Nano-scale orientation mapping of graphite in cast irons

Theuwissen, Koenraad; Lacaze, Jacques; Véron, M.; Laffont, Lydia

doi:10.1016/j.matchar.2014.06.021

Cited by 22 publications

(29 citation statements)

References 10 publications

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“…Such large values have already been reported for boundaries between neighbouring sectors though the values are most often in the range 10-30° [24,25]. The nearly radial dotted and dashed lines in the IPFX identify paths through blocks stacked on top of one another in the radial direction.…”

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confidence: 57%

Crystallography of Growth Blocks in Spheroidal Graphite

Brodu

Bouzy

Fundenberger

et al. 2018

MSF

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Abstract.A better understanding of spheroidal graphite growth is expected in a near future thanks to widespread use of transmission electron microscopy. However, common transmission electron microscopy is quite time consuming and new indexing techniques are being developed, among them is transmission Kikuchi diffraction in a scanning electron microscope, a recent technique derived from electron backscatter diffraction. In the present work, on-axis transmission Kikuchi diffraction in scanning electron microscope, completed by transmission electron microscopy, was used with the objective of producing new observations on the microstructure of spheroidal graphite. This study shows that disorientations between blocks and sectors in spheroidal graphite are quite large in the early growth stage, which may be indicative of a competition process selecting the best orientations for achieving radial growth along the c direction of graphite.

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confidence: 57%

Crystallography of Growth Blocks in Spheroidal Graphite

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Bouzy

Fundenberger

et al. 2018

MSF

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“…Nevertheless, the stacking is not perfect, and rotations about the c-axis occur on an almost regular basis, defining domains of similar orientation [29].…”

Section: Theorymentioning

confidence: 99%

A micro-mechanical analysis of thermo-elastic properties and local residual stresses in ductile iron based on a new anisotropic model for the graphite nodules

Andriollo¹,

Thorborg²,

Tiedje³

et al. 2016

Modelling Simul. Mater. Sci. Eng.

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In this paper, the thermo-elastic behavior of the graphite nodules contained in ductile iron is derived on the basis of recent transmission electron microscopy investigations of their real internal structure. The proposed model is initially validated by performing a finite element homogenization analysis to verify its consistency with the room-temperature elastic properties of ductile iron measured at the macro scale. Subsequently, it is used to investigate the formation of local residual stresses around the graphite particles by simulating the manufacturing process of a typical ferritic ductile iron grade, and the results are compared with preliminary measurements using synchrotron X-rays. Finally, the obtained accurate description of the stress & strain field at the micro scale is used to shed light on common failure modes reported for the nodules and on some peculiar properties observed in ductile iron at both micro and macro scale.

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Section: Introductionmentioning

confidence: 99%

“…1. The change in orientation of the c axis at the boundary between two sectors may amount from 10 to several tens of degrees, while the orientation changes within sectors are more limited [1,2].It has long been recognized that graphite layers within spheroids are arranged in growth blocks which are elongated along the prismatic a direction of the graphite structure [3]. This would imply that graphite grows along the prismatic (tangential) direction during spheroidal growth even though the overall (apparent) growth direction is the radial one.…”

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A 2-D nucleation-growth model of spheroidal graphite

2017

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a b s t r a c tAnalysis of recent experimental investigations, in particular by transmission electron microscopy, suggests spheroidal graphite grows by 2-D nucleation of new graphite layers at the outer surface of the nodules. These layers spread over the surface along the prismatic direction of graphite which is the energetically preferred growth direction of graphite when the apparent growth direction of the nodules is along the basal direction of graphite. 2-D nucleation-growth models first developed for precipitation of pure substances are then adapted to graphite growth from the liquid in spheroidal graphite cast irons. Lateral extension of the new graphite layers is controlled by carbon diffusion in the liquid. This allows describing quantitatively previous experimental results giving strong support to this approach. IntroductionGraphite spheroids in spheroidal graphite cast iron are known to consist of piling up of graphite layers having their c axis oriented parallel to the spheroid radius. To accommodate for the change in orientation in the tangential direction, the spheroids appear to be divided in adjacent sectors which are easily observed by optical microscopy as illustrated in Fig. 1. The change in orientation of the c axis at the boundary between two sectors may amount from 10 to several tens of degrees, while the orientation changes within sectors are more limited [1,2].It has long been recognized that graphite layers within spheroids are arranged in growth blocks which are elongated along the prismatic a direction of the graphite structure [3]. This would imply that graphite grows along the prismatic (tangential) direction during spheroidal growth even though the overall (apparent) growth direction is the radial one. Two types of models have been suggested in the past to account for this tangential growth: i) those based on screw dislocations [4] or cone-helix growth [5e7]; and ii) those based on the continuous growth of a graphite layer folding around the spheroid [8,9]. In the first type, tangential growth proceeds around screw dislocations or cones emanating from the spheroid's centre (Fig. 2-a), giving features that would agree with the observation of sectors. However, transmission electron microscopy (TEM) observations have shown that the orientation of the c axis along a sector tilts at random and in either ways [10] which implies that continuous growth around a screw dislocation did not occur. The second type of models (Fig. 2-b) would hardly explain the formation of sectors as already stressed by Gruzleski [9]. However, a slight modification where nucleation of new layers proceeds at the step between two neighbouring sectors which was suggested by Double and Hellawell [11] would (Fig. 2-c).There has been a renewed interest these last years for investigating the growth mechanism of spheroidal graphite [12e14]. Qing et al. [14] report observation of defects and dislocations in graphite, but do not seem to have observed long range ordered arrangements of these defects that would support the ...

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Nano-scale orientation mapping of graphite in cast irons

Abstract: International audienc

Cited by 22 publications

References 10 publications

Crystallography of Growth Blocks in Spheroidal Graphite

Crystallography of Growth Blocks in Spheroidal Graphite

A micro-mechanical analysis of thermo-elastic properties and local residual stresses in ductile iron based on a new anisotropic model for the graphite nodules

A 2-D nucleation-growth model of spheroidal graphite

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