Young Bum Chun

Bio: Young Bum Chun is an academic researcher from Monash University. The author has contributed to research in topics: Recrystallization (metallurgy) & Slip (materials science). The author has an hindex of 20, co-authored 35 publications receiving 1337 citations. Previous affiliations of Young Bum Chun include Inha University & Monash University, Clayton campus.

Effect of deformation twinning on microstructure and texture evolution during cold rolling of CP-titanium

Abstract: The evolution of microstructure and texture during cold rolling of commercial-purity titanium (CP-Ti) was studied with particular reference to deformation twinning and dislocation slip. For low to intermediate deformation up to 40% in thickness reduction, the external strain was accommodated by slip and deformation twinning. In this stage, both compressive ( { 1 1 2 ¯ 2 } 〈 1 1 2 ¯ 3 ¯ 〉 ) and tensile ( { 1 0 1 ¯ 2 } 〈 1 0 1 ¯ 1 ¯ 〉 ) twins, as well as, secondary twins and tertiary twins were activated in the grains of favorable orientation, and this resulted in a heterogeneous microstructure in which grains were refined in local areas. For heavy deformation, between 60 and 90%, slip overrode twinning and shear bands developed. The crystal texture of deformed specimens was weakened by twinning but was strengthened by slip, resulting in a split-basal texture in heavily deformed specimens.

Distribution Characteristics of In-Grain Misorientation Axes in Cold-Rolled Commercially Pure Titanium and Their Correlation with Active Slip Modes

Abstract: The distribution characteristics of in-grain misorientation axes (IGMA) in cold-rolled pure titanium were investigated using electron backscatter diffraction (EBSD). Depending on the orientation of individual grains, two distinct IGMA distribution patterns were observed: one with strong intensities of IGMA around ⟨0001⟩ and the other with those around ⟨uvt0⟩. Analyses based on the Taylor axes and Schmid factors of possible slip modes suggested that the former pattern arises from predominant activation of prism ⟨a⟩ slip, while activation of $$ \{ 11\bar{2}2\} \langle \bar{1}\bar{1}23 \rangle $$ slip under the suppression of prism ⟨a⟩ slip results in the latter pattern. It was also found that prism ⟨a⟩ slip becomes more active with increasing strain, playing a critical role in the plasticity of pure titanium. The present work demonstrates that IGMA analysis of EBSD data may be used to explore the active slip mode in polycrystalline hexagonal-close-packed (hcp) metals deformed to moderate to large strains.

Investigation of Prism 〈 a 〉 Slip in Warm-Rolled AZ31 Alloy

Abstract: Based on analysis of texture and in-grain misorientation axes (IGMA) distribution, we investigate the effects of initial orientation and deformation temperature on the rollability of magnesium alloy AZ31 and the associated deformation mechanisms. Plate samples oriented favorably for basal 〈a〉 slip exhibited the best rollability at room temperature, whereas under the warm-rolling condition, surprisingly, the plate oriented for prism 〈a〉 slip exhibited the best rollability. The enhanced rollability of the latter plate is attributed to increased activity of prism 〈a〉 slip, which exhibits a lower texture hardening rate than basal 〈a〉 slip. The increased activity of prism 〈a〉 slip is shown experimentally by the development of the \( \langle 10\bar{1}0 \rangle \)//RD texture and 〈0001〉-type IGMA distribution. Asymmetric texture is also suggested to impair the rollability of plate oriented for basal 〈a〉 slip.

Twinning-induced negative strain rate sensitivity in wrought Mg alloy AZ31

Abstract: This paper reports the effects of the texture and strain on the strain rate sensitivity of wrought magnesium alloy AZ31. Specimens were prepared from strongly textured AZ31 plate such that the uniaxial loading direction was either parallel or perpendicular to the basal planes of the majority of grains. The strain rate sensitivity of the specimens was determined from strain rate jump tests in tension and in compression, and the microstructure evolution during the tests was tracked by electron backscatter diffraction microscopy of ex situ samples. Specimens oriented unfavorably for { 0 1 1 ¯ 2 } tension twinning show a decreasing strain rate sensitivity with increasing strain. In contrast specimens oriented favorably for tension twinning exhibited negative strain rate sensitivity at low strains followed at higher strains by positive strain rate sensitivity. The flow stress and consequently the strain rate sensitivity was modeled using an analytical constitutive equation. This model was able to account for not only the negative strain rate sensitivity of the samples undergoing tension twinning at low strains but also the observed trend of strain rate sensitivity with strain for all samples. From this we deduce that an increase in twinning activity with strain rate is responsible for the strain rate sensitivity.

Six decades of the Hall–Petch effect – a survey of grain-size strengthening studies on pure metals

Abstract: Refining a metal’s grain size can result in dramatic increases in strength, and the magnitude of this strengthening increment can be estimated using the Hall–Petch equation. Since the Hall–Petch equation was proposed, there have been many experimental studies supporting its applicability to pure metals, intermetallics and multi-phase alloys. In this article, we gather the grain-size strengthening data from the Hall–Petch studies on pure metals and use this aggregated data to calculate best estimates of these metals’ Hall–Petch parameters. We also use this aggregated data to re-evaluate the various models developed to physically support the Hall–Petch scaling.