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Journal of Materials Science

, Volume 42, Issue 14, pp 5307–5311 | Cite as

Microstructural evolution during direct laser sintering in the Al2O3–SiO2 system

  • Jürgen G. Heinrich
  • André GahlerEmail author
  • Jens Günster
  • Martin Schmücker
  • Jingxian Zhang
  • Dongliang Jiang
  • Meiling Ruan
Article

Abstract

The microstructural evolution during direct laser sintering of LSD (Layerwise Slurry Deposition)—samples in the Al2O3–SiO2 system has been investigated. Slurries with a water content of 34 wt.% and a SiO2/Al2O3—ratio of about 3:1 have been used to manufacture layers which—after consecutive drying—have been sintered and laminated by laser treatment. Densified samples can be obtained with laser irradiances from 190 to 270 kW/cm2 and scan velocities between 35 and 65 mm/s. Elemental mappings of the layers’ cross sections suggest an inhomogeneous phase distribution in the laser sintered LSD samples with a slight alumina concentration gradient. A lower degree of particle melting in the bottom region of the layers is plausible due to attenuation of the laser beam intensity. SEM and HRTEM micrographs show that after a few seconds of laser treatment relictic starting phase, crystalline alumina plus amorphous silica, occur together with needle like mullite, the latter formed within an amorphous aluminosilicate phase. The resulting phase assemblage reflects the non-equilibrium conditions which can be expected for short time laser treatments. Mullite nucleation within the bulk of the liquid phase rather than in the vicinity of the parent alumina phase suggests that dissolution of alumina is the rate controlling step. Subsequent thermal post treatment in air in a conventional sintering furnace causes an increase of density to about 96% and leads to additional phase reactions. Amorphous silica transforms into cristobalite and the amount of alumina is reduced by additional mullite formation. By both coalescence of individual crystals and grain growth the morphology of the newly formed mullite changes during post heat treatment.

Keywords

Amorphous Silica Disperse Silica Laser Beam Intensity Mullite Formation Post Heat Treatment 

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Copyright information

© Springer Science+Business Media, LLC 2007

Authors and Affiliations

  • Jürgen G. Heinrich
    • 1
  • André Gahler
    • 1
    Email author
  • Jens Günster
    • 2
  • Martin Schmücker
    • 3
  • Jingxian Zhang
    • 4
  • Dongliang Jiang
    • 4
  • Meiling Ruan
    • 4
  1. 1.Institute of Non-Metallic Materials Clausthal University of TechnologyClausthal-ZellerfeldGermany
  2. 2.Laser Application Centre Clausthal University of TechnologyClausthal-ZellerfeldGermany
  3. 3.German Aerospace CenterCologneGermany
  4. 4.Shanghai Institute of Ceramics, Chinese Academy of SciencesShanghaiP.R. China

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