Impact of gravity-related phenomena on the grain structure formation: comparative study between horizontal and vertical solidification of a refined Al-20wt.%Cu alloy

Abstract

On earth, gravity-related phenomena are unavoidable, such as thermo-solutal convection caused by density gradients in the melt and buoyancy when the liquid phase is denser than the solid phase. Such phenomena can drastically affect both the grain density and their morphology during equiaxed solidification processes. For these reasons, fundamental studies comparing the influence of solidification parameters with and without gravity effects are important to obtain benchmark data, which are useful to understand and then control the final structure of materials in industrial processes. In the present work, the impact of the solidification parameters on the dendritic grain structure formation and on the final grain size and shape was investigated in situ by using X-radiography for different growth orientations with respect to gravity. In a first step, experiments were carried out with various solidification parameters and with the furnace in horizontal position, with the main surface of the sample being perpendicular to gravity to limit gravity-related phenomena. In a second step, experiments were carried out with identical solidification parameters but with the furnace in a vertical position, and for two solidification directions (upward and downward). A comparative study between horizontal and vertical experiments was carried out. Phenomena related to gravity have been highlighted and their respective impact on the solidification front propagation was analysed.

Impact of gravity on directional solidification of refined Al-20wt.%Cu alloy investigated by in situ X-radiography

“…4b) and grain growth orientation (Fig. 4c) for the experiment A1, which agrees with a recent detailed analysis of the impact of growth velocity on those distributions for a similar experimental configuration [39,47]. The distribution of grain diameter was well-fitted by a Gaussian-type curve and the microstructure was rather homogeneous in size in the FoV.…”

“…It is worth noting that buoyancy effects became negligible with the increase of cooling rate [47,54]. Indeed, for a cooling rate of about 0.9 K/s (not shown in this paper), the growth velocity ( 120 µm/s) and the grain flotation velocity ( 100 µm/s) were of same order, yielding to an attenuation of the impact of flotation.…”

Gravity effect on thermal-solutal convection during solidification revealed by four-dimensional synchrotron imaging with compositional mapping

“…2 j) and no radial macro-segregation was observed. Solute plumes have been reported [9] via in situ radiography during downwards solidification, but it is not observed here. During downwards solidification, it is likely that some of the segregated solute is immediately transported into the hot liquid below the growth front and is mixed due to a convection current established in this region.…”

“…Experimentally, in situ and real-time observation has been a method of choice to enlighten gravity effects on solidification, which includes optical microscopy using transparent organic alloys [17] and 2D X-ray radiographs [2 , 15 , 22 , 23] of metallic alloys. Experiments have been carried out on Earth [5] , aboard the International Space Station [2 , 23] , parabolic flights [9] , and sounding rockets (for example the MASER-12 mission in 2012 [24] ). These studies have greatly enhanced our understanding of the gravity effects.…”

Investigation of Al-20Sn-10Cu alloy directional solidification by laboratory X-radiography

“…The SFINX facility available at IM2NP laboratory was used and was described in detail in [16]. It has been developed within the framework of the ESA MAP named XRMON (In-situ X-ray monitoring of advanced metallurgical processes under microgravity and terrestrial conditions), devoted to the application of X-radiography during microgravity experiments [17].…”