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원심주조법으로 제조된 Ti-(2 ~ 6) A1-4Fe-(0.5, 1) Si 합금의 미세조직과 기계적 특성
현용택,김승언,이용태,정희원 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.1
Ti-4Fe-(0.5, 1)Si had been investigated as a preliminary study for the development of a new titanium alloy having a low cost and high strength. The tensile strength of these alloys was comparable to that of a Ti-6Al-4V at room temperature, while lower at 400℃. For this reason, Ti-4Fe-(0.5, 1)Si-xAl (x = 2∼6 wt%) alloy system was redesigned to improve tensile strength even at 400℃ as well as at room temperature. In general, the new alloys exhibited the prior β grain size and the aspect ratio of a phase decreased with increasing Al content. The Ti_5Si₃ phase was precipitated mainly at β grain boundary in as-cast specimens. However, almost of the Ti_5Si₃ phase was transformed into Ti₃Si phase after HIP. The addition of Al to Ti-4Fe-(0.5, 1)Si alloy made the size of silicides finer, while in the case of Ti-4Fe-1Si-(2∼6)Al system coarse silicides were formed. The coarse silicides were formed mainly at grain boundary and decreased the ductility of the alloys at room temperature and at 400℃. After systematic investigation of these alloy system, suggested optimum composition is Ti-6Al-4Fe-0.5Si. Ultimate strength of this alloy was 1191 ㎫, and 930 ㎫ at room temperature, and at 400℃, respectively. These properties are superior to those of Timetal 62S as well as those of Ti-6Al-4V.
Ti-6Al-2Sn-4Zr-6Mo 합금의 고온압축 변형거동
현용택,이용태,이찬규,Hyun, Yong-Taek,Lee, Yong-Tai,Lee, Chan-Gyu 한국재료학회 2001 한국재료학회지 Vol.11 No.2
Ti-6Al-2Sn-4Zr-6Mo(Ti6246) 합금의 고온 변형거동을 조사하기 위하여 $\alpha$+$\beta$ 영역 및 $\beta$영역의 온도에서 $10^0s^{-1}$에서 $10^{-3}s^{-1}$의 변형속도로 압축시험을 수행하였다. 유동응력은 변형속도가 증가하고 시험 온도가 감소함에 따라 증가하였다 90$0^{\circ}C$ 이하에서 시험한 결과로부터 얻어진 유동곡선은 가공연화 현상을 나타내었으나, 이 합금의$\beta$영역인 95$0^{\circ}C$ 이상에서는 유동응력이 지속적으로 증가하다가 정상 상태를 나타냈다. 압축시험 결과로부터 얻은 유동곡선 분석을 통하여 유동응력의 변형량, 변형속도 및 온도에 대한 관계로부터 이 합금에 대한 구성방정식을 구하였다. The hot deformation behavior of Ti-6Al-2Sn-4Zr-6Mo(Ti6246) alloy was investigated in both the $\alpha$+$\beta$ and $\beta$-phase fields by conducting compression tests over a strain rate range of $10^{-3}s^{-1}$ to $10^0s^{-1}$. The flow stress was increased with increasing strain rate and decreasing test temperature. The flow curves obtained at temperatures below 90$0^{\circ}C$ exhibited a flow softening. However, in the $\beta$-phase field, above 95$0^{\circ}C$, the flow stress increased monotonically with plastic strain approaching steady state values. Constitutive equations for the dependence of flow stress on strain, strain rate, and temperature were developed through the analysis of the flow curves.
저비용 고강도 Ti-Fe-Si 합금의 상온 및 고온 인장 특성
현용택,김승언,이용태,정희원 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.9
A TFS(Ti-xFe-ySi) alloy system has been newly designed for a high strength titanium alloy with low cost. In this study, Fe was selected as β-stabilizer to replace expensive β-stabilizing elements such as V, Mo. In addition, Si was selected as third element to compensate the high temperature mechanical properties. Fe contents of over 4 wt% stabilize β phase even at room temperature. Coarse silicide chain was formed at prior β grain boundary in TFS alloys containing over 2 wt% of Si, and deteriorated the mechanical properties. Fe was dissolved in Ti matrix as solid solution and increased α/β phase boundaries. Si was also dissolved as solid solution or precipitated finely in Ti matrix. The optimum composition range was Ti-4Fe-(0.5∼1)Si. Ultimate tensile strength was a range of 799∼831 ㎫ at room temperature and 532∼585 ㎫ at 400℃ which are comparable to Ti-6Al-4V.