The coarsening of lamellae in Ti-48Al-2Mn-2Nb
- Univ. of Birmingham (United Kingdom)
The thermal stability of as-cast Ti-48Al-2Mn-2Nb alloys has been investigated as a function of time at temperatures of 1,200, 1,350 and 1,420 C. The resultant structures have been characterized using optical microscopy, electron probe microanalysis and transmission electron microscopy. The as-cast structure consists mainly of lamellae of [alpha][sub 2] and [gamma]. Annealing at 1,350 and at 1,420 C resulted in the continuous and discontinuous coarsening of the primary lamellae. Discontinuous coarsening, which often originates at the sample surface, results in branched irregular secondary lamellae. The average interlamellar spacing of the secondary lamellae is up to a thousand times larger than the primary interlamellar spacing. The extremum principles of maximum velocity and maximum rate of entropy production, used to predict the secondary interlamellar spacing, are inconsistent with the experimental observations. The theoretical predictions of the velocity of the discontinuous coarsening by Livingston and Cahn are used to estimate the value of grain boundary diffusivity at 1,350 C. The temperature dependence of discontinuous coarsening is weak, in contrast to the strong effect of lamellar orientation on the rate of discontinuous coarsening.
- OSTI ID:
- 6930033
- Journal Information:
- Acta Metallurgica et Materialia; (United States), Journal Name: Acta Metallurgica et Materialia; (United States) Vol. 42:8; ISSN 0956-7151; ISSN AMATEB
- Country of Publication:
- United States
- Language:
- English
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