Transmission Electron Microscopy Analysis of Grain Boundary Behavior in Superplastic Doped Aluminas

Lartigue-Korinek, Sylvie; Carry, C.; Dupau, F.; Priester, L.

doi:10.4028/www.scientific.net/msf.170-172.409

Cited by 9 publications

(5 citation statements)

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“…Several authors have observed faceting of predominantly basal [0001] planes and other low index planes such as ͓1120͔ and ͓1010͔ in contact with glassy phases of various compositions. 14,15,18,[20][21][22]30,31,33 Furthermore, anisotropic and abnormal growth of these faceted grains were reported in several studies. Bae and Baik determined critical concentrations of silicon, calcium, and mixtures below which no anisotropic or abnormal grain growth was observed.…”

Section: Introductionmentioning

confidence: 89%

Atomistic Structure of Sodium and Calcium Silicate Intergranular Films in Alumina

Litton

Garofalini

1999

J. Mater. Res.

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Sodium silicate intergranular films (IGF) in contact with the [0001] basal plane of α-alumina were studied using the molecular dynamics computer simulation technique. The results were compared to previous simulations of calcium silicate and sol-gel silica IGF's in contact with alumina. An ordered, cagelike structure was observed at the interface. Sodium ions segregated to the cages at the interfaces. Calcium and hydrogen ions were also observed to segregate to the cages in the previous simulations. The modifier ions were surrounded by more oxygen ions in the cages at the interface than in the bulk of the IGF. This explains the segregation of modifiers at the interface. Interface energy decreased as the sodium content of the IGF increased. Interface energy decreased faster as a function of Na2O content than as a function of CaO content. However, interface energy decreased slower as a function of Na+ content than as a function of Ca2+content.

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Section: Introductionmentioning

confidence: 89%

Atomistic Structure of Sodium and Calcium Silicate Intergranular Films in Alumina

Litton

Garofalini

1999

J. Mater. Res.

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“…Second, direct measurement of the coefficient of oxygen grain boundary diffusion by Le Gall et al 10 recently showed a 3 orders of magnitude reduction with a doping level of 500 ppm Y, while the oxygen lattice diffusivity increased slightly. Finally, although it has been proposed [19][20][21] that the role of the dopant ions is to modify the grain boundary structure and increase the frequency of special boundaries, recent research by the present group 22 utilizing EBKD (electron backscatter Kikuchi diffraction) has found no evidence of this. This emerging picture of inhibited Coble creep, in turn, implies that blocking effectiveness is essentially a geometrical issue related to dopant size and the local geometry of a particular boundary.…”

Section: (4) Size Effect-single Dopantsmentioning

confidence: 85%

“…[6][7][8][9][10][11][12] Assuming a diffusional creep mechanism, segregants at the grain boundaries could inhibit grain boundary diffusion [8][9][10] or possibly retard the interface reaction believed to be controlling the rate of ion transport along the grain boundaries. 11,13 Indeed, grain boundary diffusion experiments by Le Gall et al 10 recently revealed a 3 orders of magnitude reduction in diffusivity by doping alumina with 500 ppm Y. In a study by Wakai et al, 5 the creep rate reduction due to Zr addition was attributed to a decrease in the interface reaction rate resulting from zirconia particles formed at the alumina grain boundaries.…”

Section: Introductionmentioning

confidence: 99%

Codoping of Alumina to Enhance Creep Resistance

Wang

Chan

et al. 1999

Journal of the American Ceramic Society

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The tensile creep behavior of both singly and multiply doped alumina samples has been investigated in order to understand better the impact of dopant segregation to grain boundaries on observed creep resistance. Previous studies have suggested that the segregation of the oversized dopant ions reduces the grain boundary diffusivity and thus the creep rate. The aims of the present work are to examine the possibly beneficial effects of selective codoping in enhancing creep resistance, and to elucidate the role (if any) of precipitates in creep inhibition. The specific singly and codoped systems considered in this work were as follows: hot-pressed alumina samples containing nominally (i) 100 ppm zirconium, (ii) 100 ppm neodymium, (iii) 100 ppm zirconium codoped with either 100, 350, or 1000 ppm neodymium, (iv) 100 ppm zirconium codoped with 1000 ppm scandium. Microchemical mapping using secondary ion mass spectrometry revealed direct evidence of cosegregation of the dopant ions to grain boundaries. Tensile creep tests were carried out in the temperature range of 1200-1350°C, utilizing stresses ranging from 20 to 100 MPa. In the case of the Nd/Zr codoped alumina, it was found that the creep rate decreased by 2 to 3 orders of magnitude relative to undoped alumina. This improvement was greater than that achieved by doping with either Nd or Zr alone, and demonstrates that the incorporation of ions of differing sizes may be beneficial. The observed enhancement in creep resistance was obtained for compositions both above and below the solubility limit of Nd in alumina; hence the phenomenon is primarily a solid solution effect.

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“…It is significant, therefore, that recent research findings have underscored fundamental deficiencies in our understanding of transport mechanisms along grain boundaries and structural and chemical transitions that can occur within grain boundaries. For example, several groups have shown that the incorporation of oversized dopant ions at alumina grain boundaries can significantly influence the high temperature mechanical and transport behavior . It is generally accepted that the dopant ions segregate to the grain boundaries .…”

Section: Grand Challenges For Ceramic Sciencementioning

confidence: 99%

Challenges in Ceramic Science: A Report from the Workshop on Emerging Research Areas in Ceramic Science

et al. 2012

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In March 2012, a group of researchers met to discuss emerging topics in ceramic science and to identify grand challenges in the field. By the end of the workshop, the group reached a consensus on eight challenges for the future:—understanding rare events in ceramic microstructures, understanding the phase‐like behavior of interfaces, predicting and controlling heterogeneous microstructures with unprecedented functionalities, controlling the properties of oxide electronics, understanding defects in the vicinity of interfaces, controlling ceramics far from equilibrium, accelerating the development of new ceramic materials, and harnessing order within disorder in glasses. This paper reports the outcomes of the workshop and provides descriptions of these challenges.

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Transmission Electron Microscopy Analysis of Grain Boundary Behavior in Superplastic Doped Aluminas

Cited by 9 publications

References 0 publications

Atomistic Structure of Sodium and Calcium Silicate Intergranular Films in Alumina

Atomistic Structure of Sodium and Calcium Silicate Intergranular Films in Alumina

Codoping of Alumina to Enhance Creep Resistance

Challenges in Ceramic Science: A Report from the Workshop on Emerging Research Areas in Ceramic Science

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