Duplex stainless steels (DSSs) produced via laser powder bed fusion (LPBF) exhibit excellent strength and plasticity compatibility. In this study, in-situ electron backscatter diffraction (EBSD) was ...employed to investigate the coordinated deformation behavior of 2205 DSSs fabricated by LPBF with heat treatment at 1050 °C for 1 h, including strain distribution behavior and mechanism of stress concentration release. The results indicate that the initial deformation of LPBF samples is primarily concentrated in the austenite phase. As the tension progresses, austenite gradually transitioned to hard orientation, and the strain in austenite can pass through the phase boundary into the ferrite grain. To coordinate the deformation, ferrite transitioned to soft orientation through rotation towards the slip systems of {110}<−111> and {1–21} . The stress concentration in ferrite can be alleviated by forming dislocation walls and cells through planar and cross-slip dislocations. In contrast, the stress concentration in austenite can be released by stacking faults and deformation twins. Compared to the as-cast samples, the yield strength of LPBF samples is improved from 472 ± 13 to 641 ± 17 MPa due to fine grain strengthening and dislocation strengthening. This study offers guidance for further enhancing the strength and plasticity of materials prepared by LPBF.
•Duplex stainless steel with excellent strength and plasticity compatibility was produced by laser powder bed fusion.•The strain distribution behavior in ferrite and austenite was characterized and analyzed.•The mechanism of stress concentration release was investigated.•The mechanisms of strength enhancement were clarified.
•The application of ultrasonic vibration delays the occurrence of the dynamic recrystallization of AZ31.•Ultrasonic vibration enlarges the region of the steady-state deformation.•Ultrasonic vibration ...facilitates the transition from LAGBs to HAGBs, accelerating the CDRX process.•A dislocation evolution of magnesium alloys occurs under the influence of ultrasonic vibration.
Ultrasonic vibration-assisted tensile tests of AZ31 magnesium (Mg) alloy sheets are carried out at different temperatures (150 °C, 200 °C) and amplitudes (0–11.2 µm). The influences of the ultrasonic vibration on the stress-strain responses, microstructural evolution, fracture morphology, dynamic recrystallization (DRX), and dislocation structure of the material during hot deformation are discussed. The results show that both flow stress and elongation of the material are significantly influenced by the temperature and amplitude. The application of ultrasonic vibration delays the occurrence of DRX. However, it accelerates the continuous dynamic recrystallization process, thereby increasing the percentage of the DRX. Furthermore, an evolution of the dislocation structure occurs under the impact of ultrasonic vibration, offering valuable insights into the plasticity improvement of the material. The underlying mechanisms of ultrasonic vibration-assisted hot deformation of AZ31 Mg alloys can be described as below. Ultrasonic vibration affects the motion and distribution of dislocations, which have an effect on the dynamic recrystallization behavior, ultimately leading to changes in mechanical behavior of the material.
•Central defect formation is due to small impact angle during parallel impact process.•Big impact speed and angle results in the formation of end unwelded zone.•Nano grains and amorphous phase forms ...at the interface of welded zone.•Location scheme can eliminate the defect by changing the impact angle.
Experimental and numerical methods are carried out to analyze the interface formation and defect elimination mechanism during electromagnetic pulse welding T2 to 304L tube by changing the inner tube morphology from original scheme to stage scheme, ramp stage, and location stage. When the original scheme is operated with 13mm lap length, the morphology of interface is divided into four zones containing end unwelded zone, first welded zone, central unwelded zone, and second welded zone due to the different impact velocity and angle during the initial impact process, parallel impact process, and final impact process. The parallel impact leads to the formation of the central unwelded zone, containing (Cu, Fe) solid solution, oxides, nano grains, and amorphous phase. By providing a suitable impact angle, the ramp scheme (α = 7°) and location scheme (L = 6.5 mm) can eliminate the defect in the central unwelded zone.
Specimens of duplex stainless steel (DSS) fabricated by selective laser melting (SLM) exhibit excellent strength but poor plasticity, which has limited their applications. To improve the plasticity ...and to achieve a strength-plasticity matching, the effect of the laser scanning speed on the density, phase, microstructure, and mechanical properties of 2205 DSS specimens fabricated via SLM is investigated. The results reveal that the molten metal is solidified according to the kinetic sequence L → δ + L → δ → δ + γ for the SLM forming process, and the sample is completely composed of the ferrite phase. The content of austenite cannot be effectively enhanced by a change in the laser scanning speed. The mechanical properties of the samples are primarily affected by the presence of pores. A scanning speed of S700 (700 mm/s) results in the formation of fewer pores, which gives rise to a high yield strength of 896.80 MPa but a poor plasticity of 15.34 %. Decreasing the scanning speed to below 700 mm/s reduces the yield strength, but it also significantly increases the elongation. The elongation of the specimens fabricated using a laser scanning speed of 500 mm/s increases to 23.09 %, and they exhibit excellent strength-plasticity matching. This increased elongation at lower scanning speeds is attributed to higher density, lower dislocation density, decreased number of grain boundaries and the higher proportion of high-angle grain boundaries (HAGBs) of the specimens. Therefore, a significant decrease in the scanning speed can improve the plasticity of the specimens fabricated by the SLM method. By changing the laser scanning speed, the density, microstructure and mechanical properties can be optimized to further improve the plasticity of the specimens.
•The mechanism of phase transformation mechanism and the effect of scanning speed were investigated.•The effects of scanning speed on grain size and dislocation density were investigated.•A specimen of 2205 was fabricated by SLM with excellent strength-plasticity matching properties.•The mechanism of elongation enhancement was explained.
Cu-Nb microcomposite wires drawn to different strain values were studied by means of scanning electron microscopy and transmission electron microscopy. The Cu and Nb near the interfaces show a ...typical Kurdjumov-Sachs relationship with a deviation angle of 12°. This deviation accommodates internal stresses and slip discontinuity between Cu and Nb. The dislocations are mainly stored around the interface near the Cu matrix. Lattice distortion occurred near the interfaces, where Nb is believed to mix into Cu matrix. Microhardness is affected by interface area density as well as by strain-induced lattice distortion, which can produce a supersaturated solid solution.
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•The investigated Cu-Nb wires are fabricated by accumulative drawing and bundling process.•The tested microhardness values were found far beyond the estimated ones at large strains.•Interface area density is shown to be crucial to the microhardness.•Solid solution and lattice distortion nearby the interface in ADB wire were analyzed.•Solid solution was suggested to account for the discrepancy between the tested hardness values and the estimated ones.
Selective laser melting (SLM) has been attracting increasing attention as a suitable route for fabricating personalized orthopedic implants to address patient–prosthesis mismatches and has been used ...for producing Co29Cr9W3Cu alloys in our previous study. However, SLM technology can result in the formation of mesh-like random high-angle grain boundaries (indicated as molten pool boundaries) and accumulation of residual stress in the microstructure, possibly causing an unstable mechanical property. In this study, the research on the relationship between microstructural evolution and mechanical properties was performed on the SLM-produced Co29Cr9W3Cu alloys with different heat treatments to improve the reliable mechanical property of the SLM-produced Co29Cr9W3Cu orthopedic implants. It was found that the microstrucutre with mesh-like random high-angle grain boundaries could be eliminated during recrystallization, replaced by the one with equiaxial structure containing the Σ3 grain boundaries (annealing twin). Most importantly, the combined effect of eliminating the mesh-like random high-angle grain boundaries and residual stress and generating the Σ3 grain boundary contributed to an increase in elongation from 12.49% of the as-SLM-produced one to 23.38%. Proper heat treatment is considered to be an efficient strategy to improve the mechanical properties of the SLM-produced Co29Cr9W3Cu alloy with a desired tensile ductility.
•Carbide-reinforced MMCs coatings were prepared via plasma transferred arc.•The MMCs coating has a high hardness of 1121.1 HV1.0.•The wear amount increased first and lowered then as the main arc ...current increased.•The wear amount influenced by the carbide volume fraction.•Wear performance was enhanced by the MMCs coatings.
MC-type carbide-reinforced metal matrix composites (MMCs) coatings are additively manufactured by plasma transferred arc (PTA) on Q235 steel under different arc currents ranging from 120 A to 160 A. The microstructure, elemental distribution, hardness, and wear resistance of MMCs coatings are studied. The results show that the MMCs coating possesses a high hardness up to 1112.1 HV1.0, 30.3 % volume fraction of carbides, and excellent wear resistance when PTA main arc current is 140 A. The mechanical performance improvement is in that the MMCs coatings manufactured at 140 A have the highest density of finer fishbone-shaped carbides and favorable size uniformity, compared with other main arc currents.
In this work, the corrosion resistance of CD4MCu (UNS J93370) duplex stainless steel both at cold-rolled and annealed states was studied with respect to microstructure, α'-martensite, α/γ phase ...boundaries, LAGBs (low-angle grain boundaries), Σ3 and textures. A series of characterization methods including optical microscopy, electron backscatter diffraction (EBSD), x-ray diffraction (XRD) and electrochemical testing were applied to analyze the microstructure and interpret the corrosion resistance changes. The results show that as the cold rolling deformation increases, the phase spacing decreases and the γ/α interphase boundary ratio increases. Strain-induced martensite forms during plastic deformation and the amount increases as the deformation goes on. After cold rolling, Cu, S, brass and Goss textures form in γ phase, and weaker α- and γ-fiber textures form in α phase. After annealing, the texture intensity in the γ phase is weakened, while the γ-fiber texture in the ferrite phase is enhanced. The corrosion resistance can be improved by appropriate deformation and annealing. The increment of LAGB and Σ3 grain boundary with low interfacial energy and the favorable textures induced during deformation are suggested to be responsible for the improvement in the corrosion resistance. They offset the negative effects of α'-martensite and defects on the corrosion resistance. As a function of deformation level, the corrosion resistance of both the deformed and annealed samples enhanced first and then decreased, reaching the best corrosion resistance at 60% deformation.
With the widely use of high-strength steel sheets in the automotive industry, the twist springback phenomenon of the steel sheets under multi-step forming conditions has received extensive attention. ...In this work, the Dual Phase steel DP500 is taken as the research object to investigate the complex non-linear elastoplastic behaviors and twist springback under two-step loading paths. The large specimen with a pre-strain of 4% true strain in rolling direction is carried out on a large tensile testing machine, and several specific blanks are extracted from it at different directions for a subsequent P-channel forming. The influence of twist springback associated with the pre-strain is analyzed. The finite element model based on the non-linear elastic model and the homogeneous anisotropic hardening model (HAH) is also established for the springback prediction and stress analysis. The results indicate that the pre-strain has a considerable impact on the twist springback. The non-linear strain path changes resulted from pre-straining not only influence the residual stress but also affect the elastic modulus distribution.
