Documents disponibles écrits par cet auteur

Primary crystallization in Al-rich metallic glasses at unusually low temperatures / J. Bokeloh in Acta materialia, Vol. 58 N° 11 (Juin 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3919–3926 Titre : Primary crystallization in Al-rich metallic glasses at unusually low temperatures Type de document : texte imprimé Auteurs : J. Bokeloh, Auteur ; N. Boucharat, Auteur ; H. Rösner, Auteur Année de publication : 2011 Article en page(s) : pp. 3919–3926 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nanocrystallization  Metallic  glasses  Modulated  differential  scanning  calorimetry  Phase  separation Résumé : The initial stage of the primary crystallization reaction and the glass transition of the marginal metallic glass Al89Y6Fe5 were investigated by conventional differential scanning calorimetry (DSC) and modulated differential scanning calorimetry (MDSC), microcalorimetry, X-ray diffraction (XRD) and transmission electron microscopy. A sharp onset of the primary crystallization was found by microcalorimetry and XRD studies at temperatures which were 120 °C below the primary crystallization peak observed in conventional DSC. A systematic MDSC study of annealed samples revealed a wide spectrum of glass transition onsets, which show a strong dependence on the annealing conditions. In addition, the glass transition onsets can be linked to the initial stage of the primary crystallization. The spectrum of glass transition onsets observed is discussed with respect to the occurrence of phase separation preceding the nucleation and growth of dendritic aluminium nanocrystals. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001904 [article] Primary crystallization in Al-rich metallic glasses at unusually low temperatures [texte imprimé] / J. Bokeloh, Auteur ; N. Boucharat, Auteur ; H. Rösner, Auteur . - 2011 . - pp. 3919–3926. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 11 (Juin 2010) . - pp. 3919–3926 Mots-clés : Nanocrystallization  Metallic  glasses  Modulated  differential  scanning  calorimetry  Phase  separation Résumé : The initial stage of the primary crystallization reaction and the glass transition of the marginal metallic glass Al89Y6Fe5 were investigated by conventional differential scanning calorimetry (DSC) and modulated differential scanning calorimetry (MDSC), microcalorimetry, X-ray diffraction (XRD) and transmission electron microscopy. A sharp onset of the primary crystallization was found by microcalorimetry and XRD studies at temperatures which were 120 °C below the primary crystallization peak observed in conventional DSC. A systematic MDSC study of annealed samples revealed a wide spectrum of glass transition onsets, which show a strong dependence on the annealing conditions. In addition, the glass transition onsets can be linked to the initial stage of the primary crystallization. The spectrum of glass transition onsets observed is discussed with respect to the occurrence of phase separation preceding the nucleation and growth of dendritic aluminium nanocrystals. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001904

Strain mapping in a deformation-twinned nanocrystalline Pd grain / H. Rösner in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2610–2620 Titre : Strain mapping in a deformation-twinned nanocrystalline Pd grain Type de document : texte imprimé Auteurs : H. Rösner, Auteur ; N. Boucharat, Auteur ; K.A. Padmanabhan, Auteur Année de publication : 2011 Article en page(s) : pp. 2610–2620 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Strain  mapping  Nanocrystalline  plasticity  Twinning  High-resolution  electron  microscopy Résumé : Strain in a deformation-twinned nanocrystalline Pd sample of about 24 nm grain size was mapped by means of geometric phase analysis based on an individual high-resolution transmission electron microscopy image. The in-plane components of the strain tensor were calculated and charted. Strains with magnitudes of about 0.8% were found in the grain interior. Twins and matrix were significantly distorted relative to each other (by about 3° on average) and showed a strong rotation gradient from top to bottom, revealing that the whole grain is bent. An estimate of the strain energy stored in the Pd grain yielded a value of View the MathML source. Based on the strain distribution observed, a temporal deformation scenario has been developed. In our judgement, deformation twins had formed first and subsequently dislocations were activated, most likely by the misfit strain/stress concentrations generated by the twins themselves. The interaction of the dislocations with the twin boundaries left behind Shockley partials and this accounted for the strain concentrations finally observed along the twin boundaries. It is concluded that in the temporal evolution of deformation in a nanocrystalline material, twinning must be by far the fastest deformation mode, which accounts for the abundance of deformation twins, especially at high strain rates. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409009057 [article] Strain mapping in a deformation-twinned nanocrystalline Pd grain [texte imprimé] / H. Rösner, Auteur ; N. Boucharat, Auteur ; K.A. Padmanabhan, Auteur . - 2011 . - pp. 2610–2620. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2610–2620 Mots-clés : Strain  mapping  Nanocrystalline  plasticity  Twinning  High-resolution  electron  microscopy Résumé : Strain in a deformation-twinned nanocrystalline Pd sample of about 24 nm grain size was mapped by means of geometric phase analysis based on an individual high-resolution transmission electron microscopy image. The in-plane components of the strain tensor were calculated and charted. Strains with magnitudes of about 0.8% were found in the grain interior. Twins and matrix were significantly distorted relative to each other (by about 3° on average) and showed a strong rotation gradient from top to bottom, revealing that the whole grain is bent. An estimate of the strain energy stored in the Pd grain yielded a value of View the MathML source. Based on the strain distribution observed, a temporal deformation scenario has been developed. In our judgement, deformation twins had formed first and subsequently dislocations were activated, most likely by the misfit strain/stress concentrations generated by the twins themselves. The interaction of the dislocations with the twin boundaries left behind Shockley partials and this accounted for the strain concentrations finally observed along the twin boundaries. It is concluded that in the temporal evolution of deformation in a nanocrystalline material, twinning must be by far the fastest deformation mode, which accounts for the abundance of deformation twins, especially at high strain rates. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409009057