Ti-15V-7AI合金の焼戻しに伴う組織変化

摘要

P型Ti合金は軽量，高強度，耐食性，生体親和性に 優れ，構造材料だけでなく機能材料としても注目され ている.しかし，時効処理で形成されるω相は非常に 脆いため，ω相の生成を抑制する目的で一般にA1が添 加される.β下限組成にA1を7%添加した合金では 形状記憶や形状進展といった特異な現象が現れること が最近明らかになってきた.この現象は焼戻しによ ってβ母相からα"マルテンサイトが形成されることに 起因する。本研究では，この組成条件を満たす Ti-15V-7Al(以後15VAと呼称）合金の焼戻しに伴う組 織変化を調べた.%Microstructure, crystal structure, and hardness evolution with tempering on Ti-15V-7Al alloy have been investigated. A rapid quenching from the β-field to an iced water retained most of p-phase. Short time tempering at 550℃ formed acicular products observable by OM overall. Because the composition distribution of the products was hardly detected by STEM-EDS, they were regarded as martensites. However, these products disappeared in OM level by prolonging time more than 3min, and the hardness remarkably increased. With heating of the U-shaped quenched specimen, the shape recovery slightly occurred preceding the spontaneous bending.