Resulting morphologies on quenching of titanium aluminide alloys

• Published in: Materials science and technology Vol. 15; no. 5; pp. 510 - 517
• Main Authors: de Farias Azevedo, C.R., Flower, H.M.
• Format: Journal Article
• Language: English
• Published: London, England Taylor & Francis 01.05.1999; SAGE Publications; Maney; Taylor & Francis Ltd
• Subjects: Applied sciences; Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Metals. Metallurgy; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Quaternary alloys; Phase transformations; Ternary alloys; Metallography; Experimental study; Titanium base alloys; Quenching; Binary alloys; Alloying elements; Aluminium alloys; BCC lattices; Domain structure; SEM; HCP lattices; Microstructure; TEM; Transition element alloys
• ISSN: 0267-0836; 1743-2847
• DOI: 10.1179/026708399101506201

The effect of alloying elements (aluminium, silicon, niobium, and zirconium) on the mechanism and morphology of the allotropic transformation Ti-β(bcc) → Ti-α(hcp), occurring during the quenching of binary, ternary, and quaternary titanium aluminide alloys, has been studied. The alloys investigated were (at.-%) Ti-16Al, Ti-16Al-1Si, Ti-16Al-3·5Si, Ti-14Al-1Si-1Nb, Ti-14Al-1Si-1Zr, Ti-22Al, Ti-22Al-1Si, Ti-22Al-3·5Si, Ti-20Al-1Si-1Nb, and Ti-20Al-1Si-1Zr. The allotropic transformation in these alloys presented a very narrow temperature range for the formation of all possible α morphologies resulting from quenching. The different morphologies of α phase observed have been correlated with the competing mechanisms of β decomposition. The morphological observations indicated that small variations in thermodynamic and kinetic conditions in the β phase might account for changes in the mechanisms of formation and growth of the α phase. Additionally, the effect of the alloying elements on the ordering reaction α → α 2 occurring during quenching has been investigated. Silicon addition promoted the formation of columnar α 2 domains during quenching.