Novel joining of dissimilar ceramics in the Si{sub 3}N{sub 4}-Al{sub 2}O{sub 3} system using polytypoid functional gradients Metadata

Title

• Main Title Novel joining of dissimilar ceramics in the Si{sub 3}N{sub 4}-Al{sub 2}O{sub 3} system using polytypoid functional gradients

Creator

• Author: Lee, Caroline Sunyong
  Creator Type: Personal

Contributor

• Sponsor: United States. Department of Energy. Division of Materials Sciences.
  Contributor Type: Organization
  Contributor Info: USDOE Director, Office of Science. Office of Basic Energy Studies. Division of Materials Sciences (United States)

Publisher

• Name: Lawrence Berkeley National Laboratory
  Place of Publication: Berkeley, California
  Additional Info: Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA (United States)

Date

• Creation: 2001-08-22

Language

• English

Description

• Content Description: A unique approach to crack-free joining of heterogeneous ceramics is demonstrated by the use of sialon polytypoids as Functionally Graded Materials (FGM) as defined by the phase diagram in the system, Si3N4-Al2O3. Polytypoids in the Al2O3-Si3N4 system offer a path to compatibility for such heterogeneous ceramics. The first part of the dissertation describes successful hot press sintering of multilayered FGM's with 20 layers of thickness 500 mm each. Transmission Electron Microscopy was used to identify the polytypoids at the interfaces of different areas of the joint. It has been found that the 15R polytypoid was formed in the Al2O3-contained layers and the 12H polytypoid was formed in the Si3N4-contained layers. The second part of the dissertation discusses the mechanical properties of these polytypoidally joined Si3N4-Al2O3. The thermal stresses of this FGM junction were analyzed using a finite element analysis program (FEAP) taking into account both coefficient of thermal expansion (CTE) and modulus variations. From this analysis, the result showed a dramatic decrease in radial, axial and hoop stresses as the FGM changes from three layers to 20 graded layers. Scaling was considered, showing that the graded transition layer should constitute about 75 percent or more of the total sample thickness to reach a minimal residual stress. Oriented Vickers indentation testing was used to qualitatively characterize the strengths of the joint and the various interfaces. The indentation cracks were minimally or not deflected at the sialon layers, implying strong interfaces. Finally, flexural testing was conducted at room temperature and at high temperature. The average strength at room temperature was found to be 581 MPa and the average strength at high temperature (1200 degrees C) was found to be 262 MPa. Scanning electron microscope observation of fracture surfaces at a different loading rates indicated that the strength loss at higher temperatures was consistent with a softening of glassy materials present at grain junctions.
• Physical Description: vp.

Subject

• Keyword: Mechanical Properties
• Keyword: Silicon Nitride Alumina Functionally Graded Material Polytypoid
• Keyword: Silicon Nitrides
• Keyword: Phase Diagrams
• STI Subject Categories: 36 Materials Science
• Keyword: Thermal Expansion
• Keyword: Aluminium Oxides
• Keyword: Joining Silicon Nitride Alumina Functionally Graded Material Polytypoid
• Keyword: Thermal Stresses

Source

• Other Information: TH: Thesis (Ph.D.); Submitted to University of California, Berkeley, CA (US)

Collection

• Name: Office of Scientific & Technical Information Technical Reports
  Code: OSTI

Institution

• Name: UNT Libraries Government Documents Department
  Code: UNTGD

Resource Type

• Thesis or Dissertation

Format

• Text

Identifier

• Report No.: LBNL--48986
• Grant Number: AC03-76SF00098
• Office of Scientific & Technical Information Report Number: 791793
• Archival Resource Key: ark:/67531/metadc738341

Note

• Display Note: OSTI as DE00791793