In situ observation of hot tearing formation in succinonitrile-acetone

Farup, Ivar; Drezet, Jean‐Marie; Rappaz, M.

doi:10.1016/s1359-6454(01)00013-1

Cited by 143 publications

(92 citation statements)

References 11 publications

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“…In this respect, the smooth grain model leaves isolated liquid pockets at triple junctions and thus induces a departure from Carman-Kozeny earlier as compared with the edgy grain model. This situation is actually closer to observations on organic or metallic alloys, which reveal liquid droplets in between grains (or dendrites) [1]. Despite the fact that these liquid droplets have a positive curvature, the effect of which is not taken into account with the present model, the smooth grain model is nevertheless a much better approximation and will be used exclusively hereafter.…”

Section: Localisation Of Feedingsupporting

confidence: 79%

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A granular model of equiaxed mushy zones: Formation of a coherent solid and localization of feeding

Vernède

Jarry²,

Rappaz

2006

Acta Materialia

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The gradual transformation of a mushy zone during alloy solidification, from a continuous liquid film network to a fully coherent solid, has been simulated using a granular model. Based on a Voronoi tessellation of a random set of nucleation centers, solidification within each polyhedron is computed considering back-diffusion and coalescence. In the network of connected liquid films, a pressure drop calculation is performed assuming a Poiseuille flow in each channel, Kirchhoff's conservation of flow at nodal points and flow Losses compensating solidification shrinkage (KPL model). In addition to intergranular liquid pressure maps, the model shows the progressive formation of grains clusters, the localisation of the flow at very high solid fraction, and thus natural transitions of the mushy zone.

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Section: Localisation Of Feedingsupporting

confidence: 79%

“…Hot tear surfaces reveal an intergranular profile exhibiting a smooth surface with a few small spikes (∼ 10µm) resulting from local plastic deformation of solid bridges or solidification of last liquid menisci [1].…”

Section: Introductionmentioning

confidence: 99%

A granular model of equiaxed mushy zones: Formation of a coherent solid and localization of feeding

Vernède

Jarry²,

Rappaz

2006

Acta Materialia

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“…Because small elements result in convergence issues during FE analysis, coalescence between two grains is assumed to occur when the thickness of the liquid channel between two elements is less than 0.4 pct of the average diameter of the grains. Although this hypothesis is not physically accurate, because the presence of thin liquid films of a few nanometers in size have been previously observed near the end of solidification, [35] these small films are highly viscous and also tend to stick two surfaces together. Thus, for hot tearing, thin liquid channels act similar to solid-solid bonds.…”

Section: A Generation Of Discrete Elements Using a Solidification Modelmentioning

confidence: 99%

Simulation of Semi-Solid Material Mechanical Behavior Using a Combined Discrete/Finite Element Method

Sistaninia

Phillion

Drezet

et al. 2010

Metall Mater Trans A

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As a necessary step toward the quantitative prediction of hot tearing defects, a three-dimensional stress-strain simulation based on a combined finite element (FE)/discrete element method (DEM) has been developed that is capable of predicting the mechanical behavior of semisolid metallic alloys during solidification. The solidification model used for generating the initial solid-liquid structure is based on a Voronoi tessellation of randomly distributed nucleation centers and a solute diffusion model for each element of this tessellation. At a given fraction of solid, the deformation is then simulated with the solid grains being modeled using an elastoviscoplastic constitutive law, whereas the remaining liquid layers at grain boundaries are approximated by flexible connectors, each consisting of a spring element and a damper element acting in parallel. The model predictions have been validated against Al-Cu alloy experimental data from the literature. The results show that a combined FE/DEM approach is able to express the overall mechanical behavior of semisolid alloys at the macroscale based on the morphology of the grain structure. For the first time, the localization of strain in the intergranular regions is taken into account. Thus, this approach constitutes an indispensible step towards the development of a comprehensive model of hot tearing.

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“…Des observations sur les organiques ontété conduites a l'aide du dispositif expérimental décrit sur la figure 2 [11,12].À l'aide d'un moteurélectrique, les dendrites sontécartées dans le sens perpendiculaire au gradient thermique. L'apparition de fissuresà chaud est alors filmée par une caméra située au-dessus de la cellule contenant l'organique.…”

Section: Observation Sur Les Alliages Organiquesunclassified

Fissuration à chaud : des alliages organiques aux superalliages

Drezet

Grasso

Rappaz

2004

Mécanique & Industries

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Résumé -L'apparition de fissures ou criquesà chaud pendant la coulée des matériaux métalliques représente un défaut sérieux. L'EPF-Lausanne a développé un critère d'initiation de fissures qui est basé sur l'équation de conservation de la masse appliquéeà la zone solide-liquide (zone pâteuse) et qui prend en compteà la fois une déformation subie par le squelette solide perpendiculairement aux dendrites et l'appel de liquide induit par le retrait de solidification. Le modèle introduit une chute de pression dans les films liquides au-delà de laquelle la cavitation, i.e. la germination d'un premier pore, a lieu. Des observations in situ sur des alliages organiques transparents permettent de mettre enévidence l'importance de la coalescence entre les dendrites ; en effet, la prise de rigidité mécanique de la zone pâteuse se fait par l'établissement de ponts solides entre les dendrites. Enfin, le critère est appliqué successivementà la coulée semi-continue d'alliages d'aluminium,à la coulée continue des aciers et au traitement par laser des superalliages.Mots clés : Solidification / fissurationà chaud / coalescence / alliages organiques / coulée continue / alliages d'aluminium / aciers / superalliages Abstract -Hot tearing: from organic alloys to superalloys. The appearance of solidification cracks or hot tears during casting is a serious defect. EPF-Lausanne has developed a criterion for the appearance of hot tears which is based upon a mass balance performed over the liquid and solid phases and which takes into accounts for the tensile deformation of the solid skeleton perpendicular to the growing dendrites and for the induced interdendritic liquid feeding. This model introduces a critical pressure drop beyond which cavitation, i.e., nucleation of a first void, occurs. In situ observations on transparent organic alloys point our the importance of coalescence between dendrites; indeed the mechanical rigidity of the mushy zone is completed by the appearance of solid bridges between the dendrites. Eventually, the criterion is applied successively to the semi-continuous casting of aluminium alloys, to the continuous casting of steel and to the laser treatment of superalloys.

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In situ observation of hot tearing formation in succinonitrile-acetone

Cited by 143 publications

References 11 publications

A granular model of equiaxed mushy zones: Formation of a coherent solid and localization of feeding

A granular model of equiaxed mushy zones: Formation of a coherent solid and localization of feeding

Simulation of Semi-Solid Material Mechanical Behavior Using a Combined Discrete/Finite Element Method

Fissuration à chaud : des alliages organiques aux superalliages

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