EFFECT OF APPLIED STRESS ON FORMATION OF OMEGA-PHASE IN BETA-TI ALLOYS

Since omega-phase crystals in beta-Ti alloys formed by aging become nu cleation sites of omega-phase crystals due to further or high temperat ure aging, it is thought that this phenomenon can be utilized to produ ce stronger and more ductile (beta+alpha) duplex Ti alloys. In order t o form high density omega-phase crystals, the effects of a stress-agin g and hydrostatic pressurizing on the formation of omega-phase crystal s in Ti-20Mo and Ti-15Mo-5Zr alloys (mass%) were investigated using hi gh resolution electron microscopy and dark field imaging methods. The results obtained are as follows: (1) An aping under a stress of a half of the yield stress promotes the precipitation of high density omega- phase crystals. (2) Hydrostatic pressurizing also promotes the formati on of omega-phase crystals, and it is recognized that a hydrostatic pr essure of 0.7 GPa initiates to form omega-phase crystals in a Ti-20Mo alloy.