Growth and transformation mechanisms of 18R and 14H in Mg-Y-Zn alloys

Yuman Zhu, Allan James Morton, Jian Feng Nie

Research output: Contribution to journalArticleResearchpeer-review

Abstract

The growth of and transformation between 18R and 14H phases in a Mg–8Y–2Zn–0.6Zr (wt.%) alloy have been examined using conventional transmission electron microscopy and atomic resolution high-angle annular dark-field scanning transmission electron microscopy. The growth of both 18R and 14H within the α-Mg matrix occurs via a ledge mechanism, with the thickness of the particle increasing by the height of the ledge as it propagates. The unit height of the growth ledges or disconnections is 1.563 nm for 18R and 1.824 nm for 14H, and the displacement vector is a/3〈1̄010〉α . 18R transforms in-situ to 14H during prolonged heat treatment at 500 °C. The 18R to 14H transformation is shown to occur most readily in regions where the 18R structure has irregularities in the building block stacking, in particular where a pair of adjacent building blocks is separated by four rather than two α-Mg layers. It is proposed that the diffusional-displacive 18R to 14H transformation rate is controlled by the diffusion rate of Y and Zn atoms into the segregation layers.
Original languageEnglish
Pages (from-to)6562 - 6572
Number of pages11
JournalActa Materialia
Volume60
Issue number19
DOIs
Publication statusPublished - 2012

Cite this

Zhu, Yuman ; Morton, Allan James ; Nie, Jian Feng. / Growth and transformation mechanisms of 18R and 14H in Mg-Y-Zn alloys. In: Acta Materialia. 2012 ; Vol. 60, No. 19. pp. 6562 - 6572.
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title = "Growth and transformation mechanisms of 18R and 14H in Mg-Y-Zn alloys",
abstract = "The growth of and transformation between 18R and 14H phases in a Mg–8Y–2Zn–0.6Zr (wt.{\%}) alloy have been examined using conventional transmission electron microscopy and atomic resolution high-angle annular dark-field scanning transmission electron microscopy. The growth of both 18R and 14H within the α-Mg matrix occurs via a ledge mechanism, with the thickness of the particle increasing by the height of the ledge as it propagates. The unit height of the growth ledges or disconnections is 1.563 nm for 18R and 1.824 nm for 14H, and the displacement vector is a/3〈1̄010〉α . 18R transforms in-situ to 14H during prolonged heat treatment at 500 °C. The 18R to 14H transformation is shown to occur most readily in regions where the 18R structure has irregularities in the building block stacking, in particular where a pair of adjacent building blocks is separated by four rather than two α-Mg layers. It is proposed that the diffusional-displacive 18R to 14H transformation rate is controlled by the diffusion rate of Y and Zn atoms into the segregation layers.",
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Growth and transformation mechanisms of 18R and 14H in Mg-Y-Zn alloys. / Zhu, Yuman; Morton, Allan James; Nie, Jian Feng.

In: Acta Materialia, Vol. 60, No. 19, 2012, p. 6562 - 6572.

Research output: Contribution to journalArticleResearchpeer-review

TY - JOUR

T1 - Growth and transformation mechanisms of 18R and 14H in Mg-Y-Zn alloys

AU - Zhu, Yuman

AU - Morton, Allan James

AU - Nie, Jian Feng

PY - 2012

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N2 - The growth of and transformation between 18R and 14H phases in a Mg–8Y–2Zn–0.6Zr (wt.%) alloy have been examined using conventional transmission electron microscopy and atomic resolution high-angle annular dark-field scanning transmission electron microscopy. The growth of both 18R and 14H within the α-Mg matrix occurs via a ledge mechanism, with the thickness of the particle increasing by the height of the ledge as it propagates. The unit height of the growth ledges or disconnections is 1.563 nm for 18R and 1.824 nm for 14H, and the displacement vector is a/3〈1̄010〉α . 18R transforms in-situ to 14H during prolonged heat treatment at 500 °C. The 18R to 14H transformation is shown to occur most readily in regions where the 18R structure has irregularities in the building block stacking, in particular where a pair of adjacent building blocks is separated by four rather than two α-Mg layers. It is proposed that the diffusional-displacive 18R to 14H transformation rate is controlled by the diffusion rate of Y and Zn atoms into the segregation layers.

AB - The growth of and transformation between 18R and 14H phases in a Mg–8Y–2Zn–0.6Zr (wt.%) alloy have been examined using conventional transmission electron microscopy and atomic resolution high-angle annular dark-field scanning transmission electron microscopy. The growth of both 18R and 14H within the α-Mg matrix occurs via a ledge mechanism, with the thickness of the particle increasing by the height of the ledge as it propagates. The unit height of the growth ledges or disconnections is 1.563 nm for 18R and 1.824 nm for 14H, and the displacement vector is a/3〈1̄010〉α . 18R transforms in-situ to 14H during prolonged heat treatment at 500 °C. The 18R to 14H transformation is shown to occur most readily in regions where the 18R structure has irregularities in the building block stacking, in particular where a pair of adjacent building blocks is separated by four rather than two α-Mg layers. It is proposed that the diffusional-displacive 18R to 14H transformation rate is controlled by the diffusion rate of Y and Zn atoms into the segregation layers.

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