Mechanical Blocking Mechanism for the Columnar to Equiaxed Transition

Biscuola, Vinicius Bertolazzi; Martorano, Marcelo Aquino

doi:10.1007/s11661-008-9643-x

Cited by 76 publications

(31 citation statements)

References 37 publications

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“…Ad (ii): In a previous section, we mentioned that the precise value of the threshold for coherence of the equiaxed grains is not agreed upon in the literature (ranging from 0.2 [33] to 1 [34]). To study the sensitivity of our results to this threshold value, we simulated solidification of a weld pool using a coherency threshold of 0.49 and 0.6, leading to a 15% difference in the volume of equiaxed structure in the weld (figure 9).…”

Section: Sensitivity To Numerical and Model Parametersmentioning

confidence: 99%

An integrated model for the post-solidification shape and grain morphology of fusion welds

Kidess

Tong

Duggan

et al. 2015

International Journal of Heat and Mass Transfer

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Through an integrated macroscale/mesoscale computational model, we investigate the developing shape and grain morphology during the melting and solidification of a weld. In addition to macroscale surface tension driven fluid flow and heat transfer, we predict the solidification progression using a mesoscale model accounting for realistic solidification kinetics, rather than quasi-equilibrium thermodynamics. The tight coupling between the macroscale and the mesoscale distinguishes our results from previously published studies.The inclusion of Marangoni driven fluid flow and heat transfer, both during heating and cooling, was found to be crucial for accurately predicting both weld pool shape and grain morphology. However, if only the shape of the weld pool is of interest, a thermodynamic quasi-equilibrium solidification model, neglecting solidification kinetics, was found to suffice when including fluid flow and heat transfer.We demonstrate that the addition of a sufficient concentration of approximately 1 µm diameter TiN grain refining particles effectively triggers a favorable transition from columnar dendritic to equiaxed grains, as it allows for the latter to heterogeneously nucleate in the undercooled melt ahead of the columnar dendritic front. This transition from columnar to equiaxed growth is achievable for widely differing weld conditions, and its precise nature is relatively insensitive to the concentration of particles and to inaccurately known model parameters.

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Section: Sensitivity To Numerical and Model Parametersmentioning

confidence: 99%

An integrated model for the post-solidification shape and grain morphology of fusion welds

Kidess

Tong

Duggan

et al. 2015

International Journal of Heat and Mass Transfer

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“…[8,9] Columnar-to-equiaxed transition (CET) during nugget solidification has been proposed to be caused either by a pileup of equiaxed crystals that block the growth of the columnar grains or by attachment of equiaxed crystals from the liquid to the columnar dendrite front. [10,11] The criteria for CET are tip growth rate and temperature gradients ahead of the dendrite tips. [9,12] Various techniques have been employed to promote CET and increase the percentage of equiaxed grains in the weld, such as magnetic arc oscillation, [13] ultrasonic vibration, [14] exciting the electric arc, [15] or double-sided arc welding.…”

Section: Introductionmentioning

confidence: 99%

Resistance Spot Welded AZ31 Magnesium Alloys, Part II: Effects of Welding Current on Microstructure and Mechanical Properties

Liu

Xiao

Feng

et al. 2010

Metall Mater Trans A

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Resistance spot welding of AZ31 magnesium alloys from different suppliers, AZ31-SA (from supplier A) and AZ31-SB (from supplier B), was studied and compared in this article. The mechanical properties and microstructures have been studied of welds made with a range of welding currents. For both groups of welds, the tension-shear fracture load (F C ) and fracture toughness (K C ) increased with the increase in welding current. The F C and K C of AZ31-SA welds were larger than those of AZ31-SB welds. The fracture surfaces of AZ31-SB welds were relatively flatter than those of AZ31-SA. Microstructural examination via optical microscope demonstrated that almost all weld nuggets comprised two different zones, the columnar dendritic zone (CDZ), which grew epitaxially from the fusion boundary, and the equiaxed dendritic zone (EDZ), which formed in the center of the nugget. The nature and extent of the CDZ seemed to be critical to the strength and toughness of spot welds because of its position adjacent to the inherent external circular crack-like notch of spot welds and the stress concentration in this region. The width and microstructure of the CDZ were different between AZ31-SA and AZ31-SB. The AZ31-SA alloy produced finer and shorter columnar dendrites, whereas the AZ31-SB alloy produced coarser and wider columnar dendrites. The width of the CDZ close to the notch decreased with the increase of current. The CDZ disappeared when the current was higher than a critical value, which was about 24 kA for AZ31-SA and 28 kA for AZ31-SB. The microhardness of the two base materials was the same, but within the CDZ and EDZ, the hardness was greater in AZ31-SA than AZ31-SB welds. It is believed that the different microstructures of spot welds between AZ31-SA and AZ31-SB resulted in different mechanical properties; in particular, K C increased with the welding current because of the improved columnar-to-equiaxed transition.

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“…Under 0.5, 0.85, and 1.2 MPa, the experimental average distances from CET position to the edge of ingot are 19.8, 22.1, and 27.4 mm, respectively . In order to accurately detect the CET position during simulation process, the average aspect ratio (the shortest axis in a grain divided by the longest axis in a grain) is evaluated for determining the type of grain . When the average aspect ratio is larger than 0.4, the grain is equiaxed grain.…”

Section: Model Validationmentioning

confidence: 99%

Effect of Solidification Pressure on Compactness Degree of 19Cr14Mn0.9N High Nitrogen Steel Using CAFE Method

Zhu

et al. 2017

steel research int.

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The cellular automaton‐finite element (CAFE) model is used to simulate solidification structures of 19Cr14Mn0.9N high nitrogen steel under different solidification pressures. The effect of solidification pressure on model parameters is firstly investigated. After validation, this model is used to clarify the effect of solidification pressure on compactness degree with number of grains and primary dendrite arm spacing (λ1). The results show that increasing solidification pressure from 0.5 to 1.2 MPa exhibits a significant increment (200 W m2 K−1)) on heat transfer coefficient and slight change for other model parameters. The model validation indicates CAFE model can accurately simulate solidification structure under higher solidification pressure. Under higher solidification pressure, the primary dendrite arm spacing (λ1) of central equiaxed grain becomes smaller and the number of grains of the whole ingot increases obviously, revealing a further improvement on the compactness degree of ingot. At a given pressure, the decrement in the number of grains is obvious away from the edge of ingot. With increasing solidification pressure, a more significant increment in the number of grains exists at columnar grain zone than that at central equiaxed grain zone, suggesting a greater increasing tendency of compactness degree at columnar grain zone.

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Mechanical Blocking Mechanism for the Columnar to Equiaxed Transition

Cited by 76 publications

References 37 publications

An integrated model for the post-solidification shape and grain morphology of fusion welds

An integrated model for the post-solidification shape and grain morphology of fusion welds

Resistance Spot Welded AZ31 Magnesium Alloys, Part II: Effects of Welding Current on Microstructure and Mechanical Properties

Effect of Solidification Pressure on Compactness Degree of 19Cr14Mn0.9N High Nitrogen Steel Using CAFE Method

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