Search Results (10)

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

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

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

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

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

Fatigue life tests and fatigue crack growth rate (FCGR) tests in the air and water environment were conducted on X80 pipeline steel welded joints (welded by CO₂ arc welding). Scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) were utilized to investigate the internal influential mechanisms of the water environment during fatigue crack initiation and propagation stages, respectively. Results show that a great many oxide particles induced by the water environment gradually formed the fatigue crack initiation site and decreased fatigue life of welded joints. Meanwhile, the preferred grain orientation of <001>//ND and CSL boundaries of Σ3, Σ11, Σ13c, Σ17b, Σ25a, and Σ25b are both prone to fatigue propagation when loading in the water environment. In addition, a coalescence of the stress intensity factor (SIF) range and water environment accelerated FCGR by motivating secondary slip systems of {112}<111> and {123}<111> in bcc crystalline structures. Full article

This study investigated the susceptibility to intergranular corrosion (IGC) in austenitic stainless steel with various degrees of sensitization (DOSs) from a microstructural viewpoint based on the coincidence site lattice (CSL) model. IGC testing was conducted using oxalic acid and type 304 stainless steel specimens with electrochemical potentiokinetic reactivation (EPR) ratios that varied from 3 to 30%. As a measure of IGC susceptibility, the width of the corroded groove was used. The relationship between IGC susceptibility, grain boundaries (GB) structure, and EPR ratio of the specimens was evaluated. As a result, the IGC susceptibility cannot be characterized using the Σ value, irrespective of the DOS of the specimen. The IGC susceptibility increases with increasing unit cell area of CSL boundaries, which is a measure of the stability of the CSL boundaries, and then levels off. The relationship between the IGC susceptibility and unit cell area is sigmoidal, irrespective of the DOS of the specimen. The sigmoid curve shifts rightward and the upper bound of IGC susceptibility decreases with decreasing DOS of the specimen. Full article

High-energy beam welding was introduced for pipeline steel welding to reduce pipeline construction costs and improve the efficiency and safety of oil and gas transportation. Microstructures and their distribution in X100 laser-welded joints, which determine the joints’ strength and toughness, are discussed in this paper. Welded joints were prepared by an automatic 10,000-watt robot-based disc laser-welding platform for 12.8 mm thick X100 pipeline steel. Then, the grain, grain boundary, orientation, and distribution pattern of each zone of the welded joints were studied by optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and electron backscattered diffraction (EBSD) analysis techniques. The results showed that the grain boundary density, contents of the high-angle and low-angle grain boundaries, distribution states, and evolution trends of coincident site lattice (CSL) grain boundaries were essentially the same in each zone from the base metal (BM) to the weld of the X100 pipeline steel laser-welded joint. The relative content of grain boundaries above 55°, which were composed of the Σ3 type CSL grain boundary, showed a considerable impact on the mechanical properties of the joint. The content of twin grain boundaries was closely related to the thermal cycles of laser welding, and the effect of the cooling rate was greater than that of the process of austenization. Full article