| 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. |
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