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Abstract

An investigation including the use of transmission electron microscopy has been carried out into the solid state transformations in Ti–Al–Ru alloys in the composition range 17–37 at.-%Al and 1–5 at.-%Ru. Ruthenium is shown to be a strong β stabiliser: a 5 at.-%Ru addition produced complete or substantially complete retention of metastable β on quenching from 1250°C (within the stable β range). Three types of martensite can result by quenching from the β field, depending on the composition: a hexagonal martensite α′ in α + α₂ alloys with 1 at.-%Ru, an ordered hexagonal (DO₁₉) in alloys close to Ti₃Al stoichiometry with 1 at.-%Ru; an orthorhombic martensite in α + α₂ alloys with 2 at.-%Ru. On heating martensite or retained β in the range 1100–770°C, various transformations occur depending on composition and temperature, e.g. tempering of martensite to α₂ + β or α₂ + γ + G, or reversion of martensite to β followed by precipitation of one or more of the phases α, α₂ and γ.

MST/1029

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Solid state phase transformations in Ti–Al–Ru system

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