• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.126-129
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• 2005

Microstructures and tensile properties of low carbon steels, 5083 Al alloy and Ti-6Al-4V alloy fabricated by equal channel angular pressing (ECAP) were examined in order to understand their deformation response associated with a formation of an ultrafine grained (UFG) structure. Room temperature tensile properties of UFG low carbon ferrite/pearlite steels and UFG ferrite/martensite dual phase steel were compared for exploring a feasibility enhancing the strain hardening capability of UFG materials. In addition, low temperature and high strain rate superplasticity of the two grades of the UFG 5083 Al alloy, and Ti-6Al-4V alloy were presented. From the analysis of a series of experiments, it was found that UFG materials exhibited the enhanced mechanical properties compared to coarse grained counterparts.

• Journal of Mechanical Science and Technology
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• v.16 no.10
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• pp.1246-1252
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• 2002

Ultrafine grained (UFG) low carbon (0.15 wt.% C) steel produced by equal channel angula. pressing (ECAP) was tested for investigating the effect of load ratio on the fatigue crack growth rate. Fatigue crack growth resistance and threshold of UFG steel were lower than that of asreceived coarse grained steel. It was attributed to the less tortuous crack path. The UFG steel exhibited slightly higher crack growth rates and a lower △Kth with an increase of R ratio. The R ratio effect on crack growth rates and △Kth was basically indistinguishable at lower load ratio (R >0.3), compared to other alloys, which indicates that contribution of the crack closure vanishes. The crack growth rate curve for UFG steel exhibited a longer linear extension to the lower growth rate regime than that for the coarse grained as-received steel.

• Corrosion Science and Technology
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• v.5 no.1
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• pp.23-26
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• 2006

Recent development of ultrafine grained (UFG) low carbon steels by using equal channel angular pressing (ECAP) and their room temperature tensile properties are reviewed, focusing on the strategies overcoming their inherent mechanical drawbacks. In addition to ferrite grain refinement, when proper post heat treatments are imposed, carbon atom dissolution from pearlitic cementite during ECAP can be utilized for microstructural modification such as uniform distribution of nano-sized cementite particles or microalloying element carbides inside UFG ferrite grains and fabrication of UFG ferrite/martensite dual phase steel. The utilization of nano-sized particles is effective on improving thermal stability of UFG low carbon ferrite/pearlite steel but less effective on improving its tensile properties. By contrast, UFG ferrite/martensite dual phase steel exhibits an excellent combination of ultrahigh strength, large uniform elongation and extensive strain hardenability.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.263-266
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• 2009

Transformation induced plasticity (TRIP) steel consisting of ferrite, austenite, and bainite phases was regarded as an excellent candidate for automotive applications due to the good combination of ductility and strength. The aim of the present study was to understand the microstructural characteristics of ultrafine grained (UFG) TRIP low-carbon steel fabricated via equal channel angular pressing accompanied with intercritical- and isothermal-annealing treatments. When compared to coarse grained counterpart, only the volume fraction of austenite phase in UFG TRIP steel remained unchanged, but all other microstructural variables such as size and morphology were different. It was found that UFG TRIP steel showed the homogeneous distribution of each constituent phase, which was discussed in terms of annealing treatments done in this study.

• Transactions of Materials Processing
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• v.15 no.2 s.83
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• pp.105-111
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• 2006

A study was made to investigate the microstructure and the mechanical properties of low-carbon steel, Al-Mg alloy and Ti-6Al-4V alloy each representing bcc, fcc and hcp crystal structures, respectively fabricated by equal-channel angular(ECA) pressing. After a series of ECA pressings was performed, most grains were significantly refined below ${\mu}m$ in diameter with high mis-orientation of grain boundaries irrespective of different crystal structure used. Regarding the strain hardening capability, tensile tests of ultrafine grain (UFG) dual-phase (ferrite/martensite) steel which was different from UFG ferrite-pearlite steel were carried out at ambient temperature, and corresponding mechanical properties were discussed in relation to modified C-J analysis. Low-temperature and/or high strain-rate superplasticity of the UFG Al-Mg alloy and UFG Ti-6Al-4V alloy were also studied. Based on the analysis used in this study, it was concluded that UFG alloys exhibited the enhanced mechanical properties as compared to coarse-grained (CG) counterparts.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.263-265
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• 2009

In this study, ultrafine grained (UFG) oxygen free high conductivity copper (OFHC Cu) having two different grain morphologies, one the severely elongated and the other the equiaxed, was prepared by equal channel angular pressing (ECAP) with routes A and $B_c$, respectively. The results of quasi-static tensile tests at $10^{-1}\;s^{-1}$ and $1\;s^{-1}$ and dynamic compression tests at $10^3\;s^{-1}$ order revealed that the equiaxed UFG Cu exhibited higher strength and less ductility compared to the elongated one. The difference of the plastic flow characteristics between the two were rationalized by considering their dislocation mean free length based on the orientation relationship between the possible slip planes and the loading direction.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.6.2-6.2
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• 2009

Ultra-fine grained (UFG) Al alloys, which have submicron grain structures, are expected to show outstanding high strength at ambient temperature and excellent superplastic deformation at elevated temperatures and high strain rate. In order to get the UFG microstructure, various kind of severe plastic deformation (SPD) processes have been developed. Among these processes, accumulative roll bonding (ARB) process is a promising process to make bulky Al sheets with ultrafine grained structure continuously. The purpose of the present study is to clarify the grain refinement mechanism during the ARB process and to investigate on the effects of ultra-fine grained structure on the mechanical properties. In addition, UFG AA8011 alloy (Al-0.72wt%Fe-0.63wt%Si) manufactured by the ARB had fairly large tensile elongation, keeping on the strength. In order to clarify the reason for the increase of elongation in the UFG AA8011 alloy, detailed microstructural and crystallographic analysis was performed by TEM/Kikuchi-line and SEM/EBSP method. The unique tensile properties of the UFG AA8011 alloy could be explained by enhanced dynamic recovery at ambient temperature, owing to the large number of high angle boundaries and the Al matrix with high purity.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.215-218
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• 2006

A study was made to investigate microstructural evolution and mechanical properties of ultra-fine grained (UFG) pure-Ti produced by equal channel angular (ECA) pressings. The deformed structures were analyzed by finite element method and transmission electron microscopy with the increment of straining. After 4 isothermal ECA pressings, initial coarse grains ($30{\mu}m$) were significantly refined to ${\sim}0.3{\mu}m$ with homogeneous distribution of microstructure which was resulted from $180^{\circ}$ rotation of the sample between pressings. UFG pure-Ti exhibited the considerable improvement in yield strength while losing strain hardening capacity as compared to coarse grained microstructure at ambient temperature, which was mainly attributed to ultra-fine grain microstructure with non-equilibrium grain boundaries.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.30-30
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• 2008

• Korean Journal of Materials Research
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• v.22 no.11
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• pp.615-619
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• 2012

Recently, ultrafine grained (ufg, typically 100 > d > 500 nm) Ti-Fe eutectic materials have been highlighted due to their extraordinarily high strength and good abrasion resistance compared to conventional coarse grained (cg, d > $1{\mu}m$) materials. However, these materials exhibit limited plastic strain and toughness during room temperature deformation due to highly localized shear strain. Several approaches have been extensively studied to overcome such drawbacks, such as the addition of minor elements (Sn, Nb, Co, etc.). In this paper, we have investigated the influence of the addition of Gd and Y contents (0.3-1.0 at.%) into the binary Ti-Fe eutectic alloy. Gd and Y are chosen due to their immiscibility with Ti. Microstructural investigation reveals that the Gd phase forms in the eutectic matrix and the Gd phase size increases with increasing Gd content. The improvement of the mechanical properties is possibly correlated to the precipitation hardening. On the other hand, in the case of Ti-Fe-Y alloys, with increasing Y contents, primary phases form and lamellar spacing increases compared to the case of the eutectic alloy. Investigation of the mechanical properties reveals that the plasticity of the Ti-Fe-Y alloys is gradually improved, without a reduction of strength. These results suggest that the enhancement of the mechanical properties is closely related to the formation of the primary phase.