STRUCTURE AND STABILITY OF PRECIPITATES IN 500-DEGREES-C EXPOSED TI-25V-15CR-XAL ALLOYS

The effects of thermal exposure on microstructural changes in beta Ti- 25V-15Cr-(2-4)Al alloys (all compositions in wt%) have been investigat ed. Plasma melted alloys were either HIPped, extruded or forged before being exposed at 550 degrees C for 24-1000 h. It was found that alpha precipitation occurred in samples of Ti-25V-15Cr-3Al which were expos ed at 550 degrees C for 24 h. The amount of precipitation increased wi th exposure time and the composition of the alpha phase changed gradua lly. EDX analysis on TEM samples showed increasing Al and Ti and decre asing V and Cr in the precipitates with exposure time. In samples whic h were exposed at 550 degrees C for over 100 h alpha(2) was observed. The variation of Al from 2 to 4 wt% increased the precipitation and th e kinetics of alpha to alpha(2) ordering. The results are discussed in terms of the effects of Al and oxygen on alpha(2) precipitation in be ta TiVCrAl alloys. (C) 1998 Acta Metallurgica Inc. Published by Elsevi er Science Ltd. All rights reserved.