The mechanical characteristics of polycrystalline metallic materials are influenced significantly by various microstructural parameters, one of which is the grain size. Specifically, the strength and ...the toughness of polycrystalline metals exhibit enhancement as the grain size is reduced. Applying severe plastic deformations (SPDs) has a noticeable result in obtaining metallic materials with ultrafine-grained (UFG) microstructure. SPD, executed through conventional shaping methods like extrusion, plays a pivotal role in the evolution of the texture, which is closely related to the plastic behavior and ductility. A number of SPD processes have been developed to generate ultrafine-grained materials, each having a different shear deformation mechanism. Among these methods, linear twist extrusion (LTE) presents a non-uniform and non-monotonic form of severe plastic deformation, leading to significant shifts in the microstructure. Prior research demonstrates the capability of the LTE process to yield consistent, weak textures in pre-textured copper. However, limitations in production efficiency and the uneven distribution of grain refinement have curbed the widespread use of LTE in industrial settings. This has facilitated the development of an improved novel method, that surpasses the traditional approach, known as the nonlinear twist extrusion procedure (NLTE). The NLTE method innovatively adjusts the channel design of the mold within the twist section to mitigate strain reversal and the rotational movement of the workpiece, both of which have been identified as shortcomings of twist extrusion. Accurate anticipation of texture changes in SPD processes is essential for mold design and process parameter optimization. The performance of the proposed extrusion technique should still be studied. In this context, here, a single crystal (SC) of copper in billet form, passing through both LTE and NLTE, is analyzed, employing a rate-dependent crystal plasticity finite element (CPFE) framework. CPFE simulations were performed for both LTE and NLTE of SC copper specimens having or directions parallel to the extrusion direction initially. The texture evolution as well as the cross-sectional distribution of the stress and strain is studied in detail, and the performance of both processes is compared.
In this paper, the Zn additions combined with a novel severe plastic deformation (SPD) technology, screw twist extrusion (STE), is used to prepare Mg-xZn-1Mn alloys (x=0, 2, 4, 6) with fine grains ...and high ductility. By observing the microstructures, it is found that a gradient microstructure is obtained perpendicular to the extrusion direction (ED) in all four samples after STE. The STE process introduces twist extrusion strain into the samples, which causes the grain to twist and break, resulting in the weakening of the texture and the refinement of the grain. In addition, MgZn2 phase is formed by the addition of high Zn, and the combination of MgZn2 with twist shear strain further promoted dynamic recrystallization (DRX) to refine the grain and obtain the preferred texture, resulting in the increase of fracture elongation (FE). The FE of Mg-6Zn-1Mn sample improved from 18.4% to 27.8%, an 51.1% increase. This is mainly associated with the DRX mechanisms of continuous dynamic recrystallization (CDRX), discontinuous dynamic recrystallization (DDRX) and particle simulated nucleation (PSN). Meanwhile, the Schmid factor (SF) of basal slip increased with the addition of Zn, the basal slips in various samples are promoted obviously and FE is further enhanced. Thus, the novel STE technology combining with Zn additions provides an effective approach to improve the ductility of Mg-Zn-Mn alloys.
•The ductility of Mg-Zn-Mn alloy is enhanced by Zn addition combined with STE process.•A variety of DRX behaviors have been studied in STEed Mg-χZn-Mn alloys.•The method proposed in this paper to enhance the ductility of Mg-Zn-Mn alloys is a good choice for the application of degradable biomedical devices.
To improve the comprehensive properties of CLAM steel and expecting good performance in service conditions, twist extrusion and upsetting (TEU) based thermo-mechanical treatment (TMT) was introduced ...into the steel at 600 °C, 670 °C, and 740 °C. Optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) was used to characterize the microstructural evolution during the deformation. Uniaxial tension test was used to evaluate the tensile mechanical property. The results show that the grain size and dislocation density of the processed samples decrease from the as-received condition, but are higher than that in the as-tempered conditions. The particle sizes of M23C6 and MX in the TEUed samples are lower than that in the as-tempered case, which contribute a lot to the yield strength. The yield strength of the TEUed CLAM steel decrease with the increase of deformation temperature and a good match in strength and ductility, relating to heterogeneous microstructure, has been achieved at the deformation temperature of 670 °C (yield stress: 853.59 MPa, ultimate tensile stress: 992.4 MPa, elongation: 15.7%). The K value and exponent in the Hall-Petch relationship should be modified owing to the volume fraction of martensite, which is harder than ferrite and causes interface elastic mismatch stress, is different at different temperatures.
Useful properties of twist extrusion Beygelzimer, Y.; Varyukhin, V.; Synkov, S. ...
Materials science & engineering. A, Structural materials : properties, microstructure and processing,
03/2009, Letnik:
503, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We present an experimental study of the kinematics of twist extrusion (TE) and show that TE has the following properties: (i) as in equal-channel angular pressing (ECAP), the mode of deformation in ...twist extrusion is simple shear. Unlike in ECAP, there are two shear planes; one of them is perpendicular and the other is parallel to the specimen axis. (ii) The following processes are present during twist extrusion: vortex-like flow with large strain gradient, stretching and mixing of metal particles. We argue that, due to these properties, TE opens possibilities for investigating and forming new microstructures. It has already been successfully used to obtain ultrafine-grained microstructures with good properties in Al, Cu and Ti alloys.
Twist extrusion (TE) is known as one of newly developed, but still moderately studied severe plastic deformation methods. This research was initiated to conduct a detailed study of ...structure–properties relationship evolution during TE processing. The evolution of macrostructure, Vickers hardness and tensile properties was studied in 99.99% purity aluminum during twist extrusion processing at room temperature up to 4 TE passes (total average equivalent strain of ∼4.8). The process resulted in almost homogeneously refined structure that cannot be resolved optically. Significant increase in Vickers hardness, yield strength and ultimate tensile strength with moderate degradation in ductility of Al was observed. Apart from some structural inhomogeneity, all the mechanical properties were almost homogeneous and isotropic after four TE passes.
In the current study, a comprehensive evaluation of AA5083 processed via the novel Multi-Channel Spiral Twist Extrusion (MCSTE) method was conducted. The induced stress-strain state and the ...deformation mechanism of multiple pass deformation via MCSTE dies with twist angle β (30°) and (40°) were analyzed using finite element analysis. Nanohardness measurements were carried out along the billet surfaces to validate the numerical model output. The micro-hardness, tensile-up-to-fracture, fracture behavior and microstructural properties were investigated. The numerical model and the empirical findings reveal that the increase in the mechanical properties of the billets processed via MCSTE die with a twist angle β (40°) was associated with a plastic strain of 0.9 (mm/mm) compared to 1.2 (mm/mm) for conventional twist extrusion dies of β (60°). For the MCSTE die with angle β (30°), the hardness and tensile properties increased as a function of increasing the number of passes, with an insignificant reduction in ductility. Processing via a die angle β (40°) was limited to one pass due to excessive strain hardening, which resulted in shear localization during the second pass. The detailed analysis presented herein validates the effectiveness of MCSTE processing as a severe plastic deformation tool with a favorable potential for industrial applications.
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Planar Twist Extrusion versus Twist Extrusion Beygelzimer, Y.; Prilepo, D.; Kulagin, R. ...
Journal of materials processing technology,
03/2011, Letnik:
211, Številka:
3
Journal Article
Recenzirano
A modification of Twist Extrusion (TE) process, Planar Twist Extrusion (PTE) with a die having two flat parallel walls moving by the plunger, was designed and implemented in the present study. ...Characteristics of the deformed state after PTE and TE as well as pressures involved in the processes were studied by means of experiments on aluminum samples and finite element modelling. The differences in a character of the strain distribution and mechanisms of its accumulation during PTE and TE were established. Both processes permitted mixing of the samples on a microscale.
•Hydrostatic twist extrusion (HTE) is introduced as a new SPD method.•The process was successfully applied on CP Aluminum.•Relatively long UFG and NG samples was processed compared to that in former ...twist extrusion.•Substantial grain refinement was achieved.•Remarkable improvement of mechanical properties was obtained.
In this study, hydrostatic twist extrusion (HTE) has been introduced for processing relatively long ultrafine grained (UFG) bulk samples. By using high-pressure fluid surrounded the sample, surface contact between die and sample was eliminated. The high-pressure fluid causes high hydrostatic pressure, which leads to improvement of material properties and increased the aspect ratio of the sample (length/diameter). The HTE process was applied to commercial pure aluminum samples at room temperature, and then microstructure and mechanical properties were examined. The results demonstrate that after HTE process, the grain size was reduced from 54 µm to ∼800 nm, and microhardness was increased from 29.2 HV to 37.7 HV. Also, yield and ultimate strength were noticeably increased from 78 MPa and 103 MPa to 166 MPa and 175 MPa, respectively. This process seems to be very promising and interesting for the future industrial application.
Recently, several severe plastic deformation (SPD) techniques have been developed with the aim of incorporating grain refinement and strengthening metal forming technology into the industry without ...dimensional changes. Multi-channel spiral twist extrusion (MCSTE) was innovated and patented in an attempt to provide an effective, cost-saving SPD process that would attract the industrial uptake of the renowned twist extrusion (TE) method. The MCSTE process is based on the use of customized stacked disks that host non-circular cross-sectioned billets extruded through a die with a twist angle (β). Hence, an empirical study was conducted on AA1100 to investigate the influence of 4 successive MCSTE passes on the mechanical behavior and microstructural evolution of the extrudates compared to the as-received (AR) condition. Electron backscatter diffraction (EBSD) was employed for mapping the structural evolution, misorientation angles and the texture developed as a function of the processing passes. Additionally, hardness and tensile properties were evaluated and correlated with the EBSD findings. EBSD analysis revealed the formation of almost equiaxed grains after 1 pass, which were evolved into elongated grains aligned at approximately 45° relative to the extrusion direction after 2-passes. Moreover, MCSTE processing 1-pass produced a structure with 64% and 36% HAGB and LAGB, respectively, while 2-passes via MCSTE increased HAGBs to 80%. Processing 4-passes increased the amount of recovery depicted by the percentage of LABs within the grains, which was associated with a noticeable increase in the fraction of fine grains < 8 µm. MCSTE produced a very strong texture that increased in intensity with an increasing number of passes. The results demonstrated a significant increase of 73% and 40% in the average hardness and tensile strength, respectively, with an increasing number of passes up to 4, which was coupled with an insignificant 2% reduction in ductility. The displayed results validated the effectiveness of MCSTE as an SPD tool for grain refinement with a favorable potential for industrial applications.
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