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Study of Direct Joining of Nanostructured-Zirconia to 430L Stainless Steel Produced by Co-sintering Process

Dourandish Yazdi, Mahdi | 2009

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 39614 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Simchi, Abdolreza
  7. Abstract:
  8. In this study, the joint of co-sintered zirconia/stainless steel is investigated. To this end ZrO2-3mol%Y2O3 (TZP) and 430L stainless steel powders were utilized. The joining parameters of co-sintering in zirconia/metal were studied. In order to study the microstructure, diffusion and probable reactions at the joint boundary, HRSEM, HRTEM, EPMA and micro-focused XRD methods were employed. Shear strength of the joint was also measured. Finite element simulation of residual stresses and thermodynamic studies are utilized in the next step to analyze the experimental results. It is found that the direct joining of zirconia to 430L stainless steel is feasible by co-sintering at 1350 °C under low oxygen partial pressure (argon and vacuum). The shear punch test showed the higher strength of TZP/430L stainless steel bilayers sintered under vacuum (~ 66 MPa) compared to argon (~ 47 MPa). However, the thermodynamic studies proved the impossibility of chromium oxidation, the microscopic investigations showed the diffusion and segregation of chromium from steel to zirconia surface plays a key role in joining. Under vacuum atmosphere, the chromium diffusion can be mostly attributed to the evaporation and condensation of chromium on the zirconia surface. Moreover, the formation of liquid phase and its spreading between zirconia particles improves the wetability of zirconia, increases the diffusion rate of elements and forms mechanical locks. The diffusional distance was found up to 8 μm in the presence of liquid phase. Consequently, the joint strength was improved in both atmospheres; i.e. 91 MPa and 88 MPa for argon and vacuum sintering, respectively.
  9. Keywords:
  10. Zirconia ; Stainless Steel ; Microstructure ; Finite Element Simulation ; Thermodynamics ; Ceramic-Metal Joint ; Cosintering

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