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Ti-6Al-4V 합금의 α 상 형상이 초소성 변형거동에 미치는 영향
김용석,장영원,송진화 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.10
The superplastic deformation behavior of Ti-6Al-4V alloy with two different microstructures, a banded microstructure with continuous a phase and an equiaxed microstructure, was investigated by performing both strain-rate-change and constant-strain-rate tests in a longitudinal direction. It was found that the continuous a phase significantly affect the superplastic deformation behavior of the alloy. At 925℃ the continuous α phase remained unbroken during deformation causing higher flow stress at lower strain rate range and tow value of strain rate sensitivity, m. At lower temperature below 880℃, on the other hand, the α phase was broken up to recrystallize dynamically resulting in higher m values at 850 and 880℃. The m values of the cross rolled materials which do not have the continuous α phase steadily increased with temperatures up to 880℃ and did not show a significant decrease at 925℃ contrary to the unidirectionaliy rolled materials.
김용석,장영원,송진화 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.10
Erosion tests were performed on mild steel, 304, 310, 410 stainless steel and Inconel 600 superalloy in the air at room temperature using round Al₂O₃ pariticles. Erosion rates were calculated and eroded surfaces were examined using SEM. SEM observations indicated that platelet formation was a major erosion mechanism and size of the platelet was inversely proportional to the erosion rate. The erosion characteristics was investigated using the localized deformation model. It was found that the localized deformation model characterizes the erosion test results and strain hardening coefficient is the most influential parameter to the model Strain hardening coefficient at the early stage of plastic deformation during simple tensile tests of the alloys could qualitatively explain the difference of erosion rates among the tested materials.
김용석,장영원,송진화 대한금속재료학회(대한금속학회) 1997 대한금속·재료학회지 Vol.35 No.3
Isothermal forgings of mill-annealed, unidirectionally-rolled, and cross-rolled Ti-6Al-4V alloys were performed at temperatures of 830, 880 and 925℃ with the true strain rates of 1×10^(-3)/sec and 5×10^(-3)/sec. Flow stresses and microstructural evolution of the specimens during the forging were characterized. The flow behavior and microstructural changes during forging have been found to depend on initial microstructure of the specimens and forging conditions. Dynamic recrystallization and strain softening occurred in unidirectionally-rolled specimens, which had elongated α grains. On the other hand, mill-annealed and cross-rolled specimens, of which initial microstructure do not have elongated α grains, did not show distinct dynamic recrystallization under the same forging conditions. It was also shown that the Zener-Hollomon parameter is a good factor to characterize the steady-state stresses and the final grain size of the unidirectionally-rolled specimens during/after the forging under the given conditions.
Cr-N 피막처리된 쾌삭 Ti-3Al-2V 합금의 미끄럼마모 거동
김용석,이용태,이영백,송진화,정재인 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.1
The sliding wear behavior of the chromium nitride (CrN and a composite CrN+Cr₂N) coated Ti-3Al-2V free machining titanium alloy against heat-treated tool steel was investigated. The wear test was carried out using a ring--on-disc type tester under dry and lubricated conditions. Under the applied stress of 6.5 MPa and dry wear condition the chromium nitride coatings started to be peeled off from the substrate through pitting and micro fragmentation processes. The hard debris of the detached and crushed coatings worked as abrasives, which accelerated the wear even though the coefficient of friction was lowered by them. The effect of precleaning, such as sputtering, on the wear resistance was more significant under the dry wear condition than under the lubricated condition. Under the lubricated condition the wear resistance of the coated specimen increased a lot compared with the dry condition and the variation of the friction load decreased. Good correlation between the wear rates and low coefficient of friction was also observed under the lubricated condition.
김용석,송진화 대한금속재료학회(대한금속학회) 1996 대한금속·재료학회지 Vol.34 No.12
The solid particle erosion behavior of Fe-25 at.% Al iron aluminides(Fe₃Al) at room temperature has been investigated. It was found that the erosion rate of the aluminide increases as the impingement angle decreases, which is ductile erosion behavior. SEM observations revealed that lip formation and its subsequent detachment from the surface is the major erosion mechanism of the aluminide. Aluminides with the B2 structure showed higher erosion resistance than those with the DO₃ structure, however, the rate difference was not significant. The different erosion resistances among the aluminides with different phases were explained by the strain-hardening-rate differences.