Search Results (28)

Using additive friction stir deposition (AFSD), the poor weldability of 1045 steel can be solved, facilitating the efficient and high-performance additive manufacturing of its components. This study selected spherical 1045 steel powder and investigated key factors influencing mechanical properties, including deposition temperature, tool rotational rate, and axial force. The results showed that dynamic recrystallization (DRX) occurred in AFSD 1045 steel, which produced randomly oriented fine equiaxed grains with a size range of 1–3 µm and was sensitive to changes in tool rotational rate and axial force. The AFSD 1045 steel, with a maximum surface hardness of 477.2 HV, ultimate tensile strength of 1061.9–1172.3 MPa, and elongation of 8.6–19.0%, has superior overall mechanical properties compared with other forming processes. Moreover, by analyzing tensile fracture morphology, geometrically necessary dislocation (GND) density, and coincidence site lattice (CSL) boundary distribution characteristics, the strengthening mechanism in AFSD 1045 steel was discussed. The research findings serve as a reference for optimizing the AFSD process for 1045 steel and supply a new alternative for joining and manufacturing this material. Full article

This study introduces a strain-annealing approach to tailor the grain boundary characteristics of additively manufactured AlSi10Mg alloy produced by Laser Powder Bed Fusion (LPBF). By combining KOBO extrusion and subsequent annealing treatments, we aim to increase the proportion of low-Σ coincident site lattice (CSL) grain boundaries, particularly Σ3 boundaries. Through grain boundary engineering (GBE), specifically focused on inducing a high fraction of symmetrical CSL boundaries, our approach allows for the optimization of microstructural features that inhibit defect propagation and improve material stability. Microstructural analysis using electron backscatter diffraction (EBSD) revealed a substantial increase in Σ3 boundaries (60° <111> twin relationship) in the early recrystallization stages of the KOBO-processed LPBF AlSi10Mg alloy, demonstrating the effectiveness of this method. The findings presented in this manuscript highlight a new strategy for advancing the microstructural characteristics of LPBF AlSi10Mg alloy, with promising implications for applications requiring high-performance materials, such as in the aerospace, nuclear, and automotive industries. Full article

The effects of tensile and compressive strain, originating from U-bent deformation, on the corrosion behavior of 304 L stainless steel were studied via analyses of the material’s microstructure and electrochemistry in a 3.5% NaCl solution. In contrast with the as-received 304 L steel with the largest grain size, the deformed 304 L material with a small grain size had the lowest number of Σ3 grain boundaries and an overall low fraction, with special low-Σ values (≤29). Moreover, the dislocation density increased to 1.13 × 10¹⁶/m² and 1.4 × 10¹⁶/m² for the tensile and compressive 304 L steel testing, respectively. The decrease in E_pit and increase in i_pit suggested that there was a decrease in anti-corrosion properties due to tensile and compressive deformation. This might be attributed to the higher plastic strain found in deformed 304 L steel, which can induce the rupture of passive film and have a harmful influence on corrosion resistance. In particular, the compressive 304 L steel with the highest content of deformed grains (42.12%) promoted the formation of microgalvanic cells, thereby facilitating the nucleation of pits. Then, these pits grew to a large size through grain shedding. Subsequently, massive chloride ions were generated during metal dissolution and diffused along grain boundaries, which promoted the initiation and propagation of intergranular corrosion cracks. Full article

In this study, the grain boundary character distribution (GBCD) of a B10 alloy was optimized, employing thermomechanical processing consisting of friction stirring processing (FSP) and annealing treatment. Using electron backscatter diffraction, the effects of rotational speed of FSP and annealing time on the evolution of GBCD were systematically investigated. The GBCD evolution was analyzed concerning various parameters, such as the fraction of low-Σ coincidence site lattice (CSL) boundaries, the average number of grains per twin-related domain (TRD), the length of longest chain (LLC), and the triple junction distribution. The experimental results revealed that the processing of a 1400 rpm rotational speed of FSP followed by annealing at 750 °C for 60 min resulted in the optimum grain boundary engineering (GBE) microstructure with the highest fraction of low-Σ CSL boundaries being 82.50% and a significantly fragmented random boundary network, as corroborated by the highest average number of grains per TRD (14.73) with the maximum LLC (2.14) as well as the highest J2/(1 − J3) value (12.76%). As the rotational speed of FSP increased from 600 rpm to 1400 rpm, the fraction of low-Σ CSL boundaries monotonously increased. The fraction of low-Σ CSL boundaries first increased and then decreased with an increase in annealing time. The key to achieving GBE lies in inhibiting the recrystallization phenomenon while stimulating abundant multiple twinning events through strain-induced boundary migration. Full article

It is well known that the properties of polycrystalline metals are related to grain boundaries (GBs), which are fundamental structural elements where crystallographic orientations change abruptly and often exhibit some degree of symmetry. Grain boundaries often exhibit unique structural, chemical, and electronic properties that differ from bulk crystalline domains. Their effects on material properties, including mechanical strength, corrosion resistance, and electrical conductivity, make grain boundaries a focus of intense scientific investigation. In this study, the microstructural transformation of an AlSi10Mg alloy subjected to KoBo extrusion and subsequent annealing is investigated. A notable discovery is the effectiveness of a strain-annealing method for grain boundary engineering (GBE) of the LPBF AlSi10Mg alloy. In particular, this study shows a significant increase in the population of coincidence site lattice boundaries (CSL), which embody the symmetry of the crystal lattice structure. These boundaries, which are characterised by a high degree of symmetry, contribute to their special properties compared to random grain boundaries. The experimental results emphasise the crucial role of strain-induced boundary migration (SIBM) in the development of a brass texture in the microstructure of the alloy after annealing. In addition, the presented results demonstrate the feasibility of applying GBE to materials with high stacking fault energy (SFE), which opens up new possibilities for optimizing their properties. Full article

The interest in the crystallography of structural transformations is driven by emerging capabilities in texture control and by the resulting anisotropy of the physical-mechanical properties of functional materials and products. The recrystallization texture of cold-drawn Cu and Al samples after recrystallization annealing at different temperatures was studied using EBSD. Equivalent deformation textures of Al and Cu are transformed into different recrystallization textures. The recrystallization nuclei in Al are formed at high-angle boundaries between deformed grains close to Σ3 CSL boundaries. The recrystallization nuclei in Cu are formed inside the deformed grains at twin boundaries (Σ3). The recrystallization nuclei in both Al and Cu are the crystallites whose boundaries approximately correspond to misorientation rotated about the <772> axis at an angle of 52–70° from a deformed matrix. The physical interpretation of the results will allow for the development of new models and the enhancement of existing models of texture inheritance. Full article

Grain boundary engineering (GBE) enhances the properties of metals by incorporating specific grain boundaries, such as twin boundaries (TB). However, applying conventional GBE to parts produced through additive manufacturing (AM) poses challenges, since it necessitates thermomechanical processing, which is not desirable for near-net-shape parts. This study explores an alternative GBE approach for post-processing bulk additively manufactured aluminium samples (KoBo extrusion), which allows thermo-mechanical treatment in a single operation. The present work was conducted to examine the microstructure evolution and grain boundary character in an additively manufactured AlSi10Mg alloy. Microstructural evolution and grain boundary character were investigated using Electron Back Scattered Diffraction (EBSD) and Transmission Electron Microscopy (TEM). The results show that along with grain refinement, the fraction of Coincidence Site Lattice boundaries was also increased in KoBo post-processed samples. The low-Σ twin boundaries were found to be the most common Coincidence Site Lattice boundaries. On the basis of EBSD analysis, it has been proven that the formation of CSL boundaries is directly related to a dynamic recrystallisation process. The findings show prospects for the possibility of engineering the special grain boundary networks in AM Al–Si alloys, via the KoBo extrusion method. Our results provide the groundwork for devising GBE strategies to produce novel high-performance aluminium alloys. Full article

The influence of the ultrafine-grained (UFG) structure on the fatigue endurance limit and the nature of fatigue failure have been studied. It is shown that the formation of the UFG structure containing carbides and the coincidence site lattice relationship (CSL) and twin boundaries leads to an increase in the fatigue endurance limit. To study the mechanisms of fatigue failure, scanning and transmission electron microscopy and X-ray diffraction analysis were used. Studies have shown that the formation of the UFG structure as a result of rolling and subsequent heat treatment above the temperature of the ferrite/austenite phase transition leads to an increase in the fatigue endurance limit by more than 70%, from 475 to 800 MPa, compared to coarse-grained samples. The dynamic aging observed during fatigue tests was more pronounced in materials with a UFG microstructure. The influence of the CSL and twin boundaries on the nature of the fatigue failure of ferritic–martensitic steel is discussed. Full article

The change in the grain boundary network during recrystallization and grain growth was studied in a 316L austenitic stainless steel subjected to 5% cold rolling reduction. The primary recrystallization rapidly developed upon heating to 1000 °C, resulting in the development of relatively coarse-grained microstructure with a grain size about 100 μm. The recrystallized microstructures contained large fractions of annealing twins with their ∑3ⁿ SCL boundaries. The latter ones served as interrupters of the ordinary grain boundary network. The fraction of ∑3ⁿ CSL boundaries increased with increasing the grain size during prolonged annealing. On the other hand, the number of interruptions per unit area remained nearly the same during annealing. Hence, the number of interruptions per a grain increased in accordance with a power law function of the grain size with an exponent of 2. The relationships obtained for the grain boundary network evolution can be used to predict the microstructure evolution in austenitic stainless steels during primary recrystallization followed by grain growth. Full article

A Ni-Cr-Mo-based C276 superalloy was cold rolled to 5–40% and annealed at 1050 °C for 30 min. The microstructure and grain boundary character distribution after cold rolling and annealing were characterized. Grain refinement and a certain amount of coincident-site lattice (CSL) boundaries were obtained through recrystallization. The fraction of CSL boundaries reached peak at the cold rolling of 15% and annealing at 1050 °C for 30 min, which was the critical condition for completed recrystallization. In addition, sensitization treatments and double-loop electrochemical potentiokinetic reaction (DL-EPR) tests were applied to the cold rolled and annealed samples. The samples with a high fraction of CSL boundaries showed higher intergranular corrosion resistance as compared to the ones with a low fraction of CSL boundaries. It implies that the intergranular corrosion resistance of C276 superalloy can be enhanced by optimizing the grain boundary structure through cold rolling and annealing. Full article

To understand the relationship between microstructure and corrosion, in this study, underwater bead-on-plate laser welding was compared with the in-air laser welding of 10-mm-thick 304 stainless steel plates at different laser powers (2, 4, and 6 kW). Welding was performed via local dry underwater laser welding (UWLW) using a custom-designed nozzle and a fiber laser at a water depth of 70 mm. The best weld quality was obtained in both underwater and in-air environments using 2 kW of laser power. To understand the relationship between the microstructure and corrosion resistance of 304ss in underwater laser welding (UWLW), this study was conducted using a custom-designed nozzle. The grain boundary analysis revealed that the specimen prepared by UWLW had high-angle grain boundaries content approximately 1.5 times higher than that of the specimen produced by in-air laser welding, and the fraction of the coincidence site lattice (CSL) boundaries was increased remarkably. High residual stress and microchromium precipitation were observed in the UWLW specimen, and the corrosion rate of the same at 2 kW laser power was considerably similar to that of the in-air laser weld specimen. Full article

X2CrNi12 ferritic stainless steel has a wide range of application prospects in the railway transportation, construction, and automobile fields due to its excellent properties. The properties of X2CrNi12 ferritic stainless steel can be further improved by cold-rolling and subsequent annealing treatment. The purpose of this work is to investigate the effect of cold-rolling reduction on the microstructure, texture and corrosion properties of the recrystallized X2CrNi12 ferritic stainless steel by using SEM, TEM, EBSD and electrochemical testing technology. The results show that the crystal orientation characteristics of the cold-rolled sheet could be inherited into the annealed sheet. The higher cold-rolling reduction could promote the deformed grains rotating into the {111}<uvw> orientation, increasing storage energy and driving force for recrystallization, which could reduce the recrystallized grain size. The orientation densities of α-fiber and γ-fiber were low at 50% cold-rolling reduction. After recrystallization annealing, a large number of grains with random orientation could be produced, and the texture strength was weakened. When the cold-rolling reduction rose to 90%, the γ-fiber texture at {111}<110> was strengthened and the α-fibers, particularly the {112}<110> component, were weakened after recrystallisation annealing, which could improve the formability of the steels. The proportions of special boundaries, i.e., low-angle grain boundaries and low-Σ CSL boundaries, among the grain boundary distribution of the recrystallized X2CrNi12 stainless steel were higher when the reduction was 90%, especially when the annealing temperature was 770 °C. Additionally, the proportion of LAGBs and low-Σ CSL boundaries were 53% and 7.43%, respectively, which improves the corrosion resistance of the matrix, showing the best corrosion resistance. Full article

In this paper, the S32101 duplex stainless steel welded joints were produced by a K-TIG welding system. The weld geometry parameters under different welding speeds were analyzed by combining the morphological characteristics of the keyhole. The microstructure and impact toughness of the base metal and weld metal zone under different welding speeds were studied. The experiment results show that the welding speed has quite an effect on the geometry profile of the weld. In addition, the characteristic parameters of the keyhole can effectively predict the geometry profile of the weld. The test results prove that the microstructure, Σ3 coincidence site lattice grain boundary, and phase boundary of ferrite and austenite have an effect on the impact property of the weld metal zone. When the proportion of the austenite, Σ3 coincidence site lattice grain boundary and random phase boundary increased, the impact property of the weld metal zone also increased. Full article

The current paper is related to the study of the microstructure and texture of two machinable lead-free brass alloys, namely CuZn42 (CW510L) and CuZn38As (CW511L), which were evaluated in the as-drawn and post heat treated condition. Electron backscatter diffraction (EBSD) was employed for the examination of the brass rods’ crystallographic properties in order to correlate the effect of post processing heat treatment on the evolution of phase structure and texture towards the interpretation of dynamic (impact) fracture properties. It is shown that α- and β-phase volume fractions, mean grain size, and grain boundary misorientation are the most influential factors altering the fracture resistance of single- and dual-phase brass alloy rods. The role of grain boundary engineering, through the formation of coincidence site lattice (CSL) boundaries and their evolution during thermomechanical processing, is of major importance for the design of the mechanical behaviour of new eco-friendly machinable brass alloys. Full article

High-strength aluminum alloys are widely used in industry. Hydrogen embrittlement greatly reduces the performance and service safety of aluminum alloys. The hydrogen traps in alumi-num profoundly affect the hydrogen embrittlement of aluminum. Here, we took a coinci-dence-site lattice (CSL) symmetrically tilted grain boundary (STGB) Σ5(120)[001] as an example to carry out molecular dynamics (MD) simulations of hydrogen diffusion in aluminum at dif-ferent temperatures, and to obtain results and rules consistent with the experiment. At 700 K, three groups of MD simulations with concentrations of 0.5, 2.5 and 5 atomic % hydrogen (at. % H) were carried out for STGB models at different angles. By analyzing the simulation results and the MSD curves of hydrogen atoms, we found that, in the low hydrogen concentration of STGB models, the grain boundaries captured hydrogen atoms and hindered their movement. In high-hydrogen-concentration models, the diffusion rate of hydrogen atoms was not affected by the grain boundaries. The analysis of the simulation results showed that the diffusion of hydro-gen atoms at the grain boundary is anisotropic. Full article