A high-resolution time-resolved study of incoherent interface motion during the massive transformation in TiAl alloy

Frame-by-frame analyses of in-situ high-resolution transmission electron microscope (HRTEM) heating experiments performed on a high-index incoherent massive transformation interface in TiAl alloy at 575°C show that the interface displays dynamic fluctuations in its trace that can be described in terms of a wavelike function with an amplitude of 0.21 nm and a fundamental wavelength of 1.15 nm. The interface moves forward with a constant average velocity of 0.023 nm/s, due to spreading of criticalsize advancing fluctuations along the interface at different locations, which causes it to remain relatively planar as it advances. This interface behavior is remarkably similar to that observed during previous in-situ optical microscopy studies on massive transformation interfaces in Cu−Ga alloy and is distinctly different from the behavior of highly faceted interphase boundaries. This article is based on a presentation made in the “Hume-Rothery Symposium on Structure and Diffusional Growth Mechanisms of Irrational Interphase Boundaries,” which occurred during the TMS Winter meeting, March 15–17, 2004, in Charlotte, NC, under the auspices of the TMS Alloy Phases Committee and the co-sponsorship of the TMS-ASM Phase Transformations Committee.