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Formation of Large Size Precipitate-Free Zones in β Annealing of the Near-β Ti-55531 Titanium Alloy

Authors :
Xueqi Jiang
Xiaoqiang Shi
Xiaoguang Fan
Qi Li
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