Heterogeneous nucleation and grain growth of inoculated aluminium alloys: An integrated study by in-situ X-radiography and numerical modelling

Abstract

A comprehensive study on the heterogeneous nucleation and grain growth of Al-10wt.%Cu alloys inoculated with Al-5Ti-1B was carried out. To further reveal the solute segregation stifling mechanism, in-situ near-isothermal melt solidification experiments with constant cooling rates and greatly suppressed melt convection were realized by in-situ microfocus X-radiography study. The kinetics of heterogeneous nucleation and grain growth under the isolated influence of cooling rate and addition level of inoculant particles has been quantitatively studied. Moreover, novel image processing and analysis approaches have been proposed, to determine the maximum

Revealing the heterogeneous nucleation behavior of equiaxed grains of inoculated Al alloys during directional solidification

“…The sample was aligned in a configuration where the broad surface (X-Y plane) of the sheet-like sample is perpendicular to the gravity (Z || g), by which the melt convection and grain motion were reduced to a large extent. The Bridgman furnace was operated in the so-called near-isothermal mode [12,57], and later in standard directional solidification mode with imposed temperature gradients G along the sample length direction (G || Y). In the near-isothermal mode, the furnace temperature (melt temperature) at the commencement of the experiment is 630 o C;…”

“…Recalescence has long been understood to be the effective nucleation stopping mechanism for most of the castings where recalescence is non-negligible [5,11]. For those castings where recalescence is not present, for example, unidirectional solidification, it has been proven, both experimentally and by numerical modeling, that the nucleation stops due to solute segregation stifling [12].…”

“…To understand the heterogeneous nucleation and grain growth behavior, and to predict the grain size in castings of inoculated aluminum alloys, many numerical and analytical models have been developed in the last decades [5,11,12,[36][37][38][39][40][41][42][43][44][45][46][47]. The early models [5,11,37,43,44,47] are mostly based on the spatially isothermal melt assumption and recalescence nucleation-stifling mechanism, following the framework of Maxwell-Hellawell model [11].…”

“…In a recent work, Du and Li [46] did a more rigorous treatment of the thickness of the solute diffusion layer and the soft impingement zone around growing grains, and proposed a new grain size prediction model based on the solute segregation stifling nucleation mechanism, applicable for solidification cases without recalescence. After a further development to include the dendritic growth kinetics of grains, the model has been validated by the in-situ isothermal melt solidification experiments with constant cooling rate [12]. Though intended for directional solidification, the above models are still based on a local isothermal melt solidification assumption, while the effects of temperature gradient on the heterogeneous nucleation of equiaxed grains are neglected.…”

Atomic insights in crystallization of liquid Cu on single crystal Ta and amorphous Ta

“…Heteronucleation is a ubiquitous phenomenon, which has attracted extensive interest because of its importance in fundamental research and materials engineering [1][2][3][4][5][6][7]. In this complex process, the nucleation mechanism may vary dramatically upon change of conditions, such as the nucleant, impurity, undercooling and so on [2,7]. In practical perspectives, the understanding of heteronucleation mechanism in different conditions would inspire the control of materials properties towards diverse applications [8].…”