Search Results (33)

The martensitic transformation mechanism in the heat-affected zone of DP1180 steel plays a decisive role in the strength of welded joints. In this work, the nucleation and growth kinetics of martensite laths in the coarse grain heat-affected zone (CGHAZ) are analyzed by a high-temperature laser scanning confocal microscope (LSCM). The grain distribution and stress distribution of the samples after in situ observation are analyzed by electron backscatter diffraction (EBSD). The results reveal that austenite grain growth is realized by continuous grain boundary annexation and grain boundary migration of small grains by large grains during the heating process. Seven growth modes of CGHAZ martensitic laths under laser welding conditions are proposed. Additionally, the end growth of martensitic laths is mostly attributed to the collision with grain boundaries or other laths to form a complex interlocking structure. The results of this study could provide important data support for the development of dual-phase steel materials and improvement of welding quality. Full article

In this study, we investigated the two-phase hardening behavior and microstructural evolution of S32750 duplex stainless steel during the tensile deformation process. The analysis was conducted using in situ electron backscatter diffraction (EBSD), scanning electron microscopy (SEM), and microhardness testing. It was observed that strain transfer occurred between the two phases in the position away from the fracture. The ferrite phase exhibited softening, while the austenite phase underwent hardening. In the region less than 1 mm from the fracture site, both phases experienced a rapid hardening, with the maximum hardness difference between the two phases near the fracture reaching approximately 45 HV. In situ EBSD results indicate that the kernel average misorientation (KAM) value for the ferrite phase consistently exceeds that of the austenite phase during the initial stages of deformation. Conversely, in the final stages of deformation, the KAM value for austenite surpasses that of ferrite. In the initial stage of deformation, the type of grain boundaries in both phases remains largely unaltered. However, in the later stages of deformation, there is a marked increase in the number of small-angle grain boundaries within ferrite, which become approximately three times that of the large-angle grain boundaries. As deformation progresses, the maximum orientation distribution density of the ferrite phase is reduced by approximately 50%, with the preferred orientation shifting from the {100} plane to the {111} plane. In contrast, the orientation distribution of the austenite remains relatively uniform, with no significant change in the maximum orientation distribution density observed. This indicates that after substantial deformation, the rotation of ferrite grains significantly increases the deformation resistance, whereas the austenite phase continues to harden. This differential behavior leads to the continuous accumulation of strain at the phase boundaries, ultimately causing cracks to form at these boundaries and resulting in the sample’s fracture. Full article

Fast nanoindentation technology is a new method used to generate performance maps showing the hardness and elastic modulus distribution of each position, and it has become a research focus. In this paper, nanoindentation combined with scanning electron backscatter diffraction (EBSD) is used to analyze the micro-regional properties of single-phase interstitial-free (IF) steel. Hardness, elastic modulus and the orientation of a 200 μm × 200 μm area were characterized in situ. The relationships between hardness, elastic modulus and orientation were analyzed. The experimental results showed that the hardness varied from 1.25 GPa to 2.57 GPa, while the modulus varied from 122 GPa to 227 GPa with different crystallographic orientations. The hardness value of the (111) crystal plane was particularly high, with an average hardness of about 1.84 GPa, which is due to its higher work hardening rate. This result is consistent with the EBSD kernel average misorientation (KAM) micrograph. The harder locations with greater misorientation are more difficult to deform compared to locations with small hardness regions, for example, the (001) crystal plane. However, there seems to be no obvious strong relationship between modulus and orientation. The modulus of the regions with lower hardness seems to be smaller. The results of the KAM diagram are consistent with those of hardness mapping. Full article

An investigation was conducted on electron beam-welded and additively manufactured joints on a thick-walled titanium alloy utilizing in situ laser beam deposition and electron beam welding techniques. The surface morphology, microstructural characteristics, and mechanical properties of both joint types were comprehensively analyzed using stereomicroscopy, scanning electron microscopy (SEM), microhardness and tensile strength testing, and electron backscatter diffraction (EBSD) techniques. The electron-beam-welded joint exhibited distinct fusion and heat-affected zones, whereas the laser-beam-deposited joint exhibited a smoother surface that was free from excess spatter. Both joints featured a sharp microstructural boundary with a pronounced hardness gradient across the interface, lacking a gradual transition area. During tensile testing, both joint types demonstrated a mixed brittle-ductile fracture mode; however, the electron beam-welded joints surpassed the laser-beam-deposited joints in terms of tensile strength, achieving over 1183 MPa with an elongation of more than 7.3%, compared to 1123 MPa and 5.9% elongation, respectively. Full article

Grain boundary (GB) precipitation-induced cracking is a significant issue for S31254 super austenitic stainless steel during hot working. Investigating the deformation behavior based on precipitate morphology and distribution is essential. In this study, continuous smaller and intermittent larger precipitates were obtained through heat treatments at 950 °C and 1050 °C. The microstructure evolution and mechanical properties influenced by precipitates were experimentally investigated using an in situ tensile stage inside a scanning electron microscope (SEM) combined with electron backscatter diffraction (EBSD). The results showed that continuous precipitates at 950 °C had a stronger pinning effect on the GB, making grain rotation difficult and promoting slip deformation in the plastic interval. Continuous precipitates caused severe stress concentration near GB and reduced coordinated deformation ability. Additionally, the crack propagation path changed from transcrystalline to intercrystalline. Furthermore, internal precipitates were a crucial factor affecting the initial crack nucleation position. Interconnected precipitates led to an intergranular fracture tendency and severe deterioration of the material’s plasticity, as observed in fracture morphology. Full article

Pure shear tests of textured magnesium AZ31B sheet samples were carried out using a 5 kN Kammrath & Weiss in situ tension-compression stage in a scanning electron microscope in combination with real-time electron backscatter diffraction lattice orientation mapping. The sample design was optimized to produce a pure shear stress in the central gauge zone. Distributions of the deformation twins were correlated with finite element simulations using a linear-elastic constitutive law considering large deformations to show that twins form in areas where the principal compressive stress ${\mathsf{\sigma }}_3^{*}$ is a maximum and that they form normal to the trajectories of that minor principal stress. Mappings of the same area at different load values revealed the formation and growth of individual twins and their relationship to the internal elastic strain of individual grains as indicated by the internal grain disorientation. All twins observed were of the extension type, with an 86.3° disorientation with respect to the parent grains. A more detailed study was conducted using transmission electron microscopy to correlate with the EBSD observations and to further elucidate the twin structures within samples. Full article

This study aims to investigate in situ the three-dimensional (3D) morphology and distribution of primary carbides (PCs) in electro-slag remelting (ESR) forged 30Cr₃Ni₃Mo₂V steel. A facile non-aqueous electrolytic etching method was applied to prepare 3D PCs on the matrix. The morphology, composition, and element concentrations of PCs were characterized using a combination of optical microscopy (OM), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), and electron back-scattered diffusion (EBSD). The precipitation, type, and composition of PCs in the same steel were also simulated using Thermo-Calc software Version 2015a. The results indicate that PC is rich in Nb, which is a potential heterogeneous nucleating agent. Both the size and number of PCs increase from the edge to the center of the ingot. The large-sized PCs present three dominant types of morphology, which vary in different regions, i.e., a bulky type dominates in the edge region, a lamellar type dominates in the middle region, and a stripy type dominates in the core region. The results of EBSD analysis show that the orientation of PCs with different morphologies is different and that more nanosized V-rich type carbides are precipitated on the matrix. The thermodynamic calculations show that MC precipitates from the liquid phase when the solid phase fraction is greater than 0.985 and that the MC-type carbides are rich in Nb, which agrees well with the experimental results. Full article

Small specimen technologies, such as the small punch test, the indentation test, and the in situ Scanning Electron Microscope (SEM)/Electron Back Scatter Diffraction (EBSD) test, provide important data support for understanding mechanical properties when the size of testing materials is limited, such as for alloys, 3D printing metals, and welding joints, as illustrated in Figure 1 [...] Full article

The nucleation and growth processes of pure Fe/pure Al intermetallic compounds (IMCs) during heat treatment at 380 °C and 520 °C were observed through in situ scanning electron microscopy (SEM). The size of the IMCs were statistically analyzed using image analysis software. The types and distribution of IMCs were characterized using transmission electron microscopy (TEM) and electron backscattering diffraction (EBSD). The results showed that: at 380 °C, the primary phase of the Fe/Al composite intermetallic compounds was Fe₄Al₁₃, formed on the Fe side and habituated with Fe. The IMC was completely transformed from the initial Fe₄Al₁₃ to the most stable Fe₂Al₅, and the Fe₂Al₅ was the habitus with Fe during the process of holding at 380 °C for 15 min to 60 min. At 380 °C, the initial growth rate of the IMC was controlled by reaction, and the growth rate of the thickness and horizontal dimensions was basically the same as 0.02–0.17 μm/min. When the IMC layer thickness reached 4.5 μm, the growth rate of the thickness changed from reaction control to diffusion control and decreased to 0.007 μm/min. After heat treatment at 520 °C (≤20 min), the growth of IMC was still controlled by the reaction, the horizontal growth rate was 0.53 μm/min, the thickness growth rate was 0.23 μm/min, and the main phase of the IMC was the Fe₂Al₅ phase at 520 °C/20 min. Full article

Due to their higher strength and lighter weight compared to conventional metals, graphene-nickel (Gr-Ni) composites have recently gained growing interest for use in the automotive and aerospace industries. Homogeneous Gr dispersion, the metal powder dispersity and processing conditions play a key role in obtaining the desired grain size distribution, an amount of high angle grain boundaries thus reaching the desired balance between strength and plasticity of the composite. Here, we report an approach to fabricating graphene-nickel composites with balanced strength and ductility through the microstructure optimization of the nickel matrix. A graphite platelets (GP) content of 0.1–1 wt.% was used for the optimization of the mechanical properties of the material. In situ, conversion GP-to-Gr was performed during the milling step. This paper discusses the effect of bimodal nano- and micro-sized Ni (nNi and mNi) on the mechanical properties and microstructure of Gr-Ni composites synthesized using a modified powder metallurgy approach. Specimens with varied nNi:mNi ratios were produced by two-step compaction and investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, electron back-scattered diffraction (EBSD) and nanoindentation. The best combination of ultimate tensile strength (UTS), yield limit (YL), elongation and hardness were obtained for 100nNi and 50nNi matrices, and the best composites were those with 0.1% graphene. The addition of more than 0.5 wt.% GP to the nickel matrix induces the fracture mechanism change from tensile to brittle fracture. Dedicated to the 300th anniversary of the St. Petersburg University Foundation. Full article

In this work, we investigate the impact of Bi addition on the heat resistance of as-extruded AZ31 alloy during high-temperature annealing and hot compression. Electron backscattered diffraction (EBSD) technique and quasi in situ scanning electron microscopy (SEM) are used to analyze the evolution of microstructures during high-temperature annealing and hot compression, respectively. The test results show that with a prolonged annealing time, the as-extruded AZB313 alloy exhibited a lower grain growth rate, due to the pinning effect of Mg₃Bi₂ phases distributed at grain boundaries. On the other hand, as the compressive temperature increased, the downtrend of strength is delayed in the as-extruded AZB313 alloy. Thermally stable Mg₃Bi₂ phases dispersed within the grains act as barriers, hindering the motion of dislocations, which not only provides a more effective precipitation strengthening effect, but also increases the resistance to deformation of grains. Moreover, grain boundary sliding can also be restricted by Mg₃Bi₂ phases located at grain boundaries. This work provides a new idea for the development of heat-resistant wrought Mg alloys. Full article

The hot tensile deformation and fracture mechanisms of a Ti-5Al-5Mo-5V-1Cr-1Fe alloy with bimodal and lamellar microstructures were investigated by in situ tensile tests under scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The results show that the main slip deformation modes are prismatic slip ({1$\overline{1}$00}<11$\overline{2}$0>) and pyramidal slip ({1$\overline{1}$01}<11$\overline{2}$0>) under tension at 350 °C. In the bimodal microstructure, several parallel slip bands (SBs) first form within the primary α (α_P) phase. As the strain increases, the number of SBs in the α_P phase increases significantly and multislip systems are activated to help further coordinate the increasing deformation. Consequently, the microcracks nucleate and generally propagate along the SBs in the α_P phase. The direction of propagation of the cracks deflects significantly when it crosses the α_P/β interface, resulting in a tortuous crack path. In the lamellar microstructure, many dislocations pile up at the coarse-lath α (α_L) phase near the grain boundaries (GBs) due to the strong fencing effect thereof. As a result, SBs develop first; then, microcracks nucleate at the α_L phase boundary. During propagation, the cracks tend to propagate along the GB and thus lead to the intergranular fracture of the lamellar microstructure. Full article

This research utilises a novel heat stage combined with a Zeiss scanning electron microscope to investigate phase changes in iron alloys at temperatures up to 800 ℃ using SE and EBSD imaging. Carbon steel samples with starting structures of ferrite/pearlite were transformed into austenite using the commercial heat treatment process whilst imaging within the SEM. This process facilitates capturing both grain and phase transformation in real time allowing better insight into the microstructural evolution and overall phase change kinetics of this heat treatment. The technique for imaging uses a combination of localised EBSD high temperature imaging combined with the development of high temperature thermal-etching SE imaging technique. The SE thermal etching technique, as verified by EBSD images, enables tracking of a statistically significant number of grains (>100) and identification of individual phases. As well as being applied to carbon steel as shown here, the technique is part of a larger study on high temperature in situ SEM techniques and could be applied to a variety of alloys to study complex phase transformations. Full article

An iron loss in the motor core was often enhanced by formation of plastically affected zones in piercing the electrical steel sheets. A platform methodology to carry out quantitative evaluation of these affected zones in the pierced electrical steel sheets was proposed to search for the way to minimize the affected zone widths. A coarse-grained electrical steel sheet was employed as a work material for a fine piercing experiment under the narrowed clearance between the plasma-nitrided SKD11 punch and core-die. The shearing behavior by the applied loading for piercing was described by in situ measurement of the load-stroke relationship. The plastic straining in the single-crystal electrical steel sheet was characterized by SEM (scanning electron microscopy) and EBSD (electron back-scattering diffraction) to define the affected zone size and to analyze the rotation of crystallographic orientations by the induced plastic distortion during piercing. Integral and differentiation of spin rotation measured the affected zones. The effect of punch edge sharpness on these spin-rotation measures was also discussed using the nitrided and ion-milled SKD11 punch and core-die. Full article

The present work systematically investigated the initiation mechanism of localized corrosion induced by Al₂O₃-MnS composite inclusion in E690 steel under a simulated marine environment. The results showed that a micro-gap exists between the Al₂O₃-MnS inclusion and the matrix, and electron backscattered diffraction (EBSD) analysis revealed significant lattice dislocation zones around the Al₂O₃-MnS composite inclusion. The presence of the micro-gap and the lattice dislocation both promoted the localized corrosion initiation. The Volta potential of Al₂O₃ detected by scanning Kelvin probe force microscopy (SKPFM) was approximately 149.33 mV higher than that of the steel matrix, and the Volta potential of MnS was 10 mV lower than that of the steel matrix. The current-sensing atomic force microscopy (CSAFM) results showed that the Al₂O₃ was not conductive, while the MnS had good conductive properties. Therefore, it was not possible for a galvanic couple to be formed between Al₂O₃ and the adjacent steel matrix. A galvanic couple effect between the MnS and the adjacent steel matrix was directly demonstrated for the first time. The MnS acted as the anode phase for preferential dissolution in the corrosion process. The in situ immersion experiments and the Pourbaix diagram results confirmed that the dissolution of MnS was an electrochemical reaction process and the dissolution of Al₂O₃ was a chemical reaction. Full article