Science 347, 635–639 (2015)

Credit: AAAS

Introducing solute into a crystalline lattice is a known approach for strengthening materials; solute atoms cause localized lattice strain, making the passage of a dislocation more difficult. It is assumed however that screw dislocations do not substantially interact with solute, making only a small contribution to material strength. Qian Yu, Liang Qi and colleagues now perform a detailed mechanistic study of how oxygen solute can interact with screw dislocation cores in α-titanium. By performing in situ nanopillar compression and electron tomography of alloys with varying interstitial oxygen solute content, they observe that screw dislocations become tangled and pinned in samples with higher oxygen content, resulting in an approximate 8-fold increase in yield strength. Atomic-scale imaging and first-principles calculations reveal that the displacement of oxygen interstitials is more tightly confined at screw dislocation cores in higher oxygen samples, associated with which is a strong short-range repulsion for oxygen, causing pinning of screw dislocations.