Byungmin Ahn

Learn More
Aluminum alloys with nanocrystalline (NC) and ultrafine grain (UFG) size are of interest because of their strengths that are typically 30 pct greater than conventionally processed alloys of the same composition. In this study, UFG AA 5083 plate was prepared by quasi-isostatic (QI) forging of cryomilled powder, and the microstructure and mechanical behavior(More)
Al–Mg alloy powder was mechanically milled in liquid N2 (cryomilling) to produce thermally stable powder with nanocrystalline (NC) microstructure for the manufacture of high-strength alloys. A multi-scale microstructure was achieved by blending unmilled coarse-grained (CG) powder with cryomilled powder and subsequently consolidating. The final bulk alloy(More)
Dynamic observations of deformation in an ultrafine-grained Al-Mg alloy with bimodal grain structure " Abstract: The tensile properties and deformation response of an ultrafine-grained (UFG) Al–Mg alloy with bimodal grain structure were investigated using a micro-straining unit and a strain mapping technique. Atomized Al 5083 powder was ball-milled in(More)
To assess potential routes for the production of high-strength Al 5083, gas-atomized powder was cryogenically ball-milled, to obtain a nanocrystalline structure, then hot vacuum degassed and consolidated by two methods: (1) hot isostatic pressing (HIPping) and extrusion, and (2) two-step quasi-isostatic (QI) forging. The consolidated billet in both cases(More)
Uniform GaN nanorod arrays are grown vertically by selective area growth on (left angle bracket 0001 right angle bracket) substrates. The GaN nanorods present six nonpolar {1⁻100} facets, which serve as growth surfaces for InGaN-based light-emitting diode quantum well active regions. Compared to growth on the polar {0001} plane, the piezoelectric fields in(More)
Al–Mg alloy powder was cryomilled to achieve a nanocrystalline (NC) structure having an average grain size of 50 nm with high thermal stability, and then consolidated by quasi-isostatic forging. The consolidation resulted in a bulk material with ultrafine grains of about 250 nm, and the material exhibited enhanced strength compared to conventionally(More)
We demonstrate that nonpolar m-plane surfaces can be generated on uniform GaN nanosheet arrays grown vertically from the (0001)-GaN bulk material. InGaN/GaN multiple quantum wells (MQWs) grown on the facets of these nanosheets are demonstrated by cross-sectional transmission electron microscopy. Owing to the high aspect ratio of the GaN nanosheet structure,(More)
Lower green density Lower green density ƒ ƒ Smaller Smaller porosity porosity ƒ ƒ Smaller Smaller inter inter-particle distance particle distance Higher green density Higher green density 500 500 º ºC C 415 415 º ºC C 440 440 º ºC C ∴ ¾ The prior particle boundaries are still clearly observed The prior particle boundaries are still clearly observed ¾ ¾(More)
Disks of commercial Al-1050 and ZK60A alloys were stacked together and then processed by conventional high-pressure torsion (HPT) through 1 and 5 turns at room temperature to investigate the synthesis of an Al–Mg alloy system. Measurements of microhardness and observations of the microstructures and local compositions after processing through 5 turns(More)
  • 1