Structure and stability of precipitates in 500°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 investigated. 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 exposed at 550 degrees C for 24 h. The amount of precipitation increased with exposure time and the composition of the alpha phase changed gradually. EDX analysis on TEM samples showed increasing Al and Ti and decreasing V and Cr in the precipitates with exposure time. In samples which 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 the 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 beta TiVCrAl alloys. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.