Abstract
The effect of the addition of oxygen on the formation of microstructure cooled from the β phase of Ti-Fe alloy was examined. The alloy ingots of Ti-(4, 5, 6, 7, 8, 9 and 10) at.% Fe and Ti-8 at.% Fe-(1 and 3) at.% O were arc-melted. They were homogenized at 1200 °C for 3.6 ks and then hot-rolled at 850 °C into 1.5-mm thick sheets. The disk specimen was fabricated and then put in the differential thermal analysis (DTA) apparatus. The disk in the DTA was heated at 1000 °C for 0.6 ks in the β phase and then cooled to room temperature at a rate of 50 °C/min. The microstructure was examined by an optical microscope after the DTA experiment. In the Ti-(7 and 8) Fe alloys the ω phase formed during cooling. The addition of oxygen in the Ti-8Fe alloy promoted the β→α transformation. Furthermore, the addition of one at.% oxygen in the Ti-8Fe alloy promoted β→ωi transformation, while the addition of three at.% oxygen suppressed the β→ωi transformation during cooling.
Highlights
Titanium alloys are used for aircraft, automobile, and medical materials because of their high specific strength, high heat resistance, and excellent corrosion resistance [1,2,3,4,5]
The exothermic peak of the transformation of ωi phase appeared at a temperature of 20 °C higher than that in the Ti-8Fe alloy, indicating the oxygen addition promoted the ωi phase formation
The temperature of the exothermic peak of ωi phase in Ti-8Fe-1O alloy appeared at a higher temperature than that in Ti-8Fe alloy, implying that the oxygen played as an ωi phase former in titanium alloy
Summary
Titanium alloys are used for aircraft, automobile, and medical materials because of their high specific strength, high heat resistance, and excellent corrosion resistance [1,2,3,4,5]. The addition of iron in a titanium alloy works as a β phase stabilizer. The addition of oxygen in a titanium alloy, on the other hand, works as an α phase stabilizer. The β→ωa and β→ωi transformation would be suppressed by the addition of oxygen [11,12]. The authors' group showed the β→ωa transformation in Ti-Nb alloy was suppressed by the oxygen addition [13]. Niinomi et al revealed the oxygen addition stabilized the ωi phase in the Ti-29Nb-13Ta-4.6Zr alloy [14]. The effects of oxygen addition on the transformation of the β→ωi phase are still under discussion. The effect of the oxygen addition on the formation of the ωi phase during cooling from the β phase in Ti-Fe alloy
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