Naslov
Phase transitions in the system Al-Zn

Autori
Popović, Stanko ; Gržeta, Biserka

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Book of Abstracts of the 6th Powder Diffraction Conference EPDIC-6 / Ungar, Tamas ; Svab, Erzsebet - Budimpešta : Diffraction Division of the Roland Eotvos Physical Society, Hun, 1998

Skup
6th Powder Diffraction Conference EPDIC-6

Mjesto i datum
Budimpešta, Mađarska, 22.08.1998. - 25.08.1998

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
Phase transition. solid solutions. thermal expansion. XRD

Sažetak
Phase transitions and the formation of solid solutions at elevated temperatures in Al-Zn alloys having 8, 24, 40, 48, 54 and 62 at% Zn were followed in situ by X-ray powder diffraction. In the equilibrium state at RT, after quenching from the solid solution temperature and prolonged ageing, these alloys are two-phase systems: alpha -phase (fcc, with 99 at% Al) and beta -phase (hcp, with more than 99.5 at% Zn). As the temperature of the previously annealed alloy increased, a decrease of the peak intensities of diffraction lines took place due to increased thermal vibration amplitudes. Also, a shift of diffraction lines due to thermal expansion was observed. The beta -phase exhibited an anisotropy in thermal expansion, this being several times larger along the c-axis than along the a-axis. A partial dissolution of the beta -phase in the alpha -phase started at approximately=490 K. For the alloys with 24, 40 and 48 at% Zn the phase transition beta to alpha '(fcc) took place at approximately=550 K. The beta -phase was not present above 555 K. At 560 K the unit-cell parameter of the alpha '-phase was smaller for 0.9% than that of the alpha -phase. As the temperature further increased, the alpha - and alpha '-phases merged together and the solid solution, alpha /sub ss/ (fcc), was formed. For the alloys with 54 and 62 at% Zn the shape of beta -phase precipitates changed on heating. Above approximately=550 K a partial transition beta to alpha ', took place. The alpha -phase disappeared at approximately=650 K, the alpha '-phase remaining in coexistence with the beta -phase. The beta -phase finally disappeared at approximately=700 K, and alpha /sub ss/ was formed. In the cooling cycle, a temperature hysteresis in reversal phase transitions was observed. During a repeated heating of the same specimen, a temperature delay in phase transitions for several tens of K's took place. The present results indicate that minor corrections are necessary in the phase diagram of the system Al-Zn.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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