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질소 이온 주입시킨 7050Al 합금의 표면 미세구조 변화와 저주기 피로거동
이창우,권숙인 ( C . W . Lee,S . I . kwun ) 한국열처리공학회 1994 熱處理工學會誌 Vol.7 No.4
The surface microstructure modification by N^+ ion implantation into 7050Al alloy and its low cycle fatigue behavior were investigated. Ion implantation method is to physically implant accelerated ions to the surface of a substrate. High dose of nitrogen(5×10^(17)ions/㎠) were implanted into 7050Al alloy using current density of accellerating voltage of 100KeV. The implanted layers were characterized by Electron Probe-Micro Analysis(EPMA), Auger Elecron Spectroscopy(AES), X-Ray Diffraction(XRD), X-Ray Photoelectron Spectroscopy(XPS), and Transmission Electron Microscopy(TEM). The experimental results were compared with computer simulation data. It was shown that AlN was formed to 4500Å deep. The low cycle fatigue life of the N^+ ion modified material was prolonged by about three times the unimplanted one. The improved low cycle fatigue life was attributed to the formation of AIN and the damaged region on the surface by N^+ ion implantation.
SM40C 강의 열처리가 피로균열전파속도에 미치는 영향
금창훈,권숙인 ( C . H . Keum,S . I . Kwun ) 한국열처리공학회 1990 熱處理工學會誌 Vol.3 No.2
The effect of the microstructural change on the near threshold fatigue crack growth rate in SM40C steel has been studied using the ΔK decreasing method. Below the total strain amplitude of 0.56%, cyclic softening occured, whereas above this value cyclic hardening occurred in the pearlitic lamellar structure. However, in the spherodized structure the cyclic hardening solely occurred. The crack growth rate in the near-threshold region was decreased with increasing prior austenite grain size and this was due to surface roughness. The crack growth rate of the spherodized structure was lower than that of the pearlite lamellar structure and the ΔK_(th) of the former was higher than that of the latter. It was understood that the crack propagates preferentially through the ferrite phase. The intergranular facets in the near-threshold region appeared in the spherodized structure.