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Ti-4Al-4Fe-0.25Si 합금의 고온변형거동과 미세조직발달에 관한 연구
원종우,이용문,염종택,이기영,이종수 대한금속재료학회(구 대한금속학회) 2016 대한금속·재료학회지 Vol.54 No.5
Hot deformation behavior of Ti-4Al-4Fe-0.25Si alloy with martensite microstructure was investigated by compression tests at temperatures of 1023 - 1173 K (α+β phase region) and strain rates of 10-3 - 1 s-1. By analyzing the deformation behavior, plastic deformation instability parameters including strain rate sensitivity, deformation temperature sensitivity, efficiency of power dissipation, and Ziegler’s instability were evaluated as a function of deformation temperature and strain rate, and they were further examined by drawing deformation processing maps. The microstructure evolution was also studied to determine the deformation conditions under which equiaxed α phase was formed in the microstructure without remnants or kinked α phase platelets and shear bands, these last two of which cause severe cracks during post-forming process. Based on the combined results of the processing maps and the microstructure analysis, the optimum α+β forging conditions for Ti-4Al-4Fe-0.25Si alloy were determined. (Received January 20, 2016)
원종우,Chan Hee Park,이태경,이종수 대한금속·재료학회 2014 METALS AND MATERIALS International Vol.20 No.6
The aim of this work is to develop a constitutive model that can predict the flow behavior of pure Ti withdifferent interstitial concentrations and grain sizes. To build a database required for identifying materialconstants, three different grades of Ti were subjected to tensile tests at temperatures of 223, 300, 473, 673or 773 K and at a fixed strain rate of 103 s1. In the modeling procedure, the mechanical threshold stressmodel was further modified to capture both the hardening effects attributed to the changes in equivalentoxygen concentration (Oeq) and the softening effect caused by deformation heating at high strain rates. Thedeveloped model can reasonably predict the flow behavior of pure Ti having different Oeq (0.14-0.32 wt%),and grain size (14.5-90 μm) over a temperature range of 135 to 673 K, and a strain rate range of 2×104 to1400 s1.
Edge‑Cracking Behavior of CoCrFeMnNi High‑Entropy Alloy During Hot Rolling
원종우,Minju Kang,Heoun‑Jun Kwon,Ka Ram Lim,Seong Moon Seo,Young Sang Na 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.6
This work investigated edge-cracking behavior of equiatomic CoCrFeMnNi high-entropy alloy during hot rolling at rollingtemperatures 500 ≤ TR ≤ 1000 °C. Edge cracks did not form in the material rolled at 500 °C, but widened and deepened intothe inside of plate as TR increased from 500 °C. Edge cracks were most severe in the material rolled at 1000 °C. Mn–Cr–Otype non-metallic inclusion and oxidation were identified as major factors that caused edge cracking. The inclusions nearedge region acted as preferential sites for crack formation. Connection between inclusion cracks and surface cracks inducededge cracking. Rolling at TR ≥ 600 °C generated distinct inclusion cracks whereas they were not serious at TR = 500 °C, sonoticeable edge cracks formed at TR ≥ 600 °C. At TR = 1000 °C, significant oxidation occurred at the crack surface. Thisaccelerated edge crack penetration by embrittling the crack tip, so severe edge cracking occurred at TR = 1000 °C.
Role of Deformation Twins in Static Recrystallization Kinetics of High-Purity Alpha Titanium
원종우,이태경,홍성구,Yongmoon Lee,이정훈,Chong Soo Lee 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.6
The importance of deformation twins in static recrystallization kinetics of high-purity alpha titanium was investigatedby carrying out thermal annealing tests of deformed materials in combination with electron-backscatterdiffraction-based microstructural analysis. Prior to thermal annealing, the material was compressed to a truestrain of 0.22 along three directions to introduce different twinning characteristics. Our results showed thatdeformation twins substantially promoted the static recrystallization process by deepening the microstructuralinhomogeneity induced by the formation of twin boundaries and twinning-induced crystallographic latticereorientation. Twin morphology was also observed to be important because it influenced the extent of microstructuralinhomogeneity. Intersecting twin morphology, caused by the activation of multiple twin variants, was moreeffective than parallel twin morphology, caused by the activation of a single twin variant (or a twin variantpair), because it gave rise to more twin boundaries, more twin boundary junctions (intersections, triplejunctions, etc.), and greater in-grain crystallographic orientation spread.