Search Results (268)

In this study, the asymmetrical rolling technique was employed to fabricate 75 μm-thick Ti-6Al-4V ultra-thin strips from the initial 0.45 mm sheet without intermediate annealing, aiming for applications in fuel cell bipolar plates. The rolled strips exhibited good surface quality without cracking. In order to enhance both the mechanical response and the shaping capability of Ti-6Al-4V strips produced by asymmetric rolling, the material was subjected to annealing at various temperatures, and the resulting changes in microstructural features and mechanical performance were systematically examined. The findings indicated that the cold-rolled Ti-6Al-4V exhibited a microstructure primarily composed of subgrains with an average size of approximately 0.41 μm, a feature that contributed to improved corrosion resistance and enhanced ductility after annealing. When the alloy was subjected to heat treatment within the range of 650–800 °C, it was observed that annealing temperatures below 700 °C favored microstructural changes governed predominantly by recovery processes and the onset of recrystallization. At 700 °C, the grains became equiaxed and uniformly distributed, and the dislocation density significantly decreased. The tensile strength reached 887 MPa, while the elongation increased to 13.7%, achieving an excellent strength-ductility balance. Once the annealing temperature rose above 700 °C, noticeable grain growth took place, accompanied by a more pronounced grain-size gradient and a renewed increase in dislocation density. Meanwhile, the dimples observed on the fracture surface became finer, collectively contributing to a decline in tensile elongation. The Ti-6Al-4V ultra-thin strip annealed at 700 °C was used for bipolar plate stamping, producing fine micro-channels with an aspect ratio of 0.43. Finally, TiN coating was applied to the surface, which significantly improved the corrosion resistance and reduced the interfacial contact resistance (ICR), meeting the performance requirements for bipolar plates. Full article

In this work, different processing routes were investigated to evaluate the effects of hot rolling temperature, annealing before cold rolling (ABCR), and one- or two-stage cold rolling and annealing schedules to obtain more efficient electrical steels. The correlation between processing variables, microstructure, thickness, and magnetic properties was established from the analysis of 3D surface plots. It was found that the lowest core loss values (3.4 W/kg) were obtained when steel is processed by hot rolling (800 °C), ABCR (880 °C–180 min), first cold rolling (up to 0.25 mm), first annealing (850 °C–10 min), second cold rolling (up to 0.2 mm), and second annealing (850 °C–10 min). The better combination between thickness and grain size leads to the enhancement of the magnetic properties, which affects the way eddy and hysteresis losses contribute to the total core losses. Full article

In this study, we fabricated Fe-25Ni-15Cr alloy rods via vacuum induction melting, electroslag remelting, forging, hot rolling, and annealing. We systemically investigated the influence of varying cold-drawing deformation levels (10–60%) on microstructure evolution and mechanical properties, which were characterized by a variety of multi-scale characterization techniques, including optical microscopy, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The results show that when the cumulative deformation amount is less than 30%, the hardness, tensile strength, and yield strength increase significantly with the increase in deformation amount, while the elongation continues to decline; when the cumulative deformation amount exceeds 30%, the rates of increase in hardness and strength decrease significantly; and when the deformation amount increases to 50%, dislocation density accumulates preferentially at the grain boundaries and forms a cellular substructure, while the texture orientation gradually stabilizes from random distribution to the <111> direction. This alloy rod exhibits three strengthening mechanisms during cold drawing: grain refinement, second-phase precipitation, and work hardening. A predictive model for tensile strength is derived through theoretical calculations. This work has guiding significance for establishing a cold-drawing process window without intermediate annealing. Full article

In this investigation, Ni_50.9Ti_49.1 wires cold rolled to 40% and straight annealed at 480 °C, 510 °C, and 550 °C, respectively, were heat treated to shape set these wires as helical springs and enhance their SME for use as electro-mechanical actuators. These spring actuators were heat treated at 350 °C, 400 °C, and 450 °C for 30, 60, and 90 min. The wires’ performance as actuators was assessed on a custom-built testing rig, which measured both the stroke and actuation time for each wire. Additionally, the wires were characterised experimentally by DSC, XRD, and nanoindentation. The final resulting properties of the R-phase transformation helical spring actuator are controlled by the competing mechanisms of dislocation annihilation, and precipitation of Ni₄Ti₃, as well as the prior thermomechanical treatment. The optimum conditions for actuator response in Ni_50.9Ti_49.1 40% cold-worked wires were a straight annealing temperature of 480 °C and shape-setting aging conditions of 450 °C for 60 min. These parameters result in the optimum combination of defect annihilation and density of precipitates, resulting in a high-stroke (56 mm), low-hysteresis (2.68 °C) actuator with an actuation time of 6 s. Full article

The high material cost has restricted the development of concentrated solar power (CSP) systems. In this study, a low-cost alternative material was developed by adding aluminum to 304 stainless steel to form a protective oxide film, thereby enhancing its corrosion resistance to molten salt. Three material variants were tested: untreated hot-rolled plates after solution treatment and cold-rolled high-aluminum 304 stainless steel (High-Al304SS) after solution treatment and annealing treatment. After all samples were immersed in a NaNO₃-KNO₃ mixed salt at 600 °C for 480 h, corrosion products including NaFeO₂, CrO₂, Mn₂O₄, and NiCr₂O₄ were formed. The phase composition was determined by XRD, and the surface and cross-section of the corrosion layer were analyzed by SEM and EDS surface and point analysis. The corrosion rate of the samples was calculated by the weight loss method. Notably, an Al₂O₃-Cr₂O₃ composite oxide film was formed on the sample surface, effectively inhibiting corrosion. The high defect density and grain boundary energy introduced by the cold-rolling process, as well as the precipitation of the second phase during annealing, accelerated the corrosion process of the samples. However, the hot-rolled samples after solution treatment exhibited excellent corrosion resistance (64.43 μm/year) and, through further process optimization, are expected to become an ideal low-cost alternative material for 347H stainless steel (23 μm/year) in CSP systems. Full article

Improving the isotropic magnetic properties of FeSi electrical steels has traditionally focused on enhancing their crystallographic texture and microstructural morphology. Strengthening the cube texture within a ferritic matrix of optimal grain size is known to reduce core losses and increase magnetic induction. However, conventional cold rolling followed by annealing remains insufficient to optimise the magnetic performance of thin FeSi strips fully. This study explores an alternative approach based on grain boundary migration driven by temperature gradients combined with deformation gradients, either across the sheet thickness or between neighbouring grains, in thin, weakly deformed non-oriented (NO) electrical steel sheets. The concept relies on deformation-induced grain growth supported by rapid heat transport to promote the preferential formation of coarse grains with favourable orientations. Experimental material consisted of vacuum-degassed FeSi steel with low silicon content. Controlled deformation was introduced by temper rolling at room temperature with 2–40% thickness reductions, followed by rapid recrystallisation annealing at 950 °C. Microstructure, texture, and residual strain distributions were analysed using inverse pole figure (IPF) maps, kernel average misorientation (KAM) maps, and orientation distribution function (ODF) sections derived from electron backscattered diffraction (EBSD) data. This combined thermomechanical treatment produced coarse-grained microstructures with an enhanced cube texture component, reducing coercivity from 162 A/m to 65 A/m. These results demonstrate that temper rolling combined with dynamic annealing can surpass the limitations of conventional processing routes for NO FeSi steels. Full article

The increase in electrification and desire for greater electrical motor efficiency under a range of operating conditions for different products (e.g., household appliances, automotive and aerospace) is driving innovative motor designs and demands for higher performing electrical steels. Improvements in the magnetic, electrical and/or mechanical properties of electrical steels are required for high-volume electric motors and recent advances include steels with increased silicon (Si) content (from <3.5 wt% Si up to 6.5 wt%). Whilst the 6.5 wt% Si steels provide increased motor performance at high frequencies, the formation of a brittle BCC B2/D03 phase means that they cannot be cold-rolled, and therefore the production route involves siliconization after the required thickness strip is produced. The advances in computationally driven alloy design, coupled with physical metallurgical understanding, allow for more adventurous alloy design for electrical steels, outside the traditional predominantly Fe-Si compositional space. Two alloys representing a new alloy family called HiPPES (High-Performing and Processable Electrical Steel), based on low cost commonly used steel alloying elements, have been developed, cast, rolled, heat-treated, and both magnetically and mechanically tested. These alloys (with nominal compositions of Fe-3.2Mn-3.61Si-0.63Ni-0.75Cr-0.15Al-0.4Mo and Fe-2Mn-4.5Si-0.4Ni-0.75Cr-0.09Al) offer improvements compared to current ≈3 wt% Si grades: in magnetic performance (>25% magnetic loss reduction at >1 kHz), and in tensile strength (>33% increase in tensile strength with similar elongation value). Most importantly, they are maintaining processability to allow for full-scale commercial production using traditional continuous casting, hot and cold rolling, and annealing. The new alloys also showed improved resilience to grain size, with the HiPPES materials showing a <5% variance in loss at frequencies greater than 400 Hz for grain sizes between 55 and 180 µm. Comparatively, a commercial M250-35A material showed a 40% increase in loss for the same range. The paper reports on the alloy design approach used, the microstructures, and the mechanical, electrical and magnetic properties of the developed novel electrical steels compared to conventional ≈3 wt% Si and 6.5 wt% Si material. Full article

Novel structural materials, high-entropy alloys (HEAs), have attracted considerable interest owing to their tunable microstructural designs and adjustable mechanical properties. In the present work, the microstructural evolution and tensile deformation behavior of FeCoNiCrTi_0.2 HEA are comprehensively examined through cold rolling (with 80% thickness reduction) followed by annealing, combined with multiscale characterization techniques (EBSD/TEM) and mechanical tests. The results reveal that the as-rolled microstructure was characterized by the presence of strong Brass, Goss/Brass, and S textures, along with the formation of high-density dislocation walls (DDWs) and dislocation cells (DCs). As the annealing temperature increased, recrystallized grains preferentially nucleated at grain boundaries with higher stress concentrations and dislocation densities. The grain size decreased from 120.33 μm in the as-rolled state to 10.26 μm after annealing at 1000 °C. Low-angle grain boundaries (LAGBs) progressively transformed into high-angle grain boundaries (HAGBs), while the fraction of Σ3 twin boundaries initially decreased and subsequently increased, reaching a maximum of 43.7% after annealing at 1000 °C. At annealing temperatures exceeding 800 °C, deformed grains became equiaxed, with partial retention of primary texture components observed. After annealing at 1000 °C, the yield strength and tensile strength decreased compared to the as-rolled state, while the elongation significantly increased from 17.2% to 69.8% Simultaneously, the yield ratio decreased by 53%, and the strain-hardening capacity was enhanced. Ultimately, a constitutive model integrating the influences of dislocation mean free path and twin boundary obstruction was developed, providing microscopic explanations for the inverse relationship between strength and recrystallization fraction. Full article

The ordered tetragonal FeNi L1₀ phase, tetrataenite, is a promising candidate for rare earth-free permanent magnets due to its competitive magnetic properties and the low cost of the constituent elements. In this work, we have investigated the effect of molybdenum and aluminum substitution on the formation of the ordered L1₀ phase. The alloys were prepared with die casting and melt spinning techniques, further processed using cold rolling and cryomilling, and finally annealed below the estimated order–disorder temperature (T_OD). To study the influence of composition and processing of the alloys, structural characterization and microstructural analysis were performed with synchrotron radiation X-ray diffractometry (SR-PXD) and Scanning Transmission Electron Microscopy (STEM), respectively. The presence of tetrataenite in the alloys investigated in this work could not be confirmed. In situ SR-PXD and STEM indicated minimal structural changes in the temperature stability range of the materials. A full-loop hysteresis curve acquired using a vibrating sample magnetometer (VSM) indicated no signs of magnetic hardening of the alloys with the measured coercivity being below 10 Oe, and thus consistent with FeNi without ordering. Full article

This study investigated the hydrogen embrittlement behavior of Fe-28Mn-10Al-1C-(0,3) Cu austenitic low-density steels after hydrogen charging. Electrochemical hydrogen charging and thermal desorption spectroscopy (TDS) were employed to characterize hydrogen desorption behavior and identify hydrogen trap types in cold-rolled (LZ) and annealed (TH) conditions. Uniaxial tensile tests were conducted to obtain mechanical properties and the hydrogen embrittlement index (HEI), enabling quantitative evaluation of hydrogen embrittlement susceptibility. Fracture surface morphology was analyzed to elucidate the underlying embrittlement mechanisms. Results indicate that annealing treatment and Cu addition have negligible effects on the activation energy of reversible hydrogen traps, suggesting similar trap types. The reversible hydrogen content decreased by 0.1 wt.ppm and 0.2 wt.ppm in LZ-3Cu and TH-3Cu, respectively, compared to their Cu-free counterparts, indicating that Cu addition mitigates the accumulation of reversible hydrogen. Annealed specimens exhibited lower HEI values, with the HEI of TH-0Cu decreasing from 21.3% to 13.5% and that of TH-3Cu reaching only 9.6%. Fracture mode transitioned from mixed brittle-ductile to fully ductile with Cu alloying, accompanied by a shift from the coupled the Hydrogen-Enhanced Decohesion (HEDE) and the Hydrogen-Enhanced Localized Plasticity (HELP) mechanism to the HELP-dominated mechanism. Collectively, these findings demonstrate that Cu alloying significantly enhances the resistance of austenitic low-density steels to hydrogen embrittlement. Full article

Metastable titanium alloys have been developed for biomedical use due to their lower elastic modulus, combined with high strength, good ductility, and excellent corrosion resistance. In this study, the electrochemical corrosion resistance of the alternative Ti-23.6Nb-5.1Mo-6.7Zr alloy was investigated. The alloy was initially homogenized at 1000 °C for 24 h and then tested under different processing conditions: 90% cold rolling; 90% cold rolling followed by annealing at 950 °C for 1 h and water quenching; and 90% cold rolling followed by aging at 300 °C, 400 °C, and 500 °C for 4 h each. Electrochemical behavior was assessed using anodic polarization, open circuit potential (OCP), and electrochemical impedance spectroscopy (EIS) tests in a synthetic solution (Ringer’s solution) to simulate body fluid. The obtained results demonstrate the stability of the passive film formed of the conventional and modified alloys, considering long-term use in the human body, regardless of the volumetric fraction and phase distribution across the various processing routes studied as β, α, α″ and ω. The electrochemical parameters, combined with Young’s modulus and hardness of the alternative alloys, enable the definition of a multicriteria selection method of the most suitable mechanical process routes to be used. The application focused on components of functional femoral stems. Full article

The development of lightweight steels with high specific strength is critical for automotive applications and energy savings. This study aimed to develop a high-performance lightweight steel with high specific strength by designing an alloy composition and optimizing thermomechanical processing. A novel Fe-28.6Mn-10.2Al-1.1C-3.2Ni-3.9Cr (wt.%) steel was investigated, focusing on microstructural evolution, mechanical properties, and strengthening mechanisms. The steel was processed through hot-rolling, solution treatment, cold-rolling, and subsequent annealing. Microstructural characterization revealed a dual-phase matrix of austenite and ferrite (6.8 vol.%), with B2 precipitates distributed at the grain boundaries and within the austenite matrix, alongside nanoscale κ-carbides (<10 nm). Short-time annealing resulted in the finer austenite grains (~1.1 μm) and the higher volume fraction (5.0%) of intragranular B2 precipitates with a smaller size (~0.18 μm), while long-time annealing promoted the coarsening of austenite grains (~1.6 μm) and the growth of intergranular B2 particles (~0.9 μm). This steel achieved yield strengths of 1130~1218 MPa and tensile strengths of 1360~1397 MPa through multiple strengthening mechanisms, including solid solution strengthening, grain boundary strengthening, dislocation strengthening, and precipitation strengthening. Full article

This study investigates the subsequent stages of recrystallisation in Interstitial-Free (IF) steel subjected to an unconventional continuous annealing process with a controlled thermal gradient. A cold-rolled steel strip was exposed to varying annealing temperatures along its length, enabling the analysis of microstructural evolution during the course of recrystallisation. The microstructure and stored energy were assessed at various positions along the strip using Electron Backscatter Diffraction (EBSD). The results underscore the significant influence of local misorientation and structural inhomogeneity on orientation selection during recrystallisation. The remaining non-recrystallised volume fraction (NRF) strongly correlates with the average misorientation gradient, obeying a phenomenological power-law correspondence with an exponent of ~3.7. This indicates that the recrystallisation process is highly sensitive to small changes in local orientation gradients. These findings highlight the crucial role of stored energy distribution for texture evolution, particularly during the early stages of recrystallisation in continuous annealing. It is observed that g-fiber grains, in comparison to a-fiber grains, are much more susceptible to grain fragmentation and therefore develop more robust intra-granular misorientation gradients, allowing for successful nucleation events to occur. In the present study, these phenomena are documented in a statistically representative manner. These insights are valuable for optimising thermal processing in interstitial-free (IF) steels. Full article

In this paper, Cu-1.16Ni-0.36Cr alloy was obtained by adding Ni-Cr intermediate alloy, and the effects of aging parameters on its microstructural evolution and mechanical properties were studied. The results show that after secondary aging (solid solution + one time cold rolling at 87.5% + annealing at 300 °C for 2 h + secondary aging at 450 °C for 2 h), dispersed BCC structure Cr precipitates are obtained in the alloy, which shows good comprehensive properties (strength of 512.0 MPa, elongation of 17.2%, and electrical conductivity of 45.5%). The change in aging parameters significantly affects the existing form of Cr precipitates. When the aging temperature increases from 400 °C to 450 °C, the precipitated phase begins to have a stable boundary, which shows that the precipitated phase with BCC structure Cr precipitates (~10 nm in range). When the aging temperature further increases to 500 °C, the size of Cr precipitated phase begins to grow, from 5.0 nm to 16.7 nm. The strengthening mechanism of the alloy with different aging time at 450 °C is calculated, and the relationship among aging parameters, microstructure characteristics, strengthening mechanism and mechanical properties is established. It is concluded that precipitation strengthening and dislocation strengthening are the main strengthening mechanisms of the alloy. Full article

The effects of trace Ce on the microstructure and texture of non-oriented silicon steel during recrystallization and grain growth were examined using X-ray diffraction and electron backscatter diffraction. Additionally, this study focused on investigating the mechanisms by which trace Ce influences the evolution of the {114} <481> and γ-fiber textures. During the recrystallization process, as the recrystallization fraction of annealed sheets increased, the intensity of α-fiber texture decreased, while the intensities of α*-fiber and γ-fiber textures increased. The {111} <112> grains preferentially nucleated in the deformed γ-grains and their grain-boundary regions and tended to form a colony structure with a large amount of nucleation. In addition, the {100} <012> and {114} <481> grains mainly nucleated near the deformed α-grains, which were evenly distributed but found in relatively small quantities. The hindering effect of trace Ce on dislocation motion in cold-rolled sheets results in a 2–7% lower recrystallization ratio for the annealed sheets, compared to conventional annealed sheets. Trace Ce suppresses the nucleation and growth of γ-grains while creating opportunities for α*-grain nucleation. During grain growth, trace Ce reduces γ-grain-boundary migration rate in annealed sheets, providing growth space for {114} <418> grains. Consequently, the content of the corresponding {114} <481> texture increased by 6.4%, while the γ-fiber texture content decreased by 3.6%. Full article