Non-classical homogeneous precipitation mediated by compositional fluctuations in titanium alloys |
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| Authors: | S. Nag Y. Zheng R.E.A. Williams A. Devaraj A. Boyne Y. Wang P.C. Collins G.B. Viswanathan J.S. Tiley B.C. Muddle R. Banerjee H.L. Fraser |
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| Affiliation: | 1. Center for the Accelerated Maturation of Materials and Department of Materials Science and Engineering, The Ohio State University, Columbus, OH, USA;2. Center for Advanced Research and Technology and Department of Materials Science and Engineering, University of North Texas, Denton, TX, USA;3. Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright Patterson Air Force Base, Dayton, OH, USA;4. ARC Centre of Excellence for Design in Light Metals, Department of Materials Engineering, Monash University, Victoria 3800, Australia |
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| Abstract: | This paper presents experimental evidence of homogeneous precipitation of the α-phase within the β matrix of a titanium alloy, and then accounts for this phase transformation by a new, non-classical mechanism involving compositional fluctuations, based on the pseudo-spinodal concept [1]. This mechanism involves local compositional fluctuations of small amplitude which, when of a certain magnitude, can favor thermodynamically certain regions of the β matrix to transform congruently to the α-phase but with compositions far from equilibrium. Subsequently, as measured experimentally using the tomographical atom probe, continuous diffusional partitioning between the parent β- and product α-phases during isothermal annealing drives their compositions towards equilibrium. For a given alloy composition, the decomposition mechanism is strongly temperature dependent, which would be expected for homogeneous precipitation via the compositional fluctuation-mediated mechanism but not necessarily for one based on classical nucleation theory. The applicability of this mechanism to phase transformations in general is noted. |
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