| 1. |
- Jiang, Kaiyun, et al.
(författare)
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Ab initio study of effects of substitutional additives on the phase stability of gamma-alumina
- 2010
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Ingår i: Journal of Physics. - : Institute of Physics. - 0953-8984 .- 1361-648X. ; 22:50, s. 505502-
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Tidskriftsartikel (refereegranskat)abstract
- Using ab initio calculations, we have evaluated two structural descriptions of gamma-Al(2)O(3), spinel and tetragonal hausmannite, and explored the relative stability of gamma-Al(2)O(3) with respect to alpha-Al(2)O(3) with 2.5 at.% of Si, Cr, Ti, Sc, and Y additives to identify alloying element induced electronic structure changes that impede the gamma to alpha transition. The total energy calculations indicate that Si stabilizes gamma-Al(2)O(3), while Cr stabilizes alpha-Al(2)O(3). As Si is added, a bond length increase in alpha-Al(2)O(3) is observed, while strong and short Si-O bonds are formed in gamma-Al(2)O(3), consequently stabilizing this phase. On the other hand, Cr additions induce a smaller bond length increase in alpha-Al(2)O(3) than in gamma-Al(2)O(3), therefore stabilizing the a-phase. The bulk moduli of gamma-Al(2)O(3) with these additives show no significant changes. The phase stability and elastic property data discussed here underline the application potential of Si alloyed gamma-Al(2)O(3) for applications at elevated temperatures. Furthermore it is evident that the tetragonal hausmannite structure is a suitable description for gamma-Al(2)O(3).
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| 3. |
- Jiang, Kaiyun, et al.
(författare)
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On the high temperature stability of gamma-Al2O3/Ti0.33Al0.67N coated WC-Co cutting inserts
- 2012
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Ingår i: International Journal of Materials Research - Zeitschrift für Metallkunde. - : Carl Hanser Verlag GmbH. - 1862-5282 .- 2195-8556. ; 103:12, s. 1509-1516
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Tidskriftsartikel (refereegranskat)abstract
- The high temperature stability of gamma-Al2O3 films deposited using filtered cathodic arc and plasma assisted chemical vapor deposition on Ti0.33Al0.67N coated WC-Co cutting inserts is investigated. X-ray diffractometry reveals that filtered cathodic arc deposited films transform partially into the thermodynamically stable alpha-Al2O3 phase at a temperature of 1000 degrees C. The gamma to alpha-Al2O3 transformation for plasma assisted chemical vapor deposition grown films is observed at 900 degrees C. These results are in qualitative agreement with differential scanning calorimetry measurements. Transmission electron microscopy on filtered cathodic arc and plasma assisted chemical vapor deposition films annealed at 900 degrees C reveals the existence of hexagonal AlN in the Ti0.33Al0.67N interlayer, as well as Al depletion at the Al2O3/Ti0.33Al0.67N interface. After annealing the plasma assisted chemical vapor deposition sample at 900 degrees C, alpha-Al2O3 grains with a size of 100 nm are observed inside the gamma-Al2O3 matrix, while for filtered cathodic arc samples only the gamma-phase is identified. Transmission electron microscopy analysis on both filtered cathodic arc and plasma assisted chemical vapor deposition samples annealed at 1000 degrees C shows that the original Al2O3/Ti0.33Al0.67N/WC-Co layer architecture is no longer intact. The formation of TiO2 is detected along the growth direction of the Al2O3 films. The present study suggests that not only the morphology and the impurities incorporated into gamma-Al2O3 but also stability of the Ti0.33Al0.67N interlayer determine the high temperature stability of gamma-Al2O3/Ti0.33Al0.67N coated hard-metal.
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