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A study of die parameters influencing the plastic deformation for 3D finite element simulations of equal-channel angular pressing
(2025-08-01)
Wongsa-Ngam, Jittraporn
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Noraphaipaksa, Nitikorn
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Kanchanomi, Chaosuan
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Langdon, Terence G.
Equal-channel angular pressing is an effective method of severe plastic deformation that is employed to produce materials with ultrafine grain structures. This study aimed to systematically investigate the influence of the die parameters, specifically the channel angle and the outer curvature angle, on the induced plastic strain, strain inhomogeneity and the reaction force during processing of a round section copper-zirconium alloy workpiece. Three-dimensional finite element simulations were developed using ABAQUS/ Explicit to model single-pass deformation with varying channel angles of 90°, 110°, 120° and 150° and outer curvature angles of 20°, 30° and 60°. The results demonstrate that the channel angle is the dominant factor controlling the average equivalent plastic strain, which decreased from approximately 1.04 at 90° channel angle with 20° outer curvature angle to about 0.31 at 150° channel angle regardless of the outer curvature. In contrast, the outer curvature angle significantly influences the strain homogeneity at low channel angles, with the coefficient of variance increasing from 0.06 to 0.22 when the outer curvature angle increases from 20° to 60° at a 90° channel angle. Additionally, the maximum reaction force declined markedly with an increasing channel angle, dropping from 58 kN at 90° to 12 kN at 150°, thereby highlighting a strong interplay between imposed strain and forming load. These findings provide clear guidelines for optimizing the die design to balance high strain, uniform deformation and manageable pressing forces in the industrial processing of ultrafine-grained materials.
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Advances in Superplasticity from a Laboratory Curiosity to the Development of a Superplastic Forming Industry
(2022-11-01)
Wongsa-Ngam, Jittraporn
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Langdon, Terence G.
Superplasticity refers to the ability of some materials to pull out to tensile elongations of 400% or more when the strain rate sensitivity is ~0.5. The first report of true superplastic flow was published in 1934 in experiments conducted in England. However, this remarkable result attracted little interest among western scientific researchers and the result remained a laboratory curiosity for many years. Later, following extensive research on superplasticity in the Soviet Union, interest developed in the west, and superplasticity became a topic of extensive scientific research. This research was further enhanced with the demonstration that the application of severe plastic deformation provided an opportunity for achieving grain refinement to the submicrometer or even the nanometer level, and these small grains were especially attractive for achieving good superplastic properties. It is now recognized that superplastic alloys provide an excellent forming capability, especially in making high quality curved parts that are not easily fabricated using more conventional processes. This has led to the development of a large superplastic forming industry that currently processes many thousands of tons of sheet metals. This report traces these developments with an emphasis on the scientific principles behind the occurrence of superplastic flow.
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Numerical investigation of plastic strain homogeneity during equal-channel angular pressing of a Cu-Zr Alloy
(2021-12-01)
Wongsa-Ngam, Jittraporn
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Noraphaiphipaksa, Nitikorn
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Kanchanomai, Chaosuan
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Langdon, Terence G.
A three-dimensional finite element method (3D FEM) simulation was carried out using ABAQUS/Explicit software to simulate multi-pass processing by equal-channel angular pressing (ECAP) of a circular cross-sectional workpiece of a Cu-Zr alloy. The effective plastic strain distri-bution, the strain homogeneity and the occurrence of a steady-state zone in the workpiece were investigated during ECAP processing for up to eight passes. The simulation results show that a strain inhomogeneity was developed in ECAP after one pass due to the formation of a corner gap in the outer corner of the die. The calculations show that the average effective plastic strain and the degree of homogeneity both increase with the number of ECAP passes. Based on the coefficient of variance, a steady-state zone was identified in the middle section of the ECAP workpiece, and this was numerically evaluated as extending over a length of approximately 40 mm along the longitudinal axis for the Cu-Zr alloy.
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The influence of HPT on microstructure and wear resistance of Al-7wt%Si-2wt%Fe Alloy
(2021-01-01)
Wongsa-Ngam, Jittraporn
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Xu, Jie
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Phongphisutthinan, Chakkrist
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Langdon, Terence G.
An aluminum silicon-based alloy (Al-7wt%Si-2wt%Fe) was subjected to severe plastic deformation by the high-pressure torsion (HPT) method. This HPT processing was conducted at room temperature up to five revolutions under a pressure of 6.0 GPa and rotation speed of 1.0 rpm. Observations of microstructure evolution, especially intermetallic phases, was carried out by an optical microscope (OM) and a scanning electron microscope (SEM). It was found that the ironintermetallic particles decreased in size with numbers of turns. This is due to the large strain introduced during HPT processing which produced a degree of fragmentation of intermetallic phases which increased with the imposed strain. In addition, wear behaviors of the as-cast and samples deformed by HPT were also investigated using micro-tribometer UMT-2 (CETR Co., USA) following the ASTM G99-05 (2010) standard. The friction coefficient and wear volume loss were measured to evaluate the effect of imposed strain during HPT processing on wear resistance. It was found that the values of the average friction coefficient were slightly lower in deformed samples and the wear volume loss decreased with increasing numbers of turns.
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Microstructure evolution of Al-7wt%Si-2wt%Fe alloy processed by high-pressure torsion
(2018-08-14)
Wongsa-Ngam, Jittraporn
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Phongphisutthinan, Chakkrist
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Langdon, Terence G.
The microstructure evolution of an aluminum silicon-based alloy after severe plastic deformation processing was examined. An aluminum silicon-based alloy; Al-7wt%Si-2wt%Fe, was processed by the severe plastic deformation technique called high-pressure torsion at room temperature under a high pressure of 6.0 GPa and rotational speed of 1.0 rpm with numbers of revolution up to 5 turns. Microstructure evolution, especially intermetallic phase, was observed using an optical microscope and a scanning electron microscope (SEM). The effects of high-pressure torsion on the Fe intermetallic compounds in Al-Si alloy were investigated. It was found that the intermetallic particles decreased in size with increasing imposed strains.
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Effects on hardness and microstructure of AISI 1020 low-carbon steel processed by high-pressure torsion
(2017-10-01)
Marulanda Cardona, Diana Maritza
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Wongsa-Ngam, Jittraporn
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Jimenez, Hernando
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Langdon, Terence G.
Low-carbon steel AISI 1020 was subjected to high-pressure torsion (HPT) with 6.0 GPa pressure through 1/4–5 turns. The microstructures of the samples in each turn were studied by means of X-ray diffraction (XRD) analyzing the changes in micro-strain, crystallite size and lattice parameter. Vickers testing was utilized to study the microhardness behavior of the samples subjected to HPT processing. The morphology evolution of the samples and especially the changes in ferrite and pearlite structures were studied for different numbers of turns using scanning electron microscopy (SEM).
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Microstructural Evolution and Properties of a Hot Extruded and HPT-Processed Resorbable Magnesium WE43 Alloy
(2017-03-01)
Liu, Dexue X.
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Pang, Xin
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Li, Denglu L.
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Guo, Chenggong G.
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Wongsa-Ngam, Jittraporn
Disks of an extruded magnesium WE43 alloy are processed by high-pressure torsion (HPT) and the evolutions of microstructure and mechanical properties are investigated in detail. Excellent grain refinement is achieved by HPT processing with a reduction in grain size from an initial value of ≈12 μm to a final value of ≈200–300 nm after 10 turns. The microhardness increases significantly with HPT processing but low hardness values are recorded at the centers of the disks. The tensile strength initially increases and then decreases while the elongation decreases. Observations of the fracture surfaces reveal a corresponding transition of the fracture mode from ductile to brittle.
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The microstructure length scale of strain rate sensitivity in ultrafine-grained aluminum
(2015-04-14)
Kammers, Adam D.
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Wongsa-Ngam, Jittraporn
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Langdon, Terence G.
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Daly, Samantha
The mechanical properties of ultrafine-grained aluminum produced by equal-channel angular pressing (ECAP) are strongly influenced by strain rate. In this work, an experimental investigation of local strain rate sensitivity as it relates to microstructure was performed using a combination of scanning electron microscopy and digital image correlation. Uniaxial tension tests were carried out at 200 °C and strain rates alternating between 2.5 × 10-5 s-1 and 3.0 × 10-3 s-1. The results demonstrate that the heterogeneous microstructure generated by ECAP has a strong effect on the microstructure scale strain rate sensitivity. Deformation centered at grain boundaries separating regions of banded microstructure exhibits the greatest strain rate sensitivity. Strain rate sensitivity is limited in deformation occurring in regions of microstructure composed of ultrafine grains separated by low-angle grain boundaries. The tensile specimens all failed by shear bands at 200 °C and at room temperature they failed by necking with little plastic deformation apparent outside of the neck.
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Wear resistance of an ultrafine-grained Cu-Zr alloy processed by equal-channel angular pressing
(2015-03-05)
Li, Jianwei
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Wongsa-Ngam, Jittraporn
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Xu, Jie
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Shan, Debin
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Guo, Bin
A Cu-0.1 wt.% Zr alloy was processed by equal-channel angular pressing (ECAP) through 8 passes at room temperature to produce an ultrafine grain size of ~350 nm with an average Vickers microindentation hardness (200 gf) of ~140. Ball-on-disc dry sliding tests were conducted on an annealed material and on the ECAP-processed alloy using applied normal loads from 1 to 15. N. The coefficient of friction (COF), surface topography and wear volume loss were examined to evaluate the micro-wear resistance. The results show that samples processed by ECAP have lower average values for the COF than the unprocessed alloy and there is also a decrease in the wear depth and wear volume loss with increasing numbers of ECAP passes. The ultrafine-grained alloy processed by ECAP has a higher wear resistance than the annealed and unprocessed material due to the significant grain refinement and improved mechanical properties.
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Microstructural evolution and microhardness in a low carbon steel processed by high-pressure torsion
(2014-10-01)
Marulanda Cardona, Diana Maritza
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Wongsa-Ngam, Jittraporn
;
Langdon, Terence G.
A low-carbon triple-alloyed steel was processed by high-pressure torsion at room temperature for up to 5 turns under a pressure of 6.0 GPa. Microhardness, scanning electron microscopy and X-ray diffraction were used to investigate the hardness and microstructural evolution of the steel. Values of the Vickers microhardness were recorded across the sample diameters. The results show that there is a gradual evolution in both the hardness and the microstructure with increasing numbers of turns. However, the microhardness does not become fully homogeneous across the sample diameter after five turns and there remain significantly lower values in the center of the disk. These results indicate that complete homogeneity across the disks for this steel requires applied pressures higher than 6.0 GPa and/or torsional straining through more than 5 turns.

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