AGING BEHAVIOR OF TI-15MO-5ZR AND TI-15MO-5ZR-3AL ALLOY UP TO 573 K

Aging behavior of Ti-15Mo-5Zr (15-5) and Ti-15Mo-5Zr-3Al (15-5-3) allo ys isothermally aged below 573 K has been investigated mainly through resistometry. In the 15-5 alloy, resistivity at 77 K (rho(LN)) increas es only slightly, whereas the resistivity at room temperature (rho(RT) ) increases greatly. The rho of the 15-5-3 alloy shows the same tenden cy as that of the 15-5, but the increase in rho continues for a longer period and the increment is larger than in the 15-5 alloy. X-ray diff raction and hardness of the 15-5-3 suggest a long incubation period fo r the precipitation of the aged omega phase, in contrast to that of a 15-5 alloy aged between 623 K and 723 K. The increase in rho(RT) of th ese alloys might be best interpreted as the concentration separation o f beta matrix, like GP zones in Al alloys, which contributes to a sign ificant increase in rho but to only a minor increase in hardness. Also with alpha precipitation at high aging temperature, a slight increase is observed in rho(LN) during an apparent incubation period. These re sults suggest that the concentration separation of beta occurs at both high and low aging temperatures and that suppression of aged omega by Al addition makes the rho increase conspicuous.