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Formation of Large Size Precipitate-Free Zones in β Annealing of the Near-β Ti-55531 Titanium Alloy
- Source :
- Metals, Vol 9, Iss 5, p 544 (2019)
- Publication Year :
- 2019
- Publisher :
- MDPI AG, 2019.
-
Abstract
- Large size (>10000 μm2) precipitate-free zones in the absence of microsegregation were observed in the near-β Ti-55531 titanium alloy after furnace cooling from high temperature and longtime annealing in the single-β phase field. To reveal the formation mechanism of the large size precipitate-free zone, continuous cooling and isothermal heat treatment were carried out to investigate the β-α phase transformation process. It was found that the large size precipitate free zone is attributed to the heterogeneous nucleation of α phase. The nucleation site evolves in three different modes: I-random nucleation inside the β grain, II-network nucleation inside the β grain and, III-heterogeneous nucleation on the precipitated α phase. Modes I and II lead to homogeneous transformed structure while Mode III results in the large size precipitate-free zone. Both modes II and III are promoted at high annealing temperature, rapid cooling above 600 °C or slow cooling below 600 °C. Mode II is common as it can minimize the strain energy in phase transformation. As a result, the formation of the large size precipitate-free zone is not deterministic.
Details
- Language :
- English
- ISSN :
- 20754701
- Volume :
- 9
- Issue :
- 5
- Database :
- Directory of Open Access Journals
- Journal :
- Metals
- Publication Type :
- Academic Journal
- Accession number :
- edsdoj.673825f0e11e42f2b4796ae7fd64da68
- Document Type :
- article
- Full Text :
- https://doi.org/10.3390/met9050544