Search Results (13)

The advent of additive manufacturing (AM), also known as 3D printing, has revolutionized the production of titanium alloys, offering significant advantages in fabricating complex geometries with enhanced mechanical properties. This study investigates the variant-specific deformation mechanisms in HIP-treated TA15 (Ti-6.5Al-2Zr-1Mo-1V) titanium alloy, fabricated via selective electron beam melting (SEBM). The alloy exhibits a dual-phase (α+β) microstructure, where six distinct α variants are formed through the β→α phase transformation following the Burgers orientation relationship. Variant selection during AM leads to a non-uniform distribution of these α variants, with α6 (22.3%) dominating due to preferential growth. Analysis of the prismatic slip Schmid factor reveals that α4–α6 variants, with higher Schmid factors (>0.45), primarily undergo prismatic slip, while α1–α3 variants, with lower Schmid factors (<0.3), rely on basal or pyramidal slip and twinning for plastic deformation. In-grain misorientation axis (IGMA) analysis further reveals strain-dependent slip transitions: pyramidal slip is activated in α1–α3 variants at lower strains, while prismatic slip becomes the dominant deformation mechanism in α4–α6 variants at higher strains. Additionally, deformation twins, primarily {10–12}<1–101> extension twins (7.1%), contribute to the plasticity of hard-oriented α variants. These findings significantly enhance the understanding of the orientation-dependent deformation mechanisms in HIPed TA15 alloy and provide a crucial basis for optimizing the performance of additively-manufactured titanium alloys. Full article

The tensile behavior of single-crystal superalloys was investigated at room temperature (RT) and 850 °C, focusing on various secondary orientations. Transmission electron microscopy (TEM) and quasi in situ electron backscatter diffraction (EBSD) were employed to study the deformation mechanisms across length scales. Deformation at 850 °C enhanced the tensile ductility of the samples, evidenced by the more uniform coverage of dislocations across the γ and γ′ phases, and the fracture mode switched from pure cleavage at room temperature to mixed mode due to accelerated void growth. The influence of secondary orientations on mechanical properties is insignificant at room temperature. However, the ductility of the different secondary orientation samples shows significant variations at 850 °C, among which the one with [001] rotated 37° demonstrated superior ductility compared to others. Full article

An excellent Fe-3.3 wt% Si steel was fabricated by double cold rolling and final annealing. The evolution of the microstructure and texture was studied by optical microscope (OM), X-ray diffraction (XRD), ex situ, and quasi-in situ electron backscattered diffraction (EBSD) to investigate the recrystallization behavior. Double cold rolling significantly reduced the adverse γ texture in the final annealed sheets, and a stronger η texture was observed. With a reduction ratio of 50% and 65% during double cold rolling, the γ texture almost disappeared, whereas the η texture was obviously improved. Consequently, the texture factor reached its peak, leading to a reduction in iron loss and an enhancement of magnetic induction. By combining texture regulation with dislocation strengthening, the magnetic properties of Fe-3.3 wt% Si steel were improved, and the yield strength also increased. The final sheet exhibiting exceptional magnetic characteristics and enhanced strength attained a reduction in iron loss (P_10/400 = 21.84 W/kg) of 6.43 W/kg, along with an enhancement of magnetic induction (B₅₀ = 1.698 T) of 0.038 T and yield strength (R_p0.2 = 578 MPa) of 37 MPa compared to a single-stage cold rolling process. Full article

The reliability of friction stir welded joints is a critical concern, particularly given their potential applications in the aerospace manufacturing industry. This study offers a quasi-in situ observation of the microstructural response during fatigue crack growth (FCG) of a friction stir welded AA2024-T4 joint, aiming to correlate fatigue crack growth behavior with mechanical properties investigated using electron backscatter diffraction (EBSD). Notched compact tension (CT) specimens corresponding to the morphology of the stir zone (SZ), advancing side (AS), and retreating side (RS) were meticulously designed. The findings indicate that the welding process enhances the joint’s resistance to fatigue crack growth, with the base metal exhibiting a shorter fatigue life (i.e., ~10⁵ cycles) compared to the welding zones (SZ ~ 3.5 × 10⁵ cycles, AS ~ 2.5 × 10⁵ cycles, and RS ~ 3.0 × 10⁵ cycles). Crack propagation occurs within the stir zone, traversing refined grains, which primarily contribute to the highest fatigue life and lowest FCG rate. Additionally, cracks initiate in AS and RS, subsequently expanding into the base metal. Moreover, the study reveals a significant release of residual strain at the joint, particularly notable in the Structural-CT-RS (Str-CT-RS) sample compared to the Str-CT-AS sample during the FCG process. Consequently, the FCG rate of Str-CT-AS is higher than that of Str-CT-RS. These findings have significant implications for improving the reliability and performance of aerospace components. Full article

Inclusions are important phases affecting material properties in complicated ways. In this paper, a quantitative study of the addition of HfO₂ inclusions to DZ125 nickel-based superalloys was performed. Experimental results showed that the introduction of HfO₂ inclusions caused a loss of strength and ductility. The carbide morphology also changed significantly from skeletal-shaped to block-shaped, resulting in a remarkable discrepancy in the fracture behavior under quasi-in-situ tensile testing. The SEM dynamic observations showed that cracks were initiated from the skeletal carbides and almost failed to propagate into the matrix. In contrast, the damage behavior of block-shaped carbides also involved internal cracking but with a tendency to form interconnected microcracks during propagation. A crystal plasticity finite element model (CPFEM) method was further developed to study the stress/strain behavior during the deformation process, considering the crystal orientations and microstructure morphologies from the EBSD data. Those elastoplastic parameters were determined through nanoindentation experiments. Simulation results verified that blocky carbides produced a pronounced strain concentration at the interface of the carbides and matrix, thereby increasing the tendency of crack formation. This paper provides a fundamental understanding of the role of inclusions in material recycling applications. Full article

The quasi in situ EBSD test was applied to study the effect of grain orientation on corrosion behaviors of the thermomechanically affected zone I (TMAZ I) of dissimilar AA6082/AA7204 friction stir welding (FSW) joints in this work. The results show that the structure with grain orientation close to the brass texture ({110}<112>) has excellent corrosion resistance, which contributes to the better corrosion performance of the TMAZ I of the 7204-AS joint than the 7204-RS joint. Furthermore, the brass texture around by S texture ({213}<364>) in the TMAZ I of the 7204-AS joint is slightly corroded, and the orientation of the remaining structure is closer to the ({110}<112>) than before, which indicates that the corrosion, like deformation, is carried out alongside the {110} plane for the structure with grain orientation near {110}<112>. Those findings could provide new insight into the designed FSW joints and improve the corrosion resistance of the wrought aluminum alloy. Full article

The hydrogen embrittlement (HE) behavior of a selective laser-melted (SLM) 316L austenitic stainless steel has been investigated by hydrogen charging experiments and slow strain rate tensile tests (SSRTs) at room temperature. The results revealed that compared to the samples without H, the ultimate tensile strength (UTS) and elongation (EL) of specimens were decreased from 572 MPa to 552 MPa and from 60% to 36%, respectively, after 4 h of electrochemical hydrogenation with a current density of 100 mA/cm². The negative effects of hydrogen charging were more pronounced on the samples’ ductility than on their strength. A quasi in situ EBSD observation proved that there was little phase transformation in the samples but an increased density of low angle grain boundaries, after 4 h H charging. After strain was applied, the surface of the H-sample displayed many hydrogen-induced cracks along the melt pool boundaries (MPBs) showing that these MPBs were the preferred areas for the gathering and transferring of hydrogen. 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

Microscopic strain and strain-induced phase transformation during plastic deformation in metastable austenitic steel were investigated at different strain rates. Quasi in-situ tension tests were performed sequentially with well-defined elongation intervals at room temperature at strain rates of 10⁻³ s⁻¹ and 10⁻¹ s⁻¹. The tests were monitored by high-resolution optical imaging with a microscopic lens at a resolution of 0.23 µm/pixel. The macroscopic temperature was also measured with an infrared (IR) camera. The microstructure-level strain localizations were observed on the surface of the etched specimens by means of microscale digital image correlation (µDIC). Additionally, the microstructure was characterized by electron backscatter diffraction (EBSD) at the same location before and after deformation. The results of the study indicated that microscopic strain localizations favored the formation of α′-martensite particles. At the lower strain rate, high local strain concentrations formed at several locations in the microstructure, correlating with the areas where the formation of large martensite islands occurred. Martensite particles of various sizes formed nearby each other at the lower strain rate, whereas at the higher strain rate, martensite islands remained small and isolated. Although the macroscopic increase in temperature at both the studied strain rates was very low, at the higher strain rate, local heating on the microscopic scale could take place at the newly nucleated martensite embryos. This inhibited the further growth of the martensite particles, and local strain distribution also remained more homogeneous than at the lower strain rate. Full article

The anisotropic mechanical behavior and associated microstructure evolution in annealed Zircaloy-4 were investigated at room temperature, using quasi-in situ tensile tests along the typical direction, rolling direction (RD), and transverse direction (TD). Herein, the in-grain misorientation axes (IGMA) and the nominal Schmid factors were evaluated to analyze the slip mode based on the electron backscatter diffraction. The IGMA result shows that there were anisotropic slip modes within grains, whose basal poles were parallel with the TD (TB) and placed within 40 to 50 degrees from the normal direction (ND) to the transverse direction (N (40°–50°) TB)), under different loading directions. When loading along the RD, the basal <a> slips were activated in the N (40°–50°) TB and TB orientation grains, while the second-order pyramidal slips were activated in the grains when loading along the TD. The relatively higher ultimate tensile strength and elongation in Zircaloy-4 when tensile along RD occurs due to its much higher frequency of soft grains (88.54%) than the TD sample (64.29%), and the synergy deformation among local grains. The present study demonstrated that the anisotropic mechanical behavior of Zircaloy-4 was attributed to the combined effects that exist between the anisotropic slip behavior and the different compatible deformation capabilities. Many shallow dimples and cleavage regions were observed on the fracture surface in the TD sample. Such fracture features are consistent with the lower ultimate tensile strength ~470 MPa and elongation ~14.5% in the deformed tensile Zircaloy-4 along the TD. Full article

The quasi in-situ indentation behaviour of <110>||BD and <111>||BD-oriented grains in a FeCo alloy is studied in this investigation. The effect of build height on melt pool shape and melt pool size is also studied by finite element method simulations. As the building height increases, the aspect ratio of the elliptical melt pool increases. Correspondingly, the effect of the laser scan speed on the melt pool shape and size is studied by the finite element method, because, as the laser scan speed increases, the aspect ratio of the elliptical melt pool increases, too. The microstructural characterisation of the indentation area before and after indentation is performed by electron backscatter diffraction (EBSD). Based on the EBSD data grain reference orientation deviation (GROD), calculations are performed to describe the effect of indentations on the neighbouring grain orientations. High GROD angles are detected in the neighbouring grain region adjoining the indented grain. An in-depth slip trace analysis shows the activation of all three slip systems ({110}<111>, {112}<111> and {123}<111>) which is also confirmed by slip lines on the sample surface that are detected by laser scanning confocal microscopy. A high concentration of geometrically necessary dislocations (GNDs) are observed on the adjoining area to the indentation. Local surface topography measurements by laser scanning confocal microscopy confirmed the formation of pile-ups near the indentation. Full article

In this work, the tensile deformation behavior of an as-extruded AZ80 magnesium alloy under pulsed current (PC) was investigated based on microstructure observations. We found that compared with the tensile tests at room temperature (RT) and given temperature (GT), the flow stress is reduced due to both thermal and athermal effects of pulsed current. A quasi-in-situ electron backscatter diffraction (EBSD) analysis reveals that at the same strain, the geometrically necessary dislocation (GND) density of the RT sample is the highest, followed by the GT sample and the PC sample. This proves that the athermal effect can promote the annihilation of dislocations and slow down dislocation pileup, which reduces the flow stress. In addition, the twinning behavior under different deformation conditions was studied; the twins are {10−12} tension twins, which are activated with the assistance of local stress. We found that the twin fraction in the PC sample is lower than that in the RT and GT samples, due to the least accumulation of GNDs at grain boundaries, which decreases the nucleation of {10−12} tension twins. Full article

Secondary recrystallization Goss texture was efficiently achieved in rolled, binary Fe₈₁Ga₁₉ alloy sheets without the traditional dependence on inhibitors and the surface energy effect. The development of abnormal grain growth (AGG) of Goss grains was analyzed by quasi-situ electron backscatter diffraction (EBSD). The special primary recrystallization texture with strong {112}–{111}<110> and weak Goss texture provides the inherent pinning effect for normal grain growth by a large number of low angle grain boundaries (<15°) and very high angle grain boundaries (>45°) according to the calculation of misorientation angle distribution. The evolution of grain orientation and grain boundary characteristic indicates that the higher fraction of high energy grain boundaries (20–45°) around primary Goss grains supplies a relative advantage in grain boundary mobility from 950 °C to 1000 °C. The secondary recrystallization in binary Fe₈₁Ga₁₉ alloy is realized in terms of the controllable grain boundary mobility difference between Goss and matrix grains, coupled with the orientation and misorientation angle distribution of adjacent matrix grains. Full article