TY - JOUR
T1 - Oxygen in Ti-(Cr, Mn)-Si icosahedral phases and approximants
AU - Libbert, J. L.
AU - Kim, J. Y.
AU - Kelton, K. F.
PY - 1999/9
Y1 - 1999/9
N2 - Nearly single-phase icosahedral quasicrystals can be obtained in Ti-Cr and Ti-Mn alloys by rapid quenching, when the amounts of silicon and oxygen are carefully controlled. The role of phase stabilization by these elements, however, is unknown. Here, the essential role of both oxygen and silicon for the formation of phases with local icosahedral symmetry is demonstrated in these alloys. Rapidly quenched and as-cast samples of Ti-Cr-Si and Ti-Mn-Si alloys made without oxygen form primarily the β solid solution phase. In contrast as-cast alloys of Ti-Cr-Si containing more than 10at.% oxygen and Ti-Mn-Si alloys made with more than 6at.% oxygen contain significant quantities of the 1/1 crystal approxi-mant. Correspondingly, as-quenched alloys of these compositions form the icosahedral phase. Annealing studies of samples containing the 1/1 phase demonstrate that the oxygen has a thermodynamic rather than a kinetic role in phase stabilization. It is likely that the oxygen atoms bind with Ti atoms, forming a network of octahedra in the undercooled liquid. These octahedra then become natural building blocks for the double-shell Mackay icosahedra.
AB - Nearly single-phase icosahedral quasicrystals can be obtained in Ti-Cr and Ti-Mn alloys by rapid quenching, when the amounts of silicon and oxygen are carefully controlled. The role of phase stabilization by these elements, however, is unknown. Here, the essential role of both oxygen and silicon for the formation of phases with local icosahedral symmetry is demonstrated in these alloys. Rapidly quenched and as-cast samples of Ti-Cr-Si and Ti-Mn-Si alloys made without oxygen form primarily the β solid solution phase. In contrast as-cast alloys of Ti-Cr-Si containing more than 10at.% oxygen and Ti-Mn-Si alloys made with more than 6at.% oxygen contain significant quantities of the 1/1 crystal approxi-mant. Correspondingly, as-quenched alloys of these compositions form the icosahedral phase. Annealing studies of samples containing the 1/1 phase demonstrate that the oxygen has a thermodynamic rather than a kinetic role in phase stabilization. It is likely that the oxygen atoms bind with Ti atoms, forming a network of octahedra in the undercooled liquid. These octahedra then become natural building blocks for the double-shell Mackay icosahedra.
UR - https://www.scopus.com/pages/publications/0039521825
U2 - 10.1080/01418619908210418
DO - 10.1080/01418619908210418
M3 - Article
AN - SCOPUS:0039521825
SN - 0141-8610
VL - 79
SP - 2209
EP - 2225
JO - Philosophical Magazine A: Physics of Condensed Matter, Structure, Defects and Mechanical Properties
JF - Philosophical Magazine A: Physics of Condensed Matter, Structure, Defects and Mechanical Properties
IS - 9
ER -