (increase of 90.9%) was also achieved. More importantly, the high strength-plasticity (“double high”) Al-Cu-Mg alloy was attributed to a cobweb-like sub-grain structure, which was proposed for the first time by utilizing reverse thinking to enhance plasticity through elevating dislocations, due to the formation of high-density dislocations from high-strain-rate rolling and rearrangement effect of dislocations from cryogenic treatment. Furthermore, the strength-plasticity mechanism was verified using in-situ tensile electron back scatter diffraction (EBSD), molecular dynamics (MD) simulations, and crystal plasticity (CP) models. The results indicated that the cobweb-like sub-grain structure, resembling countless walls, formed barriers that hindered dislocation migration towards high-angle grain boundaries (HAGBs) and absorbed them, thereby reducing the occurrence of stress concentration zones, i.e., the dislocation absorption and stress-strain sharing mechanisms. Additionally, the strengthening mechanism was associated with synergistic strengthening by multiscale microstructures, including micron-sized grains, micron-sized high-density dislocation lattices, and nanosized Al2CuMg phases, which were activated by successive deformation processes. Consequently, the concept of biomimetic structure design, which may serve as an effective method for achieving structural materials with high strength-plasticity synergy, can be extended to transportation fields, such as railway tracks and body structure design.

An innovative thermal simulation study of microstructure improvement by delay forging during solidification

The solid fraction at the beginning of the forging process is an important factor affecting the performance of the casting-forging integrated forming, which is an innovative and efficient process. The solid fraction depends on the delayed forging time during the casting-forging integrated forming. This paper investigates the effect of delayed forging time on the microstructure of aluminum alloy forged during solidification using an innovative physical simulation method. In this work, a solidification-forging device compatible with the Gleeble system has been developed. Then, experiments were conducted at various delayed forging time. Temperature and force data were collected using the Gleeble system for analysis. Microstructural evolution was investigated using methods including Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Electron Backscattered Diffraction (EBSD), and Three Dimensional Computed Tomography (3D-CT). The results demonstrate that with the extension of the delayed forging time, the grain size of the alloy decreases gradually, and the coarse dendrite structure changes to the rose-shaped grains, and the local misorientation in the grain increases. Moreover, the effect of forging under different forging time on the casting defects of the alloy is studied. When the forging delay is extended to 8 s, the forging promotes the porosity caused by the liquid phase convection. However, with further extension of forging delay, the reduction of the liquid phase and the fracture of dendrites lead to the complexity of liquid phase channels, resulting in the increase of porosity. Additionally, forging near solidification can close shrinkage porosity.

Corrosion resistance and wear behavior of CoCrFeNiMn@Gr high entropy alloy-based composite coatings prepared by laser cladding

In this study, we utilize laser cladding to apply a CoCrFeNiMn HEA with 2 wt.% few-layer graphene (Gr) coating onto the surface of Q235B mild steel. Alcohol stirring method was used for HEA and Gr preparation of composite powder. Raman spectroscopy and energy dispersion spectroscope (EDS) indicate the successful mixing of HEA and Gr powders, with Gr adhering to the surface of the HEA powder in a lamellar structure. The X-ray diffraction (XRD), scanning electron microscope (SEM), EDS, and Electron backscatter diffraction (EBSD) analyses revealed that grain refinement and the formation of fine carbide-hard phases in the HEA/Gr coating improve microhardness and wear resistance. The average Schmidt factors of the coating decreased from 0.47 to 0.45 with the addition of Gr, indicating enhanced resistance to plastic deformation and anisotropy. Nanoindentation experiments demonstrated that the HEA/Gr coatings exhibit superior resistance to plastic deformation, effectively enhancing the coating’s durability against spalling under stress and wear conditions. The microhardness of the HEA/Gr coating increased by 99.25%, and the wear rate decreased by 86.31% compared to the HEA coating alone. The open circuit potential (OCP), linear polarization curve, Tafel curves, electrochemical impedance spectroscopy (EIS), and Mott-Schottky tests all indicated that the HEA/Gr coating possesses superior corrosion resistance. X-ray Photoelectron Spectroscopy (XPS) results suggest that the passivation film of the HEA/Gr coating, which contains more oxides and less hydroxide, is more protective and denser, thereby slowing the corrosion rate.