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Author: search.filters.author.Langdon, Terence G.Subject: search.filters.subject.High-pressure torsion

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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
    ;
    Xu, Jie
    ;
    Phongphisutthinan, Chakkrist
    ;
    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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    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 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.