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ARPGE: a computer program to automatically reconstruct the parent grains from electron backscatter diffraction data.

Cayron C - J Appl Crystallogr (2007)

Bottom Line: A computer program called ARPGE written in Python uses the theoretical results generated by the computer program GenOVa to automatically reconstruct the parent grains from electron backscatter diffraction data obtained on phase transition materials with or without residual parent phase.The misorientations between daughter grains are identified with operators, the daughter grains are identified with indexed variants, the orientations of the parent grains are determined, and some statistics on the variants and operators are established.Variant selection phenomena were revealed.

View Article: PubMed Central - HTML - PubMed

Affiliation: CEA-Grenoble, DRT/LITEN, 17 rue des Martyrs, 38054 Grenoble, France.

ABSTRACT
A computer program called ARPGE written in Python uses the theoretical results generated by the computer program GenOVa to automatically reconstruct the parent grains from electron backscatter diffraction data obtained on phase transition materials with or without residual parent phase. The misorientations between daughter grains are identified with operators, the daughter grains are identified with indexed variants, the orientations of the parent grains are determined, and some statistics on the variants and operators are established. Some examples with martensitic transformations in iron and titanium alloys were treated. Variant selection phenomena were revealed.

No MeSH data available.


Related in: MedlinePlus

Bainitic steel (courtesy of P. H. Jouneau). (a) Quality index map. (b) Orientation map of the austenite phase. (c) ARPGE finds six austenitic grains (only the information on the bainitic phase has been taken into account in the reconstruction). The experimental orientations of the bainitic grains inside the reconstructed austenitic grains and the calculated orientations of the austenitic grains are represented by the 〈111〉 directions in the pole figures by blue and red spots, respectively. (d) The experimental orientations of the residual austenite corresponding to the six reconstructed grains are reported and the calculated orientations are superimposed with red circles. One may check the perfect agreement between the calculated and the experimental orientations of the austenitic grains. The other spots come from twinned austenite (blue arrows) and some bainitic grains misindexed as austenite.
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fig3: Bainitic steel (courtesy of P. H. Jouneau). (a) Quality index map. (b) Orientation map of the austenite phase. (c) ARPGE finds six austenitic grains (only the information on the bainitic phase has been taken into account in the reconstruction). The experimental orientations of the bainitic grains inside the reconstructed austenitic grains and the calculated orientations of the austenitic grains are represented by the 〈111〉 directions in the pole figures by blue and red spots, respectively. (d) The experimental orientations of the residual austenite corresponding to the six reconstructed grains are reported and the calculated orientations are superimposed with red circles. One may check the perfect agreement between the calculated and the experimental orientations of the austenitic grains. The other spots come from twinned austenite (blue arrows) and some bainitic grains misindexed as austenite.

Mentions: The second example is a bainitic steel (courtesy of P. H. Jouneau, INSA-Lyon, France). Since the proportion of residual austenite is more important in that material, both bainite (b.c.c.) and austenite (f.c.c.) phases have been taken into consideration during the EBSD acquisition. The quality map is presented in Fig. 3 ▶(a). The orientation of the retained austenite is given in Fig. 3 ▶(b). We then tested ARPGE to check if it could effectively find the austenitic grains and their orientations only from the bainitic data. Only the experimental bainitic orientations were loaded into the ARPGE program. Assuming a bainitic transformation with a Nishiyama–Wasserman (NW) orientation relationship, ARPGE finds six austenitic grains, represented in Fig. 3 ▶(c). Their orientations are given by the red spots in the pole figures. The experimental orientations of the retained austenite corresponding to these reconstructed areas are reported in Fig. 3 ▶(d). In that figure, we have also superimposed the calculated austenitic orientations of Fig. 3 ▶(c) by using red circles. All the experimental austenitic orientations are located inside the calculated red circles. This proves the efficiency and the high precision of the reconstruction algorithms used in ARPGE. Nevertheless, some other orientations have not been detected [blue arrows in Fig. 3 ▶(d) and other small dots]. These orientations correspond to twins of the austenitic grains 1, 3, 4 and 6 and also to bainite wrongly indexed as austenite (see footnote 1). By a careful examination of the data, we have concluded that the twins could not have been found because they have generated only ‘common’ variants. Let us explain. We have proved in §9.2 of Cayron (2006 ▶) that, assuming an NW orientation relationship, four variants are always sufficient to reconstruct without ambiguity the orientation of the austenitic crystal, and we have shown that an austenitic crystal can share three common bainitic variants with its Σ3 twin. These common variants are those encountered in the case of Fig. 3 ▶. We believe that the presence of only these common variants in the twinned austenite is not a coincidence but results from stress accommodation mechanisms during the bainitic transformation. Such a hypothesis would need deeper study. This example shows the intrinsic limit of our reconstruction program; there is no method based only on orientation measurements that allows the distinction between untwinned and twinned austenite if the twinning process generates only the three common variants.


ARPGE: a computer program to automatically reconstruct the parent grains from electron backscatter diffraction data.

Cayron C - J Appl Crystallogr (2007)

Bainitic steel (courtesy of P. H. Jouneau). (a) Quality index map. (b) Orientation map of the austenite phase. (c) ARPGE finds six austenitic grains (only the information on the bainitic phase has been taken into account in the reconstruction). The experimental orientations of the bainitic grains inside the reconstructed austenitic grains and the calculated orientations of the austenitic grains are represented by the 〈111〉 directions in the pole figures by blue and red spots, respectively. (d) The experimental orientations of the residual austenite corresponding to the six reconstructed grains are reported and the calculated orientations are superimposed with red circles. One may check the perfect agreement between the calculated and the experimental orientations of the austenitic grains. The other spots come from twinned austenite (blue arrows) and some bainitic grains misindexed as austenite.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2483492&req=5

fig3: Bainitic steel (courtesy of P. H. Jouneau). (a) Quality index map. (b) Orientation map of the austenite phase. (c) ARPGE finds six austenitic grains (only the information on the bainitic phase has been taken into account in the reconstruction). The experimental orientations of the bainitic grains inside the reconstructed austenitic grains and the calculated orientations of the austenitic grains are represented by the 〈111〉 directions in the pole figures by blue and red spots, respectively. (d) The experimental orientations of the residual austenite corresponding to the six reconstructed grains are reported and the calculated orientations are superimposed with red circles. One may check the perfect agreement between the calculated and the experimental orientations of the austenitic grains. The other spots come from twinned austenite (blue arrows) and some bainitic grains misindexed as austenite.
Mentions: The second example is a bainitic steel (courtesy of P. H. Jouneau, INSA-Lyon, France). Since the proportion of residual austenite is more important in that material, both bainite (b.c.c.) and austenite (f.c.c.) phases have been taken into consideration during the EBSD acquisition. The quality map is presented in Fig. 3 ▶(a). The orientation of the retained austenite is given in Fig. 3 ▶(b). We then tested ARPGE to check if it could effectively find the austenitic grains and their orientations only from the bainitic data. Only the experimental bainitic orientations were loaded into the ARPGE program. Assuming a bainitic transformation with a Nishiyama–Wasserman (NW) orientation relationship, ARPGE finds six austenitic grains, represented in Fig. 3 ▶(c). Their orientations are given by the red spots in the pole figures. The experimental orientations of the retained austenite corresponding to these reconstructed areas are reported in Fig. 3 ▶(d). In that figure, we have also superimposed the calculated austenitic orientations of Fig. 3 ▶(c) by using red circles. All the experimental austenitic orientations are located inside the calculated red circles. This proves the efficiency and the high precision of the reconstruction algorithms used in ARPGE. Nevertheless, some other orientations have not been detected [blue arrows in Fig. 3 ▶(d) and other small dots]. These orientations correspond to twins of the austenitic grains 1, 3, 4 and 6 and also to bainite wrongly indexed as austenite (see footnote 1). By a careful examination of the data, we have concluded that the twins could not have been found because they have generated only ‘common’ variants. Let us explain. We have proved in §9.2 of Cayron (2006 ▶) that, assuming an NW orientation relationship, four variants are always sufficient to reconstruct without ambiguity the orientation of the austenitic crystal, and we have shown that an austenitic crystal can share three common bainitic variants with its Σ3 twin. These common variants are those encountered in the case of Fig. 3 ▶. We believe that the presence of only these common variants in the twinned austenite is not a coincidence but results from stress accommodation mechanisms during the bainitic transformation. Such a hypothesis would need deeper study. This example shows the intrinsic limit of our reconstruction program; there is no method based only on orientation measurements that allows the distinction between untwinned and twinned austenite if the twinning process generates only the three common variants.

Bottom Line: A computer program called ARPGE written in Python uses the theoretical results generated by the computer program GenOVa to automatically reconstruct the parent grains from electron backscatter diffraction data obtained on phase transition materials with or without residual parent phase.The misorientations between daughter grains are identified with operators, the daughter grains are identified with indexed variants, the orientations of the parent grains are determined, and some statistics on the variants and operators are established.Variant selection phenomena were revealed.

View Article: PubMed Central - HTML - PubMed

Affiliation: CEA-Grenoble, DRT/LITEN, 17 rue des Martyrs, 38054 Grenoble, France.

ABSTRACT
A computer program called ARPGE written in Python uses the theoretical results generated by the computer program GenOVa to automatically reconstruct the parent grains from electron backscatter diffraction data obtained on phase transition materials with or without residual parent phase. The misorientations between daughter grains are identified with operators, the daughter grains are identified with indexed variants, the orientations of the parent grains are determined, and some statistics on the variants and operators are established. Some examples with martensitic transformations in iron and titanium alloys were treated. Variant selection phenomena were revealed.

No MeSH data available.


Related in: MedlinePlus