Aging behaviour of Ti15Mo5Zr and Ti15Mo5Zr3Al alloy up to 573 K

Aging behavior of Ti15Mo5Zr (15-5) and Ti15Mo5Zr3Al (15-5-3) alloys isothermally aged below 573 K has been investigated mainly through resistometry. In the 15-5 alloy, resistivity at 77 K (ϱLN) increases only slightly, whereas the resistivity at room temperature (ϱRT) increases greatly. The ϱ of the 15-5-3 alloy shows the same tendency as that of the 15-5, but the increase in ϱ continues for a longer period and the increment is larger than in the 15-5 alloy. X-ray diffraction and hardness of the 15-5-3 suggest a long incubation period for the precipitation of the aged ω phase, in contrast to that of a 15-5 alloy aged between 623 K and 723 K. The increase in ϱRT of these alloys might be best interpreted as the concentration separation of β matrix, like GP zones in Al alloys, which contributes to a significant increase in ϱ but to only a minor increase in hardness. Also with α precipitation at high aging temperature, a slight increase is observed in ϱLN during an apparent incubation period. These results suggest that the concentration separation of β occurs at both high and low aging temperatures and that suppression of aged ω by Al addition makes the ϱ increase conspicuous.