Shogo Saeki 1, Sengo Kobayashi 1 and Satoshi Okano 1
1 Department of Materials Science and Biotechnology, Graduate School of Science and Engineering, Ehime University
The effect of oxygen addition on the spinodal decomposition and hardness variation of α″ martensite during aging in the Ti-4at%Mo alloy was investigated.Ti-4at%Mo-(0, 1.0, 1.5 and 3.0)at%O alloys were arc-melted. The alloy ingots were homogenized at 1473 K for 3.6 ks and then hot-rolled at 1123 K into a 1.5 mm thick sheet. Specimens were solution-treated at 1473 K for 0.6 ks and then quenched in iced brine. The solution-treated specimens were aged at 773 K for up to 86.4 ks. The addition of 3.0at% oxygen in the solution-treated Ti-4at%Mo alloy increased hardness about 200 Hv. The hardness of the alloys during aging at 773 K increased and then decreased showing maximum. The maximum hardness decreased as increasing in oxygen content in the alloy. A modulated structure formed in the α″ martensite laths during aging due to spinodal decomposition. The wave length of modulated structure by spinodal decomposition increased as increasing in oxygen content of the alloy, resulting in decrease of maximum hardness. Oxygen addition in the alloy suppressed spinodal decomposition due to increase of elastic energy for decomposition.
titanium, oxygen, alpha double prime phase, spinodal decomposition, hardness
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