[SY-C9] Interstitial Shuffling Mechanism for Solute-Induced Embrittlement of Titanium
Invited
The exceptional sensitivity of the strength of Ti alloys to low concentrations of interstitial O arises from a mechanism akin to steric hindrance [1]. The equilibrium interstitial sites of the O atoms are highly distorted and compressed during the passage of a dislocation. The presence of an O atom at this site resists this distortion and compression inhibiting the passage of the dislocation and strengthening the metal. However, this strength increase is also correlated with embrittlement of the metal. We identify a dislocation-induced interstitial shuffling mechanism that can explain the observed O-induced embrittlement of Ti [2]. Molecular dynamics simulations show that the passage of a dislocation can move a fraction of the O interstitials from their equilibrium octahedral sites into adjacent hexahedral sites. The excess number of O interstitials in hexahedral sites is metastable and will eventually return to equilibrium. However, simulations of the dislocation/O interstitial interaction predict that an O atom in the hexahedral site presents a weaker obstacle to dislocation slip than an O atom in the octahedral site. Under typical strain rates, the time between dislocation passage on the slip plane is less than the estimated typical residence time for an O atom in the hexahedral site. The implication is that the passage of the first dislocation on the slip plane leads to softening for the subsequent dislocations. Subsequent dislocations may the further soften the slip plane through the same mechanism. This slip plane softening is expected to lead to planar slip, and the stress concentrations associated with planar slip then lead to the embrittlement of the metal. This work is supported by the U. S. Office of Naval Research under grant N00014-16-1-2304 and employed computational resources of the National Science Foundation under grant ACI-1053575.
[1] Q. Yu et al., Science 347, 635-639 (2015).
[2] M. Poschmann et al., to be published.
[1] Q. Yu et al., Science 347, 635-639 (2015).
[2] M. Poschmann et al., to be published.