Origin of dramatic oxygen solute strengthening effect in titanium

チタンにおける劇的な固溶強化機構の起源

Yu, Q.*; Qi, L.*; 都留 智仁   ; Traylor, R.*; Rugg, D.*; Morris, J. W. Jr.*; Asta, M.*; Chrzan, D. C.*; Minor, A. M.*

Yu, Q.*; Qi, L.*; Tsuru, Tomohito; Traylor, R.*; Rugg, D.*; Morris, J. W. Jr.*; Asta, M.*; Chrzan, D. C.*; Minor, A. M.*

溶質元素がらせん転位の長距離弾性場と弱い相互作用をすることを考慮して、固溶硬化は可動転位と比較的弱い影響しか持たないとこれまで考えられてきた。この考えは転位芯との強い相互作用を示した第一原理計算によって覆されようとしている。我々は六方晶のチタンを対象に実験と計算から顕著な強化機構について検討を行った。高解像度その場観察電子顕微鏡を駆使して、柱面を運動するらせん転位と酸素が非常に強い相互作用をすることを示した。また、第一原理計算から、格子間型の溶質酸素が転位芯と短距離ながら強い結合を生じることを明らかにした。これらは酸素原子近傍の転位のピン留め機構を生じ、従来の知見と異なり格子間固溶元素が強化機構に重要な役割を持つことを示している。

Given that solute atoms interact weakly with the long-range elastic fields of screw dislocations, it has long been accepted that solution hardening is only marginally effective in materials with mobile screw dislocations. This accepted wisdom has recently been questioned by first-principles calculations suggesting that solutes may interact much more strongly with the screw dislocation core. We report here the results of a combined experimental and computational study undertaken to elucidate the profound hardening effect of oxygen in pure hexagonally-close-packed structured -Ti. High resolution and in situ transmission electron microscopy nanomechanical characterization establish that the strengthening is due to the strong interaction between oxygen and the core of screw dislocations that mainly glide on prismatic planes. First-principles calculations of the screw dislocation core reveal a simple crystallographic source for the oxygen-dislocation interaction that is consistent with experimental observations. The distortion of the interstitial sites at the dislocation core creates a very strong but short-range repulsion for oxygen atoms. These mechanisms effectively pin the dislocation near the oxygen interstitial. These results establish a highly effective mechanism for strengthening by interstitial solutes that, contrary to prior understanding, may be significant in many structural alloys.