In situ synchrotron radiation measurements of orthorhombic phase formation in an advanced TiAl alloy with modulated microstructure. Issue 1760 (2nd February 2015) - Baker, I.
ABSTRACT New low aluminium high niobium TiAl alloys exhibit a nano scale modulated microstructure consisting of lamellae with a tweed substructure. These tweed like appearing lamellae are a modulated arrangement of at least two phases. One constituent of the crystallographic modulation in the lamellae is an orthorhombic phase, which is closely related to both the hexagonal Î±2-Ti3Al phase and the cubic B2 ordered Î²o-TiAl phase. In this study the nature and formation of this orthorhombic phase has been investigated by high-energy X-ray diffraction. Measurements have shown that the newly formed orthorhombic phase is structurally comparable to the O phase (Ti2AlNb). It forms in the temperature range of 550 Â°C to 670 Â°C from the Î±2 phase by small atomic displacements and chemical reordering. The in situ experiments yielded information about the thermal stability of the orthorhombic phase. After dissolving at temperatures above 700 Â°C the phase can be re-precipitated by annealing within the temperature range of formation.