In situ studies of precipitate formationin Al-Pb monotectic solidification by X-ray transmission microscopy

Abstract

Al-1.5 wt pct Pb monotectic alloys were unidirectionally solidified. X-ray transmission microscope (XTM) observations, both during and after solidification, revealed various new morphological/compositional features in the melt and solid. In the melt, nonuniform lead-rich interfacial segregation layers and droplets were observed to form well ahead of the interface. In the solid, periodic striae formed at translation/solidification velocities as low as 6 ϫ 10 Ϫ6 m/s. The striae shape does not replicate that of the interface. The striae spacing decreases from 4 to 2 ϫ 10 Ϫ4 m with an increasing solidification rate between 6 and 16 ϫ 10 Ϫ6 m/s. High resolution postsolidification XTM examination reveals that these striae consist of Pb-rich particles of 2 to 3 ϫ 10 Ϫ6 m diameter. At translation/solidification velocities below 6 ϫ 10 Ϫ6 m/s, Pb incorporation into the solid occurs in the form of continuous fibers and strings of particles of about 5 ϫ 10 Ϫ6 m diameter. Bands, parallel to the interface, in which these fibers were aligned in the solidification direction, alternated with bands of poor fiber alignment. The width of these bands is comparable to the striae spacings obtained at the high solidification rates.

In-Situ and Real-Time Analysis of the Formation of Strains and Microstructure Defects during Solidification of Al-3.5 Wt Pct Ni Alloys

“…Later, microfocus X-ray sources producing increased incident photon flux were used by Koster, who investigated fluid flow in molten Ga and the global solidification microstructures in Ga-In, [7] and by Kaukler et al, to study the formation and engulfment of lead droplets in Al-Pb alloys. [8] It is only in recent years that the high brilliance of the third generation synchrotron radiation was taken advantage of to carry out in-situ and real-time observations of microstructure formation by radiography on different alloy systems with satisfying spatial and time resolutions. [9][10][11][12] In the field of solidification processing of materials, the dynamics of a series of phenomena, such as columnar-to-equiaxed transition (CET) in refined Al-Ni alloys, [13] or fragmentation of dendritic crystals during columnar growth of Al-Cu alloys [14] could be analyzed for the first time.…”

Time-resolved x-ray imaging of aluminum alloy solidification processes

“…Apart from very special cases, [5] where model systems can be alloyed with optically opaque elements, variations in alloy composition in the solid and liquid are not visible, measurements have been used to characterize solidification where the real part, 1 Ϫ ␦ r , describes refraction, whereas the imaginary part, i␤ r , is due to the absorption of the processes in terms of spatiotemporal variations in attenuation of the X-ray field by the material. [6][7][8][9] However, these methelectromagnetic wave. The refractive index of vacuum is n vac ϵ 1.…”

“…DISCUSSION high resolutions obtained in this experiment exceed those obtained with other X-ray transmission electron microscopy As illustrated by the figures, the image series collected were phenomenologically rich. In addition to the results techniques [6][7][8][9] by more than one magnitude, both spatially and temporally. The ability to exploit the local variations in analyze the relative X-ray transmission, in order to extract and interpolate contours for a local liquid constitution ahead refraction by the sample as another source of contrast in addition to attenuation is unique in work with solidificationof the interface.…”

Lei de Crescimento em Função da Posição para Ligas do Sistema Monotético

“…As distintas morfologias dos sistemas monotéticos têm sido alvo de intensos estudos CALBERG;BERGMAN, 1985;DERBY;FAVIER, 1983;LOGRASSO;HELLAWELL, 1984;HELLAWELL, 1981;KAMIO et al, 1984;KAUKLER;ROSEMBERGER;CURRERI, 1997;OZAWA;MOTEGI, 2004;RATKE, 2005;RATKE;MULLER, 2005;GARCIA, 2009a, 2009b, SILVA et al, 2010YANG;LIU, 2001) durante as últimas décadas. Um dos parâmetros microestruturais normalmente investigados é o espaçamento interfásico, λ, sendo bastante comum a utilização da clássica relação para crescimento de sistemas eutéticos de Hunt e Jackson (GARCIA, 2007;STOCKER;RATKE, 1999): λ 2 v = C para representá-lo, ou ainda a relação de crescimento dendrítico proposta por Calberg e Bergman (1985), .…”