Effect of the solution treatments on the precipitation of a phase and the formation of precipitates free zone (PFZ) in a β titanium alloy, Ti-15V-3Cr-3Sn-3Al, is studied by optical and transmission electron microscopy. a phase precipitates homogeneously inside the β grain at the aging temperatures between 573 and 723K. However, the precipitation delay and the PFZ are observed in the vicinity of the β grain boundaries. These phenomena are strongly affected by the solution conditions and are considered to be caused by a effect of the excessive vacancies in the β grains.βチタン合金，Ti-15V-3Cr-3Sn-3Al，中のα相の析出と無析出帯(PFZ)の形成に及ぼす固溶化熱処理の影響を光学顕微鏡法と透過型電子顕微鏡法により研究した。α相は573-723Kの時効温度でβ結晶粒の内部に均一に析出する。しかし，β結晶粒界の近傍では析出の遅れとPFZが観察される。これらの現象は固溶化熱処理条件に強く影響され，β結晶粒中の過剰空孔の影響によって引き起こされているものと考えられる
