Lamellar transformation in near-γ TiAl alloys—Quantitative analysis of kinetics and microstructure

This paper supplies new quantitative data on the global kinetics of the α → α2 + γ transformation and the α2 + γ lamellar microstructures produced through continuous cooling from the α domain as applied to the representative near-γ TiAl-based alloy Ti–48 at.% Al–2% Cr–2% Nb. The evolution of α-transformed volume fraction during cooling is followed by dilatometry. A novel method based on the combination of electron back-scattered diffraction (EBSD) and image analysis is presented to measure the distribution of true (3D) lamella widths supplied by scanning electron microscopy (SEM) observation of 2D surfaces of the samples treated. The transformation start and finishing temperatures, the lamellar-grain size, the α2 phase volume fraction, the width of the α2 lamellae and the inter-α2 lamellar spacing are supplied for various durations of isothermal treatment in the α domain and over a wide range of cooling rates. Quantitative relations between these kinetics, structural and thermal parameters have been established and are discussed.