Wongsangam, Jittraporn

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Wongsangam, Jittraporn
Alternative Name
Wongsa-Ngam, Jittraporn
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Email
jittraporn.wo@kmitl.ac.th

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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
    ;
    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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    An examination of the saturation microstructures achieved in ultrafine-grained metals processed by high-pressure torsion
    (2014-10-01)
    Sabbaghianrad, Shima
    ;
    Wongsa-Ngam, Jittraporn
    ;
    Kawasaki, Megumi
    ;
    Langdon, Terence G.
    Experiments were conducted on two commercial alloys, a Cu-0.1%Zr alloy and an Al-7075 aluminum alloy, to investigate the significance of the saturation microstructure which is achieved after processing by high-pressure torsion (HPT). Samples were processed by HPT and also by a combination of equal-channel angular pressing (ECAP) followed by HPT. The results show that the saturation conditions are dependent upon the grain size in the material immediately prior to the HPT processing. Additional grain refinement may be achieved in HPT by initially processing the material to produce an ultrafine-grain size before conducting the processing by HPT.
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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.
    ;
    Pang, Xin
    ;
    Li, Denglu L.
    ;
    Guo, Chenggong G.
    ;
    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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    Wear resistance of an ultrafine-grained Cu-Zr alloy processed by equal-channel angular pressing
    (2015-03-05)
    Li, Jianwei
    ;
    Wongsa-Ngam, Jittraporn
    ;
    Xu, Jie
    ;
    Shan, Debin
    ;
    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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    The effect of microstructure heterogeneity on the microscale deformation of ultrafine-grained aluminum
    (2014-01-01)
    Kammers, Adam D.
    ;
    Wongsa-Ngam, Jittraporn
    ;
    Langdon, Terence G.
    ;
    Daly, Samantha
    A combined approach of scanning electron microscopy and digital image correlation was used to examine microstructure-scale strain localization and active deformation mechanisms in ultrafine-grained (UFG) high purity (99.99%) aluminum processed by equal-channel angular pressing (ECAP). The results from tensile tests demonstrate a strong relationship between the heterogeneous microstructure and strain localization. The localized deformation was investigated in areas that contain significantly different microstructural features typical of ECAP processed aluminum. It was found that areas of the UFG microstructure containing primarily low angle grain boundaries deformed by dislocation slip and behaved similarly to a coarse-grained material. The greatest strain localization occurred at high angle grain boundaries (HAGBs) separating distinct microstructure regions and with median surface trace angles of approximately 26.6°. In areas of banded microstructure, shear strain localization as high as 30% and shear displacements of up to 500 nm occurred at the HAGBs separating bands, suggesting grain boundary sliding. Copyright © 2014 Materials Research Society.
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    Microstructure evolution of Al-7wt%Si-2wt%Fe alloy processed by high-pressure torsion
    (2018-08-14)
    Wongsa-Ngam, Jittraporn
    ;
    Phongphisutthinan, Chakkrist
    ;
    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
    ;
    Wongsa-Ngam, Jittraporn
    ;
    Jimenez, Hernando
    ;
    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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    The microstructure length scale of strain rate sensitivity in ultrafine-grained aluminum
    (2015-04-14)
    Kammers, Adam D.
    ;
    Wongsa-Ngam, Jittraporn
    ;
    Langdon, Terence G.
    ;
    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<sup>-5</sup> s<sup>-1</sup> and 3.0 × 10<sup>-3</sup> s<sup>-1</sup>. 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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    Microstructural evolution and grain refinement in a Cu-Zr alloy processed by high-pressure torsion
    (2014-01-01)
    Wongsa-Ngam, Jittraporn
    ;
    Langdon, Terence G.
    A copper alloy, Cu-0.1% Zr, was processed at room temperature by high-pressure torsion (HPT) in order to evaluate the microstructural evolution and grain refinement mechanism. Transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) techniques were employed to measure the grain morphology, grain size distributions and the distribution of the misorientation angles. The results demonstrate that this processing procedure has a potential for producing an ultrafine-grain structure containing reasonably equiaxed grain with high-angle boundary misorientations. The grain refinement mechanism is primarily governed by dislocation activities. © (2014) Trans Tech Publications, Switzerland.
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    Microstructural evolution of cryomilled Ti/Al mixture during high-pressure torsion
    (2014-02-28)
    Bahmanpour, Hamed
    ;
    Sun, Yu
    ;
    Hu, Tao
    ;
    Zhang, Dalong
    ;
    Wongsa-Ngam, Jittraporn
    To provide insight into the influence of the length scale on the kinetics of phase evolution during severe plastic deformation, we studied the microstructure evolution of cryomilled Al and Ti mixture, which is further subjected to high-pressure torsion (HPT). The cryomilled microstructure consisted of elemental Al and Ti, and the subsequent HPT deformation at ambient temperature led to the solid state formation of Al-rich intermetallics. X-ray diffraction peaks originating from TiAl2 and TiAl3 were observed after one revolution of HPT, suggesting a shear strain-assisted formation of the intermetallics. A high resolution transmission electron microscope confirmed the formation of TiAl2 following HPT for one revolution. Further HPT straining led to microstructure refinement and a mixing of the Ti and Al, as well as of any phases formed initially. The solid state formation of the intermetallics and the overall evolution of the microstructure are discussed based on the generation of a high density of lattice defects that evolve under the strain conditions present during HPT.