Modeling and characterization of grain structures and defects in solidification

Abstract

a b s t r a c tThe paper by Karma and Tourret (this volume) in this special issue focuses on multiscale modeling approaches ranging from atoms to microstructure. In the present one, the most recent and significant modeling contributions dealing with the scale of solidification from microstructure to grain structure are briefly reviewed. The paper also covers modeling of defect formation during the last stage of solidification, namely porosity and hot tearing. As will be shown, the field of solidification has taken advantage of several simulation and experimental tools which have become increasingly powerful and accessible over the past decade. The emphasis will be put on complex 2D and 3D models for which correlations with in situ observations using synchrotron radiation and/or combined orientation and metallography imaging have been made.

Atomistic to continuum modeling of solidification microstructures

“…This gap stems from the fact that, while 3D volumes up to about a mm 3 are within reach of today's large scale phase-field computations, those volumes are still minute on the scale of a casting. In contrast, Cellular Automata coupled with Finite Elements (CAFE) models [119,51,118] can access those much larger scales and predict grain structures of castings [26]. However, those models do not resolve dynamical interactions between branches of hierarchical dendritic networks, which can strongly influence both intra-grain microstructure selection and the growth competition of different grains [139].…”

“…For this reason, Dc is a key parameter in continuum models of hot tearing [120,150,5] reviewed in Ref. [118].…”

“…Those simulations typically use a million atoms and interatomic potentials modeled by the embeddedatom method (EAM). They have also yielded useful quantitative insights into solute-trapping in rapidly solidified alloys [158,70], as well as interface coalescence phenomena that control crystal cohesion during the late stages of solidification [67,46,111] and are relevant to hot tearing, reviewed in the article by Rappaz in this issue [118].…”

“…We leave out two-phase microstructures, reviewed in the separate article by Plapp in this issue [114]. In Section 4, we discuss recent progress to bridge the gap between http phase-field modeling on the microstructure scale and grain structure modeling [118]. This gap stems from the fact that, while 3D volumes up to about a mm 3 are within reach of today's large scale phase-field computations, those volumes are still minute on the scale of a casting.…”

Particle-induced morphological modification of Al alloy equiaxed dendrites revealed by sub-second in situ microtomography

“…At 4.35 s in Figure 2, porosity is already visible in the solidifying sample when UST was not performed but represents only 0.02% in volume fraction (red curve, Figure 3a). During further cooling, the sudden increase in porosity content on the red curve arises when dissolved hydrogen present in the aluminium melt diffuses inside the pores due to a decrease of hydrogen solubility in the melt during solidification [35]. The size of pores then raises leading to an increase in the overall volume fraction of defects in the solid state (1% in volume fraction).…”