Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5456007 | Materials Science and Engineering: A | 2017 | 27 Pages |
Abstract
The precipitation-hardening phenomenon is well-known in nitrogen-supersaturated ferrite and its precipitation sequence has received extensive attention. Thus far the αâ³-Fe16N2 phase has been known as the main hardening precipitates in the alloy upon ageing at low temperatures. Here we report that distinct precursors (pre-αâ³) of the αâ³-phase exist and they also play a crucial role in the precipitation-hardened alloy. Using (in-situ) high-resolution transmission electron microscopy, property characterization and first-principle energy calculations in association with varying thermal processes, it is shown that lying on the {001}α planes, the pre-αⳠprecipitates have a plate-like morphology and are the major hardening precipitates in natural aged Fe-N ferrite. They are stable without much change even after tempering at 60 °C for 2 h. Furthermore, the plate-like pre-αⳠprecipitates typically consist of needle-like domains, due to energy minimization. The in-situ observations demonstrate that the precipitation sequence upon ageing is as follows: N-supersaturated α-FeâN-rich clustersâpre-αⳠ(GP zones)âαâ³, where GP zones stands for Guinier-Prestone zones. The pre-αⳠprecipitates can have even more significant effects on properties of the alloy, as compared with the well-known αⳠprecipitates.
Related Topics
Physical Sciences and Engineering
Materials Science
Materials Science (General)
Authors
Y. Hong, C.L. Wu, L. Tian, N. Li, Q. Xu, J.H. Chen,